A roof has a “low pitch” if it slopes anywhere from 2/12 to 4/12 inches—meaning that for every foot the roof extends horizontally, the level of the roof rises two to four vertical inches. Some roofs have extremely low slopes and appear to be nearly flat. No roof, of course, should actually be completely flat. If it is, puddles of water will accumulate on the roof and ultimately damage it.
Low-slope roofs are seen on both commercial and residential buildings, although they are primarily associated with businesses. There is a reason for this: in commercial buildings, it is generally considered more prudent to maximize the use of space, leading to a flatter roof. Residential homes, on the other hand, tend to have a much steeper incline for cosmetic reasons.
Regardless of whether you’re looking for low roof pitch options for your home or your place of business, you’ll need to consider what materials are best. In this article, we’ll take a look at the choices available to you and other variables to consider when putting in a roof.
The Trouble with Low Roof Pitch
The primary advantage of a low roof pitch is maximizing space. It will allow you to utilize the space in your area all the way up to the top. This can create a number of advantages. Heating and cooling are easier in a building with a flatter roof, for example. However, low-slope roofs come with disadvantages that don’t trouble steeper roofs. The primary problem with a low slope has to do with drainage: water damages roofs, and water can begin to pool on a roof with too low of a slope. Ice and snow can also be a problem, depending on the climate. If water accumulates on your roof and can’t drain properly, it will eventually cause decay.
Direct sunlight can be another problem for a low-pitch roof, although this is certainly not an issue unique to these types of roofs. In fact, ultraviolet light can do a number on any type of roof, unless the proper materials are used.
This brings us to the primary disadvantage of a low slope roof: you are somewhat limited in the materials you can use to construct them. This is because of the importance of waterproofing. On a roof with a higher pitch, water will easily roll off, and that means you don’t need to concern yourself as much with waterproof materials. A low-pitch roof, on the other hand, absolutely must be waterproofed.
Low-pitch roofs are usually waterproofed through the use of a roof membrane, which can be made from synthetic rubber, a thermoplastic such as PVC, or modified bitumen. Any of these materials can effectively carry water off the roof without allowing it to pool anywhere or penetrate vulnerable areas and cause damage. Occasionally, asphalt roofing systems are also still in use, and while these types of roofs were extremely common in the past, they’ve largely been supplanted by synthetic membranes. This is because asphalt roofs don’t seal as effectively as other membranes do.
Types of Low-Pitch Roofs
There are several options when having a low-pitch roof installed for your building. These options, however, are more limited than those for a gable roof or other higher-pitch roof. Even so, there are several choices you can make as far as the construction of your roof, each with its own set of pros and cons.
Asphalt shingles are, as their name suggests, shingles made from asphalt and layered on your roof over felt, a synthetic underlayment, or thicker “ice and water shield”–type membrane. Shingles can be a controversial option for a low-slope roof. Most manufacturers allow shingles on slopes of 2/12 and greater, but most roofing contractors insist on greater slopes, as shingles aren’t “waterproof” but water shedding. Shingles are popular primarily because of their relatively low cost, ease of installation, and aesthetic benefits. However, installing shingles on a low-slope roof might be asking for problems. Consult a professional roofing contractor with many years of experience.
Unlike with other roofing systems, where the material is built up over the membrane or layered on top of other materials, single-ply membranes are installed without the help of other layers. A thermoset or thermoplastic membrane is laid across the surface of the roof (generally over rigid insulation) and hot-air welded together. The most popular materials for single-ply membranes are PVC and TPO, which are usually reinforced with the addition of polyester or fiberglass. Single-ply membranes are a great, relatively inexpensive option that’s easy to install. However, because they’re only one layer, maintenance is critical.
Torch Down Roofing
This roofing system is made from sheets of modified bitumen—a hydrocarbon-based material—which is then sealed to the surface of the roof through the use of a handheld propane torch. The seams of the bitumen will melt and fuse together as a result of the welding process, creating seams that are completely waterproof.
This roofing material is great if you live in a particularly harsh climate. While other materials may expand or contract if the weather is hot or cold, modified bitumen will not. This material also has a long life span and is easy to repair, though it can be extremely difficult to install due to the use of the torch. As most of the roof decks in the Pacific Northwest are made of wood, the risk of fire should be a significant consideration. Only use a contractor with the CERTA certification.
For commercial buildings, one of the other popular low-pitch roof options is coated metal. Metal roofs aren’t waterproof in and of themselves, but they can be treated with a coating that makes them so. This coating helps reduce the instances of rust, increasing the life span of the roof. Generally, the coating that’s applied is a fluoropolymer paint, which allows the metal roof to become resistant to water and ultraviolet radiation. This option, of course, isn’t practical for commercial buildings that don’t have metal roofs.
If you’d like to discuss roofing options for your building, contact the professionals at Interstate Roofing. We’ve been serving Pacific Northwest for over 20 years and are always ready to share our expertise.