5 step plan
1) Try to plan your roofing project in warm weather so new shingles can properly seal to the layer below. Most storage buildings, sheds, detached garages and outbuildings today have a pitched roof of various degrees and use an asphalt shingle system. Asphalt shingles meet ASTM (American Society for Testing and Materials) standards. The most common type are strip shingles and are rectangular, 12 inches wide by 36 inches long.
2) Roof deck – Use 1/2”plywood as opposed to OSB. Along with adequate ventilation, plywood provides a better deck. There have been concerns raised among roofing contractors on the effects of moisture on OSB and the potential for problems with fasteners. Using a treated plywood for your deck would be even better, and for a smaller roof such as a storage building or shed the additional cost may be minimal.
3) Underlay – Felt paper or underlay should be installed over the roof deck before you apply the shingles. The underlay provides temporary deck protection from weather until the shingles have been installed and then act as an extra weatherproofing barrier if moisture should penetrate the asphalt shingles.
4) Shingles and Nails – Lay your shingles one course at a time, starting from the bottom working horizontally from one side to the other, working your way up the roof pitch. Use 11 or 12 gauge roofing nails. Nail heads should be low-profile, smooth, flat and long enough to penetrate through all layers of roofing materials extending through the underside of the roof deck.
5) Flashings – The majority of roof leaks occur where the plane of the roof is interrupted by a ridge, a wall or penetration such as a vent or skylight etc, or another roof intersecting at an angle. For most garage buildings and storage sheds a simple gable or shed style roof is used, so flashing is only used if you want to install a skylight or roof vent. The shape of vent flashing is round with a wide flange at the base, that is lapped into the shingles as the roofing is installed. Always remember to install flashing under shingles on the up slope of a flange and over top of the shingle on the down slope. Use roofing cement to caulk all flashing seams.