Flat Roofs & Snow Load

Posted :
November 21, 2014
Posted :
Arbor Builders
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Can flat roofs handle all that snow?



The climate here in Central Oregon lends itself to a wonderful variety of weather – including the every-so-often multiple feet of snow accumulation overnight. This is great for those powder hounds out there skiing at Mount Bachelor, but when it comes to the ability of homes to withstand the more extreme weather, many people have concerns, in particular, about those homes with flat roofs and snow load.

These flat-roofed homes, however, are designed and engineered with our local weather in mind. Go ahead and get a cool-looking, unique, mid-century modern home with a flat roof and enjoy your Central Oregon snowfall as well.

Here are ways we build our new homes to withstand all sorts of weather:

Roof Pitch

Usonian roof line

Here’s one secret – the roofs are not actually flat! They have a pitch of 1/4 in. That means that for every foot of roofing, there is a 1/4 inch slope. 10 feet of roof will drop 2.5 inches from the center to the edge. This helps the precipitation roll off the roof and also increases the structural integrity.


Usonian engineering

We also look to expert engineers to engineer these flat roofs to handle our Central Oregon snowfall. Our new homes are engineered, to code, to hold TWICE the record snowfall in Central Oregon recorded in the past 20 years. The flat, Usonian roofs are designed to hold 25 psf (pounds per square foot) of snow, which is a “live load” – meaning the snow load isn’t going to be there permanently.

Want to find out more about snow loads around Oregon? Check out this website: Structural Engineers Association of Oregon

Roofing Material

TPO Sample

We use a very strong roof covering on our flat, Usonian roofs called Thermoplastic polyolefin (TPO) single-ply roofing. TPO is typically made from polypropylene and ethylene-propylene rubber polymerized together.

TPO is known for its durability & flexability (highly resistant to tears and punctures), strong seam strength, convenient installation, UV and heat resistance, and being economical. The nature of TPO roofing that we use on our Usonian roofs keeps moisture from seeping in from snow, rain, hail, etc.

In many ways, TPO roofing is more effective at blocking moisture than composite roofing:

    • There is less room for error in installation. TPO is much easier and straight forward to apply. With large sheets and very few seams to weld.
    • TPO is more moisture-resistant than composite. Water will evaporate much more quickly and can blow off the roof more easily.

Central Oregon weather can be unpredictable, but homes, when properly engineered and built, are meant to handle the unpredictability.

sisters mountains

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