When you drew a house as a kid, it probably looked like a square with a triangle on top. Many houses in America look a lot like that. But here in Philadelphia, most of our houses look more like a tall rectangle. Which means the roof is out of sight. Maybe you can see part of your roof from an upper rear window, but for a lot of us, the roof above our heads is out of sight, out of mind. Read on for a primer on rowhouse roofs and things to keep in mind.

Progress shot of a new white EPDM roof with exterior insulation.

Your average rowhouse roof is what we call a flat roof. This is why you don’t see it from the street. The triangle you drew as a kid means you can see that pitched roof from some angles, and it is usually clad in shingles. Flat roofs aren’t really flat, because water needs to get off of there, but they are a low pitch. Sometimes only a quarter inch of drop for every foot of length.

This means the product you use has to be fully sealed, because any gaps in the membrane will let water in. It’s not unusual for water to pond on a flat roof after a rain.

If you look at the roof in the foreground of the photo above, you’ll see the most common roof in Philly. Modified bitumen. Think of as an asphalt shingle in sheet form. They use roof cement (commonly called muck), to seal the perimeter and seams. This is your weak point on a roof like this. When first installed, only the seams are coated. This roof can last indefinitely, but you need to coat the whole roof every 3-5 years. Remember where we started. If your roof is out of sight out of mind, you might not keep up with this. If you don’t know when your roof was last coated, get a roofer out to check it out, and then put it in your calendar every 3 years to have it checked. It’s a lot less expensive than having to do a full tear off.

Another thing we see a lot in Philly are situations where the old roof isn’t torn off. They just layered another one on top. That works to a point, but on a 100+ year old house, the time will come when the weight of all those roofs is too much for the rafters to bear. Below you’ll see a tear off from a recent project. We took easily 1000 pounds of material off this house.

We’ll talk about insulation in another post, but while you’ve got the roof torn off, this is a great opportunity to add continuous exterior insulation. You can see the sheets of insulation stacked in the photo below. While you can usually insulate below the roof as well, to get the R-values we look for, a combination approach is the best move.

Still with me? Alright. We talked about modified bitumen, but if you want a roof you can worry less about, go for an EPDM or TPO roof (commonly called rubber roofs). You’ll need an installer qualified to properly install these, but the seams are welded. While modified comes in a white color, it’s not as white as the roof you saw at the beginning of the post. Why white? Because it reflects the sun’s rays. This keeps your house, and the urban heat island we live in, from being as hot, and that’s a good thing.

Example of a pole gutter, lined on the inside with epdm

Last up, let’s talk gutters - or the lack thereof. Now you may be saying, that doesn’t look like a flat roof. Well, you’re right. Rowhouses also have pitched roofs. But while most suburban homes have a gutter on the edge of the roof, most rowhomes have what we call a pole gutter (otherwise known as a “Philadelphia” gutter). The way this works is it sits on the roof at an angle and directs the water to a scupper box. This is basically a copper box that directs the water into a downspout. If you have a flat roof, you won’t have the pole gutter, but you’ll still have the scupper. Make sure that scupper stays clear of leaves and debris. When roof leaks happen, it’s often because the water has backed up at the scupper.

Thanks for reading. If you have a question about your roof, or anything else in your house, use our contact form to reach out and I’ll be happy to see if we can be of assistance.

Rowhouse Roofs