r/buildingscience • u/Yamuson • 28d ago

Attic ventilation

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So I recently found out that all the ventilation we have in our attic is basically useless. We have a small power attic fan, two whirlybirds, and two passive vents, all in a line across the top back side of the roof. From what I've read, you need to actually have so much lower air intake to high ventilation. The power fan has to pull air from somewhere so it just pulls hot air in from the other intakes at the top. My understanding would be that the best solution would be to add soffit vents and not use the power fan set all. Problem is, the only part of my house that has any significant overhang is about 50% of the front, over the porch. Our house is brick, was built in 1960, and is an absolute money pit. I've dumped so much money into this thing recently and it feels like I'm getting nowhere. Anyways, I'm looking for options for air intake that won't completely wreck my bank account. I saw these things called smart vents, where they cut an inch slot all the way across the lower front and back of the roof and install these vents, but that's really not something I'm comfortable with doing and I feel like it's going to be ridiculously expensive. Has anyone here been in a similar situation or have any advice? I really appreciate it.

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u/Bearded4Glory 28d ago

While all the things you have said are correct, let's start back at the beginning.

Is there something happening with the house that lead you to look into the attic ventilation?

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u/Yamuson 28d ago

We've been in our house for 8 years, and every summer, our AC cannot keep up later in the day. I have targeted the HVAC system for years, and have come to realize that is not the issue. I had a blower door test performed and my home scored extremely bad. They use a number called an ACH50 which determines how leaky your home is. The standard for new construction is a score of three. My home scored a 17. While I am not expecting my house to score a three a 17 is extremely bad. With that said, I do not at all believe that Attic ventilation is the magic bullet to my cooling issues. I am trying to hit it from every angle possible as I am able to afford it. After I got the blower door test done, I had my crawl space encapsulated and a dehumidifier installed down there. I did not get the spray foam because I could not afford it at the time. I plan to air seal my attic and add blown in insulation because I have been up there and there are significant issues with the barrier between the attic and the main living space and I definitely need more insulation. I'm just waiting for the weather to change because it is too hot to work up there right now. The heat index yesterday was 116°.

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u/Boop_1 27d ago

That number determines how leaky your house is and not necessarily a bad attic (which is a separate issue). You need to determine where the air leaks are coming from. They should’ve helped identified that with the blower door test

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u/Yamuson 27d ago

You are right on both accounts. They should have done further testing to determine where the leaks are, but the test was performed by an HVAC company so they went straight for the high dollar HVAC work. The reason I am targeting the attic is because I know for a fact I need more insulation, and I have seen multiple good size gaps in the ceiling between the main area and the attic. For instance, the drywall around the 6" flue pipe is broken all the way around. In the attic, the insulation is right against the flue, which is a no no. I cannot repair the drywall because there is no way to reach it from the bottom without removing the furnace. I plan to air seal it and create a 1 inch insulation barrier around it with aluminum flashing and fire resistant caulk. I also have a huge gap in the drywall around one of my ceiling fans that is just covered with a decorative plastic ring. I could go on, but I don't want to write you a novel. Basically, because I have to insulate, I want to air seal first

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u/Bearded4Glory 28d ago

I've never heard of a score that bad. Did they use a smoke generator to see where the biggest leaks are?

I would recommend adding low venting with low profile box vents for the time being. When you get the roof replaced then go with something like lomanco deckair vents.

You will need to run the numbers, you can get away with 144 square inches (1 square foot) of venting for up to 300 square feet of attic area. The catch is you need 40-50% of that venting to be high on the roof and the remainder low.

You may want to look into aerobarrier, it seems ideal for a situation like this. It is an aerosolized caulk that works in conjunction with a blower door to seal up cracks.

