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Question DetailsAsked on 1/19/2014

mold & moisture problem in newly enclosed cathedral ceilings-north facing side only. R30FB insul, wood t&g ceiling

ridge and soffit vents . polyvents between FG batting and roof sheathing. do not want to tear down ceiling- need to replace roof anyway-current roof was improperly installed 13 years ago (architectural shingles with seams staggered every other row instead of every sixth row)- never noticed a problem while the attic was wide open and the space was unconditioned- but now there is condensation between the FG and the roof -dripping down in spots onto the insulation and out the soffits-some places between the polyvents and between the batting. Only on the north facing roof and some spots are worse than others. how can i determine if it is a roof , condensation or insulation problem and how can i fix it from above while the roof is being replaced if it is an insulation- /condensation issue? since we discovered the moisture we have shut off our house humidifier, pulled down some batting behind the knee walls to allow for more air, placed a dehumidifier and fan in the space.

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OK - good to see what we are talking about - like Don says, not at all what I thought you had. I was thinking a living space cathedral ceiling at one side of the house, under the outer edge of the rafters and terminating at an attic knee wall blocked off attic storage space that was unheated.

1) I hope that white insulation blanket (?) on the knee wall is the warm side, but it does not look like it was - if that is the outside of the knee wall, on the cold side, that that is a wrong side vapor barrier - should be exposed open batt on that side, or a breathable surface like batt netting (nylon net to hold batt on exposed walls like that). IF it is a fully breathable housewrap then fine - but looks pretty impervious to me in the photo. Even if a housewrap, I would be dubious - because in your environment, unless you have an excellent vapor barrier on the inside of the knee wall, moist air coming through will frost up on and in it, turning it into a vapor barrier that will then wet the insulation. I have seen this happen in cold climates where they used Tyvek on the outsdie of knee walls to hold the insulation in, and it became a solid ice wall several inches thick inside the insulation. You always (in normal climatic design with winters) want the vapor permeability to increase from inside to outside as much as possible, realizing that paint and drywall do not do that for architectural reasons, but you want to avoid any barrier to evaporation from within the walls to the outdoors.

2) One of your primary problems is that joke of a baffle, both in terms of airflow capacity and in maintaining ventilation under all of the sheathing - what you need is a complete-width baffle like these, but definitely not metal as that promotes frosting and condensation and not cardboard as that soaks up moisture -

http://1.bp.blogspot.com/-9Lc1dfm1tik...

except that in the picture they blew it at the bottom. The better type sags down a bit in the center,so any frost or condensation runs out downthe center of the baffle, not off to the rafters where it can cause rot.

3) The baffle should fully penetrate to the outside of the house so the insulation also covers the top of the wall plate, and should not leave a blocked dead air spot near the eave like they did there. Also, by penetrating all the way to the outside, with proper joint lapping (installed from top to bottom of bay so melted frost or condensation in the trough runs off one trough section onto next one rather than hitting a raised joint it can then leak through), and so water running down the trough from condensation or roof leakage runs all the way outside the attic and drips out under the eaves to the ground. However, you need full rafter bay width air flow - yours only ventilates less than half the width of the rafter bay, so where the baffle does not exist or directly touches the sheathing, you will have frost forming on the baffle and sheathing, as well on the exposed rafters - the top half of which or so should be enclosed in the baffle air space or else it will frost up too. That is why you saw about an inch of wetted line at the tops of the rafters - that is probably how thick the frost was up there.

4) Also, as Don said - any time you use fiberglass in an attic, it should be in at least two layers. Even if an 8 inch batt or roll will work if you are adding R30 for instance, it should be done as two 4" layers with staggered joints. Also, it should not touch the bottom of the baffle (should be 1 inch air gap, which is about what shows in your picture at least at that one point) except maybe right at the pinch point at the eave to allow for air flow under the baffle, and an air opening from the insulation should be provided to the ridge vent to remove the moisture that WILL get into it from the house. This air gap is usually done by terminating the baffles about 2 inches shy of the ridge centerline on each side, leaving a slot for attic air to rise up into the ridge vent.

5) Personally, I would still recommend removing the T&G, putting in full-width baffles, then the insulation underlain by continuous heavy vapor retarder (which can be progressively rolled out and stapled as the insulation is installed), with full sealing of all vapor retarder seams as well as taping. This assumes the insulation you have is regular kraft paper, which should be removed. If it is asphalt impregnated vapor retarder I guess you could leave it by code, but all the seams should be sealed, and if you ever get moisture up there again the brown drips will resume, permanently staining your T&G ceiling, so personally I would remove the paper. The asphalt layer in the kraft paper is highly likely the reason for the brown drips - one reason kraft faced insulation should never be used in attics. Personally, I would tear off the kraft paper and use a continuous large-roll vapor retarder product under drywall, then put the T&G back up. Remember, the insulation will have to be TOTALLY dried before sealing it up.

6) One big conflict you have is in the winter your insulation is likely to drop down to the 40's on the house side bacause the T&G acts as an insulator against house heat, so you may get condensation on the underside of any true vapor barrier, which would cause staining and rot of the T&G. Also, if your house is air conditioned in the summer, a true vapor barrier can accumulate condensation on TOP of it from the high summer air moisture in the attic contacting the cold air conditioned vapor barrier, so despite the fact it will let more moisture through in the winter, I think you really have to use a vapor retarder here unless you do not air condition the house.

7) If this were my house, I would have extended the rafters down (deeper) with firring for another 4-6 inches to provide space for the insulation and left most or all the rafter bay as open airspace.

