Denver has a surprisingly large stock of flat and low slope roofing across its housing inventory. Mid century modern homes built in the 1950s through 1970s, additions and sunrooms on older ranch houses, garages, commercial buildings, and mixed use properties throughout the metro all have flat or low slope roof systems. If you own one of these properties, your roofing needs are different from the typical steep slope asphalt shingle situation, and the options available to you are different as well.
What Is Considered a Flat or Low Slope Roof?
In roofing terminology, a flat roof and a low slope roof are related but distinct. A true flat roof has essentially no pitch, though even these are typically installed with a slight slope of one quarter inch per foot for drainage. A low slope roof has a pitch of less than 3 to 12, meaning it rises less than three inches per horizontal foot. Standard asphalt shingles are not appropriate for low slope applications because water drains too slowly to prevent wicking under the shingles. These roof types require membrane systems or other waterproofing methods specifically designed for low or no slope installations.
Types of Flat and Low Slope Roofing Systems
TPO, or thermoplastic polyolefin, is currently the most widely installed single ply membrane system in commercial applications and is increasingly used on residential flat roofs. It is a white or light colored membrane that is heat welded at seams to create a waterproof bond. TPO reflects solar heat effectively, which is beneficial in summer, and is relatively resistant to puncture and UV degradation. It typically lasts 15 to 20 years with proper installation and maintenance. EPDM, or ethylene propylene diene monomer, is a rubber membrane system that has been used for decades on commercial and residential flat roofs. It is black or dark gray and is typically adhered or ballasted. EPDM is durable, flexible in cold temperatures, and relatively easy to repair when punctures or seam failures occur. It is widely available and has a well understood long term performance record. Modified bitumen is an asphalt based system applied in multiple layers and is particularly common on residential flat roofs and additions in Denver. It can be torch applied, cold applied, or self adhering and provides a thick, durable membrane that performs well in our temperature extremes.
Common Flat Roof Problems in Denver
Ponding water is the single most common issue on flat roofs. When drainage is inadequate or the roof has settled unevenly, water pools and sits for extended periods after rain or snowmelt. Standing water accelerates membrane deterioration, can penetrate seams, and adds structural load. Membrane blistering occurs when moisture or air becomes trapped beneath the membrane during installation or over time, creating bubbles in the surface. Blisters weaken the membrane and can eventually break open and allow water infiltration. Flashing failures around penetrations and at parapet walls are a frequent source of leaks. Every pipe, drain, curb, and wall transition requires flashing that is properly bonded to the membrane and maintained over time. In Denver's climate with extreme temperature cycling, flashing materials expand and contract and can pull away from substrates.
How Colorado Hail Affects Flat Roofing Differently
This is an important distinction for Denver flat roof owners. Steep slope asphalt shingles are evaluated for hail damage by looking for impact marks, granule loss, and mat damage. On a flat membrane roof, hail damage looks different and is evaluated differently. TPO and EPDM can be punctured by large hailstones, especially at seams where the membrane transitions or at aged areas where flexibility has diminished. Modified bitumen membranes are more impact resistant but can still show indentation or granule loss on cap sheets. After any significant hailstorm, a flat or low slope roof should be professionally inspected regardless of visible leaks. Hail damage on membrane roofs can create conditions for future failure even when no immediate leak is present.
When to Repair Versus Replace a Flat Roof
Flat roofing systems are generally repairable up to a point. If a leak or blister is isolated and the surrounding membrane is in good condition, a targeted repair makes sense. However, if a flat roof is more than 15 years old and showing widespread deterioration, numerous blisters, multiple failed seams, or repeated leak callbacks in different locations, replacement is almost always more economical than continued patching. The economics of flat roof repair versus replacement are similar to other roofing systems: at some point, the cumulative cost and inconvenience of repairs exceeds the cost of doing it right.
Lifespan Expectations for Flat Roofing in Denver
In Denver's climate, a properly installed TPO or EPDM system can realistically achieve 15 to 20 years of service life. Modified bitumen systems installed correctly can last 20 years or more. However, improper installation, inadequate drainage, or deferred maintenance can dramatically shorten these lifespans. We have seen TPO systems fail within five years due to installation errors and EPDM systems still performing well at 25 years with proper maintenance and repairs.
Finding a Qualified Flat Roof Contractor
Not every roofing contractor who installs asphalt shingles is equally competent at flat and low slope membrane systems. They are different skills using different materials and different installation methods. When choosing a contractor for flat roof work, ask specifically about their experience with the system type you have or are considering. Ask for references from recent flat roof projects. Verify that they carry manufacturer certification for the system they are recommending.
At Gates Enterprises, we handle roof repair services and roof replacement services for both steep slope and flat or low slope systems throughout the Denver metro. Whether your flat roof needs a targeted repair or a complete system replacement, we can assess the situation honestly and give you a clear picture of your options. Call us at (720) 766-3377 for a free inspection.