Pros and Cons of Adhesives vs. Mechanical Fasteners for Roof Insulation

adhesive materials

Mechanical fasteners and adhesives are two of the most common roof installation methods on the market. Although mechanical fastening is the preferred method for many roof system installations, adhesive fastening is an option in many applications. During the past few decades, adhesive fastening technology has evolved to provide many options and solutions for every building and deck type. The decision to use adhesives or mechanical fasteners depends on a number of factors, such as the type of building, type of deck substrate, aesthetic concerns [where fasteners are visible inside the premises], noise considerations, and budget. In this article, we’re laying out the pros and cons of each method, and giving you the inside scoop on everything you need to know about these two materials. 


The Evolution of Fastening Techniques

Effective roof insulation is an essential element of all buildings constructed today as it provides a thermal blanket to keep the interior warm or cool, depending on the season. Insulation is usually installed in one or more layers. For more than a century, the commercial roofing industry has used a variety of fastening techniques and methods to secure roof membrane, cover board and insulation to deck substrates. Materials historically were affixed to building substrates with hot asphalt or held in place with pavers or stone ballast. 



Historically, there have been several insulation adhesives on the market: solvent-based asphalt and non-asphalt adhesives, water-based asphalt and non-asphalt adhesives, polyurethane-based adhesives, and hot asphalt. For more than 150 years, hot asphalt has been used as a single-source adhesive to bond insulation to monolithic roof decks, and to bond multiple layers of insulation. During the 1960s, cold asphalt-based adhesives were developed as an interlayer adhesive on built-up roof systems. These contained organic felts and fiber mats. This was followed by two-component polyurethane-based adhesives in the 1990’s and this material is widely used today.


Some facts about Adhesives: 

  • In a fully adhered fastening system, the membrane is bonded to the top layer of cover board or insulation and usually one or more layers of insulation are glued to a vapour retardant over top of the substrate.
  • The range of adhesives available to the roofing industry has expanded dramatically over the past several years, making it one of the most versatile fastening systems in the market today.
  • Just like other fastening types, adhesives used to secure roofing materials and components must be compatible with other materials. They must also be thoroughly tested by such agencies as ULC and Factory Mutual to confirm performance and durability characteristics of rated roof assemblies.


Adhesives vs. Mechanical Fasteners


Pros of Adhesives

  • Using adhesives can help reduce energy loss from thermal bridging (because several layers of insulation are glued together). This is desirable to avoid potential issues with moisture.
  • Compared to mechanical fasteners, there is a wider range of adhesives available in the market.
  • The new generation of single-component polyurethane-based adhesives is clean and easy to use.
  • Single-component polyurethane-based adhesives can be used in new and re-roofing applications on a wide range of substrates and with temperatures as cold as minus 20 degrees Celsius.
  • Two-component polyurethane-based insulation adhesives do not rely on ambient temperature or humidity for curing, thus offering a more predictable cure time. They are also odour-free. As a result, these adhesives usually are allowed on projects such as hospitals, medical facilities, and schools where strong odors cannot be tolerated.
  • Two-component insulation adhesives can be used on virtually every common roof deck (including steel, wood, concrete, gypsum, lightweight concrete, cementitious wood fiber, smooth- and granular-surfaced polymer-modified bitumen, and more). They are also compatible with various cover boards (e.g. polyisocyanurate, expanded polystyrene, high-density polyisocyanurate).
  • Unlike mechanical fasteners, two-part polyurethane insulation adhesives offer a non-penetrating application method and are not visible from inside the building.


Cons of Adhesives

  • Applying adhesives “may” be dependent on the installation temperature.
  • Humidity levels might impact the performance of adhesives.
  • Polymer-modified bitumen-based adhesives have long and unpredictable cure times, particularly when used in multilayer applications.
  • If excessive amounts of adhesive are used, roofing materials can slide out of place and take longer to cure. Additionally, trapped solvents may soften roofing materials and cause blisters. In contrast, using insufficient amounts of adhesive may result in an incomplete or weakened bond.
  • Insulation adhesives generally are more expensive than mechanical fasteners.


Adhesives vs. Mechanical Fasteners


Mechanical Fasteners

With mechanical fasteners, insulation layer(s) are fastened to the deck substrate using screws, plates, oversized washers, and/or special nails that are specially designed for the application. When fastening through the deck substrate, the correct type and length of mechanical fastener must be used. The fasteners should also be spaced out in the pattern required by the roof system manufacturer/warranty provider.


Pros of Fasteners

  • All manufacturers’ warranties allow for this method of securing insulation.
  • This is a faster installation method than working with adhesives 
  • A mechanically attached assembly is fastened directly to the structural decking. This means that, in order for the roof system to become detached, the fasteners need to back out of the structural decking. With adhesive assemblies, the insulation is only attached to the vapour retardant or top surface of the deck substrate, so if the insulation facer becomes delaminated, the membrane sheet is at risk of a blow off. With a ballasted roof system, If the stone shifts or gets blown off the roof, the roof’s attachment, including the insulation, becomes much weaker.
  • Materials are less costly compared to adhesives.


Cons of Fasteners

  • Using mechanical fasteners can detract from building aesthetics as insulation plates can sometimes telegraph through the roof membrane and also are visible on the underside of the deck substrate.
  • Mechanical fastening is not always the best option for all deck types, such as those made of concrete, gypsum, or cementitious wood fiber roof decks. Most concrete and gypsum decks must be pre-drilled to accept most mechanical fasteners. Pre-drilling is time-consuming and labour-intensive, which can drive up overall installation cost.
  • There is more energy loss due to thermal bridging.
  • Mechanical fastening is not allowed in the roofing of some industries and building types. Hospitals, medical facilities, freezer and cold storage buildings, food-processing plants, some types of school buildings, and buildings that contain potentially corrosive processes preclude the use of any mechanical fasteners that penetrate the roof deck. This is to avoid introducing contaminants into controlled environments and reduce the instance of damage in high-humidity or low temperature structures.
  • Facilities that have electrical and data conduits buried inside the deck substrate create a potential blind hazard that could be costly to repair if a fastener impacts live wire(s).
  • The process of installing mechanical fasteners is very noisy. Excessive noise is a large concern to educational, medical, health care, and hospital facilities. Building owners generally do not want students or patients to be disturbed by drilling or hammering when a roof system is being installed.


When it comes to roofing insulation, the best course of action is to work with your roofing professional to determine the specific needs of your structure and the right methods to achieve them. If you’re looking for more information, or have questions you’d like to ask a roofing professional, contact us here.  our team is here to help 24/7.