Tips on Matching a Gable Roof Addition

Getting Started

• The addition should be framed up to the point where it intersects the eaves on the existing structure. Since the tie-in framing will lie on top of the framing of the existing roof, get a structural engineer's opinion on whether the old roof can support the added weight. You have the option of removing the shingles on the space under the tie-in before you start framing, but the FineHomebuilding website recommends simply leaving them in place.

Ridge Pole

• A ridge pole, a long beam that goes on top of the rafters or trusses, will connect the top of the addition to a point on the old roof. To find the proper spot, called the ridge point, run a string horizontally from the peak of the addition roof and fasten it at the point where it meets the old roof. You will cut a ridge pole to this length to connect the top of the two roofs.

Valley

• The tie-in will form two 45-degree intersections, called valleys, with the old roof. Running string lines, also called chalk lines, from the ridge point to the point where the addition walls meet the existing wall gives you the location for your valley boards, which provide the base of the tie-in framing. After cutting the valley boards and ridge pole to length, you remove the strings and nail the boards and pole in place.

Jack Rafter

• The rafters on the tie-in, which will be shorter than normal rafters, fasten to the valley boards and the new ridge pole. You get the proper length for the new rafters, called jack rafters, by marking off every 24 inches on the ridge pole and measuring down to the valley board. You will need a miter box, a wooden or metal box with angled slots, to make the appropriate cuts on the ends of the rafters. Once framing has completed, you need to finish the new roof with shingles matching the old one.