Flat Roofing systems: The purpose of a flat roof or any roof for that matter is to keep your home or building safe and dry. The roof MUST protect your investment from the elements such as rain, snow, and even the sun’s heat. However, many flat roofing technologies on the market today have some major, inherent drawbacks that have origins in their design. In fact, most flat roofs fail to serve their main purpose just a few years after they are installed.
You are presented with so many choices for a flat roof and every roofing contractor will tell you their product is the best. But which one do you choose and how do you know that you are getting the best deal? Here we have summarized the most common and ‘popular’ flat roofing choices. You can be the judge and decide which is best for you.
Benefits of flat roof construction:
There is a common misconception among many home-improvement contractors and residential builders / architects that flat roofs = problems. The truth is that flat roofs are very convenient, easier to build, and cost less than pitched / sloped roofs. In some cases, a flat roof is the only way to go, for example, when you have a large size building. Building a reliable pitched roof in those cases will require extra engineering to accommodate for additional structural weight.
Flat roofs are also convenient for installing large HVAC equipment that otherwise would have to be installed on the ground. You can also use flat roof as a roof-top deck, patio or penthouse. Green roofs are also gaining popularity with environmentally conscious companies and organizations.
When you compare all the construction costs and environmental benefits, flat roofs by far surpass any sloped roof, for which the roof products of choice are oil-based asphalt shingles. These asphalt shingles end up in our land-fills every 12-15 years, and yet more and more of them are produced.
Limitations and Disadvantages of flat roofing:
Flat roofs also have a number of disadvantages. The main one is the fact that there is no slope and all the water/snow sits on the roof. While water can be taken care of with proper drainage, snow will sit on the roof until it melts. This requires the engineers / architects to implement building components with a higher structural load. Another disadvantage that haunted flat roof installations for over a century is ponding water. Until the invention of single ply membranes such as an IB roof, there was no effective and economical way to eliminate the leaks caused by ponding water. That had to be taken care of in the initial design/construction stage. Creating a slight pitch and multiple drains was required, and still ponding water caused over 75% of all flat roof leaks.
Now the ponding water problem is solved by either implementing a slight pitch to the roof – such as in ‘space metal buildings”, using tapered insulation to direct water flow toward drains and with the creation of IB PVC / CPA roofing with hot-air welded seams, ponding water is no longer a problem in small quantities. It is still necessary to have adequate drainage system, since a lot of ponding water can cause structural damages to your house or building.
Types of flat roof: Modern and Outdated roofing technologies.
Outdated (Multiple-Ply Roofs) – some are over 100 years old:
- Build-Up Roof (BUR)
- Tar & Gravel
- Bitumen (Modified Bitumen)
- Rolled Asphalt (usually a “single-ply” install, sometimes uses tar-paper as base ply)
Modern (Single-Ply Membranes)- created within last 30 years:
- IB Roof (PVC roofing) – IB PVC roofing membrane is one of the best low-slope and completely flat roofing products available, and that is precisely the reason why we only install IB roofs. With over 30 years of spotless reputation and leaks-free performance in many different climates – from Alaska’s frigid north-lands to Hawaii’s tropical paradise, IB roofs are protecting the buildings and everything inside, without a single material failure since 1978.
IB roofs still feature the same chemical formula as its original design, and with hot-air welded seams, will maintain complete water-tightness over your roof.
- Epdm Rubber Roof – a widely used flat roofing material, mainly popular among contractors because of its low price and no special equipment needed to install the rubber roof. Still, rubber roofs are very prone to leaks, as the seams are glued together, and adhesive tends to break down within 5-7 years. Also in the residential roofing market (and not so much in commercial) there are too many contractors who will install rubber roofing products without proper knowledge and training. As a result, we often go to rubber roof repair service calls to fix problems caused by poor workmanship, often on fairly new roofs.
- TPO Roofing – a single ply thermoplastic roofing membrane similar to PVC roofs from a first glance. But as you start digging, you’ll find numerous problems with TPO roofs, mainly as a result of manufacturers skipping on adding important ingredients into formulation of the TPO membrane, and as a result, quietly scrapping as many as three major generations of the product.
