Easiest way to Airseal an attic space

Question

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

Answer 1

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.

Answer 2

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.