8) Whether you could successfully go with closed cell foam in this situation I am not comfortable with, but you could maybe get away with it - full width solid (not vented) air troughs caulked at seams so foam cannot expand into them, spray foam on bottom, shave off flat at rafter bottoms, then vapor retarder and T&G might work, but I don't like the idea of no air gap below the troughs, which WILL be cold enough to frost up in the winter. Plus I would be very worried about the foam accumulating moisture - even most closed cell foam is not really that,, and does pick up moisture. I have seen several closed cell installation that got so wet that pices pulled out of the wet wall felt as heavy as soaking wet sponges.

9) I just don't think full rafter bay spray insulation right on the underside of the sheathing is going to work for you - I believe you will still have vapor problems at the sheathing and maybe at the T&G/foam interface, and eventually sheathing and maybe rafter rot. Enclosing rafters and sheathing in foam is just plain bad practice, in my opinion - I have seen far too many roofs get severe structural rot due to this practice. Maybe someday they will come up with a synthetic waterproof sheathing that will not rot and this whole issue will go away - something similar to the InsulBoard (I think that was what it was called) that was tried in the 70's when EPS came out, but turned out to not hold nails well enough for roofing use.

10) You can get away with spraying the underside of the roof on metal roofs because the metal has a rust-resistant finish and has a long life even if damp, though even in that case you will get premature rust through in many cases. It can also be done on exposed-bottom insulation board based built-up roofs though it does trap moisture in the roofing layers if there are any leaks.

11) IF you do decide to spray foam the underside of the roof, then that acts as a pretty effective vapor barrier - especially if closed cell, so there is no chance of any moisture getting out of the sheathing through the bottom. Be sure they add the mildewcicde additive at least. Therefore, the question would remain of whether to use a breathable underlayment under the shingles hoping that what water gets in will go back out the top (which is hopeful wishing because the vapor drive is towards the cooler sheathing), or to go the other route and totally seal the top of the sheathing with an impermeable membrane hoping to prevent any infiltration. That is what I would do - with full ice and water shield or similar self-sealing roofing membrane over the whole roof. Actually, in your sitution, I think I would be looking at a raised seam metal roof with underlying ventilation airspace, as being less likely to create moisture issues inthe rafter bays that you cannot get to to do anything about in the future.

12) I did get confused on Don's last comment - he recommends taking the T&G off, fixing the vents and insulation, then putting on a full vapor barrier under the rafters (with as few seams as possible, btw), then putting the T&G back up - basically same as I am saying would be my preferred solution. However, he then talks about removing the sheathing as the only solution - unless he means to do that only IF you decide to foam in place, then I am lost.

13) BTW - the sheathing IS a structural part of the roof, but for snow load and keeping the rafters from bending out-of-plane under load, and of course to support the shingles. During a reroof taking the sheathing off is not a problem, though it is highly recommended to do it progressively with only a few sheets off at any one time rather than all at once, to keep lateral support on the rafters. Where the sheathing becomes a major part of the structural element is under snow and wind loadings.

14) Here is a CertainTeed article and a Building Sciences.com article on vapor retarders versus vapor barriers which might help - because in the winter you need a vapor barrier against indoor moisture getting into the insulaiton, but in the summer you need a high-perm vapor retarder to let moist insulation dry back into the house.

http://www.certainteed.com/resources/...

http://www.buildingscience.com/docume...

15) On the knee-wall "dead air space" - you have to do something about that. Two possibilities - one is to put in baffles just at the eaves to keep the floor insulation from blocking the airflow like you normally would for an open attic, then restarting the baffles right at the kneewall and up to the ridge, thereby letting a lot of air flow in from the eaves to the kneewall space for ventilation. Of course, this means the knee walls and floor have to be insulated for full outside temperature. The other alternative is running the baffles continuous from eave to ridge to maximize ventilation under the sheathing, then put in large rake vents (gable vents, but low down so they ventilate the area outside the kneewalls) on the ends of the house to promote air flow through there. Personally I would do the first to maximize ventilation during calm weather. Remember you have to consider your HVAC equipment you said was up there - if it is not designed for full cold exposure you may need to build a small isolated utility room around it and provide some heating for it - especially if you have anything that contains or generates water that could freeze up. Ditto to dehumidifier - I have never heard of one that works with subfreezing air, and the condensate would freeze up. And of course dehumidifier condensate has to be piped away - having an open pan in it just puts a lot of the moisture back into the air.

16) Regarding the central beam and the T&G - I don't know how they are finished now, but I would HIGHLY recommend, if unfinished, to use nothing more than a no-build stain or similar permeable finish, rather than paint or urethane or varnish. The reason - if they get some moisture on the top from condensation at the vapor retarder in real cold weather, keeping the surface permeable allows the moisture to wick through the wood and evaporate on the inside face, rather than trapping it in the wood. Same philosophy as not painting the bottom of deck boards, so water that gets through the top finish can evaporate from the bottom- just upside down in your case.

17) Curiosity - in the second picture of the attic, with the white blanket material, it looks like you are looking toward the eaves (downhill) and there are horizontal sistered rafters or beams coming out toward the camera - could you explain what these are - for the life of me I cannot understand what they are.

Lot to think about I know, and of course you want to do the least possible at this point due to both frustration and cost, but I am afraid you are in this situation because of tuning the attic area into living space, and you certainly don't want to give up on that at this point, so you are kind of stuck on a one way road to solving the ventilation issue. Just think of how you can sit back in your graying years and talk over all the experiences you had with the neverending attic project !

Answered 3 years ago by LCD

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Votes

If you have soffit vents and a ridge vent with baffles running from eaves to ridge there is only one thing I can think of. Something is letting cold air pass between the vapor barrier and the wood ceiling allowing it to cool off.