- SFR – Sprayed Foam Roofing (not a single-ply)
Part I: Inferior and outdated flat roofing technologies
These are very common on older buildings, although many newer buildings also have these systems installed. They are rarely installed on any commercial building today. However, they continue to be produced, and many roofers still install them on residential and small commercial roofs. This is particularly due to their low cost of material, and roofers’ lack of experience with BETTER solutions. It is sad that there are some decent roofers offering such an inferior product to their customers. I often hear something along the lines of: “I’ve been doing ‘torch-down’ for 20 years, and it is the best” – very sad – so we will briefly describe them, without getting into details.
BUR / Tar & Gravel / Torch-down: Multiple-ply roof where each ‘tar-soaked’ ply is applied with a torch (yes, open flame on your roof!), or hot mopped (preheated tar transported to the roof and applied with a mop). Gravel goes on top of this ‘sandwich’ mainly as a protection layer from foot-traffic and sun’s devastating ultraviolet rays. There are many deviations from the above procedure, but they are all within a close range of similarity.
Modified Bitumen: It is also applied with a torch in a similar manner described above. It is however a different material than tar. Modified bitumen has rubber and elastomers added into the formula, so it is stronger and more flexible.
Rolled Asphalt: Similar to asphalt shingles – tar paper is saturated in asphalt, with crushed stones glued on top of it. Rolls are installed in an overlapping pattern, with cold-mop application and nails to attach it to the roof deck. Overlapping seams are sealed with tar.
Problems associated with flat roofs:
The nature of flat roofs’ problems is just that they are flat. Water does not run off the roof. Proper drainage must be in place to get rid of water accumulating on a roof. Usually older roofs are not leveled, so water puddles will appear here and there after every rain, and just sit there until it dries out. This is called standing or ponding water. Most roofing systems were not designed for ponding water. In fact, most manufacturers of the roofing systems on the market today, will void out the warranty if there is ponding water on the roof (we will get to this issue later). Other major problems for flat roofs, are penetrations such as skylights, vent or exhaust pipes, chimneys, roof hatches, drains, etc. However the biggest problem with flat roofs is the seams, because they are the most common areas where leaks occur.
Seams exist on every flat roof (except tiny ’6×10 porch-type’ roofs, which can be covered with a single sheet of roofing membrane), and are usually put together with some sort of adhesive. After a few years the adhesive breaks due to severe weather changes (here in New England, temperature can change 25 degrees or more, in a matter of one day). Another major factor affecting seams’ adhesive is condensation, which always occurs underneath the roof covering. Condensation expands both in the winter and summer. The most dramatic expansion of condensation happens in the winter time when water freezes, expands and breaks the seam. The same happens to our roads. Think of all the potholes you drive over. Those too were caused by water freezing. In the summer water heats up and also expands. When you see bubbles on the roof surface, it is the water vapor lifting the membrane. The third major factor is actually quality of workmanship and the adhesive itself. For different roofing systems the process is different, but most of them share the same shortcoming – the need for using adhesives, be it glue, hot tar, liquid resin, etc. Adhesives are also required to flash any roof penetrations listed above, but here the workmanship is actually more of a factor than the adhesive.
Conclusion – let’s get real.
It is a shame that in the 21st century we are still using 19th century technology. Even more so, because nearly 50% of roofers in the on-line construction forums will advise you to choose a clearly inferior roof. These heavy and dirty roofs, heat up to 170 degrees and make your AC run like crazy in the summer. These very roofs start leaking prematurely and are impossible to fix. Why would some one acting in good faith actually recommend these? The answer is obvious – they don’t know any better. Fortunately there is ONE modern, technologically advanced flat roofing solution available on the market today – IB Roof. In fact, this solution has been around for a few decades now, and has a proved track record of 30 years of leak-free service!
Read more: Part II – Single-Ply Roofing Membranes – PVC, TPO & EPDM Rubber Roofing.
Written by Leo - roofer with a vision. Follow Leo on Google+
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