Adding a room onto an existing home is probably the most cost effective way to increase a building’s usable interior space. In this article, an addition means what a colleague calls a “three sided” addition. This phrase intends to avoid confusion with some other home additions such as raising a building to create a new ground level space, or raising the roof to create a story between a ground level space and a roof area. The three sided addition means that the new and existing building will share an inside wall.
Begin your design thinking by trying to envision everything you consider an ideal ceiling height for your addition when finished. As mentioned, most prefer a minimum eight feet, but a few inches less than this will still work in a pinch. It is important to start here, because your new ceiling will likely be hanging from the roof framing that will, consequently, attach to the existing building. If this framing attaches to an existing building too low, your ceiling will be too low. Let’s look at a couple standard roof frame techniques to help clarify.
Gable Dormer: When most kids in the western world draw a house, it will have a gable roof. A gable roof is an upside-down “V. ” A gable dormer is this same roof shape attached to an existing main building at a right angle. It’ll have a peak as does the children’s drawing, and where its roof meets the main roof is called a valley. As people have been using gable dormers for hundreds of years, you won’t need to look far for an example. The main advantage to a gable dormer when designing an addition is that the addition’s ceiling height is determined by how high its peak is in accordance with the main building. Typically, the larger the peak, the greater the available ceiling height.
Just like any building project, there was seemingly no end to pro and cons, and compromises need be found. When utilizing a gable dormer frame for an addition, the compromise is that a lot of its weight will bear on the existing or main roof framing because it overlaps this framing. As the main roof framing was not likely designed to support this excess weight, this main roof frame will need to be strengthened. Obviously, there are a few more in and outs to know about putting a lid on your addition using the gable dormer method, but in my opinion, this method may be the slickest, and in the long term, offer better looks than most alternatives. Due to the structural bolstering, and other framing elements required when using a gable dormer, it will likely cost more, as well.
If thinking about the gable dormer method, something to bear in mind is that must be sizable addition’s roof dormer will cover up a substantial percentage of the existing roof, hold off on re-roofing until the dormer is in place. This will save burying a lot of new roofing material under the new dormer.