Though you say it is condensing on the roof decking after rereading your question and that would be more likely a breach in the vapor barrier compounded by too high a humidity in the space. Are there any bathroom exhaust fans not run through the roof or in a case I was called for just the other day a dryer vent not run through the roof. The one I have to repair next week had the dryer hose just fastened below an extisting roof vent and not sealed to it. If you do not have a continuous sheet of poly vapor barrier on the bottom of the rafters continuing down and sealed to the knee wall barrier (preferably with tape) and not just kraft faced insulation stapled to the sides of the rafters this is probably the problem and I doubt a good fix can be done from above.

It might be possible to remove the roof and roof decking and use a spray foam from above but that will be costly and you will need a large window of good weather or large tarps to protect the home while the job is being done.

You say there are baffles above the rafters but are you sure the soffits are vented. I do not know if this is a new home or an older one that had new vented soffits added over a plywood or other non vented soffit. This happens quite often with siding crews as speed is how they make money and often they are only knowledgable in siding work and not how a house works.

And by the way it is quite often just the Northern side that this happens.


Don

Answered 3 years ago by ContractorDon

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Does the polyvents (or rafter baffles) extend up from the sofft vents through the knewall to the ridge vent?

Is there a continous ceiling vapor barrier (no, not the kraft facing stapled to the rafters)?

Is the kneewall floor crawlspace to the roof insulated, and is there a thermal/vapor barrier in the floor/ceiling joist cavity directly below the kneewall bottom plate?


With a humidifer running 24x7 you may have excessive moisture, and without properly installed venting, moisture barrier and insulation these problems develop-not uncommon in cold climates. With your previously open attic there was probably enough venting to take care of the moisture. You have a T&G ceiling with seams allowing moisture into the insulation- Kraft-faced insulation will not stop the moisure, only a continous moisture barrier. The wood will continue to shrink over time allowing more moisture into the insulation which condenses, and drip,drip,drip...



Answered 3 years ago by hosey

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There is no vapor barrier, only the paper on the insulation stapled to the rafters. We are in Central North Carolina. The soffit vents are open. The ridge vent was open, at least before the insulation it was.

If we do use foam from above, what would be the process? How can we prevent it from getting in between the T&G ceiling. Would we fill the whole rafter bay with foam? How do we insure there is no gap between the foam and the roof sheathing or is that what we want? If we use foam, I assume we do away with the ridge and soffit vents.

What kind of roof underlayment would we then use?

I guess it would end up being a cost analysis as to whether we tear down the T&G ceiling and tackle from below, or tackle from above when the roof shingles are off.


UGH! we just finished the entire interior, wood floor, paint, trim etc.

I want to make absolutely sure that it isn't just a roofing problem before we go through all of that-how?

Answered 3 years ago by diydisaster

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The baffles run continous from soffit, above knee wall to ridge. The floor is insulated, I doubt it has a vapor barrier. There is nothing venting into that space that would carry moisture. How long after I shut off the humidifier should I expect to see improvement if that was the problem. We have had below feezing temps at night and 10-20 degrees above freezing during the day. Should I have expected my insulation contractor to have installed a vapor barrier? Do I have any recourse there?

Answered 3 years ago by diydisaster

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With your temperature swings that could be adding to the problem, but I don't think it is all of the problem.

If I were the GC on the job I would never have let the insulation contractor use Kraft faced insulation especially stapling it to the sides of the rafters as this is not a perfect seal. Kraft paper might have worked if it was stapled to the bottom of the rafters so as to overlap each other.

I hate to say this but your best bet would be to carefully remove the T&G ceiling. The last piece installed is the worst to get out and may have to replace that one. If you just nailed on the tongue instead of face nailing pry the board away a bit and you can slide a metal cutting blade on a reciprical saw behind it and cut the nails working your way to the original starting point. I have pulled of old boards this way and saved most all of them and with newer wood the odds are even better. If you number them as you go you could reinstall in reverse order. With carefull nailing you may not even have to paint them.

I would start at the top if possible just to see if there is a possilility that the vent was not done properly there and also look at the underside of the ridgevent to make sure that the tar paper was not left up and over the roof (I have seen this) and if you find something there you might be able to leave the rest.

I would do the whole thing though and then add a plastic vapor barrier as you can check to see if indeed the vents are continuous and no gaps are there that would allow the insulation to block the air flow. If you have found a problem at the ridge you might be able to check the vents with a strong flashlight at the ridge and looking up the chute from the bottom by the knee wall.

You can reuse the insulation if after reinstalling it you slice the paper with autility knife before installing the plastic, you do not want two barriers.

I think this is a way better way of dealing with the problem especially since with solid foam the part below the knee walls will have no ventillation.

Don

Answered 3 years ago by ContractorDon

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You know, I mis-spoke. The "kraft "paper is nailed to the bottom of the rafters overlapping each other. Do you think this is an adequate vapor barrior? Could another factor be the culprit?


Should I take the chance of changing out the roof shingles (which we had planned on doing anyway,) replacing the tar paper with a breathable synthetic underlayment, inspecting the ridge vent.....leaving the insulation as is and monitoring-then attacking from below if it turns out that the roof was not the source of the moisture.


This is sounding more reasonable to me as I hear that the "best " fix, if this is purely a condensation issue, should be from below.


The "fix" being- keep existing FG insulation but apply a vapor barrior on the ceiling side.

What sort of vapor barrier?


I am worried that the R-30 may not be enough insulation, though. The rafters are 2x 10, and with the polyvent taking up some of the room...


I would hate to close it all back up again and still have the same problem. Won't I still have condensation from the humid air which passes through the vents from the outside (if it warms due to inadequate insulation) against the cold roof?



If foam (higher R value) is the answer...could it be done from the roof side?-back to square one!

