Category: Flat Roofs

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 However, it is such an inefficient and outdated flat roofing material that we cannot recommend using it.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

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

ROOF COATINGS

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

When the time comes to replace your flat roofing system there are several things to think about that can improve the performance of your next roof. There are plenty of factors that can contribute to the failure of a flat roof, including improper slope, poor drainage, and structural problems. The location and use of the building will bring up other considerations such as R-Value, wind uplift, and fire resistance.

The guidelines in part one and part two of this post will help ensure that your next roofing system lasts longer than the one you’re replacing.

SLOPE

The slope of your roof system is the key player in how well your roof sheds water. Ponding water, the biggest problem among commercial or flat roofing systems, is caused by insufficient roof slope. When a poorly sloped roof starts to leak, the leaks will be much more severe for the fact that the water has nowhere else to go. There are older flat roofs out there that are performing satisfactorily with slopes of just 1/8″ per foot, however, it is generally recommended that the slope be a minimum of 1/4″ per foot in order to minimize ponding water on the roof surface and prevent subsequent leaks.

Roof Drainage

As your roof’s slope sheds water, your roof’s drainage system disposes of it. And, an inadequate drainage system will cause many of the same problems that improper slope will. Whether you’re using internal drains, scuppers or gutters and downspouts, the roof drainage system needs to be matched to the size and slope of your roof. As the slope of your roof increases, the volume of water that is routed to the drainage system will increase. Stop and ask yourself if there are enough drains, if the scupper openings are large enough, or if your gutter system is large enough handle the volume of water expected to hit your roof.

R-VALUE

Your insulation’s ability to resist heat transfer is determined by its R value. The higher the R value, the better. Consider your roof’s existing R-value and how it affects your heating & cooling costs. Not only will adding insulation improve your R value, but if your roof’s slope is inadequate, using tapered insulation can be a more cost-effective solution than structurally altering the roof. It is the best way to insulate a flat roof and by adding thickness to the taper, it increases your R-value.

STRUCTURAL LOADS

Another important thing to think about is the weight your roofing system can support, which is typically expressed in pounds per square foot (PSF). Roofs are generally engineered to handle projected wind and snow loads based on regional, historical data.

Let’s say your original built-up roof system was installed with a structural load of 2 PSF. This value would have also dictated the framing that was required to accomplish the desired structural strength. Now, let’s say you’re considering a modern single-ply EPDM membrane roof system as a replacement, and your prefer a ballasted system since it’s typically the least expensive. Ballasted systems usually have a structural load of around 10-12 PSF. The additional weight load placed on the roof structure (even if the old roofing system was removed) could easily cause the roof to collapse. Therefore, it is crucial to compare the weight of the new roof system to the limits of the original roof system that the building was designed around. Consult with an engineer if you aren’t sure about how much weight your roof structure can safely handle.

ROOF DECK DEFICIENCIES

If your roof deck has structural problems this is another important element to contemplate when replacing your roof system. Wood-framed roofs often have joists that have bowed from years of constant load. This can cause water to pond in the middle of the roof. Maybe your roof decking has weird elevation changes from previous instances of construction and remodeling. Whatever decking issue you may be facing, it’s critical that these aspects are factored into your roof replacement project. If your roof structure has deficiencies and you decide to install a new roof system over the existing one, the new roof will have the same problems. You will have the best opportunity to address structural issues is the existing roof system(s) are removed down to the decking.

Find the last 5 flat roofing considerations in Part 2 of this post!

If it’s time to repair or replace your flat roof, check out our commercial roofing page and contact us today.

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

WIND UPLIFT

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.

UL FIRE CLASSIFICATION REQUIREMENTS

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.

ROOF REPAIR VS. REPLACEMENT

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.

TEAR-OFF VS. ROOF-OVER

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.