Basement slab and first floor framing

Caution, lots of photos this week.

This week we finished installing the interior drainage plane for the foundation walls, insulating the floor under the basement slab and pouring the slab. We also framed out the first floor exterior walls. The weather held out till Saturday afternoon when a cold rain forced us to stop.

We used extruded polystyrene foam (XPS, the blue stuff) under the slab because of its greater compressive strength. We laid two layers of 2 inch foam, then a layer of 6 mil polyethylene as our radon gas barrier. We used acoustical sealant to attach the poly to the drainage plane on the wall to complete our radon gas barrier. Then we laid another 2 inches of XPS foam for a total for R30 under the slab. The top 2 inches of the foam lies on top of the footing. We placed another 2 inches of expanded polystyrene (EPS, the white stuff) on the walls sitting on top of the XPS foam. EPS is more environmentally friendly than XPS. This overlap isolates the concrete slab from the foundation and walls, keeping it dry and warm.

The concrete arrived Friday. They poured and leveled 4 inches of concrete on top of the foam. They also poured a small knee wall in the walkout area and the footings for the deck on the west side of the house.

Above, we raised the first floor exterior walls. You can now start to get a sense of the size of the space and the view out the framed openings. Of course it will feel a bit smaller when we frame up the interior walls, and smaller still when we put up the sheathing and finally the interior drywall.  Now you can see the house when driving up the driveway.

3 Responses to “Basement slab and first floor framing”

  1. 1 Mom 8-September-2010 at 9:49 am

    I LOVE the view from the windows! WOW!!

  2. 2 Jim Merrithew 7-January-2011 at 4:38 pm

    You mentioned that you have 6 inches of XPS under the slab. The foundation wall will be insulated to R40. At the intersection of the foundation wall and the slab, you only have two inches of EPS which is roughly R8 to 9. Is this a thermal weak point in your envelope?
    Did you lay any insulation above the drainage tiles to insulate the footings before you backfilled?

    • 3 Larry 7-January-2011 at 6:29 pm

      It would be a weak spot if there was not an R40 wall above it. This detail only works if you are highly insulating the foundation walls.

      There is no insulation on the exterior of the foundation or footings.

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