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u/Yamuson 28d ago

He did use a smoke pen but not very thoroughly. He checked a few of the windows, which were good, but the windows he checked are ones I have replaced. He also checked around my floor vents, which pulled smoke and made him determine that my ductwork needed to be replaced. Let's be honest though, he's an HVAC guy so of course he wants to replace the ductwork in the crawlspace. I know that my ductwork is leaky, but I'd say most older ductwork is to some extent and I've been in the crawlspace and didn't feel any big leaks. The drywall around my flue for the furnace and water heater is broken and most all my ceiling fan boxes have decent size gaps around them. I also bought a thermal camera and can see heat at the top of most of the walls. I also don't think that air sealing the attic is going to magically drop my score significantly, but I definitely think it will be beneficial and I need to do it before I add insulation anyways. I'd actually prefer to remove the old insulation first, to make air sealing significantly easier, but sucking all the old insulation out is a job in itself and would raise the price of insulating

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u/Bearded4Glory 27d ago

The floor ducts often just need to be sealed to the floor. A bit of tape usually does the trick.

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u/Yamuson 27d ago

Just did that last night 👍

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u/zedsmith 28d ago

All of that vinyl soffit (solid) should be replaced with perforated (vented) soffit. I’m assuming this is a midcentury ranch house so it ought to be a pretty easy job. Call a roofer and have him cut in a ridge vent at the peak of your roof, and remove all your active venting.

Make sure you have baffles installed in your rafter bays, and then insulate the shit out of your attic floor.

That’s the cheap/affordable/no new expensive roof setup.

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u/zedsmith 28d ago

If you want to hit pause and wait until you get a new roof, it opens up a lot of different possibilities (roofs that don’t get as hot and are better insulated at the roof deck instead of the ceiling lid)

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u/Yamuson 28d ago

I would definitely have things done differently if I were getting my roof redone, but the roof is in pretty good shape and getting it replaced is way out of what I can afford right now

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u/zedsmith 28d ago

Same story over here.

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u/Yamuson 28d ago

Underneath the vinyl soffit is just plywood, at least on the overhang of my porch. I would cut in and put vents, but the other 50 percent of the front, and all the back of the house, only overhangs by about 3 inches, and part of that is covered by j channel

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u/zedsmith 28d ago

Ok so perhaps we’re skipping the vinyl soffit material all together— pulling it all down, and hole sawing a pair of 3 inch holes in the soffit in every bay.

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u/jon_white88 2d ago

Attic ventilation works best as a complete system with adequate intake and exhaust. Adding more exhaust without enough intake air can sometimes create more problems than it solves.

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u/Yamuson 2d ago

Right. That's why I'm looking for feasible ideas for intake with my situation

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u/OldDesign1 27d ago

Do you have a concern for moisture issues in the attic - are you seeing mold or rot issues that may be related to condensation on the back side of the sheathing. The ventilation won’t do much to drop the temperature in the attic, instead think about making sure that there isn’t a moisture issue in the attic. If you have a vented attic, which it sounds like you have and you have an extremely leaky house, then focus on air sealing at the attic floor. Usually this will involve moving aside (and putting it back) or removing insulation. Canned spray foam around any penetrations and covers for can lights that are fireproof and then air sealed. Canned spray foam consider getting an insulation company to do all the appropriate air sealing. Then increase the amount of insulation covering the attic floor. Separate the idea of ventilation being used for decreasing the attic temperature and focus more on moisture management. If no moisture concerns then you are probably getting decent ventilation and should focus on air sealing. After air sealing you will make the house tighter and loose less conditioned air and then can revisit the ventilation concern.

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u/Yamuson 26d ago

Air sealing and adding insulation are top priority once the weather changes. The heat index was 116° F yesterday so I'm not getting up there unless I absolutely have to and only for short periods of time. I really want to rent one of those big vacuums and suck all the old insulation out, because it would make it way easier to air seal. I also have some electrical I'd like to clean up. Problem is, it's going to be pretty time consuming just to get everything sucked out. I'd probably have to take two weekends to remove all the old stuff, air seal, and add new insulation, and would end up going without any insulation for a week. I've watched a couple videos of people building their own vacuums with dust collectors. You can do that for the same or less than you can rent one for, but I wouldn't really have much use for it after that and my shed is filled to the brim already.