Most houses have shingles on them, but yours might not. Shingles work spectacularly on roofs with steep enough pitch that water sheds well. But because shingles have seams that slow-moving water can seep under, low-slope roofs need a something else entirely.
The solution is membranes with completely welded seams to become uniform. Then rainwater can travel slower down them without driving back up under any seams.
In the Pacific Northwest, there are two main types of these membrane roofs: TPO and torchdown (modified bitumen).
Torchdown was once more popular than it is today. As the name implies, the top layer of the modified bitumen is heated with a torch and applied to the base sheet. These are excellent roof styles, but they come with significant drawbacks (because of the flame). There’s always a risk of catching something on fire, and nobody wants that. And proper torch technique is harder to teach.
It’s no wonder that roofing manufacturers developed a different type of roof waterproofing membrane that contains less risk and is easier to install: TPO (thermoplastic polyolefin). Originally used as pool-liner, TPO is the most common roofing membrane for low-slope roofs today.
Even though most houses have pitched roofs that allows shingles (or metal panels) to shed water properly, a decent amount of homes have been designed with shallow pitch roofs and no attic. TPO is usually the best option for these.
What you need to know doesn’t end there, though. One of the most important components of a TPO roof is the insulation. Without adequate insulation, a low-slope roof is at great risk of failure due to condensation damage. They can rot from the inside-out and you wouldn’t know it until “leaks” started showing up. By then it would be too late and the entire roof would need to be replaced.
If your home is low-sloped and you need a new roof, you’ll want a system that consists of the following, from bottom of the roof to top:
- Plywood decking
- Vapor barrier (sometimes called retarder) like GAF Tiger Paw
- 2 layers of interlaced rigid insulation
- Gypsum fiber or glas-mat roof board like USG Securock
- TPO membrane top layer
This layered system covers all bases. Insulation is sandwiched between 2 vapor barriers (TPO is also one), allowing us to keep condensation at bay by limiting vapor travel and temperature changes between inside and outside the home. Preferably you want between about 7″ to 9″ of total insulation depth. The gypsum fiber or glas-mat boards act as secondary water resistant layer, are exceptionally fire resistant, and help protect against wind uplift.
Some roofing contractors cut corners and don’t offer these systems. On the contrary, we specialize in this comprehensive roofing system that you can rely on.
