Rockwool in a crawlspace
I recently purchased a home about 45 years old on the east coast of Virginia. I’ve been researching insulation as I intend on doing both the attic and crawl space. Due to other necessary repairs, I intend on starting in the crawl then moving to the attic. I intend on encapsulating the crawl using a dehumidifier. The property is close to a marsh and therefor the ground is fairly wet so I will be installing a drain and sump system in the crawl. I was planning on installing foam board against the brick foundation then sealing with a vapor barrier.
My question is this, can rockwool be used in place of the foam board? Is it rated for ground contact or have a termite resistance?
There are a few driving factors for me in looking into this. I like the fire resistance of the Rockwool. Rockwool is available at the big box stores. The foam board available that I’ve seen has questionable ratings on ground contact and termite resistance. If the rockwool gets wet, it looks like the moisture would just drain back down between the brick and vapor barrier and get removed via the drain system I’m going to have around the perimeter of the foundation.
Other questions that come to mind; Will I be able to match the R-value of the foam board using the rockwool? How will I install the rockwool vertically against the brick? Construction adhesive? I don’t think the nail gun system used in installing foam board will work.
Thanks in advance,
Steve
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Replies
This doesn't answer your question in any way but I was able to find Thermax sheating by locating a Dow supplier in my area, they delivered relatively cheaply and the insulation itself was priced pretty well.
Zaid
If you have a crawlspace, encapsulating is a good idea. A dehumidifier (suspended, not on the floor) is also a good idea.
I do wonder how high the swamp and local water table are relative to your crawlspace floor. If you are already close to the water table and you dig a pit for a sump pump, you may just end up continuously pumping swamp water. If you can just encapsulate and dehumidify, that may be sufficient. This does require that you have taped and sealed any seams in the encapsulating (sheeting) carefully.
If you have bricks or cement block foundation walls, you will want a vapor barrier to go all the way up the crawlspace wall to the top. It’s not clear to me that the insulation has to go on first; if you use rigid foam (and not open insulation that needs to be enclosed on all sides), then it seems like you could put the insulation on second. This seems like it would reduce the exposure of foam to bugs if you’ve done a good job encapsulating. [Specific question: does the insulation need to go onto the crawlspace wall first, before the vapor barrier? I know some encapsulation companies do this, but on poured walls. They then only go about 6” up and tape the vapor barrier to the rigid foam.]
Rockwool doesn't mind water and doesn't get eaten. I don't think anything will even nest in the rigid version of rock wool, but might in the softer rock wool batts. Total guess here, using rigid foam that has an approved fire rating would be a much easier project.
Thanks for the reply. The house grade is high enough that the water table is below the footing and would also be below the sump. There’s a decent hill in my back yard sloping down to the swampy area. I’d say maybe 20 ft elevation difference.
That’s a good question on the placement of the insulation. I’ll look into that more but making a few assumptions. The way the insulation is normally installed is by shooting a nail and plastic system through the board and into the wall. This would puncture the vapor barrier and allow moisture to penetrate. Also placing the vapor barrier before the insulation may lead to condensation forming on the inside surface of the barrier if the dehumidifier were to fail. Maybe not a huge risk but one the pros think about? I could see they there would be gaps between the insulation and barrier leaving a surface for the condensation to form.
Do they make rigid foam with a decent fire rating? I’ve not seen that and would eliminate one of my bigger concerns.
I'm not an expert on brick foundations or your climate, so I can't help that much, but I'm commenting anyway because I am hoping this will bump up the visibility of your post and attract attention from some experts. But one concern is that in the winter, your brick will be colder with the insulation in place. That will mean it will dry less, and freeze more, which could damage it over time. Mineral wool board on the outside could help, if that's feasible.
Not really feasible to place it on the exterior. The exterior brick goes from grade to roofline.
I don’t know for sure but I don’t think freezing would be an issue. Just up the wall the house has insulation inside the brick to form the rooms. The brick doesn't seem to be effected by that. I’ll look into this question as well though. I’d hate to invest thousands into this project only to damage the foundation of the house.