Comments on: Is Venting an Unconditioned Attic Necessary?

By: Jason

Jason — Wed, 02 Aug 2023 03:48:37 +0000

This post seems to focus on energy usage and means to keep your attic cool. One the main issues I see in my area is attic spaces that not vented properly, but still open to the outdoors, so hot humid outdoor air enter the attic with no where to go. Throw some leaky ductwork in the leak and now you have a slightly pressured attic space, with some cool surfaces near dew point – and a home that is slightly under negative (due to leaky supply ducts). This combination is almost always a mold fest.

I usually recommend functional outdoor air ventilation or enclosing and conditioning that attic space to control humidity. Almost all attic spaces I see that are unvented and without humidity control are moldy (usually on the backside of any adjacent interior ceiling or wall drywall).

Can you have an unvented attic without humidity control and an HVAC unit in it without moisture issues?

By: David Oblak

David Oblak — Mon, 24 Jul 2023 01:29:41 +0000

I have a two story colonial home with an unvented hip roof with dark shingles. I live in VA. My roofing company says I need a powered attic fan, a fix which you disagree with. My attic gets so hot it has melted the tar under my shingles, leaving black streaks on the shingles. So, it seems some type of venting would be helpful. What would you suggest, whirlybirds?

In regard to getting lighter shingles, I don’t know if that is good idea. My winter heating bills are four to five times my air conditioning bills. I believe the dark shingles absorb more warmth from the sun in the winter and thereby lower my heating costs, but obviously I pay a penalty in the summer.

Thank you.

By: Ally

Ally — Wed, 05 Jul 2023 20:01:13 +0000

Hi Dr. Bailes, I have a mystery for you. I have a remodeled 1927 1.5-storey house on a crawlspace in southern Oregon. The second floor has a small unfinished room containing the air handler for our heat pump, with a tiny space above the door to access the actual attic. The issue is that when the attic temp hits 98 degrees, there is a terrible “attic smell” that permeates the entire upstairs. It gets worse the hotter it gets, to the point that it is unlivable. On very hot days, it stinks downstairs too, but not as bad. We have flexible ducts in the attic but it still stinks if we don’t run the HVAC upstairs at all. We don’t know what’s causing it, but it smells kind of like tar and is not registered by air purifier particle sensors, so we think it may be roofing materials, which is concerning for our health. The roof deck is OSB so clearly not original to the house, but this is our second summer here and it’s no better. I’d expect typical off gassing to be over by now. We had 2 small gable vents originally and added static vents last year, which did not help. Asphalt shingles are in good shape, but quite dark in color. Do you have any idea what could be causing this smell or how to approach fixing it? Clearly the attic is poorly sealed, but would it be wise to seal it without identifying the smell? And is it even possible to properly seal an old attic like this, with the only access being through an unfinished room? We’ve had several HVAC and roofing pros out but no one has helped. Don’t even know who else to call at this point. We’re about at our wit’s end, so any help would be very, very appreciated!

By: Joseph

Joseph — Thu, 08 Jun 2023 01:31:36 +0000

In reply to Phil Bradon. Thanks Phil. I was planning on doing exactly that (with an attic ventilator fan, not squirrel cage) but this page seems to be saying powered ventilation is a no no. My gable vent is way too small for the 14 inch fan I have, so I will be closing the triangular gable and cutting an opening for a louver vent in front of the van. I was thinking of getting the shutters that close, but I probably want the vent open even when the fan isn't running for passive ventilation.

