Attic insulation guidance after spray foam disaster
Hello. I am specifically writing to get help with how to insulate my attic post spray foam removal. I am in climate zone 4. I recently had to undergo spray foam removal of my roof deck after dealing with foam that would not stop gassing (removal and dry ice works- VOCS in home went down 82.5%). I now have to figure out how to insulate my attic back and I’m not keen on using foam ever again. I currently have a very large attic area. On the attic floor is some batt insulation that was installed for sound purposes only. I have plenty of HVAC and duct work in attic along with ERVS and a dedicated attic dehumidifier.
1) If I install the insulation on attic floor and air seal, my HVAC and ductwork will be “outside”. I can build an insulated closet around the air handlers (and remove insulation below) but have not seen any reports of the being done successfully. Is this an option? or if tightly air seal my ducts and equipment how “bad” is it to have this equipment exposed to the elements? At this point energy efficiency is not important to me but air quality and mold control is.
2) My roof life in filled with hips and valleys so not sure If sheet rocking and venting behind sheathing is plausible. I can make the inside airtight using smart air vapor barrier and sheetrock with no penetrations but there will be areas without a clear path from soffit to ridge .
3)external insulation is not an option at this point
Am I missing anything? If I do spray foam again does it make sense to do this with air baffles under for circulation even with no soffit and ridge vents?
Thank you for the help
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It sounds like you are bringing the attic into the conditioned envelope of the house. In that case, you need to treat it like the rest of the interior. What type of wall assembly do you have? Can you use the same insulation and air-sealing strategy?
You'll also need air supply/return and some of that dehumidification in the attic itself.
Here's a video that discusses this topic, featuring Dr. Joe Lstiburek, with a few links in the description. https://www.youtube.com/watch?v=zhkGcklWB_Q
Those guys are more experienced than me, for sure, but I will leave you with my own remarks: remember that drywall is a finish material. It's there mainly for looks. If you're not living in the attic, you can skip that. It has very little insulating effect, and shouldn't be used as an air barrier (because, for a start, because every outlet and light switch is a hole). While it can add thermal mass, the main reason why any buildings use it is simply as a surface to be painted. So don't get too bend out of shape about your inability to make neat-looking drywall in your attic mechanical space.
Good luck! You got this.
Hi, the attic is already in conditioned space. But we removed the spray foam insulation so now it's just uninsulated and not vented. I am trying to figure out how to insulate without the spray foam if possible and keep it unvented. But if I need to vent it how to keep mechanicals ok..... thanks for the help and encouragement
Do you have a bit of headroom to work with? If so, I would try to stick with an insulated roof and keep the attic conditioned.
I would consider a gusseted rafter system--hang 2x4s from 1x4s attached to the sides of the rafters to create whatever depth space you need for R-value. In most cases it's ok to drill holes in the middle third of beams and headers, so do that to provide continuous ventilation. Make your own insulation baffles by attaching nailers (1x2 or similar) to the sides of each rafter, with the interior edge below the drilled holes, and attach 1/4" or thicker plywood rips to the nailers to create a baffle.
If it's hard to visualize, I have a basic drawing here: https://www.greenbuildingadvisor.com/article/design-for-low-carbon-building and attached.
At the interior, have an insulator install insulweb and dense-pack the cavities with cellulose or wood fiber insulation. Or use wood-fiber batts. Or even fiberglass batts or blown-in. Mineral wool batts would also work well, but they have higher levels of embodied carbon emissions. Then install a variable permeance membrane to limit air and vapor movement into the cavities, then install drywall. If you have no or few ceiling penetrations you could probably skip the variable permeance membrane but assuming you can't get perfect venting I think the added insurance would be worthwhile.
If possible, provide 1/300 of the floor area in ventilation, half of it at the soffits and half within 3' of the ridge. If that's not possible, add what ridge venting you can and provide 1/150 of the floor area in ventilation at the soffits.
Thank you so much. To be clear am I installing soffit and ridge vents with this even thought there are areas with soffit venting etc? Love the idea of wood fiber insulation...
The way the code reads, which started out as a placeholder but has turned out to work pretty well in practice, is that if the soffit venting and ridge venting--within 3' of the highest point on the roof--are nearly balanced in net free area, you only need a total of 1/300 of the floor area in net free vent area.
If you can't get that 50/50 split, then you need a total net free vent area of 1/150 the floor area.
It sounds like the latter will probably be your situation so add up all of your current vent area and your proposed ridge vent area, see how close it is to 1/150 of the floor area, and keep adding soffit vents until you reach 1/150 (or greater).
Martin explains it more thoroughly here: https://www.greenbuildingadvisor.com/article/all-about-roof-venting. Also check out the "related articles" with that article if you want to learn more.
If you're not sure how to do the math, post your dimensions here and I or someone else will help you.
TimberHP is now producing both blown and batt insulation, with rigid board insulation coming soon. I'm not sure how widespread their distribution is but if they haven't reached your area yet, they will eventually: https://www.timberhp.com/where-to-buy.
The way I see it the conditioned attic is only marginally 5-10% better than the bad idea of HVAC in a vented attic.
Once you move the insulation to the roof line you have created a cathedral ceiling.
This article has 5 options that are known to work.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
No spray foam knocks out 2 of them.
If you are unwilling to reroof that kills another.
The others reduce the head room and one uses sheet foam.
Seems to me the smart move is to get the HVAC out of the attic but that is always a non-starter.
Consider burying the ducts.
https://www.energyvanguard.com/blog/buried-ducts-allowed-2018-building-code/
PS Was there a law suit and are you allowed to talk about it?
Walta
Thank you for the suggestions. I will happily talk about it. No one is willing to take the blame so unfortunately we had to pay all costs associated with it which frees me to discuss it all. I will do another post detailing it including testing etc because I think its important to share the real risks associated with this product.