Many large, low rise commercial buildings such as warehouses, large retail stores, agricultural structures, aerospace facilities, etc. often do not benefit from steep roofs as residential and small commercial buildings might. This is because a steep roof slope would create undesirable height and unnecessary construction costs.
Instead, these buildings are more appropriately built with so-called “flat roofs”. This is actually a misnomer, as the roofs are actually “low pitch roofs” which the National Roofing Contractors Association (NRCA) defines as any roof with “a pitch of 3:12 or less”. Anything steeper is considered a “high pitch roof”. With that in mind, let’s look at a few key points to consider when designing and building a low pitch roof.
Roof materials with a low incline
When choosing low pitch roofing products, there are generally three basic options:
- Asphalt / bitumen products: The longstanding commercial umbrella standard, the use of asphalt / bitumen products, has declined as newer, more attractive options have emerged.
- Flexible Membrane Roof: This roofing material can be made from a wide variety of plastic / polymer based materials (commonly known as EPDM, TPO, PVC, or others). Rolls of the selected membrane are laid out on the roof structure and secured either with properly spaced mechanical fasteners (screws with large washers) or with a continuous layer of adhesive.
- Metal Roof: Sometimes overlooked, metal roof is suitable for different roof pitches. Many metal roofs that use a standing seam system are designed for use on roofs as low as ½: 12 pitch.
When considering what type of roofing material to use for a construction project, there are a number of significant differences that illustrate why metal roofing is often preferred
Designed for superior performance
Metal standing seam roofs are specifically designed and engineered for use on low pitch roofs as they meet a range of performance requirements:
- Water resistance: Water and other forms of precipitation do not penetrate through metal and / or through properly formed standing seams that connect the metal plates. This is why they can tolerate slopes that are so low that the water can slowly and predictably drain away without any leakage.
- Rigidity: The rigidity of metal means that there is no possibility of damming (i.e. standing water on a roof). This is not always the case with asphalt / bitumen or membrane roof systems.
- Drainage: Water on a metal roof usually flows to the edge of the roof where it meets gutters and downspouts that lead the water away from the building. Other roof systems are based on internal drainage inside the building. This takes up space and can leak water in the building and cause damage.
- Wind resistance: Standardized lifting tests of metal roofs show that they can work just as well or even better than membrane systems that are either mechanically attached or fully bonded.
- Durability: Due to the technical design and the use of high quality coatings, the most commonly cited benefit of metal roofs is long term strength and durability. This means that the roofs will last longer – 50 years or more compared to the other two roof types, which are only designed for 20 or 30 years.
- Puncture Resistance: Roofs with a slight incline tend to be stepped on and can also suffer direct abuse from hail and other hazards. Metal roofs are more puncture-proof than asphalt / bitumen or membrane roofs and can withstand pedestrian traffic and hail better without being punctured.
- Ease of Construction / Installation: Metal roofing panels are sized and prefabricated to fit the building in which they will be installed. This usually means that placing and installing metal roofs in the field will take less time than other types of roofs. In addition, the installation of metal panels is not limited by temperature or other weather conditions as they can easily tolerate a wide range of both and still function as intended. On roofs with a slight incline, their surface is also easy to walk on without risking falls or other safety risks.
Using metal roofs on low pitch roof systems has proven to be quite inexpensive in many ways:
- Less man hours due to the simple installation save money in construction.
- Competitive material costs, especially when the metal roof is part of an entire metal construction package from a single manufacturer.
- Minimal maintenance and an aversion to rust, mold and decay, which will save the builder money over time.
All of this adds up to very low life cycle costs.
Given the performance, cost, and life cycle of metal roofing panels, this material should always be considered a viable option for low pitch roofing systems. Metal roofing manufacturers like MBCI can not only help you select the right metal roofing products, but they can also provide the information and resources necessary for a proper installation.
View examples of low pitch metal roofing projects and Contact your local MBCI representative to start your project today.