Answered 3 years ago by diydisaster

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A moisture infiltration fix might be to caulk seal all the wood plank seams- if stained use a clear paintable caulk and apply a clear varnish or poly coat. The poly or varnish will provide the moisture barrier you need. The T&G will expand & contract so you want to use a product that will allow some flexibility so it dosen't crack from the wood expansion/contraction.

Moisture barriers in southern climates can be problematic- in the winter you have moist, warm indoor air trying to get outside and in the summer you have warm, moist outdoor air trying to get inside in cool dry indooor air.

Answered 3 years ago by hosey

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You never did answer how old the house is and if the soffit vented material is the only layer there is. As I said before if new vinyl vented soffit was installed over non vented it would cause this problem. Since you are thinking of reroofing anyway if you do a complete rip off it would not add that much cost to pull off the top 2 feet of plywood on each side of the ridge and check the vent baffles with a light and looking up from the knee walls. You also said that the rooms below may not have any insulation which means probably no vapor barrier which could be the source of the moisture. With out seeing the home it is hard to advise you as to how you could complete the envelope down the knee walls and across the cold areas of the ceiling below. An oil based primer applied heavily with your choice of paint over it might be a way to do it. And also has shutting off the humidifier helped? It is a possbility you had it set too high. While it is better to have the kraft paper stapled to the bottom of the rafters any joints between each batt of insulation should have been taped for a complete seal to be achieved. One other thing you could do when the roof is open or even now would be to do as I said and remove the top two or three feet to each side of the ridge and add a flat sort of ceiling to the peak creating a sort of plenum and add a few(depends on length of ridge) power vents with built in humidistat/thermostats. They may a bit harder to find but they are made, most at the Big Box stores have just a thermostat so you may have to look online.


Don

Answered 3 years ago by ContractorDon

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The soffits are open- original to our 13 year old house. The floor between the upstairs and downstairs is insulated, but I doubt there is a vapor barrier. I like the idea about the flat ceiling and roof fans- but without a proper vapor barrier behind the T&G wood,and having cheap 1" deep polyvents that do not extend the full width of the rafter & only r-30 insulation- would this fix the problem?

Does anyone know if we decided to use closed cell foam, can it be sprayed to the kraft facing from above (while we are replacing the roof) if we left it behind after we remove the fiberglass. My concern is that if we close off the vents ...and we do not spray the foam directly to the underside of the roof sheathing, will we have a moisture problem in this void?


If there is no good way to use the foam from above while the roof is being replaced- then my decision is easy.

Answered 3 years ago by diydisaster

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As I said before, I have not actually seen the situation but from your description I think I have a good idea. I think if you have the propervents, sorry brand name for the channels your best bet is to make sure they were done right and find where the moisture is entering the cold space. I believe that if you completely fill the rafter bays you will trap the moisture at the knee wall area. Think of it as wrapping the whole warm side of the house with shrink wrap. Any voids will let the balloon leak. You may be able to seal the downstairs barrier to the roof foam by filling between the ceiling and roof. Much like what is done with the structural foam and plywood panels on pre-engineered houses. I have built solar heated homes and have seen first hand what can happen with just one goof by installers. If after shutting down the humidifier the condensation went away it may have been the setting you had it on, I had that on one new house I built. They had it set on max right after the house was built and between the moisture in a new house with all the new concrete,drywall paint and such it was just about raining in the house.


Don

Answered 3 years ago by ContractorDon

0
Votes

You have gotten a terrific set of responses on this question - far more than most questioners get - congratulations.

I am assuming this problem has occurred at times other than just during the recent extreme temperature lows - many houses would have heavy frost and drip issues under unusually extreme low temperatures that they were not designed for.

You stated your cause - "never noticed a problem while the attic was wide open and the space was unconditioned- but now there is condensation" - clearly, your conversion of part of the attic to conditioned space failed to account for moisture control, so you have a moisture and a ventilation problem in the attic. Unless you have visible leakage from the roof, likely with dark staining of the underside of the sheathing and maybe localized rot, likely NOT a roof problem.

Tracking down the exact cause of your problem is a bit tougher, and of course all we can do here is hypothesize, not seeing the situation in detail first-hand. Here are some thoughs for you to consider - several of which were covered by the other excellent answers you got, plus a couple of others to think about and check out - which actualy apply in your case you will have to figure out, or get an insulation and building energy expert to look at:

1) The conditioned part of the attic space has to be quite vapor tight, with air transfer only between it and the living space below, not with the attic. Full vapor barrier on inside of sides and top under the drywall, fully sealed knee wall doors. The underside depends on what you did - if the underside is conditioned space to the house, then you would have had to carry the vapor barrier down through the ceiling drywall to the inner surface. Otherwise, there should have been vapor barrier under the flooring, with cold airspace below that for ventilation - typically 2x or 4x spacers to provide cross ventilation under the floor, otherwise moisture can accumulate on the bottom of the flooring and around the joists under there.

2) Gable vents should be closed off; and waterproofed if subject to EVER getting wet - seal from outside, not inside, otherwise rain and snow will accumulate between vent and sealing plywood and rot the wall. While combined eave and gable venting can work OK on a wide open attic, as I think Don or Ben said, once you put in eave troughs and knee walls the airflow from the eaves has much more flow resistance so almost all the air the ridge vents want to pull will come from the gable vents, leaving the area between the eaves and knee walls as largely dead air, subject to condensation especially on the cold side of roof - the north side and sometimes other shady sides. Also, to make it worse, by blocking off the center of the attic with the enclosed storage (?) space, much or all of the airflow from the gable vents now runs along the edges of the roof outside the kneewalls - where it fights with the air trying to come in the eaves, so you get reduced eave airflow and frequently total stagnation in that area - hence, moisture accumulation. When you have soffits it is even worse because you have additionally restricted your airflow. Unfortunately, if your kneewalls and conditioned space is well insulated this is aggravated because there is less heat to promote airflow up over the kneewall, but you are still getting moisture from below - presto, condensation and frost. Remember that not all moisture comes from inside the house - it can come in with outside air on rainy days, and then for up to several days afterwards from siding and ground below the eaves evaporating moisture accumulated in the rain.

