Name that roof?

I am looking or the correct terminology of the roofing used on many low slope roofs here in Florida.

I have watched it installed numerous times. They start with a double layer of 15# roofing felt and then hot mop what appears to be 90# mineral surface roll roofing over it. Typically they will apply the hot tar and lay the first layer even with the eaves, place the second layer over it to align it with an exposure of about 18", and fold it down. They mop the area under where the top of the strip will go with tar, lay it back down and fold the lower part back over the top. They then mop the underside of that layer and lay it back down to seal on the layer below. The better roofers will sprinkle matching granules over any tar that is exposed.

What is the correct name for this type of roof?

we call it built up/hot mop…hope that helps

The built-up roofing I am familiar with is 3 or more layers of 30# felt with each layer hot mopped down and is usually coated on the surface. With the roofing I am talking about, only the 90# (or at least that is what it looks like) is the only thing mopped down.

A roofing contractor told me that it was modified bitumen, but when I researched that, it didn’t sound right either.

BTW, I said 15# in the first post but meant 30#.

modified is a rubber like roof that you heat up with a torch and stick down. It close to like a 90#cap sheet. Modified has a granule or smooth surface. Built up can be 1 ply up to 5 or more plys…do you have photos of them. If I saw a photo I can say for sure what your looking at.

the plys are just an underlayment, on built up you would cap the plys with a cap sheet of some type.

Maybe I have been calling them the wrong names for a while. Don’t know how well you can see things in the photo, but the first one is what I am talking about. The second photo is what I am used to calling a built up roof.

Pic #2 looks like a built up hard to tell because it has a coating applied over the top of it. Looks like an aluminum type coating. is #1 the same roof as #2?

pic 1 is rolled roofing

Looks like the first photo to be “selvage” roofing. The material only has half of the base material covered in mineral with the other half having the exposed base material suitable for sealing with the tar. This basically gives double coverage as one half of the next layer overlaps half of the previous course. They do use it alot in FL particularly on shed style, low pitched roofs (sunrooms, etc). More often than not I see rolled roofing with only about a 6 inch overlap. This costs a lot less but does not give nearly the protection and coverage. Lots of people, including roofers use the two terms interchangeably. Based on what I can see is they used rolled roofing (top course is completely covered with mineral) but did it in the style of selvage by overlapping by half the width.

The terms I am familiar with in my area: Neither are recommended around here:
Rolled Roofing
Half Lap

This link may help on the subject.

Give that man a cigar, it’s commonly called “wide selvage” roofing



They must have flooded the roof with asphalt to make this product look like a BUR.
Used to install this crap as a kid. Unfortunately they still sell it. :mrgreen:

A good cigar and a couple of cold long necks sounds good right now.

there are many common names for this system, but if you to use the same terminology as the building code it would be called a " coal-tar built up roof"

Built-up roofs can be very tricky to inspect. Coal tar and bitumen can have very specific installation methods. Install them in the wrong order together on the same roof and you can have a mess. Do you know how to tell? I don’t. I disclaim flat roofs and look for obvious defects.

Probably shouldn’t see built-up on roofs above 2&12, which for many roof-covering materials is where “low-slope” starts and “flat” ends.