Closed Cell Foam Insulation

I looked into it. Its very expensive (7K for my house). But obviously would save more in the long term. I had someone else tell me you then need to pay for some kind of air filtration because the house is so tight, you can get bacteria/mold/etc build up because the same air is recirculated throughout the house. Not sure how true that is but it makes sense.

Any HVAC installer should know to add fresh air to the system. In fact, when building my house, my installer asked me if I will use sprayed foam insulation In the walls so he would know to add fresh air.

One important note....the foam can push wiring and plumbing past the studs as it expands. The insulator will use a device to mill the excess foam so as to be flush with the studs. The milling device can get into the wiring and plumbing if pushed beyond the studs. So be sure this doesn’t happen.

You also need combustion air for gas appliances in the attic.

It’s very expensive to foam the rafters, in addition to the problems it may create.

I looked into it for my home. It would have taken over 20 years to break even on straight return, not accounting for time value/interest/etc. I ended doing open cell in my walls and blown fiberglass to R-38 in the attic. It seems to work very well and my utility bills are pretty low for the size of my home.

You might spend some time researching sealed attics and moisture issues.

I think it also impacts roof warranties. The envelope of a house is a system of many parts. Walls, vapor barriers, insulation, roofing, venting, etc. all have to be designed to work together. You can't always just change one piece and be OK.

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TheBoo

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What are you attempting to accomplish or problem you wish to solve?

Your HVAC having trouble keeping up or maintaining a set temperature in your in your home? Lots of people are having this issue in this heat wave of high temperature coupled with high humidity, and it’s to be expected.

Do you currently have some type of attic ventilation -passive ventilation like ridge vents, or active ventilation like “whirlybird” roof vents or some types power ventilator? If so, are they sized properly?

What type (blown, batt) and how of insulation do you currently have in your attic? < R-30, > R-30?

I also briefly looked into attic foam insulation a couple years ago and quickly nixed that idea for all the reasons mentioned by others in this thread. Now my focus is on sealing potential larger attic leaks/heat infiltration into the conditioned living area and increasing attic insulation above R-30. I’m considering radiant barrier installation which can potentially lower attic temps 15-25 degrees F but made no decisions on that yet. Radiant barriers also seem to have a long payback or break even point relative to cost (assuming it is not DYI), but if it improves home comfort significantly then that’s a priority to me over cost - within reason.

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Why do you want to install insulation on the roof rafters?

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I'm asking if that's an option...

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What are you trying to accomplish?

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Lower the temperature in my attic in the summer. My outdoor AC unit is in direct sunlight throughout the hottest part of the day, and my attic gets extremely hot. My AC doesn't get behind but it works hard to do its job. I currently have blown open cell insulation and ridge vents and soffit vents, no whirly birds. Looking for options to lower the overall temperature in my attic during the summer to help my AC work more efficiently.
I understand heat is to be expected in the summer... I'm looking to mitigate it a bit if possible.

Last month I was doing a little organizing in the attic and brought an outdoor fan up there and kicked it on by the attic access, and the decrease in temperature was very noticeable after about a half hour. I left it on for most of the day and noticed the AC didn't have to work as hard to maintain temps in the house also. However I was told by a buddy that prolonged forced air ventilation in our climate can cause moisture issues.

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fan was near the attic stairs it was probably pulling cooler, conditioned air from the house below

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My only attic access is in my storage shed on the back side of my car porch. Had the roll up door open on that and it was pulling outside air in, on a hot day, which is what made me consider installing soffit vent fans or something. I just don't have a lot of knowledge of the results (or consequences) of applying positive pressure to an attic.

I'll look into radiant barriers.

A couple things to look at, the soffit vents typically have a bug screen on them. They can get dirty and restrict the airflow coming in to the attic. You can take them down and clean them or just buy some new ones they aren’t that expensive and it’s definitely less work to just replace than to clean. That’s if you have traditional soffit vents not vinyl or the continuous vents. If you have those you can use a blower or lightly wash them.

Ridge vents depending on the design/manufacturer can also get restricted, a little harder to fix.

Based on my research prior to building my house on insulation, you’re better off insuring that any penetrations between your conditioned space and attic are sealed as well as you can and making sure you have adequate loose fill insulation, that way you’re not pulling hot dirty humid air from your hotter attic, than less hot leaking windows/doors.