How to attach 4″ EPS foam to exterior of basement wall below grade?
I am gathering materials for an expansion and reno of an existing home in zone 7.
I will be adding 4″ EPS foam above grade wood framed portion on the renovation side of the building (850 sq ft) as well as to the new construction (1000 sq ft) using 6 1/2 inch screws (thanks Dana for pointing me in the right direction on that detail).
I am struggling with details on how I will attach the 4″ EPS to the below grade concrete AND whether to use a drain wrap product against the concrete wall like Platon Foundation Wrap.
If Platon or similar is recommended I would appreciate some guidance as to the detail of the stack up and attachment…
I understand the foundation drain wrap is mechanically fastened to the concrete by ram-set nails…how is the foam attached to the drain wrap?
and how can I finish the exterior of the foam…
I am hoping to use a product like a concrete board under grade and an concrete (imitation rock) board applied above grade to the deck ledger board.
With that in mind; given that I plan 4″ of foam from footer to top plate how can I attach the deck ledge to the house (over the foam?)?
Thanks
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Replies
Anyone have some thoughts on this.........this must be a common problem that is routinely overcome...
Tim,
Dimpled wraps, like Platon's, are usually used instead of asphalt based or elastometric foundation sealers where soil is in contact with the concrete. In your case the EPS will provide a barrier, so it is unnecessary.
The foam can be attached to the foundation wall with tap-cons and caps, or foam glue. The attachment is really only to hold it in place until it is backfilled.
There are variety of ways you can provide mechanical protection for the foam above or near grade. Cement board with a stucco coating, and metal flashing probably being the most common. Neither affords much protection from tunnelling insects.
The deck ledger can be attached in a couple of ways. There are proprietary metal ledger mounts that extend out several inches, you can also use threaded rods with spacers. Both are a second best solution compared to making the deck independently supported by a beam and posts several feet out from the house. Any of these methods should be run by an engineer to ensure they meet both the vertical and horizontal load requirements of your code.
Tim,
Here is a link to an article that discusses attaching rigid foam to concrete walls, and protecting the above-grade portion of exterior rigid foam: How to Insulate a Basement Wall.
Dimpled foundation drainage mat products can be installed on the exterior side of the rigid foam if you want, to help reduce hydrostatic pressure and to keep the wall dry. If it's installed correctly, it can help direct water to your footing drain. As Malcolm points out, it is optional; another way to achieve the same goal is to backfill with free-draining material (gravel, for example), capped with a few inches of top soil or clay-rich soil.
Thanks you both.. the soil (90% sand) is very well drained so I will use clean gravel as a backfill and omit the dimpled product.
Just so I'm clear in regards the foam...
I can glue (adhere) the first of two layers of foam (2 X 2") to the concrete after its damp proofed with foam glue and then the second layer to the first with the same glue....then the cement board onto the outside layer of foam?
Is there a source for tapcons or similar that can penetrate 4" of foam?
We have no issues with termites here so that's not a concern.
As for the ledger I had not considered a free standing deck since in the current design there is a 4 foot deck (walkway) on 3 sides of the building at the main floor level leading to a 300 sq ft deck on the lake side. I had considered it for that deck.
No carpenter ants?
Attaching the deck to the house through the foam probably requires an engineered design, although Maine Deck Brackets might solve the problem. Otherwise, I'm thinking freestanding. Include the inner deck footings in the foundation dig.
I forgot about carpenter ants.... how bast to deal with that threat?
Tim,
See if you can get treated foam or look into spraying it with a product like Bor-a-Care. With seasonal treatments you might be able to keep them from nesting in your foam, but if they get in they will do a lot of damage. There are a lot of carpenter ants here in the PNW. I'd never use foam outside a foundation.
Tim,
TapCon screws can be purchased in a variety of lengths up to 6.25 inches long. See the link below.
http://www.confast.com/products/tapcon-concretescrew.aspx