I’m a HO. My walk-out basement house is presently under construction in Southern Ontario Canada. 2X6 stick-frame, fired clay brick/stone exterior. The Tyvek wrap has been sandwiched between the sill plate and the top of the foundation wall in several areas, where possible, and not in others. The sill plate has been shimmed to allow it to be (very nicely) straight relative to the rough top of the foundation wall, which has left a few varying gaps in some areas of up to about 1/4″. (They didn’t set the sill plate in mortar or any type of gasket, so this sealup is a “retro” job). I asked my builder how they seal that (suggesting canned foam), and he said they use “tar”. He said tar would be better and last longer than foam. In my mind, “tar” means volatiles which evaporate in time, which means it dries out, which causes shrinking, which leads to cracking, which means an eventual breach of building envelope. The house is on the north shore of Lake Erie(= very high winds and CCCCCCold winter temperatures). This seems like a small detail, but anyone who reads FHB and this forum realizes that the devil is in the details (and if he’s not, then you’ve got BIG problems!) I haven’t been able to find out what R-2000 standards require for this detail. I’d really like to see foam in from both sides of the 2X6 plate, if any of you experts out there have also done it this way. Or maybe foam on the inside and tar on the outside ?
To dispel any implications to the contrary that might result from my asking this question, I must say that we are extremely pleased with this builder; workmanship quality, details, site cleanliness, timelines etc. are all meeting our expectations.
It won’t be long before they start to seal this up so if there is a good alternative to tar I’d like to hear about it. What else is used out there for this detail across the country (countries) ?
Thanks – Brian.
Replies
Your best insulation choice for the rimboard sitting atop the mudsills will be sprayed foam, and your insulation contractor will consider it part of his job to use the fine tip detail sprayer in the joint between mudsill and foundation wall. It is the foam detail sprayer he will be using to seal around window and door units. Rimboard assemblies can leak a lot of air and be a great cause of heat loss. When the archaeologists are examining our ruins, they will be wondering what all the foam is about, and the wood will have all turned to dust.
I like the tar idea, we used it for years under oak and maple door thresholds, and you're right it does harden up after a couple of years. The thing is, tar hardens up long after the wood has settled in. The area you are talking about is not terribly exposed, plus the vapour barrier should seal any off gassing of the tar. Your biggest toxic problems in R2000 construction are the off gassing of furnishings, cabinets, carpet and pigments in the paint.
I would like to differ with MR Micro and advise to NEVER use foam around windows and doors. It is almost impossible to straighten them out if even slighty over foamed. Your R2000 window and door seals are achieved by adhering the vapor barrier to the frames with accoustical sealant. Batt insulation not foam is used. Trust your builder.
( your logo here) Turtleneck
I believe that in R2000 construction, there is to be a foam gasket between the sill and the top of the concrete. I think your best bet now is the spray foam. Tar seems kinda kludgy.
I stand corrected. (Do you hear that very often on this forum?). It somewhat depends on the insulation system used.
If the foundation is insulated on the OUTSIDE, you can have a continuous run of insulation from the bottom of the basement wall up to the roofline, and eliminate air leaks on the insulation. If the foundation is insulated on the INSIDE, you need to seal the air leakage path where the insulation system crosses over from inside to outside.
If