Portland Roofing Contractor - Pacific West Roofing

When you’re looking to install or replace a flat roof, you have numerous material options and installation requirements to consider. Finding out which material is right for your flat roof can be confusing and difficult. So, we’ll help you choose the right roofing system by discussing the things you value in a roof the most; price, service-life and maintenance requirements.

First, here are two main types of flat roof applications:

  • BUR or Built-Up Roofing
  • Single-Ply

Within these categories, there are many different roofing systems. Finding the appropriate application and then selecting the preferable system usually works best. Let’s take a look at each of these applications.

BUR or Built-Up Roofing

Like it’s name implies, this type of flat roof is built up by applying layers of roofing material, such as tar or asphalt composition, or fiberglass felt. Two to four layers of rolled material are applied in a criss-cross pattern with either a roofing adhesive or hot asphalt, which serves as a waterproofing membrane. A layer of granulated cap sheet or gravel is often added on top to protect the roof from damaging UV rays.

Built-up roofs are economical, but they need specialized equipment such as expensive kettles that spew out VOC’s. They are relatively durable, but difficult to maintain due to the material’s limited expandability over time, which is due to UV breakdown– even in the first 5 years. Flashings are often separating from the asphalt due to this movement.

Bear in mind that rolled asphalt roofing, also called torch down, can also be considered a single ply roof depending on how it’s installed. However, it is such an inefficient and outdated flat roofing material that we cannot recommend using it.


Single ply is the most common commercial roofing material available today. Opposite the built-up roof, it is made of just one all-purpose layer of roofing material. Single ply roofing systems are thinner and lighter than built-up roofs, ranging between 45 and 120 millimeters. Today they are commonly made of EPDM rubber (ethylene propylene diene monomer), PVC (polyvinyl chloride) or TPO (thermoplastic polyolefin), which all have their pros and cons. This type of flat roof is installed either by gluing the layer of material to the board underneath it, hot-air welding the seams and flashings, or mechanically attaching it to the roof deck with fasteners and barbed plates.

EPDM rubber is the original single ply roofing material. It is usually black, both reinforced and unreinforced, and applied with an double sticky tape adhesive to keep the seams watertight.  Although it has its limitations, like ponding water issues and almost certain repairs after 7-10 years, it is still the most commonly used flat roofing material nationally but not in the West. Its popularity is mainly due to it’s reasonable costs and the fact that no special equipment is needed to install it.

In contrast, PVC and TPO roofs are usually white, reinforced membranes with seams that are hot-air welded for water tightness. This means that installation of either of these materials will require the use of special hot-air welding equipment to seal the seams and all the flashings. The hand welder equipment is relatively inexpensive unless the company uses a walk behind welder which can cost as much as $7-8K plus the generator to run it. This is still far less than hot tar equipment.

PVC roofing has been around 3 times longer than TPO, giving PVC a more reliable track record. TPO is considerably less expensive than PVC; however, you get what you pay for. TPO roofs have many issues that have yet to be resolved, making them a gamble for the consumer. Most track records show TPO life to fall short of warranty


If you are unsure about installing a new roof, you might also consider roof coatings, which are made for preserving existing roofs. They can be used to extend the service life of a roof by as many as 15 years, acting as an additional waterproofing layer. Although, not all coatings are sufficiently waterproof despite some manufacturer’s claims.

Roof coatings are most effective on roofs with smooth surfaces such as EPDM rubber roofs, low slope standing seam metal roofs, and some modified bitumen roofs. Coatings are not suggested for roofs prone to dirt and debris, such as tar and gravel roofs. These types of roofs are nearly impossible to clean thoroughly, which is a must before applying any coating. Also they’re not for roofs with ponding conditions because they peel underwater.

For more information or a free flat roofing estimate, contact us at 503-635-8706



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Portland Roofing Contractor Since 1980

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