I’m planning on building a 4′ conditioned crawlspace for a (SIP) home in South Carolina. I’ve narrowed my options down to 2 choices: use “superior wall” with their built in R5 insulation. Or go with traditional cement blocks and add insulation to the inside walls later. My questions are “How much insulation is enough? and which is the better way to go?” The superior wall option gives me an R7 which seems pretty low considering the SIP walls on the rest of the house would be around R21. I don’t know what the cement block option with additional insulation would give me. Obviously cost is a consideration as well.
Any info you guys might have would be greatly appreciated.
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In addition to the generally excellent advice you will receive, and while you are waiting for responses from people who have done both systems, you may want to check out this web site, if you have not already done so. http://www.buildingscience.com/housesthatwork/
It has a wealth of information you may find very handy as you go through the construction process.
Why not try an ICF(Insulated Concrete Form) foundation. I'm going to use one for the first time on the next house I build. Seems reasonably priced and I believe the r-value is much higher than the "superior wall". You could hire a subcontractor or based on the article in last months FHB you may be able to do it yourself.
I built a sealed crawlspace once with block and then went back and insulated the inside of the walls with blue board and I think we achieved like an r-7 or something but depending on how many layers you want to put on you could go much higher. I think 2" blue board is r-3 or r-5? I couldn't find 2" blue board at the time so we used several layers of 1" and 1/2" to achieve the proper r-value. We used mesh tape and mastic to seal up all the joints and to seal the top edge to the block. We then put 6 mil poly on the floor and sealed it to the walls with mesh tape and mastic.
As far as the correct amount of r-vaue, you could ask your inspector or there's a building science non-profit in Raleigh, NC called Advanced Energy that might be able to help you. I just looked at their website(advancedenergy.org) and one of the first stories is about sealed crawlspaces and an attempt to get the code council to adopt new language to include them in the code.
What will you do on the floor of your crawlspace? Use plastic? I think I'm going to pour a 3" rough slab with a moisture barrier under it so that the envelope can't be compromised by holes in the plastic later in the houses life. I believe I will have to provide for the possibility of radon, just a pvc pipe in the gravel under the slab stubbed out above the concrete so it could be tagged onto later and run out of the building if radon ever became an issue. Plus it will make a much better storage space, a good selling point.
Thanks for the info. I'll talk to a couple of ICF contractors. I was initialy concerned with termites in an ICF but I'll research that option a little more. I was also planning on pouring a rough slab for the floor for the same reasons you mentioned.Thanks for the help.
Termites apparently are a concern only because there's some uncertainty as to whether they will get into the foam or not. My ICF sub says they shouldn't be an issue if I do the conventional spray treatment. I was also thinking of bending a piece of metal over the top of the wall under the sill plate as a termite shield.
Somehow I wound up subscribing to Home & Garden online. Now cut that out! I think it was the DW's idea of a good ribbing.
Anyway, H&G has this other site called HGTVPRO.COM I think which does offer advice to the professional. It has videos on all segements of construction.
It has several on how to treat basements and crawlspaces and how to insulate and how to keep water and moisture (and mold) out.
Might be worthwhile checking out. Anyone else heard of this or visited the site?
I'm only a simple HO myself so I wouldn't know if their advice is practical, correct or worthwhile, but the site is very professionally done.
Griff