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-   -   Conditioned Crawl Space - Advice re Waterproofing AND Int or ext insulation (http://www.diychatroom.com/f19/conditioned-crawl-space-advice-re-waterproofing-int-ext-insulation-132814/)

JohnNe 02-06-2012 06:36 PM

Conditioned Crawl Space - Advice re Waterproofing AND Int or ext insulation
 
Followup on 9 Feb: Are my questions unreasonable or too general? Did I post this in the wrong forum? Is more precise information needed?

Hello to all. My situation involves new construction in SC. The crawl space will be conditioned with air from the house itself. 2x6 framing, solid-filled concrete block foundation, dirt floor (not poured concrete). This is our permanent home, never relocating. Cost is definitely a factor, but inhibiting mold is too. 2" thick natural stone veneer will be applied to the foundation wall above grade. I've read that the block wall should be waterproofed behind the stone.

May I please have guidance on: insulating, waterproofing, and drainage.

Insulating - The builder is new to this kind of crawl space and plans to insulate from the inside with 2" rigid foam board, seal it all up with heavy plastic over a sand floor and up the walls. As I look into waterproofing, I'm seeing recommendations to insulate from the exterior. Not sure which is best.

Waterproofing & drainage- We're in a clay/sand area, (about 80% clay). I want 100% gravel against the house with a drain system using perforated pvc and grading as described for most foundation walls. What waterproofing is recommended if natural stone veneer is to be applied? Paint-on or spray on? Membrane? Rigid foam? Plastic lining, then mesh for the stone?

I would like the clay-sand backfill to be kept away from the foundation wall by the gravel and landscaping fabric, similar to a retaining wall set-up. Is this practical? Too much?

Also I notice many expansion gaps in the mortar between the blocks. I presume it's still sealed inside the wall but would like to know if I (or masons) need to scrape extra mortar into the very thin gaps. Should I be concerned about this? I appreciate your time.

JohnNe 02-09-2012 06:14 AM

Hello folks! Found most of my answers elsewhere. Don't know if they're the right answers for my specific situation, but I'll go with the construction "theories" and see if they work out.

jklingel 02-09-2012 11:43 AM

I'm surprised no one chimed in here; I did not see this one till now. Have you scoped out buildingscience.com, and searched here? This has been discussed here at length.

JohnNe 02-10-2012 06:14 AM

Thanks for responding. Yes, I've researched the topic at length (including reading relevant posts on this forum) and also picked up a lot of great information from buildingscience.com. My dilemma is that I'm trying to find the solution for my *specific* situation. Conditioned crawl space (that will be below grade in some locations) + appropriate insulation (interior or exterior) + stone veneer. My builder wants to tar the exterior wall and add 2" of insulating foam boards to the interior. Sounds like a good method. But the research suggests exterior application of foam boards might be better (in general insulation applications --though maybe or maybe not for conditioned spaces).

I'm not excited about tar on the wall, but maybe it IS a good idea. I have no idea. The builder may be spot on. But this is his first conditioned crawl space and I need to help out with the research. A visit to a couple DIY centers led to recommendations that I use a type of concrete pad sealer, but I'm not sold on that either -- though maybe it's 100% correct. Maybe sealing the outside is "bad", considering that the inside will be sealed with plastic sheeting, therefore trapping any moisture inside the walls.

As for drainage, my info on retaining walls suggests to me that I want to keep wet the clay-sand away from the exterior foundation of my home as well. We're on a slope, so grading and terracing is needed and we'll end up with a crawl space that is, in effect, submerged in soil in some places. I want to keep moisture from the walls so that I reduce the chance of mold in the crawl space. It's conditioned, but that doesn't mean prolonged moisture won't create mold underneath the plastic lining. But am I wasting money by hauling in gravel when an exterior wall sealant might be sufficient?

Because the crawl space is encapsulated, there will be a layer of plastic, sealed against air, moisture, and radon on the interior wall, covering the 2" foam board. Okay, but doesn't that mean any the moisture in the walls will remain trapped in the concrete-filled block walls? But if the foam board is on the outside, will application of 2" stone veneer (presumably set on wire mesh affixed to the foam board wall) totally destroy any benefits of exterior foam application? I would think so, and that just brings me back to my original questions: tar? + interior foam board? + plastic? + gravel?

I feel like I may be making this too complicated and should just go with the proposed solution. But as this is new construction, I have a chance to do it the best way possible for the least cost with the least hassle if I can figure out what that is before we go much further in the construction process.

JohnNe 02-10-2012 06:53 AM

I think the solution is to foam board and plastic seal the inside. Waterproof the exterior ONLY where the stone veneer will be applied (so that the block underneath is protected from heavy rain. Leave the remainder of the sub-grade wall section unsealed (to allow the block to dry from the exterior) but back-fill with appropriate drainage materials and a French drain-type system that leads water away from the house. I guess it won't hurt to also lay one width of heavy-duty plastic about a foot underground that mimics the slope of the grade (or steeper), further helping to drain the water away from the foundation. I'm only doing this once. I hope.


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