# Gap between rim joist and subfloor



## Extreme84 (Nov 23, 2019)

Hi there, 

I have a 100 year old house and I was wondering if I should insulate the rim joists. I've seen people using spray foam to insulate their rim joists, but I noticed my setup looks different from the examples I've seen online.

I've attached photos for reference.

My subfloor doesn't extend to the rim joist. I can reach my hand right up into the gap between the subfloor and rim joist. I'm guessing this setup is intentional for my old home and I suspect if I spray foam that whole area I might be disrupting some sort of wanted circulation between the levels of the house.

Should I insulate this area or leave well enough alone?
I appreciate any helpful advice.


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## Windows on Wash (Aug 30, 2011)

Whats the outside look like...but the short answer is yes. 

While you "can" picture box it with rigid foam, its gonna be a million times easier with spray foam.


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## de-nagorg (Feb 23, 2014)

I'm a little rusty, but isn't that "balloon " framing?

The space eases the installation of utilities.

Other than that, it needs insulated.

ED


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## Nealtw (Jun 22, 2017)

Those holes are chimneys and a great for moving fire from the basement to the attic.
They should be fire stopped at the basement and the attic and anywhere you ever gain access to them in between.
Cover them with 1/2" plywood and seal them before you insulate the rim.


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## HandyAndyInNC (Jun 4, 2018)

You have what is known as a balloon frame structure. Do not cover those holes. older structures cannot follow modern day practices. Those gaps and holes are what feed air to the attic and keep the walls warm in the winter and cool in the summer. Air is flowing from the basement to attic all the time. If you close them off, you will begin to grow mold in the walls from the warm air inside meeting the cold clap boards on the outside. And vice versa in the summer. I have lived in a Victorian house located in different parts of the country all of my life. If you have foundation vents, they should be closed in the winter. The air in the basement will remain at around 60 - 64 degrees. That is what keeps the inside of the walls warm in the winter. It is called a Chimney effect. Why do you believe that you need to cover them?

What you can do is insulate the underside of the subfloor. But do not block the airflow up the walls. Older structures do not have ridge vents in the attic. Most houses, including mine have windows in the attic that can be opened. But this air movement in the walls keeps the attic cool in the summer and warm in the winter. We have no insulation in the attic, and the snow stays on our roof sometimes longer than the new houses in the area.
But that is your house, you do what you want with it. I am telling you that older structures are designed differently than new, and they have to be treated and maintained differently. That means you cannot follow things you see on tv on those stupid home fix-it shows.


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## Nealtw (Jun 22, 2017)

HandyAndyInNC said:


> You have what is known as a balloon frame structure. Do not cover those holes. older structures cannot follow modern day practices. Those gaps and holes are what feed air to the attic and keep the walls warm in the winter and cool in the summer. Air is flowing from the basement to attic all the time. If you close them off, you will begin to grow mold in the walls from the warm air inside meeting the cold clap boards on the outside. And vice versa in the summer. I have lived in a Victorian house located in different parts of the country all of my life. If you have foundation vents, they should be closed in the winter. The air in the basement will remain at around 60 - 64 degrees. That is what keeps the inside of the walls warm in the winter. It is called a Chimney effect. Why do you believe that you need to cover them?
> 
> What you can do is insulate the underside of the subfloor. But do not block the airflow up the walls. Older structures do not have ridge vents in the attic. Most houses, including mine have windows in the attic that can be opened. But this air movement in the walls keeps the attic cool in the summer and warm in the winter. We have no insulation in the attic, and the snow stays on our roof sometimes longer than the new houses in the area.
> But that is your house, you do what you want with it. I am telling you that older structures are designed differently than new, and they have to be treated and maintained differently. That means you cannot follow things you see on tv on those stupid home fix-it shows.


 That is not good advice, in a fire the homeowners and fire crew are in danger working in these houses. 

https://www.google.ca/search?biw=10...&ved=0ahUKEwjL_cLe9uPnAhX6CjQIHTeoBS8Q4dUDCAo


I have never seen anyone suggest it should be left open. 

https://www.firerescue1.com/cod-com...oon-frame-construction-fire-r7WTUe6QEmgytrUY/


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## Missouri Bound (Apr 9, 2011)

de-nagorg said:


> I'm a little rusty, but isn't that "balloon " framing?
> 
> The space eases the installation of utilities.


If the house is as old as the OP says then it most likely is.
Unfortunately those spaces greatly increase the chance of a fire spreading from floor to floor.
Insulation and fire stop are both needed.


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## Missouri Bound (Apr 9, 2011)

HandyAndyInNC said:


> You have what is known as a balloon frame structure. Do not cover those holes.


Terrible advice.
Balloon frame homes are disasters in a fire situation.
He needs to insulate and install fire blocks.


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