Installing Roll Roofing

Roll roofing and built-up roofing are the most common techniques used to cover flat roofs.

Experience has proven that an absolutely flat roof leads to trouble. To avoid standing water which eventually causes leaks, a roof must have a minimum pitch of 1/4 inch per foot. If you are reroofing, consider sheathing the roof to give it the minimal incline.

Composition shingles are not used on roofs with a slope of less than 2 in 12; wood shingles are not used on a slope of less than 3 in 12; and shakes are not used on a slope of less than 4 in 12. Of the two methods, roll roofing is quicker and easier to handle. Built-up roofing is best left to a professional, as it requires special equipment that cannot readily be rented.

Installing roll roofing
Roll roofing provides a quick, inexpensive roofing solution (Fig. 1). Essentially made of the same material as composition shingles, roll roofing provides only one layer of covering as opposed to three layers. Compared to shingling, roll roofing is installed very quickly. A lot of territory is covered in a short time, although it helps to have an assistant.

The life of roll roofing is typically 5 to 12 years. Given its plain appearance and short life, single-layer roll roofing is best used on sheds or in places where the roof is not visible. It may be used on slopes that are flatter than those normally covered by shingles, especially if a concealed nail application is used.

Double-coverage selvage roll roofing is used for roofs that are nearly flat. Roll roofing is more fragile than other roofing options. In temperatures below 45 degrees, the material may crack. You can work in colder conditions if you warm the rolls first. The roofing cement and lap cement must be kept at a temperature above 45 degrees, so store it indoors if you are working in cold weather.

Make sure the roofing has not curled at the edges or puckered in the middle. If it has, cut it into pieces 12 to 18 feet long and stack the pieces on a flat surface. Depending on the air temperature they will take an hour to one day to flatten.

Underlayment is not required, but since it is easy to install and so inexpensive, it is worth the extra effort. Install a drip edge at the rakes and eaves before roofing. Even small pebbles and sticks eventually poke through roll roofing, so sweep the surface with extra care.

1) Install the first course
The exposed nail method is the quickest and easiest way to install roll roofing.

First, protect each valley with an 18-inch-wide sheet, taking extra care to lay it completely flat. If the material is raised above the sheathing, it will tear later if someone walks on it.

The eaves may be uneven, so do not use them as a guide for aligning the first sheet. Instead, snap a chalk line 35-1/2 inches up from the eaves and run your first sheet so that it overhangs the eaves by 1/2 inch.

Add 2 inches of roofing cement at the eaves, and nail all seams and edges every 3 inches. Use galvanized roofing nails to penetrate the sheathing by at least 3/4 inch, but be aware that once you've "aimed" the sheet and put some nails down, you can't fix it if it is headed off course. Also avoid puckers and folds.

Cut the course long enough so that some roofing overhangs the rake. When the roof is complete, use a utility knife to trim the course flush with the edge of the drip edge. If you are reroofing and there is no drip edge, strike a line so the new roofing can be trimmed flush with the previous layer. (Fig. 3)