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Insulating/Sealing a very tight crawlspace

My 111 year old house is built on a brick pier foundation. Some time ago a skirt wall of bricks was added around the perimeter. Sagging floors were fixed with concrete blocks wherever they were needed. What I am left with is a crawl space with about 18 inches of head room to the bottom of the floor joists and concrete and brick piers scattered all around.

I have big moisture problems under the house to the point where everything gets covered in condensation under the floors and even above. I need to find a way to seal out the moisture before it hits my wood. I have watched videos about adding thick plastic and sealing it all around but I don't think that is an option with all the obstructions I have under the house.

Any suggestions? If you are interested my signature has a link to our blog about the entire rennovation.


Re: Insulating/Sealing a very tight crawlspace

The brick perimeter was a really bad idea. While it provides support, it also kills any air movement which you need to keep the underside space ventilated. The brick skirting also provides a nice highway for termites. The more room you have to see termites the better. Adding louvers to the brick skirting really doesn't provide the air flow needed. My neighborhood is built the same way and all the homes with brick skirting have sagging floors.

Re: Insulating/Sealing a very tight crawlspace

Looks like you are doing a dirt to roof shingle gut job there. Was that just for this one room or are you planning on doing the whole house this way? If so, you can remove all those obstructions. Then how to handle the problems. You need to determine the source of all that moisture. Is all that moisture from not having any drain lines? If so, then a new drainage system should solve that problem.

Check the slope of the ground around the house. It should slope away from the foundation for at least a couple of feet, but it should also have a way for water to get from the high side to the low side and then drain away from there.

If there is still a moisture problem after that, then you have a very wet soil condition.

I hope that is treated lumber that you are using around the perimeter, at least the sill plate should be treated. I see that you are going with stacked 2x to make 8x8 beams to go around the perimeter. I would have suggested that you could use 5 2x6's vertical and a 2x8 PT underneath the bottoms to make an 8x8.

You should consider spraying all the new wood that is not PT with a sodium borate solution like Timbor or Boracare. Since you have a child, this stuff is fairly safe, low toxicity and very effective against termites and any wood boring insects. It will also block rot, but it is water soluble so it doesn't work well for wood exposed to flowing water, like rain.

If you have a wet soil condition, then in the end you will need to put a plastic barrier on the ground and put a dehumidifier in the space. You will need to leave an access plate in the floor to get at the dehumidifier to service it when needed.

You could put down the plastic barrier, insulate the foundation walls with foam boards and insulate the rim joists around the house, if those 8x8's are the rim joists, you can skip that insulation. Then use the crawl space as your HVAC distribution system. As long as it is completely sealed, you wont need any additional ducts, just cut a hole in the floor where ever you need a vent.

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