# Weird rim joist want to insulate



## Mdsjohna (Sep 23, 2014)

Can I just shove fibreglass batt in that small rim joist (if it's even called that in this style of construction) and seal the entry slot with canned foam? Will this cause moisture problems?

Sorry can't edit title (want to insulation) lol


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## griz (Sep 22, 2015)

You can insulate.


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## Ron6519 (Mar 28, 2007)

What are you calling, "the entry slot"?


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## SeniorSitizen (Sep 10, 2012)

Moisture problems can occur if the joist temperature reaches dew point temperature.


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## Mdsjohna (Sep 23, 2014)

The space above the top of the foundation wall and the floor above is about 3" high and goes back around 8". It shows it in the first picture. I want to know if filling it with fiberglass then spray foaming to seal it in is ok. The pictures I have found online look nothing like this. The floor joists are set into the concrete and there is only a small space there. 


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## mikegp (Jul 17, 2011)

Honestly, I would just fill the entire space with canned spray foam. The spaces are small enough where one can should do at least two or three, maybe 5+. How many of those do you have to fill? Or just do a small area with spray foam at the rim joist and put insulation inside of that to make it cheaper.

Is that little notch all that's holding the house onto the foundation?


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## Windows on Wash (Aug 30, 2011)

Several thread about this on here. Rigid or Canned and Rigid foam combo works well here.


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## joecaption (Nov 30, 2011)

I agree with the ridged 2" foam then sealing any gaps with the canned foam.
Fiberglass will not stop air flow.
It will mold up if you did it the way you suggested.


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## Mdsjohna (Sep 23, 2014)

mikegp said:


> Is that little notch all that's holding the house onto the foundation?



The floor joists are set into the concrete foundation as seen in the second picture. 

So I can completely fill that area with canned foam or even one of those small two part kits without worrying about the expansion damaging anything? That's one of the reasons I haven't wanted to just fill it with foam. The instructions I have read warn against using it in enclosed spaces. I mean it would take a whole lot of force to buckle up a floor board I assume but who knows how much force those foams have. Also read they generate a pile of heat.


Just so I am clear. I'm not talking about the exposed concrete in the picture right now. I am only talking about the space between the foundation wall and the floor above it. There is significant air leakage there and I can hear the dogs barking through that area. I will worry about the exposed concrete later. If I used bat and foam It will be sealed from inside air I believe. But there will still be some leakage from the rim to the outside. I would have mold problems in that situation?


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## mikegp (Jul 17, 2011)

You don't want to seal fiberglass in that area. Air and moisture can still enter and cause issues. The only issue with spray foam is that it usually needs moisture to cure, so if you put too much in a large enclosed space it might have issues curing. You could solve that by doing it in multiple passes. 

So those are full size joists all the way to the rim joist that are embedded in the concrete? Are they pressure treated? I don't think I've seen that before.

Just curious, is that the original foundation or some type of retrofit?


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## Mdsjohna (Sep 23, 2014)

Yes those are full sized joists embedded in the concrete. I'm not sure if they are pressure treated. House was built in the mid 70s. I doubt it was a retrofit bit I don't know. It looks nothing like what I have seen online when looking at rim joist information. I did find one thread where a house inspector from Winnipeg (where I am from) posted and he was saying around 50% of the houses in Winnipeg are built like this. Here are a couple more pictures. First is just a clearer look. In the second picture I moved a drop tile on the finished side of the house to take a look at what was done. Looks like foam in the crevice not sure what's behind it. Winnipeg in the winter is EXTREMLY dry inside in most houses but it can also get extremely cold outside.


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## mikegp (Jul 17, 2011)

What you just posted in the last pic is what I'm saying to do. Then put foam board in front of that and roxul in front of that.


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## Mdsjohna (Sep 23, 2014)

Thanks for all the help


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## charles3526 (Oct 15, 2015)

Hello mds i actually have the same problem i my joists are comming over my foundation wall at least 2ft to 3ft. I wanted to spray foam inside them and cover thise sections up. I was wondering what did you end up doing? I would have to buy a spray foam kit not the cans cause i have it all around my bsmt. I also think thats where my cricket friends are straying in from.what was ur experience and ideas for this. 

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## mikegp (Jul 17, 2011)

Charles, your joists are 2-3 ft longer than your foundation? Like they hang over toward the outside? So the house is 4-6 feet larger than the basement? Or just post pics. Do you have an overhang on the outside?


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## Mdsjohna (Sep 23, 2014)

In my case they don't extend past the foundation (well except on the other side of the house where there is an overhang. Where as far as I can see it would be impossible to insulate properly from the inside) my case the actual joist area is super small because the floor joists are imbedded in the concrete so the actual joist is only 3" high. I haven't finished but I am spray foaming to completely fill that area and I will use board on the exposed concrete. Will post pictures tonight or tomorrow.


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## charles3526 (Oct 15, 2015)

Yes my living room and master bed room both hang over the foundation there is nothing but ply wood there and its all open inside the bsmt i want to spray foam all that area. I will post pics when i get home. 

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