How To Add Dormers to an Attic

Image of house attic

A dormer can provide a gloomy and dark attic with some available light during the day. A dormer can also give an attic more headroom. If you are in need of more rooms in your house, installing a dormer to an attic may give you the immediate solution as you can then convert the attic into an extra bedroom. Installing a dormer requires some carpentry skills. It may do you good to check with the local building code if installing a dormer is allowed and will not affect the original house plan that have been submitted as well as to know if there is necessary paperwork that needs to be submitted.

  • Take a look at the outside of your house and decide the exact location where you want the dormer to be installed. It should be in the most prominent position where it will benefit from the available light during the day.
  • Once you have determined where the dormer should be placed you can start removing the roofing materials. These include the shingles, the roofing paper as well as the sheathing from a span encompassing about three to four rafters. You should also remove the ceiling inside the attic to cut a hole for the dormer.
  • One side of the dormer should lie against one of the existing rafters. Cut lumber the same size as the existing rafter and nail it to the side. Measure the width of the dormer from the side of the double rafter you have just finished. The measurement should be taken from the inside wall to the opposite inside wall. This width will determine where you will install the next double rafter. These double rafters will be where you will attach the bottom section of the dormer walls. Install a piece of lumber between the two perpendicular headers. This will be the sill of the dormer window that you will install later.
  • Cut and nail the headers to the side to the double rafters near the lower slope of the roof. This will determine the height of the dormer roof. The headers should also be double pieces of lumber. Add the two shorter double headers to the back of the dormer frame. Install double top plates to complete the dormer shell. Add wall studs in between the top plates and the lower rafters when you will nail the dormer wall sidings. Complete the frame and the installation of the studs. The corners of the top plates should be cut an angle to conform to the pitch of the roof. It will also be necessary to cut the bottom of the wall studs near the back of the dormer frame at an angle to make them firm and flush against the double rafters.
  • Cut the lumber that will form the ridge of the roof. The wood should be straight. Measure and cut two pieces of wood that will be the dormer roof’s common rafters and attach these to the gable end to provide temporary support while you install the ridge. Check that the ridge is level and installed straight before cutting and installing the rest of the common rafters. These will be where you will attach the roofing material for the dormer. You should also install wall studs on the triangle formed by the roof and the top of the dormer window.
  • You need to take care of the back of the dormer where it meets the main roof. You have to install a nailer frame for the jack rafters that the will be installed in the valley made by the roof slope. After this all that is left for you to do is to nail the sidings and the roof and install the window before painting the dormer.

Check that the dormer is set flush against the roof and the gaps sealed before finishing it. Reinstall the shingles, roofing paper and sheathing, and repair the ceiling inside the attic. Now you are ready to enjoy a well-lit attic or your new bedroom.


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