How to Frame a Gabled Dormer The Family Handyman

How to Frame a Gabled Dormer The Family Handyman

A gabled roof looks great from the outside and adds space and light inside.

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Step 1: Is this project for me?

Building a dormer is an ambitious and challenging project. You should have a few remodeling projects under your belt before tackling a task this big and complex. If you’re a little unsure of your rough-framing or roofing skills, hire a carpenter to help with this phase of the project. The gable dormers we built are 6 ft. wide, about 9 ft. from the floor to the peak, and set back from the front wall of the house about 2 ft. Each dormer adds about 30 sq. ft. of headroom.

Projects this large and complex are expensive, especially when you add in elements like windows. Plan on a big time commitment as well. Set aside at least a four-day chunk of time for the basic framing, because once the roof’s open, you’ve got to keep at it until the dormer is weathertight. Then you can relax a little as you finish the exterior siding and trim. Plan on spending seven or eight more weekends finishing the interior and completing the exterior painting.

Building a dormer requires a tool belt loaded with all the basic carpentry tools, plus a few extrasa circular saw, reciprocating saw, framing square and 2- and 4-ft. levels. You’ll also need good equipment for working up high, an extension ladder, roofing brackets and scaffolding (see Roof Safety). We also recommend you rent or buy a personal fall arrest system (PFAS; Photos 1 and 12), consisting of a full-body harness, lanyard, rope, roof anchor and all the hardware and instructions.

Step 2: Work out dormer details on paper

Figure A: Dormer anatomy

The size of the new triple rafters and common rafters will vary with the roof and dormer size and local conditions. Have an architect or structural engineer size them.

Note: Figure A can be downloaded and printed from Additional Information below.

» class=»step2enlargePic enlargePic» href=»http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH04DJA_GABDOR_06.JPG»> Figure A: Dormer anatomy

The size of the new triple rafters and common rafters will vary with the roof and dormer size and local conditions. Have an architect or structural engineer size them.

Note: Figure A can be downloaded and printed from Additional Information below.

» class=»step2enlargeButton enlargeButton» href=»http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH04DJA_GABDOR_06.JPG»>

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Figure A: Dormer anatomy

The size of the new triple rafters and common rafters will vary with the roof and dormer size and local conditions. Have an architect or structural engineer size them.

Note: Figure A can be downloaded and printed from Additional Information below.

Like any other major remodeling project, your dormer project will progress more smoothly if you work out the details on paper or a full-size layout on your garage floor (Figure B), before beginning construction. Dormers are complex and not every house is suitable. To make sure the dormers work, we recommend hiring an architect who specializes in residential construction or remodeling. The architect will help you consider issues such as roof slope, interior headroom, exterior appearance, structural strength, roof condition and cost. If the dormer is feasible, the architect will draw up plans that include all the dimensions and special structural details. Use the plans to obtain a building permit from your local building inspections department.

How to Frame a Gabled Dormer The Family Handyman

After the plans have been approved by the building department, take them to a full-service lumberyard. A salesperson will put together a materials list and cost estimate and help you order windows and special items. Before you cut the hole in the old roof, have all of your materials delivered and rent a trash container or trailer for the debris. Buy a mesh reinforced plastic tarp large enough to cover the entire dormer area (Photo 5). Stretch one edge of the tarp so it laps over the roof ridge and secure it with 2x4s screwed into the roof sheathing. Roll the tarp back and it will be ready to pull over the roof at night or in the event of a surprise rainstorm.

Step 3: Lay out the dormer on the attic floor before opening the roof

Photo 1: Remove shingles and sheathing board

Remove the shingles from the area of the new dormer. Snap chalk lines for the inside edge of the dormer side walls, set your saw to cut through the roof sheathing and saw from bottom to top on both sides. Leave the overhang sheathing uncut. Pry off the old sheathing boards. » class=»step3enlargePic enlargePic» href=»http://hostedmedia.reimanpub.com/TFH/Step-By-Step/FH04DJA_GABDOR_03.JPG»> Photo 1: Remove shingles and sheathing board

Photo 1: Remove shingles and sheathing board

Remove the shingles from the area of the new dormer. Snap chalk lines for the inside edge of the dormer side walls, set your saw to cut through the roof sheathing and saw from bottom to top on both sides. Leave the overhang sheathing uncut. Pry off the old sheathing boards.

Photo 2: Make sure everything is plumb

Photo 2: Make sure everything is plumb

Using dimensions from your plan, draw lines on the floor to indicate the location of the front dormer wall. Plumb up from the outside face of the wall line and mark the rafters. Deduct an additional 1-1/2 in. to allow space for the new header (Photo 4) and cut off the rafters with a circular saw.

Photo 3: Install the new rafters


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