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Question DetailsAsked on 9/8/2014

Attic Ventalization ---- Trying to fiigure why my attic is not have air movement???

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 15 days ago by rmgov22
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I presume that you do not have gable vents, or at least blocked off if still there - because they have greater airflow capacity then your baffles usually and are closer to the ridge, so the ridge vent will pull air more from them rather than the eaves. If still in place, block off with waterproof material which also needs to be highly wind resistant - usually tarpaper against the vent covered with nailed-on 1/4" or thicker plywood works well - tarpaper should be directed at the bottom so any wind-driven snow or water hitting it runs back out the vent rather than accumulating in the attic. This is important because usually a little bit will come in with the wind, but evaporates as soon as it hits the insulation because of the airflow through the vent - but once you block it off, the moisture can accumulate and percolate down into the house or cause mold and rot right below the vent.


Personally I do not like the ones built like AccuVent that lay up fairly tight to the sheathing - they only ventilate half the roof area or so over them and are in contact with the rest of the area so totally block off airflow in that area, and really have very thin airflow area for the convection airflow. I use the type that fasten at the bottom of the joists, providing full joist width airflow (minus twice the thickness of the baffle material where turned up and stapled to joists) and provide almost full joist depth airflow area - so as much or more airflow area as the eaves themselves provide so they do not provide resistance to the airflow.


I would take one easily accessible baffle off completely and then use your smoke pencil to see what difference there is in airflow between it and an adjacent one - if you can then remove a section of the soffit to see what difference that makes, I think you will be surprised. Soffits commonly cause an 75-95% reduction in airflow, and low clearance baffles like yours further aggravate that problem to the point you get no noticeable airflow into the attic. Also check your eave or baffle insect screening is not plugged with insulation or outdoor lint and cottonwood fluff and such, or painted to almost blocking the screening.


Another thing I would do is check the air temp coming out of the top of the baffles - with soffits and baffles the leading 6-10 foot edge of the roof may have heated the 75 degree incoming air to 85-90 degrees before it even gets into the attic, which then heats it further with roof sheathing conduction and radiation.


To be perfectly honest, on a sunny day (hot sun exposure roof) it is not at all unusual for the attic to reach 100-120 degrees - my attic can reach 90 degrees under direct sun on days when the outside temperature is near freezing, as long as there is no snow cover of course. The ridge vents do not allow enough airflow to really flush out the hot air in the attic - so getting to 100+ is not unusual or necessarily a matter of concern - the 120+ temps are what really degrade the wood and cause overheating of the overlying shingles and water barrier - and of course imagine what a totally unventilated roof can do to the covering when the attic or flat roof crawlspace temp reaches 160, which I have seen in several cases - even worked one large commercial building in the Southwest where water dropped on a metal roof instantly boiled off, and the attic space was too hot to enter, but a laser temperature sensor directed into the attic through an air mushroom vent read over 180 degrees - as high as the probe would read.

Answered 5 years ago by LCD

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What do you think of a contractor offering to foil wrap instead of those baffles. The wrap would go 5 feet hight from bottom. Also, under my knee wall soffits, I power washed them from a far and dirt was running right down. Do you think I should try to get to the attic soffits and do same??? I can see sunlight right down the baffle and soffitt

Answered 5 years ago by rmgov22

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Answered 5 years ago by rmgov22

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We've been on this case for awhile - I don't remember - did you figure out if you have roll-out mesh type ridge vents or rigid plastic vents with baffled openings - and which brand, if you know. And can you shoot a picture ofthe soffits from underneath - showing maybe 5 foot run or so of them.


Since you say you have clear daylight through soffits and baffles, I am thinking it could be the low-profile baffles - and no, I would not go with foil - that close to the eaves will tear for sure with wind gusting - it is not unusual to get 10-20 mph gusts through attics on window days. Or could be inadequate airlfow capacity through the mesh - I have seen attics running 70-90 degrees and not producing enough air through mesh vents to melt the snow off them ! Neighbors and other houses I have looked at with mesh vents commonly show ZERO melt-through on the snowpack over the vents over an entire winter - and this in an area where the primary puspose for the ridge vents is winter attic moisture control, not summer heat.


Assuming this is something you can do yourself, I would still try pulling one baffle and soffit (in 2 separate tests) and check the airflow difference (on calmish a sunny day) with your smoke pencil and see what the difference is.


And check out the existence of open gable vents, if any.


You should be able to easily see from below the joints in the ridge vent - the roll-out type are just rolled out over the ridge cutout and nailed down and looks like oversized plastic brillo pad, with shingles nailed over it usually. The rigid type comes in 3-5 foot sections typically, will have an open peaked center which may or may not be shingled over, and then flat baffles (dividers) off both sides that the air flows around in a maze pattern which is designed to keep blowing rain and snow from making it through the baffles. Looking and sticking fingers up there should tell quickly. Baffle type should be letting strong sunlight (though indirect) through on the sunny side of the house - mesh type commonly lets some stray tiny beams through but generally block out most of the light.


One question on the photo inside the attic - I hope that darkband running horiontally across the particle board (for most of the photo width) maybe 4-5 feet off the insulation is messy gluing from the plant, not mold from a leak wetting the sheathing ?

Answered 5 years ago by LCD




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