If you definitely want a skylight, the alternative to raising and sloping the ceiling is to construct a lightwell between the existing flat ceiling and the roof. This basically is a rectangular tapered tunnel narrower at the skylight in the ceiling.
Converting a flat ceiling to a sloped one can be done, and often is, but it’s a more complicated project than it may appear to be at first. People often think they can just remove one side of the roof trusses over that room and slap up a layer of drywall under the sheathing.
The major concerns when doing this project are making sure the roof is still strong enough after altering the roof truss structure and being able to insulate it adequately. This is particularly true in cold climates where there may be a significant snow load on the roof during winter. I wouldn’t recommend the average do-it-yourselfer attempt this project without the help of an experienced remodeler or builder.
There are several options for making this ceiling conversion. One method, using vented structural foam core panels (sometimes called SIPS), is likely the simplest and one of the strongest designs. Using this method, the old roof will be entirely replaced by the panels. Once the panels are installed, adding the skylight is a very simple project.
These panels are manufactured with strong plywood skins on each side of a rigid foam insulation core. Because a roof needs ventilation to avoid heat buildup during summer and moisture buildup during winter, ventilation grooves are built into each panel. Your new ceiling will have the same slope as the roof. You'll have to install standard shingles or other roofing materials to finish the panels.
Several sources for these ventilated foam core roofing panels are Johns Manville, 800-654-3103, JM.com; and Rmax, 800-527-0890, RMax.com.
Installing scissors trusses is another option. The tops of these trusses are built to the same slope of your existing roof. The bottom surface of each truss is sloped at about half the angle of the roof slope so the ceiling will not have as steep a slope as the roof. It will still be sloped enough to be classified as a sloped ceiling, though.
Using scissors trusses is most effective in colder climates where the roof pitch is very high to withstand snow loading. In very warm climates with lower pitched roofs, the resultant ceiling slope may not be enough to make it a worthwhile project.
If your existing roof needs to be replaced and the sheathing is bad, another option is to build a new roof without trusses. There are many types of strong beams, glued laminated timber, I-beams, etc., that can be used to support an insulated, ventilated sloped roof. You may want to have them exposed indoors for a rustic decor.
