Building Affordable Houses—20 Years Later – GWC Mag

I don’t call myself a green builder, but I discovered the intersection between economy and ecology through my work in affordable housing. During my 40-year career, I have built hundreds of homes with one thing in common: they were always the lowest-priced new homes in the neighborhood. Sometimes government subsidies helped, but I never relied on these alone to reach the desired price point because it’s difficult to lower construction costs sufficiently to achieve affordability even on free land.

Building affordability into the design

The first step to cutting construction costs is “affordability by design.” This means ensuring the basic blueprint of a building is optimized to minimize costs from the start. After numerous trials, I developed techniques inspired by the discoveries of an unlikely source, biologist Carl Bergmann. Bergmann noticed that larger animals tended to live in colder climates, where their size helped them retain heat more efficiently. This observation, known as Bergmann’s Rule, suggests that larger bodies have a better volume-to-surface area ratio, allowing them to retain more heat. So, how does Bergmann’s rule help reduce construction costs?

While buildings are not animals, they have area, volume, and a perimeter. Various floor plan configurations require a range of exterior wall areas to interior volumes. To run a thought experiment, I drew two figures, one a square and the other a rectangle, both with an area of 625 square feet. Then, I calculated the perimeter of both shapes to discover that the square had a perimeter of 100 linear feet and the rectangle enclosing the same area had a perimeter of 125 linear feet. This was my eureka moment, as I realized the square shape would cost less to build because it had 25 percent less exterior wall—with its many costly layers of insulation, sheathing, water-resistive barrier, and siding.

I experimented with different shapes and sizes using a computer program to tweak building designs. Sometimes squares weren’t the most cost-effective option because they became too large for standard materials. However, my experiments showed consistent results.

One challenge was that I often had to build on narrow lots, requiring long, thin houses. So, I adjusted my formula to compare the area of the floor to the area of the exterior walls. This gave me a more precise ratio. Ideally, the ratio should be one-to-one, but that’s geometrically impossible unless you’re building a sphere. When I compared the square and rectangle examples using this new method, the square had a ratio of .78, which is good. Still, I found an even better ratio with a specific rectangle design: 24 ft. by 34 ft., which yielded a ratio of .88. If you run my earlier example, considering the wall area instead of the perimeter, you end up with a more accurate comparison.

^{My example of the square: 625 sq. ft. ÷ (25 ft x 4) x 8 = 800 sq. ft. wall = .78}

^{And the rectangle: 625 sq. ft. ÷ 1000 sq. ft. wall = .62}

^{My go-to shape is 24 x 34: 816 sq. ft. floor ÷ 928 sq. ft. wall = .88}

The square yielded a ratio of .78, which is efficient, but I could improve on this even with a rectangle. I discovered that my tried-and-true footprint of 24 ft. by 34 ft. yielded a very respectable ratio of .88 sq. ft. of floor for every square foot of wall.

At this point, you may wonder, but what about bedrooms, kitchens, and baths? I always start my design process by finding the most efficient basic box for the lot. I draw all my rooms inside this box. I generally opt for a two-story to balance building spans and the area of costly foundations and roofs.

Economical design influences energy performance

Many years ago, I built an affordable split-level home that Fine Homebuilding magazine featured in an article titled “Building Affordable Houses.” The article detailed many of the elements I used to reduce construction costs, including installing electric furnaces. I did this to avoid the expense of gas piping and flues. I also upgraded the shell construction, windows, insulation, and air-sealing to reduce heating and air-conditioning equipment size and expense.

A reader wrote to the magazine accusing me of using an electric furnace to saddle my buyers with excessive heating bills. An electric furnace is cheaper to buy and install but costs twice as much to run. The reader had a point. Although I had not heard complaints about the utility bills in my homes, I asked the local electric company to run a comparative audit of my houses vs. neighborhood homes. The results surprised me and explained why I had no complaints—despite using an energy-hog furnace, my homes were at least 30 percent cheaper to heat and cool than the neighborhood sample. I attribute this benefit to the reduced volume-to-surface ratio and upgraded shell.

Once I have decided on my basic box, I locate the utility core as close as possible to the center of the house, moving it around only as required to design a livable floor plan. This location makes for shorter runs of costly ductwork, plumbing, and heavy electrical wiring. I recently began using Gary Klein’s “hot water rectangle” to analyze my plumbing layout. Klein aims to reduce time waiting for hot water to arrive at the faucet. His approach and the ratios he recommends help optimize plumbing locations to reduce the cost of water and sewer pipes much more than simply locating bathrooms back-to-back.

Beyond the box

My go-to building shape and the hot water rectangle are just two examples of how I try to rely on principles of cost reduction to design a house. But the truth is, I have discovered a consistent, albeit imperfect, relationship between being cost-effective and being green building–friendly. I apply all the material-sparing techniques available in the residential building code, from low-dollar foundations to advanced-framing techniques.

In 2003, The Taunton Press commissioned my first book, Building an Affordable House: Trade Secrets to High-Value, Low-Cost Construction. It was published in 2004, coinciding with the rising popularity of the green building movement. During this time, CALGreen was in development, LEED 1.0 was running pilot projects, and even the Republicans (under George W. Bush) advocated for energy efficiency.

As popular interest in green building grew, I began receiving speaking engagements at green building conferences. To my surprise, my publisher informed me that my book had become a bestseller among U.S. and Canadian green building–materials suppliers. This recognition was a bit uncomfortable for me, given my self-concept as a conservative, hard-dollar guy.

However, with time, I’ve gained perspective. In the second edition of my book, available March 12, I explore the intersection of building economy and ecology in greater depth. I’ve come to realize that while I may have started as a conservative, cost-conscious builder, I now appreciate the importance of building homes that are not only affordable but also healthy, energy-efficient, durable, and environmentally considerate. I’m proud of the small contribution my homes make toward a better planet.

_______________________________________________________________________

Fernando Pagés Ruiz is a builder and an ICC-certified residential building inspector active in code development. Images courtesy of author, except where noted.