By: Phil Bradon

Phil Bradon — Tue, 06 Jun 2023 16:31:25 +0000

This is for Joseph in NJ. I escaped NJ for PA and rehabbed a house that probably killed its previous owner. I battled through mold, poor ventilation and radon (still working on that one). I loved the floor plan of the house which looks like split level but is actually two boxes pressed together, one having a basement and the other having a second floor (on slab). While working in the attic over the second floor, I experienced the skin melting temps you encountered. The house has a triangular gable vent on either side. I am a fan of squirrel-cage blower fans. I have many for different uses. I installed one in the attic next to one gable and use corrugated card board to point the narrow, focused exhaust out the close-by gable and cardboard to assure the air coming into fan is coming from the interior of the attic. The fan was a three speed thing I purchased from Amazon. Total cost was about $90. It pulled outdoor air from the vent across the attic and worked amazingly well. I put a temp switch in to turn ON the fan when temps got about 75 degrees . That was about 5 years ago. I forgot about it. Had to go up into the attic recently, was amazed how comfortable it was. The fan was running. The air being pulled in was actually refreshing. Someday, I might do something more permanent. I have since replaced the roof and had a ridge vent installed. The fan sill makes the big difference. I am working or opening up the soffit vents on this side of the house. I did on the other side (the one with the basement) which keeps the attic bearable in the summer and assures the mold is not coming back. Strangely, the previous owner, a contractor, installed cement board on all wall/ceiling surfaces when he purchased/built it. It has studs, 1/2 wall board covered by 1/2 cement board. This seals up the house amazingly well and probably saved the bones from collapsing under the problems he cause while living in it. I was curious as to why he did that and have arrived at the thought that he created a “heat store”. That is, once you warm up the walls in the winter, they stay evenly warm. I installed under floor hydronic heating and the effect is wonderful. My house is a constant 70 degrees all winter. It is also cooler inside than outside all summer. Try the cheap fan on a temp sensor to fix your attic problem.

By: Genry Garcia

Genry Garcia — Sun, 28 May 2023 20:00:11 +0000

In reply to Cat.

Pages 4 & 5. But the whole thing is a good read.
https://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

By: Joseph

Joseph — Sun, 28 May 2023 19:02:18 +0000

This is great if you have well-sealed ceilings in a modern home. My NJ split-level home was built in 1954. The sad 2×6 ceiling joists have the thickest insulation they can take. The outside walls are 2×4. There is no “air sealing” above the ceiling sheetrock. However, my problem is not a hot second floor. My problem is the attic itself. My attic’s only real ventilation (perhaps there are soffit vents as well) are 2 gable vents at 90 degrees to each other. In the summer, going into the attic is unbearable for more than a minute or two. Other than a powered ventilator, what is going to cool down the attic to make it suitable for humans? Why the concern that air will be pulled from the lower floors if there is outside air available from the other gable vent? And if pulling humid air through a bathroom vent is a problem, wouldn’t bathroom vent fans cause the same issue?

By: Sam Myers

Sam Myers — Sun, 28 May 2023 16:26:39 +0000

In reply to Cat. The reason why attic fans aren’t such a great idea is due to the fact that they can depressurize the house through leakage in the ceiling. As a result, this can bring on new issues that increase humidity inside the home, degrade comfort, and increase energy consumption. An airtight ceiling plane and adequate soffit and ridge ventilation is what will keep the attic space happy and healthy without negatively impacting the rest of the house. This is basic building science stuff. I don’t think Allison really needs to show data here. It’s simply an explanation of the physics involved.

By: Cat

Cat — Wed, 24 May 2023 17:27:49 +0000

So where’s your data? Everything you linked to, save 2 links, were to your own website. The two that weren’t, one was to the international building code, and the other didn’t show any hard data at all. Science requires data, and the plural of anecdote isn’t data.

P.S: a low wattage attic fan can be installed in a few minutes by anyone who can reach a gable vent and operate a screwdriver, and costs a few hundred dollars at most. A new roof is tens of thousands of dollars and may have been good for decades to come. How. Is it more cost effective to retrofit a roof versus install a thermostatic fan drawing 20 watts only when it’s above 90° up there?

By: Avery Ray Colter

Avery Ray Colter — Tue, 23 May 2023 21:30:48 +0000

In a previous home (which by today’s parlance would almost have been a tiny home, with 550 SF or so of CFA), I had set up a PV-powered gable vent attic ventilator. Was a cheap little thing, and not sure it did much other than maybe cool it down up there slightly faster in evenings. Then again, for a long time we had no hardwired AC there, and I was just as often using the “poor man’s economizer” in the evening, a box fan up against the laundry room window! The things one does with the DIY bug I tell ya!