What do you do when you’ve got parts of your roof that are steep, and parts that are very, very shallow? Tackling a steep-slope/low-slope roof is a scenario that requires extra knowledge, as you can’t use asphalt shingles on a slope less than 4:12. One solution is to use asphalt shingles on the steep part, and a single-ply membrane on the shallow part. That’s what Caldwell’s Roofing did on this job.
This roof was a mess when Caldwell’s Roofing got to it. As you can see in the photo above, there was 5V-Crimp metal roofing on the low-slope parts, and it was installed in the wrong direction, with the ribs going perpendicular to the slope! You can see the rust, the layer of EPDM applied above flapped back by the wind, and even a 2×4 and power cords just lying around.
First, let’s define our terms. Did you know that the terms “steep-slope” and “low-slope” can be used in at least three different applications, with different meanings? It’s true.
The common populace probably thinks of about an 8:12 roof as the borderline of what a “steep” roof is. And that’s a reasonable definition. When you’re talking about when to have harnesses on, though, you define it differently. OSHA uses the terms “steep-slope” for anything over a 4:12, and “low-slope” for 4:12 roofs and shallower. There’s a lot more to OSHA rules than that, but that is how they distinguish between steep-slope and low-slope (and in plain English, generally you don’t have to wear a harness on a 4:12, and you do on a 5:12 or greater, but this article isn’t a study on OSHA rules). Finally, manufacturers utilize these same catch-phrases, but they mean something entirely different by them. When roofing shingle manufacturers like GAF recommend that shingles only be used on “steep-slope” applications, they’re often talking about 4:12 or greater slopes. In other words, once you go to 3:12 or less, you need to use a water-proof material like a single-ply membrane, rather than just a water-shedding material like asphalt shingles. Asphalt shingle roofs rely on gravity to shed the water off, and when the slope is too shallow, water can wick up under the shingles and create leaks. In this article, we’ll be talking about roof slopes the third way (manufacturers’ definition).
Tackling a Steep-Slope/Low-Slope Roof – Single Ply Installation
We’ll look first at how they addressed the low-slope part of the roof. They first removed the old EPDM (“rubber roofing”) and 5V-Crimp metal, but then they found that there were two other layers of metal plating under that! Each metal layer was joined into a single piece, meaning they had to cut it up with shears just to get it off. Then, since the decking was sub-par, they installed some 7/16″ OSB (“Oriented Strand Board”) as a layer of better decking (homeowner’s choice due to budget constraints).
Next, they installed a “separation sheet” of 1/2″ “fan-fold” insulation board. This provides extra insulation, as well as some fire resistance and a smoother surface to attach the TPO single-ply membrane to.
Finally, they installed the TPO itself. TPO and PVC are two great roofing membrane choices for low-slope applications (1/4:12 up to 4:12 range, or greater). They last a long time, and unlike competitor options like EPDM, they don’t pull away from the edges or from pipe-penetrations in the roof. The picture below shows one reason why Caldwell’s Roofing doesn’t like EPDM (the membrane is pulling away from the pipe and creating a leak).
Additionally, EPDM is normally black (unless it has a top coating of white), and absorbs the sun’s rays horribly. TPO and PVC are white and reflect heat from the sun, thus saving you on cooling bills.
TPO stands for “Thermoplastic PolyOlefin” and PVC stands for “PolyVinyl Chloride.” They’re about 1/8″-thick usually, and they’re just sheets of plastic that can be attached to a roof deck with the overlapping joints welded together with a hot-air gun. What’s great about TPO and PVC is that they are the way to do your low-slope roof right. If you want to take care of your low-slope sections of roof, and not have them leak in the near future, you need to go with TPO or PVC. Your typical roofer is just going to install “roll roofing,” because it’s easy to put down, but it’s likely going to blister and create leaks pretty soon (plus, it won’t reflect the sun’s heat, so it’s bad on your AC bills). Besides that, TPO and PVC simply look outstanding on a roof. When your roofer uses TPO or PVC, you can rest assured that they gave the low-slope parts of your roof the attention they needed (assuming they install it correctly).
Single-ply membranes can be installed in a number of ways, including “mechanically-attached,” “fully-adhered,” or “self-adhered.” The latter two options use a chemical bond to attach the membrane to a separation sheet or to an appropriate decking material. On this job, Caldwell’s Roofing used the former option (mechanically-attached). Circular plates are screwed down to hold the TPO in place, and the overlapping seams are welded with a hot-air gun.
With TPO and PVC, the seams are hot-air-welded with a heat-gun. We’re not talking a $30 heat gun from a box store – we’re talking a $600 Leister heat gun from a professional low-slope roofing supply store. Heat-welding requires consistent temperatures, air volume, and other considerations that only professional tools can deliver.
A silicone seam-roller is used in conjunction with the heat gun while you are welding the joints. The joints are welded with a two-pass process, whereby 1″ is welded further back, and then the final 1″ is welded a bit more carefully.
Afterwords, Caldwell’s Roofing did some test cut-outs of seams to make sure they were welded adequately. When you rip-apart a heat-welded seam, you want the seam to fail at the inner-scrim of one of the layers, not at the weld. That tells you that your weld is stronger than the material itself, and can’t possibly leak.
Here’s a picture of some of the edging details.
Here’s a final look at the after picture. Caldwell’s Roofing also had to frame a small “cricket” to divert water in one direction or the other (barely visible in the photo below, due to low-slope nature of the cricket).
Tackling a Steep-Slope/Low-Slope Roof – Shingle Installation
If you thought the low-slope part was hard, the steep-slope part of this roof was worse. By far. There were an incredible 7 layers of asphalt shingles, in addition to a layer of wood shakes, that had to be removed! Codes usually stop at 1 or 2 layers of shingles as the maximum allowed, but 8?? Caldwell’s Roofing removed an estimated 40 tons of weight off this crazy house! And it was a lot of work. The shingles made a layer nearly 2″ thick on the roof! They filled a couple dumpsters and a couple pull-behind trailers with the mess. Whereas usually the crew can get a re-roof knocked out in a day, it took them 2 full days just to get a handle on the clean-up! Here’s a few pictures of the process.
Next, they went back with a layer of 7/16″ OSB (“Oriented Strand Board,” owner’s choice due to budget constraint), felt-paper, and 3-tab shingles.
Pipe boots were installed around pipe penetrations.
Here’s a before/after picture that shows the finished job.
Finally, here’s a shot of the house from the front, upon completion.