3) Your cathedral ceiling issue I am not totally clear on - I understand the new T&G ceiling, but if this was a true cathedral ceiling, you would only have 9-1/2 inches (with 2x10 rafters) rafter bay gap for both airflow and insulation. You said "R30FB" - do you mean fiberglass batt, I presume - hopefully not fiberboard ? Oh - later you say "I am worried that the R-30 may not be enough insulation, though. The rafters are 2x10, and with the polyvent taking up some of the room..." That would be about 8-1/2 inches worth of insulation - which for fiberglass batt at R3.5-4.0 depending on whether normal or high-density, would mean 7.5-8.5 inches of batt in an 8-1/2" space roughly, leaving zero air gap between trough and batt if normal density batt. Also, you said 1" deep baffles - that is no way large enough for a long run - should have been full width, 2-3 inch clerance minimum. Hopefully that is not the case, because it would be like a house across the street from me - long sloping cathedral ceilings with 2x8 rafters and a massive mid-roof cross-beam that the rafters set halfway down into, that was built with no insulation above the drywall ceiling, so ceiling frosted badly. They reroofed the rotted (from moss buildup) roof, and contractor convinced them 1/2-1 inch airgap was enough, so filled rafter space with 6 inch R24 insulation batt - now no airflow, so massive frost buildup problem in the rafter bays, which then becomes drips inside and causes heavy roof glaciering as the insulation wets and loses insulation value. If that is what was done in your case, your insulation over the T&G ceiling could be wet, causing the mold.

4) Alternative on cathedral ceiling problem, which may not be related to the attic moisture issue at all. Presumably you do not have conditioned space above that, so likely your warm, moist air is rising into that confined interior area, then cooling enough to condense moisture on the ceiling - which might only take a 10 degree or so temperature drop to happen with a humidifier running. Presto, mold. Cathedral ceilings without an air intake at the top to recirculate the air are just plain bad design. Circulation in tall ones requires a continuous run scavenger fam pulling that air and recirculating it, or a return air vent to the HVAC system (not as good as runs only intermittently). In lower ones where it is only a few feet higher than the rest of the adjacent ceilings, a large bladed ceiling fan can sometimes alleviate the problem. Other condensation solution is to superinsulate over the T&G to keep it from cooling down (which you do not have room to do), though you have to certain that your vapor barrier in that area is excellent, otherwise the extra insulation thickness will trap the moisture going up through it.

5) A word of explanation on that issue - commonly a poorly insulated attic will get rid of the accumulated moisture by vapor diffusion through the insulation, to the attic air and then out the ridge or gable vents. You add insulation you somewhat reduce the air leaks into the attic from below, therefore reducing the airflow through the insulation which used to carry the moisture on through. Also, more insulation means that in the winter the attic is now colder (getting less heat from the house side), so the freezing front (point where it is at freezing) drops from just above the insulation down into the interior of the insulation mat itself - so any moisture that is coming up from the house freezes in the insulation, forming a solid ice sheet which traps any further moisture from below as well as causing mildew, mold and rot when it melts.

6) Also, with more insulation and a colder attic, what moisture does get up there from whatever source is now colder, so it much more readily condenses on the underside of the roof and on top of the insulation - initially as moisture before the sheathing drops to freezing, then as frost after that. During the dead of winter the frost accumulation is not particularly harmful as long as it stays frozen and does not get thick enough to be dangerously heavy. However, when it melts, particularly if in a rapid outside warmup with sunshine, the frost cannot evaporate as fast as it melts, so you get drips from the underside of the sheathing and water running down under the sheathing. IT goes either down the joists to where they hit the wall, to the bug screen at the eaves and down that to the top of the wall, or down to drip onto the soffits, where it then runs to saturate either your wall area or your fascia area (as well as the soffits if wood), depending on where it drops off and which way the soffit slopes. Another of the many reasons soffits are BAD for anything but looks.

7) On the roof replacement issue - not clear to me why roof has to be redone after 13 years due to shingle spacing - as long as the slots in the shingles are about 4-6 inches away from the nearest underlying one, there is not a problem except maybe visually, but if it took 13 years to notice, probably not a big problem there. Maybe your design is "random width", actually meaning several different spacings alternated, so you ended up with basically overlapping slots ?

8) Don talked about eave troughs or baffles running from the eaves to the ridge vent, and you said "The baffles run continous from soffit, above knee wall to ridge". I hope this is not actually the case, because if so then you have zero ridge vent ventilation for the rest of the attic. The troughs should be as short as possible to avoid blocking the eaves with insulation but no longer, so the rest of the attic space and the attic insulation have access to moving air to remove any accumulating moisture. If you mean troughs over the cathedral ceiling to keep the batt insulation from blocking air fow, then those should be ventilated type - heavily slotted so they keep an airspace without blocking moisture coming up through the insulation. If they put in solid ones there, then your moisture going through the T&G is going into the insulation and being trapped there by the solid baffles, probably getting wet and maybe even freezing there.

9) As Don said, check for penetrations not sealed to airflow from below, and any type of duct or vent not fully sealed, allowing moist air to accumulate in the attic - ditto to possible poorly or unsealed attic access door or hatch. Needs tight compression seal to stop airflow. This should have been done BEFORE the insulation was installed.

10) You say ridge vents were open, at least before insulation. So now blocked ? This is definitely your #1 issue to take care of, and could be a major part of your problem, along with the attic space not having access to the ridge vent if the troughts cover the bottom of it over. That should NEVER be blocked unless replaced with equally as good ventilation, which is very hard to achieve and requires a continuously running special ventilation system.

