Why put gravel on flat roof?

Question

I will convert my flat roof into a patio. I took all the gravel off (was necessary anyway, full of organic matter and moss), checked and patched suspect areas in the tar surface, and now I'm ready to put the frame and decking wood on top. Do I still need to top-up the gravel on the tar again, despite the new deck above? If yes - why?

Answer 1

No need to reinstall gravel, which is a problematic solution even in the best of circumstances. You sleeper boards for your deck will press the gravel right through your roof system. However, you have to apply something to the exposed tar surface to keep u.v. light from destroying it. My favorite application is urethane, but you won't get a good bond to the oily tar. My second choice, and still a good one, is the aluminized roof coating, which has an aluminum mixture suspended in a tar base. Silver Dollar is the brand I use. It is difficult to mix properly, as the tar and aluminum want to seperate. But the end result is a reflective, long-lasting waterproof surface that will make a good underlayment for your wood deck. I would pressure-clean the deck, get it good and dry, seal the flashing joints with polyurethane caulk , and then roll the coating over the top.

In Florida, we just don't use much wood decking anymore, because of the damage done by u.v. light and the elements. You might want to look into the composite deck board that is made of recycled plastics. I've removed quite a few wooden decks that have rotted, split, warped and fallen apart in short order.

One last thing: when you install your sleepers (the boards that keep the deck off the surface), make sure they allow for the water to run completely off the deck with no obstructions, especially around the flashing joints. Be sure to fasten the deck with non-corrosive screws as opposed to nails, in the event you need to remove some deck to effect a repair.

Answer 2

The gravel helps hold the waterproof layer down, and protects it from heat and sun.

The heat of the day can cause the tar or whatever you used to bubble, or an edge can get picked up by the wind, or things hitting the roof can damage the layer, etc.

If you are decking over it, it needs less protection, but unless you put a really good membrane down really well, it would probably still benefit from some protection.

Answer 3

You can put an EPDM membrane on the roof which looks like a shingle but comes in a roll. It is actually called a modified bitumen roof. Check out this website for Johns Mansfield roofing systems: www.jm.com. You will need to put down treated wood sleepers (wood to sit the deck on) to avoid having too much wood resting on the roof.

Answer 4

1