Insulating the exterior of a Rubberwall foundation — hydrostatic pressure questions
(Zone 5A) 2 questions really
;
1st – have been using Rubberwall as my foundation sealer for years and been very satisfied with it. I usually will put a layer of some insulation on the rubberwall at the time of install to protect it but also when looking for a exterior insulation job. Lately I have been wondering if there are any redeeming qualities in the green colored rubberwall material. In other words is its manufacturing toxic or bad news in any way.
2nd – We are about to backfill a new home that has a drive out full basement under the whole thing and Energy guy wants two layers of 1 inch insulation on the outside of the foundation and wants a drainage plane to the footing drain to release hydrostatic pressure. Is using 1 layer of 2 inch going to be a big difference (because of the seams) and then what product and assembly do you suggest. Can I just do my layer of Rubberwall with 2 inches of foam and then backfill with stone, not worrying about additional drianage plain?
Suggestions welcome. Thanks
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Replies
Arthur,
I'm not familiar with the product you call "Rubberwall."
Perhaps you are referring to a product called "Rub-R-Wall"? (For the record, I am also unfamiliar with Rub-R-Wall.)
Q. "Lately I have been wondering if there are any redeeming qualities in the green colored rubberwall material."
A. If the manufacturer of Rub-R-Wall is to be believed, the redeeming qualities have to do with the product's ability to waterproof the foundation wall.
Q. "Is its manufacturing toxic or bad news in any way?"
A. I doubt whether the product will cause any health problems for the occupants of the building. It's more likely (but still unknown) that the workers in the plant where Rub-R-Wall is manufactured might have some type of negative health effect.
Q. "Is using 1 layer of 2 inch going to be a big difference (because of the seams) and then what product and assembly do you suggest? Can I just do my layer of Rubberwall with 2 inches of foam and then backfill with stone, not worrying about additional drainage plain?"
A. Two inches of rigid foam is better than 1 inch of rigid foam. The main reason is that 2 inches of foam gives you twice the R-value of one inch of foam. The benefit from staggering the seams of the two layers is a small benefit compared to the doubling of the R-value.
To provide an adequate path for moisture to reach the footing drain, and to relieve hydrostatic pressure, you have two choices: you either need a dimple mat (or a similar three-dimensional plastic product that provides channels for drainage), or you need to install a free-draining material like crushed stone (ideally protected with landscape fabric to prevent the migration of silt that might clog the stone). Installing crushed stone well is possible but tricky, because the installation of vertical landscape fabric isn't easy. Choose either method -- whatever you prefer.