11) You say - If we do use foam from above, what would be the process? How can we prevent it from getting in between the T&G ceiling. Does this mean you have no drywall OR vapor barrier above the T&G - WHOA. This is going to cause all kind of airflow and moisture getting into the attic - if that is the case, guess what - T&G comes down and job gets done right - vapor barrier, drywall, T&G. T&G, even if caulked and painted or stained, is still going to let a LOT of air and moisture through, ruining your attic situation.

12) You also say - "Would we fill the whole rafter bay with foam? How do we insure there is no gap between the foam and the roof sheathing or is that what we want? If we use foam, I assume we do away with the ridge and soffit vents." Answer - NO, NO, and NO. If you fill the rafter bay with foam, not only will your sheathing rot when moisture gets into it and cannot escape, but your ventilation airflow is eliminated. Bad idea. And you do not want to eliminate your eave and soffit and ridge venting either. If you were going to do that, then your only viable alternative would be to block off ALL air openings to the attic, remove the T&G to expose the rafters, condition the entire attic, and have an exposed rafter ceiling (which would get mighty cold in the winter and hot in summer). That is why this type ceiling is only properly done in mild, Mediterranean type climates like California and some low elevation mountain areas in the southeast and southwest.

13) " guess it would end up being a cost analysis as to whether we tear down the T&G ceiling and tackle from below, or tackle from above when the roof shingles are off." No way you want to tear off the sheathing to work from above unless it is rotted and needs replacement, which if reroofed 13 years ago presumably was not then and should not be now - that opens the entire house up to the rain. Maybe you misunderstand what a "tearoff" is - that is shingles and the water brrier, NOT the plywood sheathing - that comes off only if it is rotten,or you have major truss repair to do. Definitely want to work from the attic or below to do whatever you need to do if at all possible.

14) "I want to make absolutely sure that it isn't just a roofing problem before we go through all of that-how?" Easy way - check out the underside of the roof after next heavy, long rainstorm, or put a rainbord sprinkler up there and let run for a day (making sure it does not hit into any vents). However, if you had drips and water running out the eaves in several non-adjacent bays, highly likely it was condensation rather than leakage - very rare for a roof that is not in terrible visual condition to develop multiple leaks around same time.

15) "Should I have expected my insulation contractor to have installed a vapor barrier? Do I have any recourse there?" He should have known better, but as to recourse ? IF he put in batt with kraft paper in an attic floor he obviously did not know what he was doing, as that is not a suitable attic vapor barrier and is NOT recommended or approved for that use, even though he evidently thought that was what he was doing if he stapled it to the joists. The kraft paper is there to allow stapling to prevent sagging in walls, not as a vapor barrier.

16) One of the comments suggested caulking the T&G and that the clear finish would provide adequate vapor barrier - don't believe it. Not only do paints and finishes NOT provide adequate vapor barrier to walls or attics that see cold temperatures, even with most of the ones claiming to be designed to do that, but the joints WILL open up, and you WILL have end gaps between the boards and between boards and walls. You HAVE to have a true vapor barrier.

17) Not knowing how much of the house we are talking about with this cathedral ceiling, but I think your solution for a "certain" fix for that area would be remove the T&G and the insulation, replace the baffles located uphill of the eave area with vented trough, put in UNFACED insulation (can tear the facing off your current insulation if not saturated, just a bit of work), underlay that with full heavy vapor barrier (6 mill standard, 10 mil required in some areas)stapledto the underside of the rafters, drywall, then the T&G ceiling WITHOUT any sort of sealant or gluing, so it does not trap moisture between it and the vapor barrier. At least the kraft paper removal and vapor barrier and drywall installation. if I were installing this, assuming R30 was determined to be the proper insulation, I would have installed deeper, full rafter bay width baffles, and firred down the rafters to provide at least a 3-4 inch airgap under the baffles to the insulation, then the insulation and so forth. You also need to do something about airflow in the top of the cathedral ceiling area - this needs to be resolved while the T&G is off, to allow running duct or wiring and such.

18) If you want more input on this, would be helpful for us to see photos of the cathedral ceiling (at an angle if possible, not from straight below), and also of the configuration in the attic, as I am not quite clear on that yet. I am visualizing construction something like this (the Attic Truss) though maybe stick built with rafters and joists and stud kneewalls -

http://design.medeek.com/resources/tr...

Answered 3 years ago by LCD

-1
Votes

Answers from contractors- not building scientists.

The moisture vapor is infiltrating the T&G wood ceiling through the seams and through the kraft faced insulation....most likely condensing on the soffit to rafter baffles. Warm air exfiltration must be replaced with outside air which is most likely coming in through a very leaky house which would alos expalin the need for humidication as the outside air is dry. I would have a blower door test to determine how tight the house is and fix some of the infiltation problems. Condensation from the roof decking usually happens in much colder climates so unlikely. If you have a blower door test I would also suggest a thermal camera to see any insulation voids and possible condensation areas on the ceiling

Answered 3 years ago by hosey

0
Votes


The moisture that has dripped down between the insulation in some spots is an oily brown.


The tops of some roof rafters, not others have a moisture demarcation line about an inch from the top.


The osb sheathing in these rafter bays is moist, but not in others.


Although there was UNIFORM condensation and frost (it was very cold outside) when I first pulled down the the FG batting to inspect in the "behind the knee wall" storage area.


The roof shingles in some spots have less than 4 inch stagger- confirmed by another roofer.


There is algae growing on the bottom edges of the roof shingles on the north side.


The insulation went up in august, the HVAC then went on for the carpenters.


