Yesterday I took a trip into Seattle to watch the first home in Seattle to be built in modules, trucked in to the site and then assembled like building blocks with a crane. It was cool. Even better – it was designed with sustainability in mind.
The very fact that this building was built off site and out of the elements tackles one very big problem that all construction projects face – water. Undoubtedly you’ve seen partially built wooden structures getting a good soaking in a downpour. Given the right circumstances or the wrong drying opportunities, that wet wood can become a breeding ground for mold, rot, or warping. Normally contractors work hard to keep the project as dry and covered as possible and allow opportunity for it to dry out sufficiently before proceeding to the next building phase. Sometimes their good intentions fail later on down the line because the damage was already done and had not been caught or the wood wasn’t as dry as they thought. Some contractors may follow the schedule with more diligence than using best building practices to allow proper drying time. Building in a protected environment reduces the opportunity for water intrusion - and allows installation of the GWB and some of the other interior features before it arrives on site.
Keeping things dry is not the only sustainable practice that building in an off site location can offer. Material resource allotment can be better controlled with an assembly line type construction facility. Jigs to quickly & accurately layout pieces that need multiple copies can easily be arranged where there is space to allow for them. Contractors will set up site built jigs to make their projects run smoother, but not all sites will allow the same amount of room and opportunity for doing so. Another sustainable feature that is not limited to off site building, but excels with planning is waste reduction. Careful layout of the design and planning of how the material is cut and set will reduce the amount of waste that is generated on the project. Coordination between the trades and the designer can bring value engineering to the project through the wise use of materials.
Speaking of Value Engineering – by carefully examining each aspect of a project and determining the best and most efficient way to accomplish its goals you can provide a more quality product that could be cheaper and might cut time off the project. Having your materials dry and sorted ready to build even on the most inclement of days is value engineering. So is quick assembly of your project so that it can be dried in faster - less chance for mold and structure damage, less need to spend extra time mitigating that later.
The GreenFab project was not a Passive House project, but when I spoke with Johnny Hartsfield he did say that they could build to Passive House standards. As a Passive House consultant I know this would mean they would have to meet the same energy and airtight requirements as any other Passive House. Their modules would be entered into the PHPP as one build, thermal bridges would need to be identified and eliminated, and the solar heat gains and losses would need to be accounted for. Finally, once on the site, the modules would need to be sealed airtight together and a blower door test performed. This building method would lend itself to Passive House quite nicely and as with any other Passive House project, it is the planning before the build as well as the care of the build that produce the planned Passive House results. If you would like to read more about the Seattle GreenFab project and see even more detailed videos that they have put together about different aspects of the construction process, you can visit them at http://greenfab.com/
Entire building modules are not the only way to build offsite and assemble quickly. Panelization is another method. Here is a video where a buildings’ walls were built offsite and trucked in then assembled. It is the same concept as the modular style of fabrication. This is how many Passive Houses have been built in Europe and a few here in the United States. Expect to hear more about these methods combined with Passive House requirements in the future.
Up Next – Built off site and trucked in whole. The Mini-B Passive House makes its journey to its temporary home at the Phinney Ridge Neighborhood center!