Ask the Architect

The challenges of pre-fab houses, part one

Posted

Q. I thought our pre-fab house would be a better choice, since it was factory-built and went together quickly and easily when it was delivered. Now we have cracks in the ceilings near the top of the walls, and I have no idea why. Is it that the wood is shrinking because it’s drying out? What can we do about this?

A. I’ve sat with many homeowners who praised how fast their neighbors’ houses have been rebuilt with pre-fabricated homes — built, as you said, in a factory, under controlled temperature and delivered on truck beds to the job site. Not seeing the process and experiencing the time it takes to build a home, because it gets delivered nearly done, ready to fit together, makes it seem like it just appears one day, but the effort to build it is similar.

Unfortunately, there are some things that pre-fabricated homes lack that few people talk about, and there are issues that come up that are hard to deal with once the house is together. Probably the most disconcerting, at least to a homeowner, is that the attic comprises trusses spanning the home, forming ceiling, attic and roof structure all in one. Unfortunately, the attic is useless to store anything large in, because trusses are made up of lots of cross members that form a forest of vertical or angled members 16 to 24 inches apart. The last client who went to a pre-fabricated house took our plans to the company, which redrew them to develop modular room and hallway shapes, wiping out or reconfiguring spaces needed for the owner’s furniture arrangements and choice of window locations to avoid views of the neighbor’s house. The owner was disappointed that it was a “different house.”

Your problem with the wall and ceiling connections isn’t generally talked about, but the nailing of the top of the wall to the trusses has to be done with a less rigid and specially spaced technique because of a phenomenon that has to do with wind uplift. Just like the wind uplift that makes a plane fly, a roof experiences “drag” as breezes sweep across the roof surface and pull the roof upward. Because of the number of vertical connections from the top roof members to the ceiling members, there’s much more movement than a “stick-built” house lifting right at the tops of the walls.

Page 1 / 2