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House got gutted by a fire and now all of it has been demo'd down to the framing and the exterior sheathing. Location is Albuquerque.

We are looking at the easiest way to air seal the attic space. Attic is typical height truss space. I think about 6feet. Roof sheeting is a mix of plywood and 2x8s. 2/3 of the roof is truss and the middle 1/3 is beam construction. It doesnt have to be perfect just sealed well. Obviously we would have to install a ridge vent which is not beyond my capabilities i think. Also we are going to blow in fiberglass in the ceiling space up to code plus a couple rs.

We priced spray foam and that is waaaaay out of our price range. Quotes were 18k$ for just the roof and 32k$ for the whole house. Even flash and bat wasnt much cheaper.

We looked at sealing from the ceiling side but we have a lot of can lights, skylights, etc and that looks like an intensive proposition. 32 can lights would require 32 insulated boxes plus trimming plus foam seal. Plus the penetrations from skylights, fart fan vents, sewer gas vents, etc.

The other option is to run some sort of insulation or air barrier along the inner edge of the beams/trusses and sealing. We could staple then tape some plastic sheeting/ radiant barrier and that would provide an air barrier. Also cheap.

Also looked at insulation board and it is a bit expensive for what i was looking for and would require a lot of shaping to get around the framing

I found Prodex and looks to be a good compromise. Price is pretty reasonable. Easy to work with as far as shaping it goes. Radiant barrier and a better R value than plastic. Also one variety has an edge seal that can be done with a heat gun. I am leaning towards Prodex

It seems to me that it would be less effort and cheaper to run a continuous barrier against the rafters and trusses than sprayfoiming and boxing penetrations.

Also no ducts. Only minisplits. And we are only going to be in the house about 5 more years

Did I miss anything? Is there an easier way to air seal an attic space that i am missing?

Thanks

Ya Guy Godzilla
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  • Consider blown-in cellulose rather than fiberglass for the insulation - considerably less air movement in the insulation, also usually cheaper (may vary by locale) and definitely less scratchy. – Ecnerwal Nov 28 '22 at 17:33
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    "Easiest" is a matter of opinion. Pricing is off topic. Are you looking to air seal, insulate, or both? Your question bod and your title don't quite line up. The only question you've asked is "did I miss anything", and I'm not sure that question is on-topic here. Please take the [tour] and look at the [help] on asking questions, then [edit] to better focus your question to a good, on-topic, single question. As it stands, this is broad and vague and doesn't really ask something we can answer here. – FreeMan Nov 28 '22 at 18:16
  • Easiest way to Airseal an attic space.....i mean i dunno what to tell ya. Title pretty much states everything. But just to help people out i added. Is there an easier way to air seal an attic space that i am missing? – Ya Guy Godzilla Nov 28 '22 at 19:14
  • In many cases, unless the attic is finished, you do not want to air-seal it; you want airflow to reduce risk of roof rot. You *should* airseal between the attic and the rest of the house, and of course make sure your insulation is adequate. Note that in many areas the utilities offer services which will evaluate your place and give you a prioritized list of improvements, with the utility picking up a lot of the cost; investigate that before starting to do it yourself. – keshlam Nov 28 '22 at 19:41

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I agree with Ecnerwal on the cellulose for a one-stop-shop. The only better option would be blown-in Mineral Wool, fiberglass is typically only good for 30-years until it crushes down to worthless.

You would then want to top your blown-in with glued together (silicone caulk) Styrofoam (foil-faced if available, faced up) to ensure a dead-air situation (the only way ANY fluffy stuff works) and to provide a great convection barrier.

Iggy
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  • I will reconsider the cellulose. I did not know about the airmovement qualities it had. I am pretty sure the cost difference between it and the cotton candy fiberglass locally is negligible. Im only really concerned with vertical air movement as the walls (excepting penetrations) is air tight due to weird construction. Sheathing is plywood then has some weird 1.5 inch concrete board then concrete stucco and then a very thick coat of acrylic stucco. With the cellulose is the air movement lessend enough i can eschew can light covers? Thanks! – Ya Guy Godzilla Nov 28 '22 at 19:26
  • If the lights are rated IC (insulation contact), and they should be, then you're all set. If not, then you may have to provide clearance or get new fixtures. But yep, Cellulose does very well at air-sealing. It's usually sprayed into place as damp that makes it an insulating crust. You can even add to it in stages if affordability is questionable. – Iggy Nov 28 '22 at 19:43
  • Excellent. Follow up question making dead air for the fluffy stuff. The trusses are about 4in. I'll be laying down a lot more than 4in of cellulose. So I won't be able to rest any foam boards on the truss. Would i need to build up the trusses or in some way provide something for the foam to lay on? Follow up question, if yes would a sealed/taped layer of plastic or radiant barrier layed over the cellulose work to provide "dead air" thanks! – Ya Guy Godzilla Nov 28 '22 at 20:55
  • Oh sorry, no. The Cellulose would be done just by itself, it's very self-sealing and can be layered to whatever depth. But, you could definitely do a foam-board right on top of it, since it's very structural, but that was just seal the fluffy stuff from the top. A radiant barrier is fine and should stay shiny for your stay, but will need future cleaning to keep operating as intended. – Iggy Nov 28 '22 at 21:17
  • Thanks! I understand. Foam is to keep the fluff in place. I'll probably end up using some extra thick cellulose plus foam sealing as the primary air barrier and then maybe put up the radiant barrier attached to the trusses. Heat IS our main issue I really wish i had the money/time to take off the metal roof rebuild the attic as a conditioned space with the insulation on the outside of the of the rafters. Thanks again – Ya Guy Godzilla Nov 28 '22 at 21:47
  • Best of luck, you'll be in immensely better shape than before. – Iggy Nov 28 '22 at 21:57
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Your goal is to keep the heat out of your house.

Your attic is going to be hot and your conditioned house is cool - correct?

In that case you can have a vapor barrier on top of the insulation in your ceiling joists/rafters. The cheapest thing is just 6mil poly on top of your insulation with tuck taping the joins. The interface between - I assume you have soffit vents - the vapor barrier and the soffits is likely the trickiest. You can install foam baffles to leave the soffit open to the attic.

After you've done the poly you could also do aerobarrier - a latex spray system that seals up holes in your air barrier. It might end up being too pricey though.

Fresh Codemonger
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    Ill definitely be doing a polybarrier over cellulose. Its so cheap why not. the Aerobarrier system is something i actually got a quote for at 5500 for the house. it is THE BEST way to seal house and possibly cheaper than conventional depending on the situation. Unfortunately i couldn't justify the cost between only staying here for 5 more years and the rest of the building being not advanced enough imo to be worth it. I'll definitely use it when I build my next house if I cant convince my wife to build a monolithic dome home. – Ya Guy Godzilla Nov 29 '22 at 14:37