Flat roofs require different coverings than pitched or sloped roofs, since they are more likely to hold water in pools, which can become leaks. These types of roofs are most frequently seen in the Southwest and other areas with low or infrequent rainfall. Sometimes, an entire house roof will be flat; other styles combine a flat roof with a more traditional, sloping roof, using the flat element as a design contrast. Any flat roof can be effectively sealed with the proper coating.
- Skill level:
- Moderately Challenging
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Things you need
- Prybar or roofing removal tool
- 2-inch-by-4-inch boards
- Table saw
- Oriented strand board (OSB) or plywood
- Foamboard (IsoBoard)
- Special screws with galvanised washers
- Screw gun
- Tape measure
- Ethylene propylene diene monomer (EPDM)
- Utility knife
- Paint roller with long handle
- EPDM adhesive
- Uncured rubber
- Rubber adhesive
Remove any old roofing materials with the prybar and a shovel. Take off the old decking. Check with a level for any pitch or slope; even flat roofs often are framed with a slight angle to allow for drainage. If the roof has no pitch, make a slope of at least 1/8-inch per foot by nailing small wedges--cut on a table saw from 2-inch-by-4-inch boards--to the roof joists. Make sure that the thin edge of the wedge is pointing in the direction of drainage.
Deck the roof with panels of 5/8-inch oriented strand board (OSB) or plywood. Leave a 1/8-inch gap between the panels to allow for expansion. Using screws with galvanised steel washers, screw IsoBoard on top of the panels. IsoBoard is a special foamboard that has a fibreglass backing. Fit the boards tightly together, and stagger the joints.
Sweep the roof to clear away any dirt or debris, and measure it with a tape measure to determine the size for your ethylene propylene diene monomer (EPDM), which comes in 10-foot wide rolls. Cut a piece of EPDM with a utility knife to cover the roof, leaving an extra 9 inches on all sides. When that is fitted, roll it back halfway, leaving the decking exposed on one side. Work from the top down.
Use a paint roller with a long handle to spread adhesive over the exposed decking and the back side of the folded EPDM. Let the glue dry until it is dry to the touch, then gently fold the EPDM back over the decking. The dried glue will bind on contact, so this has to be done carefully, a little bit at a time, working on hands and knees. Do not lift the EPDM, as it will tear. Smooth the EPDM firmly into place as you go.
Fold the other half of the sheet over the glued section and repeat the adhesive process. Smooth out air bubbles with the dry paint roller on the long handle. Move to the next section of the roof and install more EPDM. Overlap the sheets by 6 inches, but don't glue the overlaps until the roof is covered.
Glue the overlapped seams by putting rubber adhesive on the EPDM that is glued down and then pasting down the overlap. Cut a 4-inch wide strip of uncured rubber and glue it over the seam with rubber adhesive. Fold the excess EPDM at the edges over the side of the roof and glue it down to the framing boards around the edges. It will be covered later with fascia or trim boards.
Tips and warnings
- Get help if possible. This can be a one-person job, but a team can do it more easily.
- There are other options, including a liquid polyurethene compound and alternating layers of roofing paper and roofing cement, sealed with gravel. The EPDM is effective and easy for a homeowner.
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