Spray foam vs other insulation

so this is existing house?

if so dont, dont go spray foam unless you are wanting change your roof. I.e. change it from vented to non vented. ALso will need to change AC if you are wanting to really do it right.

as far as roof leaks, you should be using open cell on the roof anyways which allows you to see a leak pretty easily.

spray foam seals your house off, roof is completely covered in foam.

WIth traditional insulation you either have a ridge vent or whirl birds to allow the air to circulate outside. Plus traditionally the vents from the bathroom just empty into the attic.

with spray foam, all the vents have to be run out past when the foam ties in to keep the gases from building up since the roof and walls are now sealed.

also the whirly birds and ridge vent now need to be changed because they are not needed. You have to pull them off, fix wood underneath to no longer have opening and put back on shingles.

as far as AC goes

1) because of the air tight seal, your Current AC will more than likely be oversized. typical spray foam insulated homes get about 0.10 to 0.20 Air Changes per Hour or about a 5-10 hour exchange of air. This leads to a big reduction in heating and cooling loads. This can also be a big issue if you have naturally aspirating appliances from the fiberglass desing of the house.

2) humidty can build up in the spray foam without proper AC design. really need standalone dehumidifier installed and variable speed blower

3) duct work should be open air return as you want the air in the attic cirulating also

4) really need 2 stage units. Lots of differing opinions on what is best but imo
For comfort and humidity control, a variable capacity(25%-100%) heat pump system with whole house ventilating dehumidifier is the best choice

second best is 2 stage heat pump system(70%/100%) with ventilating dehumidifier

3rd and most basic system: single stage heat pump with variable speed indoor fan with ventilating dehumidifier.

this is strictly based off expierence with my houses i have lived in with spray foam and a couple friends that have it, along with talking to couple AC guys. I am not an HVAC guy.


now OP may be just wanting to do spray foam on the ceiling and not the roof which is different and I BELIEVE that in that case its simlar to regular fiberglass insulation.

I also have heard of a retrofit where they left fiberglass on the ceiling, sprayed the foam on the roof deck but cut out the whirly birds and allowed the house to vent and used the spray foam as strictly a reflective barrier. IMO OP would be better off adding insulation and adding a radiant barrier.

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We moved into an older home and I was in the same situation. I decided to go with spray foam on the roof deck. We have/had ridge vents but those were sprayed with foam also. I put a thermometer that also detects humidity in the attic. The temperature and humidity are extremely low after the install. One day the attic hit 109. Most of the summer it was from 102 to 106. Average humidity is anywhere from 55% to 63%.

We used open cell foam. My a/c guy has been here after the foam was done and he said he thinks we're fine. We don't use our bathroom vents since they are not vented outside.

I'm not saying I made the correct choice but that's what we did. Hoping there are no issues in the long run.

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i have heard of people doing that. did you seal the attic completely on the sides?

so you just covered the ridge vent with foam?

They encapsulated the entire attic actually.

Dam, good info. Thanks

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They encapsulated the entire attic actually.

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10 bucks says you are replacing your coil within 5 years due to leak.

just from the issues i have seen and heard of in the past.

mainly from buildup of humidity in the attic due to not being open returns.

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Can that be resolved by pulling some "fresh" air from the attic?

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i have no clue. I know in my old house, spray foam was a new thing and i didnt have open air returns. At first....everything was great for about 7 years. then started having issue and having to add freon. Then after second time they started checking for leaks, found one on the coil, eventually opted to change whole air handler because it came with new warranty. Original idiot that did my original install had went out of business and had never registered the unit to get the OG warranty.

You may have no problems, but i would monitor the humidty in the attic big time.

The original a/c is still running from 2002. My plan was to have a new Trane heat pump installed this winter. I don't want to wait until the unit goes out and then deal with one possibly not being in stock or be put on a waiting list during the heat of summer.

The company I'm going to use also does spray foam so I'll ask for their input on the foam and if I need to do anything.

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Original idiot that did my original install had went out of business and had never registered the unit to get the OG warranty.

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Same here. The goofs used a 2014 coil in a home built in 2016, I guess they just bought a crap load of York coils and had em sitting around. Got freon added yesterday...hopefully getting coil quote today to decide. Will probably replace both in early spring to avoid bullcrap problems this summer. Also adding the dehumidifier in attic to try to do it all perfect.