Wednesday, January 26, 2011

5. Basement Floors

Our old house in California had a lot of problems with water-seepage during rainstorms, so waterproofing is a big priority with the new house. The exterior foundation walls were coated with a black rubberized plastic material, then a layer of pink styrofoam was added to protect this membrane. It still seems like the waterproofing contractor went a bit overboard by doing this on walls which were all going to be below the basement floor, but he would not guarantee the job unless it was done.

The empty space inside this perimeter was then filled with gravel, which was compacted every 6 inches of depth.  The gravel was "shot" into place by a special type of gravel truck.  This truck has a large hopper which feeds gravel onto a fast-moving conveyer belt. By positioning the truck on a hill above the work area, the gravel stream can be aimed very precisely and shot about 60 feet. The cost of this service is only a little more than the price of the gravel alone, and it's far more efficient than dumping it in a pile and moving it with skip loaders.

The floors in the basement and main level will be stained concrete. This can be a huge money-saver, as no floor covering (tile, wood, carpet) is needed. The downside is that cement floors can get pretty cold. So, we embedded heating tubes in the floors. When the full system is in place, water (with a bit of anti-freeze) will flow through these tubes and connect to a geothermal grid in the ground outside. A heat-pump will keep the floors warm in the winter and cool in the summer. This scheme has become quite popular around here, and homeowners report that very little additional heating or cooling is required.

With the heating tubes and rebar installed, it was time to pour the basement floors. The floors needed to be poured up against the basement walls, so the first couple of rows of Insulated Concrete Forms had to be put in. I'll talk about the ICF walls in the next chapter, but I thought I'd just mention them now because the blocks are visible in these pictures.

Pouring the floors was a very large job, so it was done in several sections over a few weeks. Expansion joints are scribed in, forming 3-foot squares. The concrete will be stained to simulate the look of large Italian floor tiles. The day after pouring each section, the cement was covered with plastic so that it would cure slowly. A couple of weeks later, the whole basement floor was covered with plywood to protect it from wear-and-tear during construction. The concrete would not be seen again for a year.


  1. Ah. So the answer is, - there is no space. :) .... That answers all my thoughts of why you hadn't used all that assumed 'space'! :)

  2. Exactly. As they were filling up the sub-basement with gravel, I was wondering the same thing - is there any way to use that space? But then I realized that it would probably just collect water and cause more problems.

  3. Probably a wise thing to do. - Some years back a friend of mine moved into a newly built house, on a previously green-field site. At the time everything was fine. But it transpired that the site developer had disturbed some ancient land drains that had been in existence across the fields for many years. - The housing development was on a hillside, and when he had need to go under the wooden floor to inspect a problem, he found the whole space was awash with water to within a few inches of the floor joists. - The disturbed land drainage was being redirected into his under-floor space, instead of being drained down the hillside. - It was a major project to get the problem corrected.

  4. So how does one size a geothermal grid and what is entailed with the installation of it

  5. Ralph - There are a large number of factors to consider, but since we have a large lot we will be using about 2000 feet of tubing outside in a closed horizontal loop. We'll have a 4-ton heat pump. Here's a pretty good overview:
    Someday I hope to install a solar array to power the heat pump, which would give us virtually free heating and cooling.

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