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Keith_MN
Diagnosing Cold Wall Spots
Keith_MN

My house was built in 1953 but flipped before I purchased it a few years ago. Parts of the house still have character from the 1950's and it is a compilation of three builds at different times. My basement is two different slabs and I also have a house above a crawlspace. The two basement sections are cinderblock walls that are not insulated on outside or in, one of the basement areas with it's own slab is considerably colder than the other area, almost 15 degrees different. I have HVAC system putting heat into my basement and crawlspace.
In one of my rooms above the basement on two exterior exposed walls I notice that a certain section of wall is extremely cold, with IR thermometer it was reading 40 degrees when the room was 68 and the outside temperature was ~0F. This part of the house is over the basement and it is a cinderblock wall that is uninsulated. The rim joists are also uninsulated, although I recently put batt insulation in the rim joists to try and help with the entire basement comfort. This is a long intro, but i'm trying to figure out how to diagnose whether or not I should work on the first floor or basement first.
Option 1. Start in first floor with wall. Pull off drywall from room, check that proper insulation is in place. I've pulled off a wall plate and examined insulation, there is some behind the drywall but it looks as if it was pressed down, so doesn't look perfect.
Option 2. Insulate basement rim joists. Area is behind an old finished area.
For insulating the rim joists I previously had a contractor use Thermax sheathing for my crawlspace and it has worked wonders. I was contemplating putting thermax sheathing in each rim joist against the external wall and then filling with batt insulation. Other option for rim joists is to contract someone to spray all of the rim joists or purchase the spray foam kit from menards.
I have a feeling that my uninsulated basement, cinderblock wall without any insulation outside or in, is causing most of my issues but wanted to make sure I wasn't missing something obvious.

Thanks
Keith

MtMan54
Re: Diagnosing Cold Wall Spots
MtMan54

Hi, You should always start in the attic first. Thanks

keith3267
Re: Diagnosing Cold Wall Spots
keith3267

Start by telling us about the section of the wall that is cold. How big? Top, middle, bottom, middle of the wall or near a corner? Can't help without this info.

Keith_MN
Re: Diagnosing Cold Wall Spots
Keith_MN

Thanks -

Had attic sealed and re insulated 1.5 years ago and also have new furnace

The cold spots are on the bottom half of the wall - under two windows in a corner, one on each wall, and they are brand new windows. So this is about 18 inches tall and stretches 6 feet. About two feet from one of the windows is the other cold spot. It goes up about two feet on the wall and is three feet wide. So the coldest spots are all on the bottom edge of the wall, which is why I tend to think the basement could be the issue.

Below the section the is not next to a window on the first floor is above a single pane window in the basement.

Thanks for the help

ed21
Re: Diagnosing Cold Wall Spots
ed21

Insulating the rim joist is easy and won't hurt.
What is the IR thermometer reading on non cold part or the wall?
It sounds like the insulation is missing or compacted at the cold locations. Seems like the IR readings are telling you that.
Opening the wall, even if partially should confirm. Insulation is often compacted behind a junction box.
A window opening might have a build up of studs, jack stud, cripples that lower the R value at those locations.
Was the insulation compromised by a water leak?

keith3267
Re: Diagnosing Cold Wall Spots
keith3267

It sounds like someone tried to insulate the walls by blowing in cellulose. This would be typical of someone flipping the house. Some cavities, particularly below windows don't get insulated. Confirm this by doing an IR scan on the outside and see if the corresponding areas on the outside are warmer than the other areas.

If the outside walls are not warmer, then it may have been insulated with faced batts. A common misconception with faced batts is to push the insulation too far against the outside of the cavity, leaving a gap between the paper and the sheetrock. This gap allows cold air to bypass the insulation, come in at the bottom, go up between the wall board and the insulation and exit through the top of the cavity. It is common that the coldest part would be near the floor as the cold air draws heat from the wall board as it rises up in the cavity.

If it is the former condition, you can usually have additional insulation blown in where there are voids. I do recommend that you insulate the rim joist as you planned, but be sure it is sealed to keep cold air from infiltrating at this point. Once it is sealed and insulated, it will trap warm air against the floor, helping to keep them warmer.