The first sign of moisture was a stain on the sheetrock at the kneewall. This as I recall was late October early November-we thought it was stain from the trim work.


Then about a month later, we noticed it had grown. The day we noticed, it was raining-so we automatically thought it was a roof leak- roofer came out-did not find anything that would cause a leak but told us about the bad install job-tore up shingles in that area and placed a waterproof membrane, then put the old shingles back on-face nailing some.- The roof is tore up from this "patch". So we do want to replace the roof-but we will not use him.


And yes, we are trying to figure this out during the coldest part of the year...


The roof sheathing where the insulation is pulled done has dried out- but in some areas there is frost on the sheathing and condesation on the vents above and below that point about a foot into where the insulation is still in place- as I said, some bays are worse than others, a few look dry.

I a have a fan running in that area- has been too cold for the dehumidifier to work.


I am not convinced that even though we have a condensation problem that we do not also have a roof problem and this may be contributing.


If the roof was proper- I would have no doubt and tackle from below- but even then am unsure of the most effective method.


And as far as the moist inside air with out a vapor barrier-

The ceiling still has open areas in it where ceiling fixtures have not yet been installed, but the worst areas do not occur in those rafter bays. So this is confusing to me- I would think this would be the worst area.


I am calling the power company to schedule a Home energy audit and another insulation contractor to give an opinion. I have a helpful roofing contractor checking into some things as well.


On a personal note:

We have spent over a year on this reno, we have had a few bad carpenters and things had to be redone. If we have to rip down the trim and ceiling after we just got it right, we may end up in the looney bin.To add to the stress- We are doing this to make space for an elderly ill parent who has moved in, taking over our downstairs space. We are so frustrated and do not want to waste money on a fix that doesn't work-especially since we are officially tapped out.


There are so many different opinions about vapor barriors, vented vs unvented, amt and type of insulation etc. Especially for the climate I have here-Central North Carolina.


Although all of this feedback is making me aware of factors which need to be taken into consideration, I am getting more confused. But now at least I can ask more educated questions of the professionals that I have come out to the house.


What type of engineer should I consult? Can you suggest anyone in my area-east triad/west triangle area.


I will continue to check this thread and post pictures. I'll let you know. I think that this experience can help others avoid the same problems in the future. Thanks

Answered 3 years ago by diydisaster

0
Votes

looking into dense packed blown in cellulose...only question here is will the T&G wood ceiling hold the dense pack?

Answered 3 years ago by diydisaster

1
Vote

Sounds like you have had a bad time of it - sorry about that, for what my sympathy is worth. My thoughts relative to your last post:

1) I would have a BPI Certified Energy Auditor consultant do an assessment, preferably one who knows he will NOT be bidding on the work to ensure an unbiased report, including thermal IR scan and smoke test (little smoke generator that shows where air is actually moving and how much). If you have been considering having a full energy audit done (though this would be putting the cart before the horse, since insulation has already been instlled and paid for), this would be the time for that with the blower door test also.

2) I don't see any way around removing the T&B and putting in proper ceiling construction - airflow gap over insulation under trough baffles or venitlated baffles, vapor barrier, drywall, then the architectural finish - the T&G.

3) You should temporarily seal up those open light fixture holes until the fixtures are installed - caulk the gap between box and drywall, then put on a blank coverplate with stickyback foam weatherstrip on the back to seal off the box itself.

4) The LAST thing I would do is use cellulose - in a situation where you know you have moisture issues, and permanent poor ventilation under the roof over the cathedral ceiling area, you do NOT want to put in an insulation that soaks up and holds water like cellulose does - not only because of the mold issue, but also the weight. With fiberglass, I would think properly nailed T&G MIGHT be able to carry 8-9 inches of insulation weight OK - of course, if you drywall first as would be normal practice, that would carry the insulation weight. Personally, considering the minimal nails used for T&G (assuming you are doing tongue and not face nailing) I would not count on the nails carrying anything more than the boards themselves. 1/2" drywall is considered OK for up to R30 fiberglass - not for cellulose, which requires 5/8" with screws - see manufacturer website for recommended spacing - usually 6 inches along edges and 7 inches field spacing for nails (nails not recommended in ceilings) and 8 inch on edges and 12 inches in field for screws on ceilings - but depends on local codes. I emphatically recommend requiring cadmium plated or Kilz priming on heads of galvanized fasteners in ceilings to prevent popouts due to rusting, ESPECIALLY where you have known moisture issues like a cathedral ceiling. BTW - if your rafters are 24 inch spacing versus 16 inch, you HAVE to use 5/8 drywall. Drywall has to run long way perpendicular to rafters.

Answered 3 years ago by LCD

1
Vote

+1


Do not...I repeat...do not dense pack with cellulose.


This has been tried and many a roof and rafter have rotted out in the process.


Best way to address it is to pull the roof and insulate and vent from the top down.



Answered 3 years ago by WoWHomeSolutions

0
Votes

Talked with county inspector- The insulation behind the knee wall is not required by code. I removed it from the north side and the rafters and osb have dried nicely in that area.

The R30 insulation was crammed into the rafter bays over the polyvents between 2x8 rafters (the rafters are 2x10 above the knee wall and 2x 8 below the knee wall).

I can still see damp osb looking up the rafter bays over the knee wall toward the ridge though.

We are going to replace the roof shingles and ridge vent when the weather improves. We will insure that the ridge and soffit vents provide the appropriate amount of ventilation. We will use synthetic underlayment- it is supposed to breath better than the felt paper that is there now. If all of that does not do the trick-then we will take down the T&G and use cc spray on foam and eliminate all of the vents. Hope we do not have to go there.The relative humidity is down to the low 30's % in the house.

I am hoping that this was all due to high house humidity and inadequate ventilation- I am keeping my fingers crossed. We have halted all work until we know.

