What to do about leaky flat carport roof?
 

I have a flat carport roof circa 1965 that is not part of the (shingled) house roof. Originally it was a rubber roof, but a couple of years ago I covered it in a white EPDM roofing membrane in an effort to stop some leaks. That helped for a short time but now the leaks are back and worse than before. I've looked online and have seen a Dow RoofMate product that allows you to angle the roof by stacking styrofoam squares then covering it. Anybody have experience/thoughts about this? Anybody have suggestions/opinions about how I should attack this? Of course I prefer to do it myself and at a reasonable price.

Jeff, first off welcome to House Repair Talk.

Yes there are materials that are designed to create slope on flat, or areas where water ponds. It comes in either 1/8 or 1/4" increments. Meaning you would have a 1/4" rise in 1 foot. This is called tapered ISO board and comes in 4X4 or 4X8' pieces.

I'd suggest taking off all the old roofing on the flat roof and shingles at least 3 courses on the sloped roof. Draw a chalk line across the roof, length and width to see if you have any swags in the structure. Install the tapered ISO and then install either of GAF "Liberty" Certainteed "Flintlastic" or ABC (if you have an ABC Supply close) Mulehide, base sheet and modified bitumen cap sheet with new drip edge.

This application will last many years. Tapered ISO is not cheap and EPDM carries no MFG warranty on residential applications.

Do you know the source of the leaks? EPDM is a pretty serious roofing material for a residential roof, and if it was installed properly I'd be very surprised if the membrane itself is already leaking. Is it possible that there's a flashing leaking? Or that the membrane was punctured during installation?

Matt

Thanks for the answer and the welcome. I'll start researching what you've suggested!

Gatorfan my guess is that a seam is leaking, but I'm not sure. I'd be surprised if it were punctured and there is no flashing.

If you're sure there is no flashing, that could be where the water is getting in. Low-slope, carport (or any other) roofs need properly-installed flashing at their intersections with abutting walls or sloped roofs. With the vertical/upright legs tucked under the wall's siding or shingles, and the horizontal legs remaining on top of the membrane, water should have a hard time finding its way in and leaking.