Illustration by Trevor Johnson
In this project, the construction that took place on the interior of the house was relatively straightforward: Take out a few walls, remove a fireplace, reroute utility connections. Up on the roof, however, the addition became more problematic.
Because the ridge of this addition is parallel to the main house, a gable "bridge" was used to fill in between the two. This created four valleys—where two downward-sloping roofs intersect. Most additions create at least two.
Because valleys collect water from both roof planes, they're prone to leaking. If you're having an addition put on, discuss how valleys will be treated with your roofer. In most cases, he'll recommend installing 28-ga. galvanized sheet metal or asphalt felt in the valley. It can then be finished off with one of three shingle patterns: woven, closed-cut or open. If your roofing is tile, wood or another rigid material, you're limited to the latter two options. The woven style provides the best weather shield, as the shingles overlap across the valley. It also gives the roof a neat, flowing look. In a closed-cut treatment, shingles are trimmed where they meet at the center of the valley. On an open valley, shingles just cover the outer edges of the flashing.
Adding on to your home also forces you to decide how much re-roofing to do. If wood shakes are worn or split, or if asphalt or fiberglass shingles are brittle or balding, consider replacing the entire roof. This way the roofing on the addition and that on the main house will match, but it can boost project costs a lot. If you decide not to opt for a new roof, consider re-roofing any sections of existing roof around the addition—stopping at ridges, valleys or hips—rather than weaving the new shingles into the old. This approach was used on the house, above; the back side of the main roof was re-shingled with the addition.