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We moved into this house late last year. It is a 1992 cape style brick house.

In short, our upstairs is miserable sitting in the mid 80s with the upstairs unit running from 11am-10pm.

After doing some poking around in the attic I noticed there were plenty of issues up there including areas missing 6”-12” of insulation against the ceiling, recessed can lights, and an A/C duct that had come off of the vent, blowing cold air into the attic and making a port straight from the ceiling to the attic. I also noticed the old yellow insulation has been compressed down in areas and it’s about only 3-4” thick.

We also have knee walls on the second floor, with very little insulation to the point where if you opened one of the little closets you could see the ceiling/soffit of the front porch.

So far I have done the following and we have seen some improvements:

  • Fixed the A/C duct
  • Used spray foam to seal air gaps at the wall plates as well as wire holes and junction boxes for ceiling fans, and any other gaps.
  • Added loose fill insulation to the gaps notably left near wall plates at the end of the bay. Also added some loose fill to the compressed down areas to bring it back up to level with the 2x6.
  • I placed some R30 unfaced above one of the bedrooms after I air sealed and added loose fill. I plan on adding this to the rest of the attic as a last step.
  • Added a 1400cfm attic fan on one of the gable ends to help exhaust some of the hot air.
  • Started sealing up the knee wall closets, stapled faced r13 and used foam board and spray foam to seal it best I can.

Concerns I have:

It doesn’t appear that there are any baffles between the insulation and the roof. If they are there they have been crushed. Is there a solution to retrofit to allow some air to move from the soffits to the attic? We have a vented roofline.

The attic fan I installed doesn’t seem to be doing a lot. The gable end is wide open and much larger than the fan, should I seal it off using plywood with the exception of the 15in hole for the fan? I figured it would be better to leave some airflow open but it may not be powerful enough to direct the air out like I hoped. It’s sitting about 6 inches from the gable screen.

Edit: thank you for the answer below, I’m unable to comment under it because I need 50 rep, sorry.

The A/C is on auto. I will try switching it to ON. The thing runs 20 hours a day anyway lol.

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  • It helps a lot to stop the sun from coming though the windows, awnings, window film alone can help with temperatures inside.
    – crip659
    Jul 4, 2023 at 20:03
  • I have considered tinting the back window. It experiences a good amount of sunlight, but we do have drapes in front of it.
    – Ncfire11
    Jul 4, 2023 at 20:45
  • gave you some points so you can use this side properly
    – Traveler
    Jul 4, 2023 at 21:21
  • Is this a typical gas forced-air system with A/C using the same forced-air system? Does the thermostat have a "FAN" switch and is it in "auto" or "on"? In the winter does it heat evenly, or is it way too hot in that room? Jul 4, 2023 at 21:29
  • Do you have eave vents (soffits)?
    – Huesmann
    Jul 5, 2023 at 13:01

1 Answer 1

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The root cause of these troubles is solar gain and the building's thermal mass relative to the insulation.

People think of heating need in relation to outdoor temperature; fair enough. However, they tend to think of air conditioning need in the same way, and it's not that way at all. Because that barely matters; the source of all that heat is solar gain. The sun makes light, and also heat. 1 square meter of sunlight is 1000 watts. 1 square foot of sunlight is 300 BTU/hr.

It would be nice if building surfaces reflected that, but they don't. Reflectivity, called albedo, is 80% on the best ultra-white paints - much worse - around 50% on fashionable house colors, and below 10% for fashionable roofs. So it's all being absorbed. The building's structure has mass, and heats up, and stores that heat. Potentially a lot! It then radiates that heat for hours after the sun sets. So there's not 80 degree air on the other side of that insulation; there's 120-150 degree building structure, roof or attic.

Of course, in heating system everything is exactly reversed - solar gain is a blessing that reduces heat needs on the sunny side of the house. So it needs less heating duct by winter and more heating duct by summer. However, there's a secret weapon to even this out: the "FAN" switch. By setting it to "ON" and circulating air continuously, you are using the thermal mass of the building inside the insulation as an air-conditioning source. You're stealing A/C from the other rooms, but that's fine because one of those rooms contains the thermostat. That will kick the A/C back on sooner, and is certainly worth a try.


The A/C ducting system, including all return ducts, must be tip-top. Broken things in this area will burden the system. I'm glad you're fixing them. In particular, you don't want the system ejecting "used" air to outside and sucking in warm, wet air to replace it.

On cooling the attic with fans, you have the right idea but fans aren't magic. You need to create a clear and direct ventilation route that forces cross-flow. Stirring the air inside the attic does nothing, and a fan ducted so air can exit right next to the fan does not work either - it will ingest its own exhaust. Be careful to balance wildfire risks with attic ventilation - many houses in western wildfires burn because the wind pushed burning embers into the attic, where it found fuel.

And there's nothing wrong with putting insulation along the top of the attic.

The insulating part isn't the plastic, glass or rock material. That's just a thermal bridge. The insulating is actually done by the air entrapped by those materials.


On all this XPS and other petroleum foam insulation, watch out. Get a scrap of it and do a "flame test" with it in your own backyard. A lot of foam products are positively terrifying* - and as a pattern, homes are getting much more deadly. (UL test on flammability of modern homes) and this test shows nothing about the lethality of the cyanates in that nasty smoke, that will shut down your nervous system and prevent your muscles from working. Your feet go out from under you and you don't get back up. This is the reason for the huge up-swing of people dying of "smoke inhalation".

And whatever you do, DO NOT fill the interior of electrical boxes with foam. I realize cheap (not really) plastic electrical boxes are very deep and go most of the way through the wall, creating a huge thermal bridge. if you want shallow electrical boxes with plenty of room for insulation behind, and wires and GFCIs inside, consider 4x4" steel boxes with a 1-gang or 2-gang mud ring coming through the drywall. These are only 1-1/4" or 1-1/2" deep. And they're cheap too!



* Better fire resistance is possible through professionally applied sprayed-on foam products; they are "2-component" (think epoxy) and must be mixed immediately before application, which requires special gear and qualified operators. The "B" part (hardener) is full of toxic BPAs or diisocyanates - these are fully consumed in the reaction, but they must be mixed in reasonable proportion to avoid creating a toxic home. They can't be sold on the hardware store shelf in a spray can for so many reasons lol.

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