How to Build a Mansard Roof

A mansard roof is a version of the hip roof. The lower section employs a deep, steep vertical slope on each of the four sides. The upper section is inset from the edge with a short, near vertical rise. This allows for additional living space in the attic or third floor. The mansard doesn't require complex framing, which saves time and money.

Confer with a builder or architect to come up with a design. She starts with a floor plan, then adds elevations to flesh out the shape and choice of material.

Review the original drawings with a structural engineer at the building site. He takes measurements, factors in weather considerations, then works up the final design and blueprints.

Consult your local code office for building code requirements and permits. Obtain all permits and set inspection dates.

Interview several contractors. Ask for recommendations from neighbors or the local home building supply store. Consider work ethic, previous experience and compatibility as well as price. Provide tools and hire skilled labor for shingling.

Choose the materials based on your budget, how long you need the roof to last and aesthetics. Climate should be your first consideration. Certain materials aren't workable in extreme weather and roof styles.

Calculate your roof area from the blueprints. Add 10 percent for waste. Divide by 100 to get the number of square feet. Round up and use this number to figure out costs and material needs. Purchase and arrange for delivery of materials. Ask for delivery directly to the roof.

Check your insurance policy for liability coverage. Check with your state for worker's compensation requirements. If you hire day laborers or specialists, you may need to withhold and file payroll taxes.

Prepare the job site. Cover plants and AC units, and rent a dumpster. Create a platform for tools.

Nail common rafters to one side of the first ridge board. Raise the ridge and nail in opposing rafters. Position the outside rafters so that the birdsmouths line up on the wall top plate and nail in place. Repeat this with the remaining three sides.

Nail in the remaining common rafters.

Nail in the ceiling beams and lay ceiling sheathing.

Build the upper extension by setting vertical rafters inside the ridge board line. Brace with common rafters inside and out.

Nail on collar ties and fascia before beginning to sheath the roof. Nail sheathing to common rafters. Lay flashing around valleys and vents. Lay the undercoating. Lay the shingles. Add any molding accents.


Use a calculator or rafter table book to cut the rafters. Determine the length of the ridge by subtracting the width of the building from its length. The thickness of the ridge board must be added to the ridge length. All common rafters are shortened half this thickness to maintain alignment.

Things You'll Need

  • Blueprints
  • Ladders and scaffolding
  • Woodworking tools
  • Work boots, gloves, hard hat, knee pads, tool belt
  • Lumber and sheathing
  • Tarps and plastic sheeting to cover plants and AC unit
  • Dumpster
  • Hardware, including nails, screws, metal ties
  • Underlayment material
  • Shingles or other finishing material
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