In Part IV of this series, we discussed two vital steps in low-slope roofing system design – considering the building’s purpose when choosing the roofing system type and, in the case of an existing roof, completing a thorough assessment of that roof to understand its components and condition. Just as important, though, is how the system’s components are attached.
If the roof is to perform over the long haul and withstand abuse from wind, hail, extreme temperatures, building movement, foot traffic, rooftop equipment and more, the insulation and cover boards must be securely fastened and the roof covering properly attached. We’ll dig into that here as we wrap up this series.
Fastening Insulation and Cover Boards
When a fully adhered roof covering becomes detached, people instinctively blame the glue that was used to adhere the membrane. It may be, however, that the failure was caused by inadequate or improper attachment of the insulation or coverboard.
The connection between insulation/cover boards and roof deck provides the holding power for the entire roofing system. It is the most crucial factor in a roofing system’s performance. To illustrate, consider a roofing system’s ability to withstand high winds – a force surpassed only by water in its power to damage a roof. If the insulation and/or cover boards are attached inadequately or improperly, uplift pressures created by high wind can exert the same types of forces that allow airplanes to fly, causing significant damage or loss.
Manufacturers, therefore, have detailed guidelines for attaching insulation and cover boards based on the roofing system type and roof deck type. They include the number and types of screws or plates to be used, along with their spacing and placement, or the types of adhesives that may be used and the pattern in which the adhesive must be applied. These specifications must be followed. Failure to do so will result in a failed warranty inspection and potentially the nightmare of a failed roofing system.
Attaching the Single-Ply Membrane
In single-ply systems, the membrane must also, of course, be attached. There are three ways of doing so – mechanical attachment, full adhesion and using ballast.
In a mechanically attached membrane system, fasteners and plates are installed at the seams. Insulation and cover boards are mechanically attached to the roof deck, too, but only at a rate needed to hold them in place. Mechanical attachment is generally the fastest and most economical option, particularly on roof decks that are easier to work on, such as steel and wood.
In a fully adhered membrane system, adhesive bonds the membrane to the insulation, cover board or roof deck. Insulation and cover boards are attached using mechanical fasteners or a low-rise foam adhesive. Adhesives are cold-weather sensitive, which limits their use in much of the country during cold seasons; contractors must carefully follow the manufacturer’s instructions. Full adhesion can be the easiest and most economical option when working with certain roof decks, such as concrete and gypsum; mechanically attaching membranes to these roof decks is more labor-intensive and requires special fasteners.
In a ballasted system, all components are loosely laid in place and then weighed down with a layer of ballast, either concrete pavers or 1.5-inch nominal size, rounded, worn river gravel. Manufacturers’ specifications indicate the amount of ballast to be installed in the roof field, along the perimeter and at the corners.
We hope that this blog series has helped demystify the world of low-slope roofing. To learn more, check out the wealth of material available on this website. And, of course, MuleHide’s territory managers and technical services team are only a phone call or email away and always ready to help.
By Rob Keating, Regional Director – Northeast