The prefab component of this starkly modern, 3,851-square-foot house in Austin, Texas, is the structurally insulated panels used for its building envelope. It was certified LEED-platinum and has a HERS rating of 35. Courtesy photo / Alison Cartwright.
Author Sheri Koones is on a mission to educate American homeowners about home building.
Her first three books focused on the basics of home construction, borne of her own experience as a frustrated homeowner trying to remodel her Greenwich, Conn., house. At that time, she said in a recent interview, there was almost no information to help her make intelligent choices as she faced an endless number of decisions about this or that flooring material, plumbing fixture, roof shingle, and on and on.
Koones’ last four books have zeroed in on prefabricated, factory-built housing. For more than 100 years, this type of housing has been promoted by designers and entrepreneurs who have touted its efficiency, speed and affordability, but with limited success. It remains a niche market, and most homeowners still equate prefabrication and modular housing with trailers, Koones said. She wants to set them straight.
With “Prefabulous + Almost off the Grid,” (Abrams, $25), Koones presents a wide variety of prefab houses that demonstrate how broad a category it is today. A modular prefab house is constructed in sections in a factory, transported on the flat bed trucks we see plying the Interstate highways and slowing down traffic, and finally joined together at the building site in only a few hours. Or, prefab can mean that the walls and framing can be partially assembled in a factory and brought to the site, where a local contractor supervises their erection and finishes the house over several weeks.
As this super-energy efficient, modestly sized, 1,500-square-foot house in Belfast, Maine, illustrates, energy efficiency is possible in a house with big windows. The prefab components are the structural insulated panels that were used for the building envelope. The HERS rating is 20. Courtesy photo / Trent Bell
Or the prefab system can be something else entirely.
The 32 prefab houses that Koones features in her latest book show that the aesthetics of prefab housing are as varied as the different types of prefabrication. Stylistically, these houses run the gamut from strictly traditional to starkly contemporary, and they all feature inviting, light filled interiors. No one will mistake them for a trailer.
The 32 houses were built in both urban and rural areas; by current standards, they are modest in size; more than half of them have less than 2,500 square feet of living space. The owners gravitated to prefab, Koones said, because they determined that it was the best way to build a new house that would be unusually energy efficient and easy to maintain.
Koones offers additional reasons to build a prefab house.
For her, one of the most important will surprise homeowners who are not familiar with the construction process. A factory built house minimizes waste, compared with a site-built house, where the large volume of waste routinely fills up a dumpster several times over. Most owners are oblivious to this but, Koones points out, they are paying for all the material that is wasted, as well as the Dumpster to hold it, the cost to haul it to a landfill and the tipping fees to dump it there.
This 2,039 square-foot, prefab house was built in sections in a factory and these were trucked to its Chicago building site. It was certified LEED platinum and the HERS rating is 48. Courtesy photo / Mike Schwartz
Factories, where the same house parts are assembled over and over, can more accurately predict what they will need, so waste is minimized and the overages can be used for other projects.
A second plus with a prefab house is its speed of construction.
While a site-built house takes several to many months to complete, a prefab generally takes weeks. Because most of the work is done in a factory, there are no weather delays and no damage to exposed framing from being deluged in a summer thunderstorm. Perhaps most importantly for owners, speeding up the construction process reduces the amount of stress that most endure as their house goes up.
Koones says prefab houses are built with higher quality control than site-built ones. In many factories, workers use sophisticated, computer-aided machinery that makes more accurate cuts so framing fits together more easily; this in turn makes all the subsequent steps in the construction sequence, including the installation of interior and exterior materials and windows, faster and easier.
Koones devotes a fair amount of text to explaining the many different ways that her 32 houses deliver the energy efficiency their owners sought.
Like all the houses in featured in Sherri Koones’ Book, this one in Maine has a light-filled interior. It clearly demonstrates that an extremely energy efficient house, even in a very cold climate, can still have big windows!
A telling detail is the HERS rating scores. HERS, which stands for Home Energy Rating System, compares the energy efficiency of a building envelope to a house built to the Model Energy Code for 2006. A house meeting that standard is rated at 100. Somewhat counter-intuitively, the lower the HERS rating, the better.
A house built to the most recent and more stringent 2012 Model Energy Code will be 30 percent more efficient and have a HERS rating of about 70. Of the 19 prefab houses with HERS scores in Koones’s book (not every house was rated), 12 have a rating below 50 and one has a HERS rating of 0.
All the houses in Koones’s book were custom built. But given the advantages of factory production, especially in creating energy-efficient houses, could an entire subdivision be built this way, especially as energy code requirements ratchet upward?
The prefab components of this Bethesda, Md., Craftsman-styled, 4,300-square-foot house are the structural insulated panels that were used for the building envelope. The HERS rating is 37. Courtesy photo/ Jim Tetro.
Daniel Gainsboro of Now Communities, a Boston home building firm whose work will be featured in Koones’ next book, is planning to do exactly that, using the Bensonwood Homes wall system featured in the “Unity House” described in her current book.
In the past, production builders have eschewed prefab, saying it costs too much. Gainsboro opted for prefab for the opposite reason — it will cost him less. The system he is using is faster, more efficient, and less costly for building the 12-inch-thick walls that he is using to make his houses 60 percent more energy efficient than conventionally built ones in the Boston area.
When he built this cumbersome, multi-layered wall on site, his crews found it frustrating and time consuming. What took them three weeks, Bensonwood can do in two and a half days.
Another plus: Bensonwood’s computerized production system allows Gainsboro to tweak the amount of insulation in each wall, depending on its orientation and sun exposure, a degree of fine tuning that the builder of a site-built house can only dream about.
Questions, queries or a topic you would like to see covered? Katherine Salant can be contacted at www.katherinesalant.com.
