Vapor barrior termination on mono slab?
FULLCIRCLEJOE
| Posted in General Questions on
Hello,
I am building a small house in TN on a mono slab. My local building inspector strongly recommends not insulating the sides of slabs due to termites in my area. So, my question is where should I stop the vapor barrier? See attached pic. My initial thought was to stop at point C, but if there is any incorrect sloping I would think water could get trapped between points C and B. Should I stop it at point B?
I very much appreciate any thoughts on this.
THANKS
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Replies
Joe,
There are two separate issues here.
Issue #1 concerns the sub-slab vapor barrier. The sub-slab vapor barrier should extend horizontally under the entire slab, terminating at point C. If you are worried about the slope at segment CB, then inspect the slope before the polyethylene is installed and correct if necessary with a rake. (I don't think that the slope of segment CB is as critical as you think, however. Stop worrying.)
Issue #2 concerns slab insulation. You really need vertical insulation at the slab perimeter. As far as I know, the best solution is to install a frost wall, and to install the insulation as shown in the detail drawing below. (This costs more than a monolithic slab, of course, but at least you end up with an insulated floor.)
I invite GBA readers who live in termite-infested regions of the country to suggest other solutions.
Every year I earn money and then use it to heat the ground around my home. I try not to think about it. But if it will save you from the same fate, consider using Roxul mineral wool bats for your perimeter insulation. Some types are approved for underslab use and termites ignore them as completely as zombies ignore sick people, according to a reliable documentary I may have seen.
Posted by a rank amateur in hopes that a reliable individual may confirm or deny.
-Pete Byar 4A