Mechanical fasteners are often the preferred method for many roofing installations, with adhesive and asphalt fastening being the other most common options. While adhesives have evolved significantly, mechanical fasteners are a tried-and-true solution for many buildings and deck substrate types. Fasteners need to be carefully selected based on each roof’s substrate, so choose wisely.
This article lays out the pros and cons of mechanical fasteners.
What are mechanical fasteners?
A mechanical fastening system uses screws, plates, sometimes oversized washers and specially designed nails to fasten insulation and/or roof membrane to the deck substrate. The roofer must ensure that the correct type, length of mechanical fastener and related plate spacing is appropriate and required by the roof system manufacturer and warranty provider.
Mechanical fasteners themselves are not the only elements to consider. Other methods of securement are very often employed in tandem with the fasteners and plates themselves, such as asphalt, adhesive, hot air welding, and thermofusible welding (also called torching).Â
When are mechanical fasteners the best option?
As with other commercial and industrial building decisions, there are often good, better and best solutions about the type of fastening system that is to be used in each specific circumstance. Your professional roofer will make recommendations based on many factors.
Metal fasteners may or may not be the right choice based on the type of deck substrate, weather, climate, aesthetics, building codes, and other factors.
Below are key pros and cons of metal fasteners that your roofing contractor will consider.
Pros of mechanical fasteners
Metal fasteners are quite versatile and can be used for many applications, making them a popular choice for many structures. Here are some of the primary benefits.
Standing up to Toronto weather and climate
Unlike adhesive and asphalt, metal fasteners have no temperature limitations. In addition, they accommodate thermal expansion to avoid warping, cracking and structural damage. When high winds are a concern, mechanical components are fastened directly to the deck substrate, making it more resistant to wind uplift. Â
Lower cost of mechanical fasteners
Materials are less costly compared to adhesives, require less maintenance over time, and are long-lasting—if they are properly installed and use high-quality materials. Premium materials may be more expensive, but they will last longer than lower quality materials prone to corrosion or other issues.Â
Less odour than adhesives and asphalt
VOCs (volatile organic compounds) from adhesive and asphalt fastening can cause disturbing odours during application or maintenance depending on factors including how much asphalt is laid, the enclosure of the space, and humidity levels.   Â
Tensile strength
Mechanical fasteners have a high load-bearing capacity, durability, and long-term stability. These positive qualities will vary based on the type and grade of the fasteners, as well as pull-out resistance, shear strength, substrate type and strength and fastener design.
Fire resistance and compliance
Most mechanical fasteners are steel, which doesn’t lose structural integrity at the temperatures required for fire testing. However, some aluminum and copper fasteners aren’t fire-resistant because they melt faster than steel.
Less risk of errorÂ
When installed correctly, mechanical fastening methods are less risky. However, poor installation can result in leaks from penetrations, misalignment, improper sealing or under- or over-tightening. The result will be higher maintenance and a shorter life span.
 Warranties
All manufacturers’ warranties allow for this method of securing insulation.
Cons of mechanical fasteners
While mechanical fasteners offer many benefits, especially with premium materials and expert installation, there are also downsides. Here are factors to consider:
Decking constraints
Mechanical fastening isn’t ideal for all decking materials. For example, concrete and gypsum must be pre-drilled, which is time-consuming and labour-intensive, driving up installation costs. Also, if the fasteners miss the top of the flute on the steel deck substrate, they will not hold at all!
Conduits and other hidden risks
One of the most critical (and expensive) risks of metal fastening occurs if fasteners hit electrical and data conduits buried on the underside of the deck, installed inside the fluted ribs instead of below the bottom of the flutes. Often the conduits are not visible, such as when the underside of the deck substrate is concealed by a T-bar or drywall ceiling. Also, the conduits are often not secured to the deck substrate so there is no deck penetration visible from the topside of the roof.
Energy loss
Thermal bridging from fasteners spanning the roof deck, insulation, and coverboard allows heat to transfer from the interior through the fasteners. In low-slope roofs, heat loss can increase up to 3-8%, rising as insulation thickness increases. In cold weather, thermal bridges can also affect the insulation.
Temperature fluctuations
When metal fasteners expand and contract with temperature changes, fasteners can loosen over time. This may lead to leaks, gaps, misalignments or structural issues if the roof system isn’t properly designed. Â
Noisy installation
Mechanical fastening is disruptive to those in the building during installation and repairs. Drilling and hammering may, for example, negatively impact those inside multi-tenant, educational and medical facilities.
Aesthetic considerations
Mechanical fasteners can detract from building aesthetics if, for example, insulation plates show through the roof membrane, fasteners can be seen on the underside of the deck substrate, or colors are mismatched. In addition, holes from the fasteners will be visible when the roof is replaced. Also, the installation of mechanical fasteners through a painted underside of deck substrate can cause the paint to start to peel.
Code restrictions
In Toronto, mechanical fastening is not allowed for some industries and building types because of building codes and fire safety regulations. Examples include certain heritage conservation buildings, low-rise construction and those constructed with combustible materials. The Ontario Building Code provides more information on this topic.Â
Read this article to learn about how mechanical fasteners compare with adhesive fasteners.
Insist on quality materials and expert installation of mechanical fasteners
Mechanical fasteners can have many roofing applications, along with pros and cons to consider. The first step is to find a qualified, expert roofer you can trust to provide the high-quality materials and installation needed for optimal performance, reduced maintenance costs, and the longevity of your roof. Elite Roofing, serving the Greater Toronto Area, delivers superior craftsmanship, backed by our 24/7 emergency service. Contact us today and get the Elite Advantage.
