How To Repair a Leaky Flat Roof and Wooden Shake Roof

As with any roof, it's important to first find the cause of the leak. How to find that leak -- and ultimately fix it -- varies depending on the type of roof. Following are some tips for mending leaks on flat roofs and wooden shake roofs.

Flat Roofs

­Flat roofs are built up of layers of roofing felt and tar. Leaks usually occur at low spots or where the roofing felt has been damaged. In most cases, the leak is directly below the damaged spot and the damage to the roofing felt is easy to see.

If there's still water pooled in the leak area, mop it up or soak
it up with rags, and let the surface dry. Brush off any gravel. Look for cracks in the felt or for large blisters where the top layer has separated.

To mend a blister:

Step 1: Use sharp utility knife to slice blister open down middle. Cut should penetrate to full depth of blistered layer
but should not reach sound roofing felt beneath it.

Step 2: Lift cut edges of blister. If there's water inside blister, press from edges in toward center to squeeze out water from between roofing layers. Soak up all the water you can with rags; then prop edges up to let layers dry.

In cold weather or if layers are thoroughly saturated, use propane torch with flame-spreader nozzle to dry out felt (be sure to wear safety goggles). Carefully move flame back and forth over inside layers of blister. Roofing felt and tar are very flammable, so don't let layers get hot enough to burn or bubble.

Caution: If there's water under a large area of the roof, the problem is more than a simple blister; water may be running in from an adjoining pitched roof surface. In this case, it's best to call a professional roofer.

Step 3: Spread thick coating of roof cement on bottom edges of loose felt and firmly press down sides of blister.

Step 4: Close blister permanently with row of 6d galvanized roofing nails along each side of slit, then spread roof cement over entire blister, making sure nail heads are well covered.

Wooden Shake Roofs

Repairing a wooden shake roof is similar to repairing a
shingle roof, although it can be a little more difficult. Use the same type of shakes or shingles to replace the damaged ones. If a ridge shingle is damaged, use a new specially cut ridge shingle instead of trying to make do with regular shingles.

To repair a wooden shake roof:

Step 1: Use hammer and sharp chisel to split damaged shake. Slant chisel up into shake at same angle as pitch of roof. Be careful not to gouge surrounding shakes. Pull out pieces of damaged shake.

Since shakes aren't flexible like shingles, it isn't possible to pry out nails. Use hacksaw to cut off nail heads as far down nail shaft as you can. You may want to wrap electrical tape around one end of hacksaw blade to protect your fingers. If
you can't reach nails without damaging other shakes, you'll have to work around them.

Step 2: Measure gap left by old shake, and cut new one
about 3/8 inch smaller than this measurement, using fine-tooth hacksaw. You must allow this 3/8-inch clearance because shake will swell the first time it rains.

Step 3: Install new shake. If you were able to cut off nails that held old shake, just slide new one up into place, with its top edge under overlapping shingles. Nail shake down with two galvanized roofing nails, one at each side of exposed top edge. If you weren't able to cut off nails, you'll have to notch new shake to fit around them.

Push shake up into gap, hard enough so edge is marked by old nails. Then carefully cut slots at marked points with coping saw. If possible, clamp shake in vise so it doesn't split. Slide notched shake into place, and nail it with two roofing nails.

Step 4: Set heads of nails with nail set, and seal them with caulking compound.

Roof leaks often occur at flashing joints, such as around chimneys or at vent pipes, and at open roof valleys. Take a look at the next section for suggestions on how to repair leaks in these areas.