How to Build Home Addition Between Building with Existing Hip Roofs
Here are the steps to follow and important considerations to make when building a room addition between two hip roofs with a shed roof:
Foundation:
The existing foundation should have load-bearing concrete footings, and a new load-bearing concrete footing will be required in the front for the new addition. Roof rafters:
The roof rafters will need to be cut back to create a flat surface for building the addition.
Slope of the roof rafters:
Determine the pitch of the roof rafters and whether you want a sloped ceiling or a flat ceiling. If you want a flat ceiling, the back end of the rafters and ceiling joists will need to be raised to allow for insulation. The minimum size for a roof rafter that will be used for ceiling joists is 2x10 to fit insulation.
Sloped ceiling: If you want a sloped ceiling, you will need to slope the ceiling joists and raise the back end of the rafters. When installing the ceiling joists, you will need to nail them to the existing roof rafters at least every four feet. Solid blocking can be used to connect the ceiling joists to the rafters.
New roof rafters:
The new roof rafters can be placed on top of the existing roof framing, including the sheathing, on sleeper boards. The rafters need to have enough support underneath them, especially at the heel and up near the peak.
Existing vs. new roof rafter spacing:
The spacing of the new roof rafters may not always match the spacing of the existing roof rafters. In the video, the existing roof rafters are spaced at two feet on center, while the new ones are spaced at sixteen inches on center. This may require additional modifications to accommodate the difference in spacing.
Drywall:
Make sure the new framing will not create problems for your drywall. For example, if you are using a sloped ceiling, you may need to frame the corners in a specific way to accommodate the drywall.
Flat ceiling:
If you want a flat ceiling, you can apply rip strips on top of the ceiling joists. These rip strips can be cut from a 2x6.
Ceiling joist intersection with existing roof:
The ceiling joists may need to extend back a little further past the framing plates to intersect with the existing roof.
Blocking over exterior wall:
A row of blocks will be needed over the exterior wall to connect the sheathing together. An engineer may specify that the pieces of plywood where they are joined together at the sloped sections should have a nail that goes through the plywood into one block.
Mid span blocks:
For a 16-foot span, mid span blocks will be required in the center of the ceiling joists.
Fascia board:
The fascia board will require a rip strip on top if it is level. If the slopes of the two roofs are different, the fascia board will need to be adjusted accordingly.
Sheathing:
When installing the sheathing, a straight edge or a straight piece of lumber can be used to set on top of the rip strips to create a line for cutting the sheathing. The engineer may require an additional framing member in the sheathing, such as a 2x4 or a shaped member.
The bottom edge of the sheathing will connect to a 2x4 or a shaped piece of lumber, which may need to be nailed to the roof rafters through the sheathing.
Bonus tips:
Hire a qualified contractor or engineer to help with the design and construction of your addition. This will ensure that the addition is structurally sound and meets all local building codes.
Pay attention to the details. There are many small details that can make a big difference in the finished product. Make sure to take your time and do things correctly.
Use high-quality materials. The materials you use will have a big impact on the durability and longevity of your addition.
Be patient. Building a room addition can be a time-consuming process. Don't get discouraged if things don't go as quickly as you would like. Just keep working away and you will eventually achieve your goal.
