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Question DetailsAsked on 5/6/2014

How do I know if I have proper ventilization in attic?I have ridge vent and baffles.

Right now its 68 and sunny outside. My attic read 108 and 19% humidity. Should I see any day light out of ridge vent. All I see is black tar paper at the apex of attic across the whole roof? Also, should I be able to see directly down baffles and see light? Some I only see very. Baffles are very close to roof. Thanks, Rick

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8 Answers

0
Votes

Sounds like you have a good handle on waht things should look like:


If you see tar paper through the sheathing slot under the ridge vent (at very peak of the attic ridges) but you have ridge vents installed, then when they shingled they must have cut the slot for the ridge vent (or it was already there) and they ran the tarpaper over it, which is normal, then they zoned out and shingled and installed the ridge vent without slicing out the slot for ventilation. You should have a slot like this under the ridge vent (first photo) -


http://www.tr-construction.com/roofin...


If no slot, you should be able to cut out the tarpaper with a utility knife or scissors - does not have to be perfect cut, just open up to the rough slot width. If above your height, since using a ladder means hauling some plywood up there to stand it on, you might be able to support yourself on truss bracing if you have trusses, or try electrical or duct taping a utility knife to a 2x2 or broom handle or such for extra reach. Hint - when doing this, tie a short string through the eye on the back end of the knife, and tape that string to the broom handle or stick also - that way, if tape comes loose or rips, you do not get a face full of knife blade. Will probably work a lot better if you take a utility work lights up there with you - especially if you have a swivel head clamp-on one that you can clamp to the rafters or trusses - or take a couple of 16d nails and a hammer with you to put in temporary hanging points,, so you can see what you are doing. Of course, once you open it up a bit, you may find you get enough light from the ridge vent to see what you are doing.


Whether you will see daylight depends on type of vent - the mesh mat type and baffled ones you would probably see a lighter area under the vent if the rest of the attic is dark, but not "daylight" as such. Eash way to check - go up there at night and take a flashlight, and shine it (may need to use a mirror) out the vent (crossways to the ridgeline) and have someone else look from out in the yard to see if light appears in the vent - even if mesh or baffled, they should see a glow through the vent, if not direct light.

=========

Baffles - should look about like these photos -


http://www.energyauditingblog.com/how...


http://inspectapedia.com/interiors/Ro...


Should NOT look like this, with almost no space between baffle and sheathing -


http://1.bp.blogspot.com/-zGbL7wCvr3w...


Ideally, they would be mounted to the bottom of the rafters, leaving pretty much full rafter depth for airflow, but many brands only allow half rafter depth or less - the IRC (generally but not universally adopted building code) requires 1 inch free air space at the eave and between the roof sheathing all insulation, which many brands obviously do NOT meet because they are not full rafter bay width - in fact, of the ones shown above, only the shiny gray one (last one) covers full bay width and appears to provide (if it was not bowed upward) one inch clearance.


You should definitely be able to see daylight through them from the attic - of course, if you have soffits, then may just be indirect light coming in through the soffit slots, but with your head tilted up against the roof sheathing (watch out for shingle nails coming through sheathing) you should be able to see the rafter tails and back side of the fascia board through them.


If after looking at it further you have any followup questions, use the Answer This Question button to do that, so it all stays in this one thread.

Answered 5 years ago by LCD

0
Votes

I should see slits when I am inside attic? How wide should they be and on both sides?

Answered 5 years ago by rmgov22

0
Votes

You should be able to see above the baffles, through the eaves, to the underside of the roo fsheathing between the rafter tails (the part supporting the roof outside the house wall) -


http://people.hws.edu/halfman/home/Fi...



but means getting your eye right up against the bottom of the roof sheathing, or using a hand mirror to look over the top of the baffles. Might be easier to look in from outside off a ladder, and see if you can see clearly up between the rafters to the inside peak ofthe roof. This assumes your roof is normal type single-plane slopes, and there is no other goofy thing going on. Should look like about this normally -


http://blog.sls-construction.com/wp-c...


Eaves look like this from outside (without soffits) - the eave is the opening into the attic between the rafters, usually along the long walls of the house, except all around on some types like hip, mansard, or full bonnet roofed houses -


http://www.regalroof.com/wp-content/u...


Eave baffles or chutes should look something like this, usually installed at least every other or third eave, but should actually be open at every eave for proper ventilation, on all sides of house that have rafters sticking out. This photo shows a normal amount of daylight to see through them, though should ahve bug screening across the eave.


http://www.energyauditingblog.com/wp-...


but not at gable end, which looks like this - usually shorter dimension "ends" of house, and while it has 2x4 or 2x6 flat supporting pieces right under the sheathing, does not have rafters showing on the outside -


http://www.vintagewoodworks.com/47.html


It is also possible your were installed upside down - I have seen several contractors who thought the baffles were to keep the insulation from touching the cold/hot roof, not to keep an airway above the insulation.


Does that help - if not, reply back again with what you are seeing and I will see if I can help further. It may be you have baffles and someone plugged them up, thinking that was energy wise.


