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Online Blog > Previous Entry 4/10/2015 > 5/01/2015 - Concrete Foundation Construction - dampproofing and french drains > Next Entry 6/9/2015

The following photos show the asphalt emulsion coat, which is just dampproofing the foundation. We like to keep all wood and siding materials at least 10" above finished grade, and we bring the damp proofing to this line on the concrete. We then place a perforated 4" PVC pipe around the base of the footer and run the pipe our to daylight. We place washed drain rock on top of the pipe and cover that with a landscape fabric before we place the topsoil. This fabric will help keep dirt out of the pipe and keep it flowing free of debris.

On the crawl space ground of this residence, before we placed a 6 millimeter polyethylene vapor retarder, we placed sand, since the rocks that were at that layer of the excavation would have quickly perforated our vapor barrier. Also, the sand will make it a lot more comfortable for our mechanical subcontractors, like the HVAC technicians and the plumber, to work in that space.

We place the 6 mil poly vapor retarder now during construction, because we have seen homes without it for a couple of months of construction, already develop mold on the bottom side of the subfloor. That is prevented by early placement of the vapor retarder.

Also, during construction of the subfloor, we keep the crawl space free of debris, especially wood scraps and other material that, if moist, would mold in the long run. We even sweep the crawlspace before the home is considered finished.

In this first photo, we have an extra large center pad as part of the continuous footer because this will be a major load bearing point for the ridge beam, and the roof, when loaded with snow, is designed to transfer 25,000 pounds of live load to that part of the foundation.

In the following photo, note that we do not backfill the foundation until we have built the subfloor. That is so that the lateral pressure of the backfill against the foundation will be resisted by the subfloor (which connects a wall to the opposing wall). Failure to do this can result in bent and bowed concrete walls, especially those that are not at a full cure (design load strength of concrete takes 28 days curing time).

I'll also call attention to the number of foundation vents. If you are going to vent a foundation, you have to do so adequately, otherwise you are creating more of a problem than a solution. The number of vents here exceeds code, which usually only specifies 1 SQF per 1500 SQF when a 6 mil vapor retarder is used, but the same code desires 100 square inches per 150 SQF when no vapor retarder is used.