Residential flat roof design comes in a variety of forms, but all of it is waterproofed in generally the same way. Most residential flat roofs are going to be about a 1:12 pitch, and on that you can use a cold adhesive modified application. The building code does not allow shingles below a 2:12 pitch, so at 2:12, you can still use a shingle. If it goes just a fraction under, you cannot use shingles, so there are several choices you might have in terms of flat roofing materials, but it has to be what you would call waterproof in a sense. A pitched roof is considered to be water-shedding, whereas as a flat roof is considered to be waterproofed. When you get below that 2:12, that’s where they apply those codes. On a 1:12 pitch or up to the 2:12 and just below it, the peel and stick cold adhesive modified roofing, which has a granulated colored granules and can match closely to the shingles is the preferred choice for residential. Now, if you get a truly flat roof, where it’s almost down to nothing, a real low pitch which is not too common in residential, but in that you can go with TPO or EPDM, which are a couple of different types of products. We have put some of those on, but we really try to stay away from that, even in residential. We get a back patio room or a patio cover or shed or something that’s low, a cold adhesive is what we usually use.

Are there other products that can be used?

In terms of different products, there’s also what’s called a modified torch down, and the torch down is pretty much the same as the cold adhesive, other than you use a torch to heat up the edges and it seals on the edges. It’s not used that often in residential flat roof design, but it is possible. The only thing is that if you use a torch, you are supposed to be rated with your insurance company. It’s totally different because the risk of burning somebody’s house down is higher; you’re working with fire. We try not to get into that because we’re not rated for that. Have we used it? Only a couple of times. We just stay away from it for liability reasons during the installation process.

Do you ever use metal materials for any flat roofs?

No. For the most part, metal is not really qualified to go on below a 3:12 pitch, so if you do put metal on below that, then you have no guarantee that you’re not going to have leaks, but metal will not be approved by building code if you’re below a 3:12. 3:12 is the minimum for a steel roof, whether it be a standing seam or something different. One of the reasons why is when you use a product like a steel shingle, these steel shingles, which have a 1 inch butt and that butt edge brings it up and then the top of the shingle effectively remains higher than the upper edge and you get a water flow that begins to cause some serious problems. Essentially, if your pitch on the roof is too low, then that butt edge stands higher than the other part of your shingle and water isn’t draining. It drains backwards, so that’s one reason you can’t use a shingle. The standing seam is typically not used below a 3:12 either, but could it be? It would probably work in certain circumstances, but codes are mostly there for a reason, and are best to follow. Having stated that, it may be something to consider if there’s nothing underneath the roof structure and you are in a place that allows for such a structure. Essentially if you live in a more rural setting and there is nothing to worry about if rain did leak through, then you can consider using it. But when you’re following the building codes, you would not be using metal on a residential flat roof design, and on a living area or even a closed-in garage, you won’t want to do that.

On a rooftop deck on a residential area, what is used underneath that deck for waterproofing?

What happens there is they’ll typically use your EPDM or your TPO, your better products, which the TPO is a thermoplastic product that welds with heat. Then the EPDM, which is like black rubber, is glued. They’re both very good systems, but usually when you have a patio like that, you shouldn’t actually be putting furniture or walking right on that roof. Typically, there are products that are made that you can set down and you build a deck on top, so you’re not actually walking on the roof but there’s a system in place where water can’t get through it and work around it. There’s different types of products. Some of them are raised up on what look like little platforms, like you would a deck on the ground, where you have a post, but it’s like a rubberized thing that sits down and you build your platform above it. Other times you can use what is called pavers. It’s like a plastic circle at the bottom of wine glass. It’s vinyl and you set it down on top of the water proofing material and water can run between it, but that way, you’re not damaging or setting furniture or planks directly on the roofing materials themselves. Anybody who puts furniture or decking material directly on top of the roofing material is risking damaging their roof and what it protects. Interested in Residential Flat Roof Design? The Littleton roofing experts at National Home Improvement are here to help with your residential flat roof design. We use the best flat roof deck materials to bring your project to life. Contact us online today to get started!