Q: When you were writing about roof repair and replacement, I never saw anything on tar-and-gravel roofs.
I just bought a house. At my prepurchase inspection, I was told the roof was in pretty good condition but that I might want to go up, add gravel and rake it around for maintenance. I have no clue how old the roof is, but I’ve had no problems.
I’ve noticed a good amount of gravel now on the ground at the mouth of several downspouts. If I get up on the roof, what should I look for and how much gravel should I add?
I also noticed that inside the house, in one small area near the fireplace, there is light-brown speckling on the painted wood that might be the first stages of a moisture/mold problem. What should I do regarding that?
A: Tar-and-gravel roofing is the generic name for a built-up roofing system used on low-slope roofs. Roofs with a rise of 3 inches for every 12 inches of run or less are candidates for a built-up roofing system.
Tar-and-gravel roofs consist of several layers of asphalt-impregnated building paper, also called roofing felt, applied over a plywood deck. Each layer is hot-mopped with liquid asphalt to form a watertight seal. The top layer is covered with a light-colored gravel. The roofing felt is sloped up at the edge to form a curb. The edge of the felt is covered with a metal flashing that extends over the eave and fascia boards.
The roof is applied with a slope so that water is directed to drains, called scuppers. The scuppers discharge water into downspouts that direct it away from the foundation. An alternative to scuppers is installing the downspouts through the soffit directly to the roof deck.
The gravel you’re finding has been washed down the roof through the downspouts and onto the ground. Gravel performs two crucial functions on a tar-and-gravel roof: It shields the roof membrane from direct sunlight and it reflects heat away from the black roofing membrane.
Get your ladder out before the rainy season hits. You’re looking for bare patches of roofing felt/tar. The felt/tar combo does not hold up really well in direct sun. If it’s exposed for any length of time, you risk the chance of breaching the roof membrane. If that happens, you’ve got a leak. If you see bare spots on the roof, check them for cracks. If you see cracks, sweep away any gravel from the area and apply a good coating of liquid roof patch. It is a viscous, black tar-like substance. It’s readily available at hardware stores.
Whether you patch or not, cover the bare spots with enough gravel to cover the felt. You may not need to add gravel, but just redistribute the gravel there.
As far as the speckling inside goes, it could be mildew. To find out, poke the wood with a screwdriver blade. If the wood is solid, it’s mildew. If the wood is punky, it’s dry rot. If it’s mildew, wash the area with a 4-to-1 solution of bleach and water. If it’s rot, the board may have to be replaced. However, before that happens, locate the source of moisture that is feeding the fungus. You may have a roof leak after all.
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