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Curtain Foundation crawlspace to vent or not??

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Reelsix

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Hi - I recently purchased a 1930s home that has an addition that was put on the back of the house in the early 2000s. The addition has a curtain foundation with concrete block piers but has lumber spanning between the piers (not brick or concrete block that seems typical). Unfortunately, a good portion of the curtain foundation is below grade by 6-12 inches and more in some areas. The builders poured rumble stone in the crawl and around the outside of the foundation and they used some sort of metal flashing to "protect" the wood spanning between the block piers. There is ductwork, plumbing etc that goes into the crawlspace from the main part of the house. There is mold and the builder put insulation in the floor joist that has to be remediated. Mold is likely from high humidty and ductwork that is poorly insulated that is condensing.

I have been told by a reputable encapsulation company that because there is not a continuous block or brick wall and there is wood spanning between the piers that they cannot fully encapsulate this space. I live down south so have a very high humidity environment. My living room and master are above this space.

I would love to know what is the best approach for insulating the flooring for this particular problem? One option I have heard is to use foam board insulation between the floor joist held in place by spray foam and then to cover the joist with pressure-treated plywood. We would seal up the foundation wall between the two crawl spaces and around ducts etc. We would add vent wells so all of the vents are open and then fans to encourage airflow.

If we take this approach would it still be a good idea to have poly covering the exposed dirt in the crawl or not a factor because we have "encapsulated" below the subfloor?

What are risk with having ductwork and plumbing running through a vented space?

Alternatively, one option is to assume that the metal flashing provides a sufficient barrier around the crawl space we seal all the vents and we cover the exposed earth as best we can by pinning the vinyl down on the edges and then have a dehumidifier running in this space. Is this likely to result in sky-high power bill with the dehumidifier having to constantly run or taking steps as outlined will likely drop the humidity a good bit and a commercial-grade unit could handle it pretty easily?

Thanks for the advice!
 

bud16415

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This type of construction seems pretty common in the southern states and I never saw it living up north until I was in my 20s and started traveling south. The first time I saw it I couldn’t believe my eyes.



Most of the time they are closed in with brick or blocks but still are not sealed off like a basement crawl space would be.



I really don’t know the answer to your question, but have a question.

How much room do you have to work from below? Headroom?
 

Reelsix

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This type of construction seems pretty common in the southern states and I never saw it living up north until I was in my 20s and started traveling south. The first time I saw it I couldn’t believe my eyes.



Most of the time they are closed in with brick or blocks but still are not sealed off like a basement crawl space would be.



I really don’t know the answer to your question, but have a question.

How much room do you have to work from below? Headroom?
Just posted a couple of pictures. It is tight. 2-3 ft max. Thanks
 

bud16415

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Again I’m not a pro but someone interested in your problem and thinking of what the pros here might like to see to help you.



You mentioned some of the wood curtain wall being below grade and covered with some sort of flashing and back filled with stone.



Could you get any photos from outside showing the grade line kind of the big picture?



Is this curtain wall made from PT materials?

How big of a job would it be to remove the wood curtain and lay up blocks? In some ways it seems like having access all around would make some of the other work easier, but if it is below grade I can see that not being the case.
 

Reelsix

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Again I’m not a pro but someone interested in your problem and thinking of what the pros here might like to see to help you.



You mentioned some of the wood curtain wall being below grade and covered with some sort of flashing and back filled with stone.



Could you get any photos from outside showing the grade line kind of the big picture?



Is this curtain wall made from PT materials?

How big of a job would it be to remove the wood curtain and lay up blocks? In some ways it seems like having access all around would make some of the other work easier, but if it is below grade I can see that not being the case.
Hi - Attached is a picture showing the grade in relation to the vents. I would say the ground level is 12-18 inches above the crawl floor. I think the lumber is pressure treated.

It would be a big job as the grade is at this level surrounding 3/4s of the crawl and for half of it a deck would need to be removed to do the work.

Thanks
 

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bud16415

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Sounds like a tough situation. It is good that it is well drained and that the wood is PT.



As to the solution for you or the best solution I’m at a loss as nothing around here is built that way even most of the pre-built double wide homes are being put on basements most of the time and when not are on a block full foundation with a crawl space floor. Single wide mobile homes are often sitting on piers with some thin skirting for wind control mostly and I believe they are floor insulated similar to what you were thinking. Around here pipe freezing is the big problem there.



Maybe others will post in that are used to dealing with this type construction.

Getting under there and placing all that cut foam and covering it with PT plywood also sounds like a project that would wear you down with the limited head room. I have done exactly what you described with outside walls that were open on the insides, cut foam and fill cracks with canned foam. It makes a nice warm wall.
 

Reelsix

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Sounds like a tough situation. It is good that it is well drained and that the wood is PT.



As to the solution for you or the best solution I’m at a loss as nothing around here is built that way even most of the pre-built double wide homes are being put on basements most of the time and when not are on a block full foundation with a crawl space floor. Single wide mobile homes are often sitting on piers with some thin skirting for wind control mostly and I believe they are floor insulated similar to what you were thinking. Around here pipe freezing is the big problem there.



Maybe others will post in that are used to dealing with this type construction.

Getting under there and placing all that cut foam and covering it with PT plywood also sounds like a project that would wear you down with the limited head room. I have done exactly what you described with outside walls that were open on the insides, cut foam and fill cracks with canned foam. It makes a nice warm wall.
Thanks for the thinking. Interesting the comparison to mobile homes and the way they are built. Certainly, welcome any other thoughts from the forum as it is a challenging situation!
 
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