Jacking up 1950’s sill plate to add capillary break
davebr
| Posted in General Questions on
After seeing a few posts on here suggesting adding a capillary break before insulating rim joists, I would like to do that on my 1958 house. However, I do not see how the sill plate is anchored to the CMU block wall (no visible bolt heads or studs/nuts) I am concerned if I try to jack up the sill plate even 1/4″, I may damage whatever fasteners lie under the floor joists and/or rim joist.
Is anyone familiar with how sill plates usually were fastened to CMU block in 1958? I’m wondering if they were nailed in, which goes to my original concern about breaking fasteners.
Any insights greatly appreciated.
Dave
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Replies
You'd be surprised how often the "fasteners" holding the sill plate to the top of the foundation wall are just gravity -- the weight of the house! If you can't find any obvious fasteners, this is likely the case. Bolts that are typically used are fairly substantial and should be very easy to spot.
What I'd do here is to jack up a few sections of the house *carefully*, while checking for any fasteners. You can use a thin piece of metal (like some 1/16" x 1" steel flat, which is usually available in hardware stores wherever they sell metal extrusions), slide it along the top of the foundation wall in the gap you open up while jacking up the house. If you don't feel it hit any fasteners over a 6-8 foot section of wall, you probably just don't have any fasteners at all.
BTW, I highly recommend the use of thin HDPE sheet, usually 1/32" - 1/16" thick for use as a capillary break in this application. HDPE is tough, slick/slippery, and fairly cheap, making it great for this. Try to get black material, which will hold up better if there is any UV exposure. Have your plastic supply house cut you pieces 4 feet long and whatever width the thickness of your foundation wall is. When you install the sheets on top of the foundation wall, overlap the ends an inch or two.
Bill
Bill,
Thank you for your detailed answer. I was wondering if maybe it wasn't anchored at all.
Follow up after reading some of Martin's responses on other posts: I'm wondering if it is worth the trouble to jack and insert capillary break in my specific situation. Most of the CMU wall on my basement is exposed more than roughly 18" above grade, with some sections 4 ft above grade. There is a section about 15 ft long that is 8-12" above grade. It seems this may be rather low risk of sill rot and potentially not worth the effort of jacking up the house to insert capillary break. I plan on treating the sill and rim joist with bora-care with mold care as well.
Any thoughts on this?
The more exposed wall you have, the less potential risk of moisture wicking up far enough to cause problems with the wood framing. Things that can increase that risk include crawlspace encapsulation projects (where you cover the wall with a membrane on the inside), painting with waterproof coatings like Drylok, etc. Pretty much anything that limits the drying ability of the wall will allow moisture to rise high.
If you're not doing any of those things, you're probably pretty safe without a capillary break, especially in the section of wall that is four feet above grade. The 8-12" section is the area at highest risk, since thats only about one course of block above grade. That would be the section I'd want to add a capillary break too, and possibly the 18" section, although that's much less of an issue. The section that is 4 feet above grade is probably near zero risk as long as you don't paint or seal the block, and even then it's probably still pretty low risk.
Bill
The block is painted with an unknown paint. I think I will forego the capillary break and maybe figure out a way to make a few locations accessible to inspection on the higher risk areas.
Thank you for your insights Bill, much appreciated.