Keith_MN
Re: Diagnosing Cold Wall Spots
Keith_MN

Thank you for the feedback

Ed - I took measurements tonight and the normal part of the wall was 64 (house is set at 68), and the cold spots below the window and next to the wall were from 58-54. It is a bit warmer outside today than the last time I took measurements. I don't believe there was a water leak but am not sure. Believe that the batt insulation is compressed, from what i can see behind the electrical plate they likely compressed it when putting in the new framing for the window.

Keith -
will plan on insulating rim joists, do you recommend trying the spray foam vs. something like thermax - i'm unsure if I should try and cover the cinderblock under the sill with some type of insulation as well.
I will likely replace the insulation in the problem areas of the wall. Will start by cutting a few holes to view the insulation and then if necessary pull down the drywall to replace the batts.

Thanks again for the advice, much appreciated!

keith3267
Re: Diagnosing Cold Wall Spots
keith3267

Spray foam by a professional would be a good idea, but expensive. If you are using spray foam in a can, that will get very expensive and messy. I would only use it around the seams that go through to the outside, normally the top and bottom seams. Then use solid foam blocks or sheets cut to fit. Also use it along the sill/block seam. You can use caulking on the seams instead and you may find that the caulking is a lot less messy.

Keith_MN
Re: Diagnosing Cold Wall Spots
Keith_MN

Keith -
I realized after I put in a new post that I could easily reply to this as well. I think I created my own problem as you describe (in bold).

How would you recommend putting insulation into this cavity, I tried my best to make sure I didn't leave any gaps and kept everything against the wall, but looks like I might have created another problem here and I just didn't realize it. I do not have much wall to work with, but wasn't sure how to blow in insulation into the small gap or put foam in.

Thanks,
Keith

keith3267 wrote:

It sounds like someone tried to insulate the walls by blowing in cellulose. This would be typical of someone flipping the house. Some cavities, particularly below windows don't get insulated. Confirm this by doing an IR scan on the outside and see if the corresponding areas on the outside are warmer than the other areas.

If the outside walls are not warmer, then it may have been insulated with faced batts. A common misconception with faced batts is to push the insulation too far against the outside of the cavity, leaving a gap between the paper and the sheetrock. This gap allows cold air to bypass the insulation, come in at the bottom, go up between the wall board and the insulation and exit through the top of the cavity. It is common that the coldest part would be near the floor as the cold air draws heat from the wall board as it rises up in the cavity.

If it is the former condition, you can usually have additional insulation blown in where there are voids. I do recommend that you insulate the rim joist as you planned, but be sure it is sealed to keep cold air from infiltrating at this point. Once it is sealed and insulated, it will trap warm air against the floor, helping to keep them warmer.

keith3267
Re: Diagnosing Cold Wall Spots
keith3267

As you can see, I responded to your new post without all the information from this post. I did not click on the provided link, I don't click on links.

I would just remove the drywall under the windows and insulate them properly with batts and a vapor barrier or faced batts. It will actually be the easiest in the long run. If you need help on how to do this, just ask.

Keith_MN
Re: Diagnosing Cold Wall Spots
Keith_MN
keith3267 wrote:

As you can see, I responded to your new post without all the information from this post. I did not click on the provided link, I don't click on links.

I would just remove the drywall under the windows and insulate them properly with batts and a vapor barrier or faced batts. It will actually be the easiest in the long run. If you need help on how to do this, just ask.

Thank you Keith -

How would you suggest taking down the wall to put the insulation in? Previously I cut a hole a few inches from the window down to a few inches above the molding so that I had enough room to smooth the joint. I did this across the entire area below the window so I could replace a few sections of insulation with a single piece of drywall. With the cavity open I cut aluminum faced batts and placed them in the wall. It was rather tricky getting them into the cavity both top and bottom without compressing the insulation. I used the vinyl vapor tape across any areas that I couldn't seal. It might have made my job easier if I had taken the molding off and the drywall down to the floor.
To give more information -
In the rim joist below the room I cut Thermax sheets (1.5in thick) and placed them in the cavity with spray foam around the edges. I then placed two pieces of batt insulation in the cavity to completely fill it. Reading the temperatures in the rim joist I do not see any difference between different cavities. Whereas if I go up to the room there is very small spot that is extremely cold relative to surrounding area.

appreciate the help
Keith

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