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Christopher
How to insulate a space under an extension
Christopher

Hi Folks,

I'm hoping I could get some advise on insulating and building walls in a room that is under an extension that was put on my house several years back. The room needs to be fairly air tight, and has a few unique features, such as:

A) plywood over the previous exterior wall

B) the original foundation, flush to plywood (A)

C) cinder block foundation for the extension

D) extension walls, set back a few inches from foundation (C)

Right now, I'm thinking closed cell spray foam insulation for the entire thing might be the easiest and most effective way to go, but would love to hear some feedback and other suggestions as well. Regardless of the approach, some additional questions I have are:

1) Should the wood and/or entire area first be treated with with something to prevent mold?

2) Is there any benefit to using spray foam over boards? Would board create an air tight space?

3) I am under the impression that lumber used to frame the walls can be placed right up against closed cell foam board. Is this also true for closed cell spray foam?

4) How should I deal with the varying depth between walls (C) and (D)?

Thanks in advance for any help you can offer!

Chris - Andover, MA

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HandyAndyInMtAiry
Re: How to insulate a space under an extension
HandyAndyInMtAiry

Christopher,

Why would you want a room to be air tight? or close to it? When you go into the room, you can hold your breath for only so long. I would be more worried about water intrusion. On the ouside surface of the foundation wall, was there water proofing of some type put on the concrete block? Concrete blocks are very pourous,  and will allow water to come thru them all the time if not. Were the concrete blocks filled with concrete to fill the voids in each block?

A few things, I cannot see your graphic file, it is not a valid format.

A) There is nothing wrong with using plywood as a wall covering, especially in a basement, or garage, or places like that. I would not put sheetrock in this types of places, it contains paper which mold loves to eat.

B) The wall is firred out to be flush with the concrete foundation footing, not the other way as you described

C) Code requires concrete blocks or solid concrete walls as foundation walls. There is nothing else that is allowed.

D) No, the foundation is usually 12 to sometimes 16" wide, while a concrete block is only 8" wide. You want the wall to be centered on the footing.

1) If you allow the area to breathe, mold will not be a problem.

2) No, the spray foam would help in making the area more air tight.

3) Yes, there is nothing wrong with spray foam touching wood. How else would you use it?

4) Since I cannot see your graphic file, I am assuming that there is a dog leg down one wall. You merely build the wall to suite your liking, or follow what the architect states on the drawing that was approved. You may leave the dog leg or build the wall to hide it.

Not to be mean, but I think you have been watching too many tv shows. Hire an architect / engineer, and they will know exactly how to design the structure for the space in the area where the structure is located.

Andrew

Handy Andy In Mt Airy NC

Christopher
Re: How to insulate a space under an extension
Christopher

Thanks for the feedback, Andy. 

The picture attached is a supported format (jpg) and I was able to download and view. Perhaps you can try again?

I would like the space to be nearly air tight as there is no heating, and I need the space to be around 80F all winter long with only a portable electric heater. If there is airflow, the incoming air will be below freezing and at best, the heater would run continuously. There will be a dehumidifier as well, so I am not so concerned about moisture.

For items A-D, can you please try the pic again? I think things would be more clear if you could see the space that I have to work with.

For items 1-4:

1) Allowing the area to breath is not an option. Are there any other ideas/concerns?

2-3) Thank you! I will plan to use the spray foam

4) Please try the pic again :)

Also, I do not watch TV. I haven't had cable for almost 20 years, so all this is straight from my imagination! The scope of the project does not warrant an engineer or architect. I simply am looking for some piratical advise from folks that have experience with this sort of thing.

Thanks again!

Christopher
Re: How to insulate a space under an extension
Christopher
HandyAndyInMtAiry wrote:

On the ouside surface of the foundation wall, was there water proofing of some type put on the concrete block? Concrete blocks are very pourous,  and will allow water to come thru them all the time if not. Were the concrete blocks filled with concrete to fill the voids in each block?

The concrete blocks are dry. On the exterior surface, they are covered with the same shingles that are all around the house. I do not know if the voids are filled as I did not build the sapce.

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