Unless you work in specific fields (roofing, construction, architecture, real-estate), you’ve probably not heard the term “low slope roof”. But you undoubtedly have heard the term “flat roof” before. These are actually the same thing, more or less. This may sound counterintuitive, but when you look into a flat roof, you realize that the term is actually a significant misnomer.
Flat roofs are not in fact, flat. A truly flat roof would be disastrous because when rain or snow fell, it would have nowhere to go, it’d pool in various places, and never drain. A flat roof may seem flat when you look at it, and even when you stand on it. However, if you were to drop a golf ball on the roof, it’d roll in a very predictable direction, though possibly gradually. A level would show some amount of slant to the surface.
Depending on whom you ask, not all low slope roofs are “flat roofs” (as some varieties of roofs with a very, very gradual but visible slope are categorized as such), but all flat roofs are indeed low slope roofs.
Today, we’re going to demystify all this, because we at JDT Construction believe that customers should be in the know, so they can make the best decisions when it comes to their roof. After all, a roof is a major make or break for curb appeal, resale value, and the integrity of a structure. It’s not to be taken at all lightly.
Most flat/low slope roofs consist of a continuous membrane material, of which there are various types. These come in rolls, and are applied considerably more quickly (and easily) than shingles or tiles. Some use a hot adhesive material (such as asphalt or a special compound) to adhere to the roof, while others have an adhesive already present, sometimes requiring heat to activate, sometimes not.
Depending on the material, a small-grain layer of loose gravel is applied over the material, to provide extra protection/resistance, though this approach is gradually falling out of favor due to the fact this loose gravel can clog drainage systems.
Uses of Low Slope Roofs
Low slope roofs see their larges application with commercial/industrial structures. This is because sloped roofs are not the most practical thing to install on such vast structures, and they become a maintenance nightmare as a result. Furthermore, these low slope designs allow ventilation, HVAC and other utility components to be more easily placed, accessed, and maintained as well.
Chances are, pretty much every store, restaurant, or other professional building you spend much time in, has a low slope roof for these reasons. They’re not nearly as common for homes, due to some maintenance problems (which are trivial for commercial properties, but a financial drain for a homeowner), and the absence of any aesthetic contribution. This is not to say a flat roof can’t work for a home, nor that it’s never done. It is very common, also, for these roofing systems to be used for outbuildings such as sheds, detached garages, and so on.
Types of Low Slope Roofing Systems
There are multiple types of low slope roof systems, but the following three are the most commonly used.
Built-Up Roof (BUR)
Built up roofs consist of multiple layers of material, starting with a rigid layer above the deck surface. A layer of asphalt is applied, followed by a cover board, and then more asphalt. Then, a series of ply sheets are laid on, each with another layer of asphalt. Finally, a reflective coating is placed atop this. BUR roofs tend to use the small-grain gravel we touched on earlier.
The advantage of BUR is that it’s been around for a very long time, so it’s time-tested, and the construction very much refined. However, it can develop seams and leaks quickly, it’s not very environmentally sound, and the expense depends on crude oil prices at the time of its installation/repair.
Modified Bitumen Roof (MBR)
Modified bitumen is a more modern process (using a modified, enhanced asphalt formula), with an advantage of having a longer life cycle, less tendency to leak or develop seams, and being easier to install. While costlier than BUR on average, MBR is often regarded as worth the extra cost.
MBR roofs consist of a corrugated steel deck, and then a layer of polyester/fiberglass, followed by mechanically-attached roof board. A base sheet of asphalt membrane is then laid over this, followed by a cap sheet resembling asphalt shingle in texture and appearance. A reflective coating is then applied over this.
Singe ply roofs are the easiest, fastest sort to apply, but is a newer process, so it lacks the time testing that BUR and MBR have.
Single ply uses a corrugated steel deck, a rigid poly insulator layer, a mechanically-applied top board, and a single layer of mechanically-applied roofing membrane. Concerns over its likelihood to develop seams, buckling, or gouge damage from maintenance, remain in the air, with this approach, for the time being.
To learn more about low slope roofs, fill out our contact form today.