Answered 5 years ago by LCD

0
Votes

I just cut a slit in the tar paer down the middle, when I cut the paper almost is like a steel wool. Is that correct? Also, I can now phyically see the mesh on both side, is that correct? i hope.

Answered 5 years ago by rmgov22

0
Votes

Hmmm - do you know what Tyvek or Kevlar looks - like - a woven plastic geotextile with string artificial fibers encapsulated in the plastic ? Sort of looks like a colored plastic covered jeans like or fiber boxing tape type weave. I think that is what you cut, which would be sheet roof underlayment - which is what lies over the sheathing and under the shingles, as a backup leak defense in case of shingle failure or blowoff. Is supposed to be cut away at the slot for the ridge vent, but is commonly applied in large sheet over the stripped off roof and not cut at the slot, partidcularly on multi-dahy roofing jobs, then cut afterwards when the ridge vent is put on at the end of the job - looks like yours was not cut, which is all too common an occurrence.


Sounds like you have the mesh type ridge vent - looks like a black nylon coarse opening scouring pad material, which should be open to the attic.


Now - only thought - make sure the mesh either has a solid plastic top surface on the mesh like this -


http://www.oakhurstcontractors.com/ph...


, or that it is shingled over like this, but hopefully without the waves in the mesh before they put the shingles on over it -

http://nabinkbhattarai.com/wp-content...


The only thing about your description that worries me a little bit is if they had put the mesh on upside down and it was the plastic-top type that does not have to be shingled over, then you may have cut through the "top" and the mesh is now open to the weather on the top, if not shingled over. From your description, I don't see how that could be because the top surface is shiny and not at all like a felt or roof underlayment, and is also bonded ot the mesh, not separate, but make absolutely sure your mesh has either a smooth plastic top surface, or is shingled over.


I think you are there - but please respond back to confirm what what you cut was a thin (like thickness of paper grocery bag) plastic sheeting, not a hard plastic layer attached on mesh (about as thick as a plastic rubbermaid or hefty food storage container). If this was an upside down applied mesh and NOT shingled over, you would be able to see daylight filtering down through the mesh from directly above.


I think you are there - the unlderlayment can be cut back tothe slot width, or cut dwonthe middle and stapled back to the underlayment at each side. On new installations the center cut is my preference, because the stapled-back underlayment protects the exposed edge of the plywood from any moisute penetration from melting snow in the mesh.




Answered 5 years ago by LCD

0
Votes

It was more like a felt that steel wool was coming out when I cut. Cut both side and tried to pull back. This really did not help much. Attic read 120 when it was only like 78 out. I did a smoke test and air went out a little bit but only on one side.

Answered 5 years ago by rmgov22

0
Votes

OK - some tar paper has coarse fiberglass fibers in it to keep it from tearing when walked on during roofing, so can be quite hard to cut, and impossible to tear by hand. If it felt like it had tar on it, then that was roofing felt.


The smoke would only go out one side in almost all cases - because there is almost always at least a slight breeze over the roof, even if only caused by the heat convection due to the sun on one side and shade on the other. Only at night when the roof temp has stabilized, and during dead calm, would you expect it to go out both sides - or when snow covered and the snow if baffling any breeze, as the inside heat rises through air holes in the snow.


The outside temp has relatively little to do with attic temp on sunny days - I have had 110 degree attic temp (up under the rafters) on a freezing winter day with strong sun on a snow-free side of the roof. It may well be be that your attic will run in the 110-125 range on sunny days even with ridge vent. The ventilation will hopefully avoid the 130-160 degrees that degrades shingles and sheathing and structural wood, but arguably the most important reason for the ventilation requirement is moisture removal to prevent mildew, mold, or dry rot.


If you have that tarpaper pulled and held back (sliced at rafters and stapled to underside of sheathing to leave slot wide open ?) or cut away at the slot, check your attic some day when it is hot AND there has been several hours of full sunlight on it - and see what your temp is. I think you should be OK, provided you found your eaves are open to the outside. Did not hear back on that from you.


If you have the mesh type vent, they do not allow free flow of air like the open-slot baffled ones do, particularly when the only driving force is the heat inside rather than wind pressure. The primary ventilation force, contrary to what most homeowners and contractors think, is not the hot air inside rising - which only generates a small fraction of a psi in pressure differential. It is a combination of the negative pressure of the wind blowing over the ridge (which causes a partial vacuum on the lee or downwind side of the vent, sucking the inside air out), and the pressurization of the attic by the wind blowing against the side of the house, forcing air up into the eaves on that side - which can reach a couple of psi in heavy wind.

Answered 5 years ago by LCD

0
Votes

Ok. I had a new ridge vent installed and it did not help. I know it works becuase when I put a smoke pencil near it. I see the smoke being sucked out. I also, fixed most of my baffles with Accu Vent Baffles. The crew who istalled my baffles prior had them exteding over the soffts, so air would not come up. I have about 70 percent of attic done, the other 30% is to a hard for me to get down. I am still feeling very little air flow coming up the baffle shoots and I checked and they are not clogged. Any suggestions why air is not coming in the attic? Its a beautiful day 75 degrees and NO humidity. However my attic says 110. Please help me. Rick

Answered 4 years ago by rmgov22




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