By the way the county inspector said that dense packed cellulose with no venting is not allowed by code here. Also, they do not recommend any "vapor barrier" in this climate. And yes I know that sheet rock is an air barrier not a vapor barrier. See how much I am learning...


Answered 3 years ago by diydisaster

0
Votes

How many square feet is the roof?


By the way, most synthetic underlayments are polypropylene and therefore class 1 vapor retarders.


There are breathable underlayement but I do not recommend them in this case.


The roof does not need to breath through the sheathing...it needs to breath through the ridge.


There are other way to fix that roof and feel free to update with information on the square footage and we can give you more feedback.

Answered 3 years ago by WoWHomeSolutions

0
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2376 sq feet by my rough estimate-half being on the north side.

Answered 3 years ago by diydisaster

0
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Sounds like you are making progress - and probably never want to buy a house with a roof or attic again :{

1) The reason the insulation was not required behind the knee wall is because the knee wall does not divide warm and cold space - it would be required if the attic area in the center of the attic (between the knee walls) was enclosed and heated - "in the HVAC envelope".

2) The insulation stuffed over the polyvents is a common mistake by insulators, who generally are about the lowest paid and least trained workers and know basically nothing about insulation principles, was undoubtedly a major portion of your problem, and probably the reason you had this moisture situation go from maybe minor or unnoticeable to a significant issue.

3) The OSB wetness - if you can reach up there, you may find it is stained, not still wet - OSB and some plywoods tend to stain darkish from the glue when they get wet, and stay that darker brownish color pretty much forever afterwards.

4) When you say replacing shingles and ridge vent I presume you also mean the underlayment - the roofing felt or roof wrap also, as well as ice and water shield where called for. Oops - now I see where you will be doing that.

5) You talk about, in the extreme case, about removing the T&G and using spray in foam and removing vents - I hope you mean removing the polyvents and spraying foam on top of the T&G, leaving a larger full-width air gap in the rafter bays over it, not filling the rafter bays totally with foam. That would be disastrous as it would eliminate all evaporation from the bottom of the sheathing in that area, and eliminate all attic ventilation - you would be at least as bad off as you were, and likely worse. Unless you air condition (heat and A/C) the ENTIRE attic space from eave to peak, blocking off eave ventilation will make for very poor conditions. And of course, if you did that, you would have to remove the ridge vents too, then insulate the entire rafter area, then put a moisture-resistant finish surface over it - putting the attic "in the envelope" rather than outside air conditions. The other alternative would be leaving the rafter area and attic uninsulated but within the envelope, which would actually be better for the sheathing probably, but the energy cost would go way up, and in very cold weather you could get frosting or condensation on the sheathing still - no improvement at all.

Again - Good Luck,, and it does sound like you are making good progress, especially with the discovery of the blocked polyvents.

Answered 3 years ago by LCD

0
Votes


Thank you for taking an interest in try to correctly solve our problem. I am afraid that I have not described the space very well.

The entire upstairs was open with no insulation except the floors for 13 years. We insulated the whole thing recently-(see picture), although only the space on the living side of the knee walls is conditioned (although the air handler for the hvac heat pump system is in the storage area behind the south knee wall). When we discovered the condensation issue, I removed the insulation only from the ceiling of the storage side of the North knee wall (see picture)-the insulation within the knee wall proper is left undisturbed.


As I understand it, The closed cell foam can only be applied to the underside of the sheathing from below. This is the recommended method, eliminate the vents and maintain a ventless system "hot roof" so to speak. BY eliminating the ability for moisture to enter, you eliminate the moisture problem. Certain teed warranties their shingles on hot roof applications-backed up by studies.


If we did spray the foam on the back side of the T&G from above, it would be very difficult to obtain even coverage without removing all of the sheathing-per a foam company I spoke to. This was not recommended due to the fact that the sheathing is fairly structural and this would also leave the entire house subject to the elements for a period of time.

And again, moisture would still be able to enter through the vents. As I understand it, I might end up with the same problem, even though we could increase r-value and create a vapor barrier between the vented space and the living space- thus eliminating warm humid house air from condensating against a cold roof. We were also concerned that the foam would ooze between the boards or loose it's integrity when the boards expanded and contracted.


Wish us luck!

Answered 3 years ago by diydisaster

0
Votes

Tell me more about why a breathable mesh synthetic underlayment would not be recommended here. We were planning on using one.

Answered 3 years ago by diydisaster

0
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This like the story that never ends. Just kidding! It is nice to get follow up. I wish you had posted pictures in the beginning. As soon as I saw that the insulation was batts it explains the problem. Your vapor barrier is not continuous with all those joints and by the lights the pape was pulled completely off. The joints should have been taped if batts were used instead of rolls and even then any joints should have been taped. And the hi hats are another weak link in the envelope. It is in my opinion a definite condensation issue and aside from pulling the T&G off and installing a full SEALED vapor barrier I would not bet on anything. Even with your polyvents you will have a moisture problem since they may become the place the moisture will condense. I hate to say it but removing the roof sheathing when you do a new roof may be the only answer. You may be able to salvage some of the sheating after it is foamed.


Don

Answered 3 years ago by ContractorDon

0
Votes

Sorry to see all the difficulty. There seems to be quite a few of these T&G/venting issues creeping up with the supremely cold temps.



Answered 3 years ago by Windows on Washingto

0
Votes

I didn't read all of the lengthy responses. We had the same problem. I live near the beach where the humidity is high. I sealed and had workers seal off every gap on the roof which made it worse. Basically the roof was like an umbrella or cooking hood trapping all of the moisture. I had a vented ridge crest installed and that resolved the problems.

Source: Stephen

Answered 3 years ago by stephsato




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