Architect and builder Andrew DiGiammo faces an interesting challenge with one of his current projects. DiGiammo's company, Master Builders of New England, is designing and building a new second story for an existing high-end house in Swansea, Massachusetts. For this custom project, DiGiammo needs to create interesting and dramatic forms in the new living space. But during construction, he also has to take care to protect the structure, finishes, and furnishings on the home's existing first floor area.

DiGiammo decided to do something he's never tried before: Build the new roof in place before tearing out the old roof underneath. "We did it this way because it seemed like the most efficient way to get the job done," DiGiammo says. After drawing up the plans, DiGiammo entrusted the job to site foreman Peter Latour, and didn't visit the site again until after the roof was mostly built. "It wasn't until I took some pictures that I realized how cool it looks. I said 'Wow, it looks like it's hovering.' We've basically built a big umbrella, then we're going to fill in the walls, and then after that we're going to rip out the roof deck and put the floors in. We won't remove the old roof until the upstairs windows are in and the space is dry."

In order to pursue this strategy, DiGiammo had to visualize the roof structure a little differently. "It has to be supported before all the walls are built, and so I had to include some redundant structure. Some of the carrying timbers that are required to hold it up now won't be needed when the project is completely built," he explains. "I used some structural valleys where I otherwise wouldn't have to."

"The other nice thing," adds DiGiammo, "is that it allows us to use the existing roof to support our staging while we're framing the new roof. It gets us up nice and high, higher than we would be if we had just ripped the roof off and put down a floor deck. And the existing roof is also a nice surface to walk on. It's working out good."

At the moment, the roof is held up by multiple structural valleys and ridges that converge on just a few points. This required DiGiammo to visualize the intersection of the roof ridge and valley beams at the design stage, and make sure that the intersection point occurred above the existing bearing wall in the house below, so that a simple post could support the whole structure. "I made sure that lined up right from day one," DiGiammo says. But that's his usual practice anyway, DiGiammo explains: "I wanted to work with the existing structure. If I was going to do structural valleys, I wanted to make sure I had a point from the beginning. Whenever I put an addition onto existing, I start with existing structural points that I want to hit, rather than just laying out a structural system and then figure out how I'm going to get to those structural points — rather than saying, 'Here's my design, this structural point is twelve feet away, how do I transfer the load over to that point?'"