Expert: Richard Taylor, AIA - 11/1/2003

Question
Because I'm working with a limited budget, and have had some house building experience, I'm exploring the idea of building a Frank Lloyd Wright “Usonian” house in the future. On a remote parcel in southern Ontario, actually it's his “Jacobs House” design, I'm primarily interested in. The L shaped design is orientated to make maximum use of solar energy and it incorporates radiant heating that is installed during the original concrete pour. Which eliminates a major heating expence right off the bat? His brilliant ideas are well ahead of there time and I could go on and on about this house. However, I'll spare you this and get to my questions of flat roofs & frost lines. I intend to build myself and fulfill the natural desire of man to build his own dwelling, as well as saving money. Wrights design saves money by eliminating the pitched roof and basement expenses, which I believe amount to about 60%. With this in mind, in preparation for the slab pour, is it possible to dig trenches around the building perimeter and support walls that are filled with tamped gravel as a foundation support instead of a concrete foundation? I'm not sure if I'm accurately describing this method, as it's not a common one?  And since it calls for a flat roof, what modern waterproof coverings are there, besides tar? Could you explain the difference between a warm and cold roof? Regards.  Bill  

Answer
Mr. Stark:

Thanks for your question!

Wright did two houses for the Jacobs; the second was the "solar hemicycle" so I'll assume you're talking about the first, built in Madison in 1936.  It's one of my favorite Usonians, too. Nice and clean.

A layout like this can be energy efficient, but it'll depend upon the amount of sunshine your location gets in the winter.  Without the direct sunshine, solar gain will be negligible and you'll probably lose more energy than you gain (that's a major problem here in central Ohio!).

When considering the energy benefits of a Wright design, you must remember that he wasn't working with fiberglass insulation, housewrap, high-performance glazing and other things that we take for granted today (especially the glazing).  He was overcoming a relatively poor building envelope technology.  Combining high-performance construction with solar gain strategies can result in OVERheating!  Consider it carefully.

You will benefit from technology in the roof construction.  The spans are easy to make with "flat" roof trusses (I'd suggest you have them pitched slightly, not absolutely flat).  The trussed construction will make insulation and utilities easier, too.  You have a couple of choices in flat roof coverings.  One is single-ply rubber membrane (manufactured by GoodRich and Carlisle).  Check out their respective websites for info and installation details.  Another is Hypalon by DuPont Dow.  It's also a single-ply membrane.  Both are appropriate for your situation.

A warm roof is the standard method of roof construction.  It is essentially an air space over the insulation with soffit and ridge vents.  A cold roof is used with vaulted ceilings.  It has no air space next to the insulation, but instead has an additional layer of construction on top of the main structure that acts to create an air channel and isolate the insulated construction.  It's useful in preventing ice damming.  Since your roof is flat, ventilation will be trickier.  Research this carefully.  I'd recommend Rob Thallon's "Graphic Guide to Frame Construction" as a start.

Your foundation idea is fine, as long as it's properly engineered and you take the frost depth into account.  That method is widely used here in basements by a company called "Superior Walls".  They do a precast foundation wall on a gravel footing that works great.  You may want to look up Superior to see if they have a dealer near you.

Good luck with the house - it sounds like a great project.  Send me a photo when it's done to rich@rtaylorarchitects.com.

Hope this helps!

Richard Taylor, AIA
Richard Taylor Architects, LLC
www.rtaylorarchitects.com