Building the Sun Cottage Part IV: Walls and Beams

Follow an architect as he leads us through the planning, pouring, and pounding involved in constrcuting the reinforced walls for your low-cost sun cottage.


| November/December 1983



Concrete Wall Detail

Here is the diagram showing how to put up your concrete wall for your sun cottage.


ILLUSTRATION: ANGUS W. MACDONALD

Follow an architect as he leads us through the Planning pouring, and pounding involved in...

All too many of us have found that building an energy-efficient home seems to be a dream... a fantasy that's kept just out of reach by escalating prices and high interest rates. Of course, MOTHER EARTH NEWS has long been exploring ways of breaking this vicious circle of waste, and one inventor of solutions — whose work we've shown you before (see Building the Sun Cottage Part I: Site Selection) — is architect Angus W. Macdonald. Angus has developed a number of housing designs that apply low-cost building techniques to passive solar, earth-tempered homes... and he's agreed to relate, in a set of articles that will span at least six issues of MOTHER EARTH NEWS, much of what he's learned about planning and building such structures. The series is following the actual construction of one of the architect's standard designs — Sun Cottage — and includes photos and illustrations.

In the last article of this series, we discussed the pouring of the footings, foundation, and floor slab for our earth-sheltered, passive solar home. And now (finally!) it's time to get started with the three-dimensional fun... beginning with the construction of the masonry or concrete retaining wall shell. Because of the terrific lateral forces that the earth imposes upon below grade walls, this is one of the most critical stages of the entire planning and construction process: You must carefully follow all of the provisions of your building code that apply to constructing bearing and retaining walls.

To give an example of the scale of these forces, the sideways pressure exerted on a retaining wall by 8 feet of backfill is 600 PSI (pounds per square inch) at floor level! So beware of contractors (or any other "experts") who claim that you're over structuring your dwelling. Many of them have never built a house even remotely like the Sun Cottage... and the risk of a cracked and leaking wall isn't one you'll want to take with your home.

Choosing Methods and Materials

If your site is near an urban area, you may have a choice of materials for your walls. Check the Yellow Pages (under "Concrete", "Contractors", "Concrete Contractors", and "Concrete Forms") to find out whether there's a company close by that rents forms. In locations where prefabricated metal forms are available, pouring a solid concrete wall will probably be less expensive than would be building with concrete block masonry. In any case, a poured wall will be stronger and more waterproof than will a masonry one. What's more, only an 8" thickness is required for the below-grade portions of a poured structure (as opposed to the 12 inches of masonry needed in the same location)... the sides will be smooth (or in a brick pattern molded by the appropriate metal form work), making them easier to waterproof and paint than blocks... and less reinforcing steel is required, as shown in Fig. 1 in the Image Gallery. Most companies that do this sort of work will quote a price for pouring both the footings and the walls, since a linking "key" must be provided to prevent the walls from slipping across their footings after backfilling. Of course, the poured walls won't follow the roof line on the east or west ends... instead, they'll rise to 8 feet high (to the top of the forms), and you'll just frame triangles, in timber and plywood, on top of the concrete to conform to the slope of the roof.

A third construction option is to dry-stack block to form the walls. This involves using a specially formulated fiberglass cement troweled on both sides of a concrete block wall that's laid up without mortar. As is the case with poured concrete, dry-stacking produces smooth, water-resistant surfaces that are easy to paint and seal. However, just as is the case with normal block construction, retaining walls must be reinforced and alternate cavities must be filled with concrete grout. Then again, you might save some money by using this technique, since even novice block-layers can do the work themselves. (The approach is also appealing in instances when a mason is simply unavailable.) On the other hand, some of those savings would be absorbed by the cost of the more expensive fiberglass cement.





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