Can I use foam board insulation in attic?
 

The previous owner, for whatever reason, did not finish insulating the attic. As you can see, they used foil back insulation. I want to go ahead and finish up insulating the attic. I hate installing fiberglass insulation! Is there any reason why I could not use foam board insulation? Or is it too much of a fire hazard?
http://forums.pelicanparts.com/uploa...1635175046.jpg

Foam board is fine, it's just a lot more expensive, I think.

Several years ago, I was able to get Johns Manville "encapsulated" insulation at Lowes. It's fiberglass, but has a thin plastic barrier all of the way around (except the ends). It was much, MUCH better to work with. I insulated our old attic with it and never had any of the usual fiberglass problems.

I'm not sure if you'll find it now or not due to the supply chain issues that the entire world seems to be having. (I wonder if China has a surplus of a bunch of crap or if they're having issues too).

Are you insulating the ceiling, the floor or the gable of the attic?

You can use foam in the ceiling but be sure to leave a gap for ventilation between the foam and roof decking. I don’t know about the fire hazard with foam.

As much a fire hazard as exposed wood methinks. And many foams even less of a fire hazard.

Like Steve I purchased fully encapsulated fiberglass bats. But setting only above the ceiling. (more efficient - less area needing covering = less insulation)

of course if you get more space with the roof insulated.

You could but it would be extremely expensive to get proper R value.

http://forums.pelicanparts.com/uploa...1635176573.jpg

I found this online. "Thermax foamboard, a Dow product, has the fire rating to be left exposed without a fire-rated sheathing."

If I were trying to make that space usable I would use foam panels (leaving a venting gap with the roof underside) ) with sheetrock for extra protection.

If I am looking at the picture correct that is the area under the roof shingles? Really the area you want to insulate would be the lower section that you are standing on, unless you are finishing that area and turning into living space? Out here uncovered foam is allowed as long as it is not exposed to finished living space, can always call your building department and verify.

I'd just get it blown in. Easy peasy.

I hate that crap. And if they aren't careful, they'll cover stuff they shouldn't, like the soffit vents.

When I had mine done they sent an insulation monkey into the corners to place baffles.

If the baffles don't extend to the floor and seal, spray or cellulose insulation will get past and block them up hidden inside.
(That is a crucial step and often over-looked.)

Rot:
If the floor of the attic is insulated don't bother with the underside of the sheathing.
In fact that might be very counter-productive!

Unless the attic space is completely sealed...and there are both supply and return furnace vents to it..........that space is considered "unconditioned" and open to atmosphere.
The conditioned envelope is the living space.

Summer sun on the roof heats up the attic space underneath. It probably has a ridge vent or gable ends to exhaust the trapped hot air with soffit intakes under the eaves to bring in fresh cooler air. This flow removes attic moisture which would collect and pool to damage/mold/freeze/etc. Anywhere there are hot-cold surfaces next to each other, vapor wants to collect from "dew point". That's why there are carburetor heaters to keep them from freezing up.

If that space was completely sealed tight it would literally expand like a balloon. Even steel tanker trucks have crumpled up like aluminum cans when drivers forget to open the vent.

Adding insulation will make the attic even hotter and all the wood flex more. Some of that would radiate inside and increase A/C costs.

(edit: Nevermind. Just saw the next post. That is totally do-able. You do need vents to move air, and low collar-ties/exposed beams to hold the walls together..)

I would call it “semi usable” space. This is an an older home that has regular stairs up to the attic. I could tell that someone in the past has used it for a hobby area as it is well lightrd and has plenty of outlets. Right now, we just use it for storage. Total area up there that you can stand up in is probably 900 square feet. All of the areas I need to cover are easily reachable either by standing or with a ladder. Here is a better picture of part of the attic. It has several leaded glass windows that tilt inward for ventilation in the summer.

http://forums.pelicanparts.com/uploa...1635183013.jpg

Wow!

That looks totally useable to me (except for lack of insulation).

Lots of space up there, Check what John70t said above. Need to be careful to not get a leak and have moisture trapped above the insulation and rot the roof. Do a search on non vented roof assembly.

Thanks everyone! I guess I need to go to the big box stores and see what insulation they actually have in stock!

Yep, that's going to be huge. Around here, I've only ever seen 1" thick foam, which is not adequate. I think 4x8x1" is $20/sheet.

I understand that "they" make thicker sheets, but I've never seen it.

Blown in rockwool or FG......R-19 or better.

Everything about rockwool/mineralwool looks great:
It doesn't burn, mold resistant, mice hate it, good R-value, etc

My only concern is that it would become the next asbestos..cough composite material cough..as if there are no other health hazards out there.
Only the pipe wrap was a true killer afaik.
But the dense shingles were also nasty when hammered to put in trash bags and hide from government agencies.

I once read a blip about a foam product called "Spraycrete" which was similar but haven't seen much since.

A spray insulation product that is dummy-proof to use, fireproof, no nasty chemicals off-gassing, or dust when removed, sticks to application, doesn't shrink or lose values.. would be the next sliced bread.