Things To Consider Before Replacing Your Flat Roof

In a conclusion to our previous post, here are five more things to think about if your flat roof needs some TLC.


Your roofing system experiences positive air pressure as wind passes across your roof. This suction effect pulls the roof system away from the structure. If your roofing system is insufficiently anchored when this happens, it could fail. And, if the decking underneath is inadequate; enough uplift can cause substantial structural damage. In the Portland area, typical wind speeds vary from 0 mph to 17 mph, and rarely exceed 26 mph. However, historically, the area has experienced winds in excess of 100 mph.

A flat roof membrane can be attached to the roof deck in two ways; either with mechanical fasteners or be being adhered directly to the insulation or DensDeck cement board, which is then attached to the decking. Each method has its pros and cons. In the case of a mechanically fastened system, the fasteners take the brunt of the pressure and the insulation is largely protected. In the case of a fully adhered membrane, the insulation is put under more pressure.

To minimize the chance of roofing system failures, consider the quality of material being used, the type of fasteners used as well as fastener spacing, and consider modifications that will improve wind uplift resistance like ½ sheets of membrane due to distance between the fasteners in the corners and edges of the building.


Underwriters Laboratories (UL), an independent testing agency, sets standards for fire resistance for all kinds of different products. They give ratings specifically for roofing systems based on their resistance to flame spread. There are three classifications of UL ratings: UL Class A, UL Class B and UL Class C; Class A being the most resistant to flame spread. As a general rule of thumb, and part of many building codes, any publicly occupied building, commercial structure or apartment building must have a UL Class A rated roofing system.


When deciding on a roof system replacement versus just a roof repair, cost is always an important factor. If you think about these expenses in terms of cost-per-year, it can help you make a smart financial decision, but you’ll need to know how long something will last. For example, let’s say a new roof system will cost $50,000 and is expected to last for 30 years. A repair for the same roof will cost $14,000 and the expected life of the repair is 5 years. Not factoring for inflation, the replacement would cost you about $1,700 per year, and the repair would cost you $2,800 per year. While the option requiring the least amount of capital is usually the favored option, cost per year can also influence this kind of decision.


Deciding whether or not to tear off an existing roofing system before installing another can be tricky. But, considering the topics discussed above can help you find peace of mind. Some situations can make the decision to tear-off for you, such as water damage, multiple existing roof systems, and extreme structural problems. Others may yield options which do not require the removal of the existing roof system. Just keep in mind that the new roof you install will only be as good as the roof system and structure that it is installed over.

Pacific West Roofing can help you determine whether a tear-off or roof-over is best. We’ll walk you through a thoughtful consideration of all options and conditions that will impact your flat roof‘s performance, and find the method that is right for you.


What is roof pitch and how does it impact the roofing process?

10 Things To Consider Before Replacing Your Flat Roof10 Things To Consider Before Replacing Your Flat Roof

10 Things To Consider Before Replacing Your Flat Roof , Part One

Portland Roofing Contractor Since 1980

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