Dormers are very popular in homes on the East coast˳ They are used to allow for more space in a steep pitched roofing system˳ For most dormers, you will need to frame the roof first and then raise the gables and set the ridge beam˳ It is also important to understand where the roof load is designed to distribute the weight on the rafters and floor joists˳ Then you will know where your bearing points are so you can install extra framing beams to carry the load and transfer down to the home’s foundation˳
Framing Gable Dormers
Gable dormers are built perpendicular to the existing roof plane, extends out the edge of the existing roof line and includes a gable roof˳ Gable dormers are designed to have the weight of the dormer rafters carried through the side walls and on to the existing roofs rafters˳ Knowing this, you will want to double or triple the roof rafters on either side of the new dormer so the side walls of the dormer have a strong support to rest on˳ By doing this you will not have to add additional joists under the attic sub-floor˳
Just like framing a new skylight, you will need to cut and head the existing rafters that run through the opening of the dormer˳ You can use a recip saw to do the job˳
If you are framing a wide gable dormer, you can expect the load to require extra attention˳ You may need to use steel I-beams on the floor system to hold up the roof˳ You may also need to add extra beams in your first floor walls to help carry the weight to the foundation˳ You can do all of this before you cut into your roof to limit the amount of time your home is exposed to outside elements˳
Shed Dormers
Framing a shed dormer is easier than framing a gable dormer˳ All the weight of the shed dormer is placed on the end wall instead of the side walls so there is no load-bearing issue if the end wall is framed on top of the exterior walls of the home˳ If the end wall of the dormer is located away from the exterior wall, the floor joist will need to be doubled or trippled to provide adequate support˳
The top of the shed dormer can either meet with the main ridge or existing roof˳ If the top meets below the ridge, you will need to install a header to support the load of the dormer rafters˳ The header must be correctly sized to carry the tail joists and connect the rafters and the ridge˳ The side walls of a shed dormer do not carry any weight of the dormer so you will not need to reinforce the rafters on either side under the sidewalls˳
To save on the amount of time your home is open, try and have all of your materials pre-cut˳ You should be able to frame a gable or shed dormer in less than a day˳
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