The concept of using a flat roof comes up nearly every day in discussions with clients. Here’s how it always goes:
Client: There’s no way I’d do a flat roof.
Architect: Why?
Client: Because they will leak.
Architect: Have you been downtown, or to Walmart or Target or Costco?
Client: Yea.
Architect: Do the flat roofs on high rise buildings and other commercial buildings like those leak?
Client: No, well, maybe sometimes.
Architect: Do you know anyone who has a leak on there shingled roof at their home?
Client: …sigh… yea.
Architect: You can get a warranty for multiple decades for flat roofs and also shingle roofs. They just need to be installed properly. If you have trees that will dump leaves on your roof, I wouldn’t do a flat roof, but I also don’t suggest allowing trees to dump leaves on your sloped roof either since it causes moss growth, clogs gutters, and leads to leaks.
Client: hmmm.
Architect: Flat roofs aren’t actually flat. They usually slope down a quarter of an inch for each foot, so a 10’ long roof slopes down 2.5”.
Client: Really?
Architect: Yep. The material on flat roofs is like a sheet of rubber called TPO or PVC. They actually heat weld/melt the seams together, so it creates a permanent bond that water can’t get through. That’s why they use them on high rise buildings and shopping plazas where they can’t take on the risk of leaks. They are installed only by an installer who is certified by the product manufacturer, and they get it flood tested to ensure they don’t leak. Flat roofs are better than sloped roofs with attics.
Client: Why?
Architect: Because they are less likely to leak. Also, since they are flat, you don’t need an attic, you don’t need attic access, you don’t need the layer of extra structural framing known as collar ties, you don’t need attic ventilation, and the light color of a flat roof also decreases excess heat gain. It saves you on a lot of infrastructure. Flat roofs are much easier to build than sloped roofs with attics.
Client: I still don’t trust a flat roof.
Architect: …slams hand on head…
This is the common (frustrating) dialogue I have several times each week. Hopefully this post will save me from repeating it at least a few times:) and hopefully prevent a few head smacks.
There’s a reason commercial buildings tend to use flat roofs and that commercial building products tend to be differentiated from residential projects: commercial products tend to be more durable and long lasting than residential. I have always found it strange that many product suppliers for roofs, windows, etc tend to offer a residential model and a commercial model. The roof and windows of a house undergo the same exact weather as an office. When I contact a material supplier about purchasing a product, they will commonly ask me, “is it for a building or house.” I can’t resist, and I say, “both.” The confused salesperson says, “well which is it.” I say, “the BUILDING is a HOUSE.” The salesperson then tries to sell me a residential product, and then I ask them for a comparison between the commercial counterpart. It usually turns out that the commercial version has a better warranty and is more durable.
A flat roof membrane is commonly thought of as a commercial material, but if we are being smart, rational, decision makers, a flat roof is the most durable and beneficial roof system since it is simpler to frame, saves energy (due to not needing an attic), and it is less likely to leak. If your architect suggests a flat roof, give it some honest consideration.
If you’d like to learn more about our design process, visit www.josharch.com/process, and if you’d like to get us started on your project with a feasibility report, please visit www.josharch.com/help