Standard half lap rolled roofing is a 90-lb. bitumen based fibrous roofing felt that is suitable for selvage installation on flat and low sloped roofs with a minimum 1/12 pitch. The 36-inch width rolled roofing comprises a 17-inch wide mineral granular coating and a 19-inch wide smooth surface that provides a double layer concealed fastening system. The half lap roofing rolls come in 50 feet lengths and need to install in ambient temperatures above 45 degrees Fahrenheit to prevent surface cracking. The installation procedure is straightforward and depends upon correct preparation techniques to complete the roofing project successfully.
Install a roof deck of a minimum 1/2-inch roofing grade plywood or an OSB equivalent for the correct substrate for half lap rolled roofing. Using a push broom, sweep the deck of debris and grit to clear the surface of material that can damage the roofing felt.
Using a utility knife and straight edge, cut lengths of rolled roofing to size according to the width of your roof. The rolled roofing applies parallel to the eave edge or parallel with the lowest roof edge. Include a 1/2-inch overhang to either side of the roof to allow for water run-off.
Use a utility knife to cut along the join between the mineral coating and the smooth surface on one length of rolled roofing. Position the smooth piece along the lowest slope edge or eave edge on the roof. Using 1 1/2-inch roofing nails and a nail gun, fasten the felt into position at 4-inch intervals along the eave and side edges and at 12-inch intervals along the edge opposite to the eave edge.
Pour roofing tar into a paint tray and use a paint roller to apply the tar over the surface of the installed felt. Position a full width of half lap roofing over the installed felt so that it overhangs the eave edge and side edges by a 1/2 inch.
Fasten it into place along the side edges of the smooth half lap with three equally spaced nails. Fasten 1 inch in from the smooth half lap edge along its length at 12-inch intervals and an additional row of nails inset 1 inch in from the granular join on the smooth half lap surface.
Apply roofing tar to the smooth half lap surface that you just installed. Position the next length over the tar so that the granular edge butts up to the granular edge of the previous length. Fasten the felt into position in the same way as before making sure that you nail into the smooth half lap only.
Continue to install the roofing using the same procedure to produce a selvage double layered application with a concealed fastener system for the half lap rolled roofing.