Happy game day!!! BTHO Mo State!

I have a question regarding attic insulation that I am hoping someone can provide info on as I have heard conflicting answers.
I have a home that we built in 2004 that has fiberglass insulation on the ceiling joists, mostly blown in, with batting later added to the garage. The house has under soffit vents, a ridge vent and one solar roof exhast fan.
I was curious about adding foam to the rafters, either blow-in or the 4x8 panels.
Any issues with this? I have heard about venting issues, but nothing definitive.

THANKS!

The correct way to retrofit spray foam in an attic is to remove the existing joist insulation and then foam the back of the attic decking.

If there are any gas appliance/furnance in the attic you will have to add make up air from the outside for them to burn properly. Also sometimes the ac system may become oversized once foamed leading to possible humidity issues which can then require fresh air to the hvac as well as a possible dehumidifier as well as dryer and vent hood pressure issues

Thanks for responding! We have no gas heater, and what you are telling me is what I have heard some folks say as well, however, no mention of the A/C unit becoming oversized. I have a neighbor who left the fiberglass on the ceiling joists and had foam blown in on the roof decking later is why I am asking.

why are you wanting to foam the attic ?

ac cant keep up now ?

Just curious. Our house is fine but the garage gets toasty. Mainly I was curious because my neighbor added foam and didn't remove the fiberglass.

It would certainly be cheaper! Thanks for the feedback!

Thanks for the information!!!!

AgDadx2 said:

---

Just curious. Our house is fine but the garage gets toasty. Mainly I was curious because my neighbor added foam and didn't remove the fiberglass.

---

west facing metal garage door ?


does the door have windows ?


is there insulation above the garage now ?

Agree with all that's been said above and best return + EZ for you.
Shade on the West side will be your best friend as well.

As to curiosity
Designed one of these for big new custom house in South Aggieland acerage subdivision.
Phase I (as built)
Attic soffit, rigde & gable vented
Rockwool on open floor joists below (insulation now and sound proofing later)
Foam on roof deck, metal roof

Results were of course better than foam roof, no attic floor insulation

Phase II Future (if ever)
Begin to develop attic into interior spaces
Deck the floor
Finish foaming/sealing the rest

The only other thing (more insulation, ventilation, shading)
would be to nail foil faced insulation sheating to roof joist, allowing ventilation to continue = overkill.

Weird but works for some
Some have taken surplus foil faced insulation sheets and tossed them top of ceiling insulation to report some emissivity ala radiant barrier sheets and of course some min. R-3.8 values ... even reduced "blow" displacement if blown in insulation up there.

Rockwool is your friend, Google why.

No
No
Yes

Lot of information! Thanks to everyone for your replies. I have known several people who added foam to older homes and after reading all of the replies it sounds as if there are risks involved. My question has been pretty much answered.

Does your attic have a radiant barrier?

No

You should investigate adding radiant barrier under the rafters and also maybe the back of the garage door if it gets direct sun. Spray foam retrofit would not be on my radar at all.

Sounds like good advice! I will investigate that option. Thanks!!