A Few Good Pointers for Installing Self-Adhering Roofing Underlayments

This content is made possible by our sponsors. Click here to add your content.

Properly flash all roof penetrations to create a watertight barrier against the elements at these critical leaks.

For more than 30 years there have been self-adhesive or “self-adhesive” roofing underlays that protect building structures from moisture damage caused by wind-driven rain, ice dams or the failure of the finished roof surface.

A number of insurance companies and code bodies have begun requiring contractors to cover the entire roof with a self-adhesive pad to protect the interior of the home from unnecessary water damage. One reason for the change was that mechanically attached roofing felts and newer synthetic underlays cannot offer the same protection if water or moisture penetrates the roofing system. Another reason is that self-adhesive underlays protect the structure before, during and after the installation of the roof system.

MFM roofing tapeSealing the plywood and OSB roof decks is a great way to provide your customers with additional waterproofing protection before, during and after the underlay is installed.

Blown shingles, ice dams or seam leaks on metal roof systems allow water to get under the finished roof system. Self-adhesive underlays provide secondary water protection for the entire roof in the event of a roof break. Most of these self-adhesive pads are also self-sealing around roof attachments to maintain a waterproof barrier. No wonder that there are more self-adhesive products today than single-layer and built-up membranes combined.

While self-adhesive pads are easy to install, there are several installation keys that should be followed carefully for maximum performance after the product is installed:

  • Building regulations – Before installing a roof underlay, be familiar with all applicable building regulations and the installation instructions recommended by the manufacturer. Self-adhesive substrates often have minimum installation temperatures, roof pitch restrictions and exposure levels to ensure that the product is installed as intended.
  • Product approvals – Self-adhesive backing can be certified or meet industry standards to ensure their performance on the job site. Issuing bodies such as the International Code Council (ICC), Miami-Dade County, and Florida Building Code document the intended use and limitations of a product. Always check to see if your rooftop project requires a Code Approved Document.
  • ventilation – Self-adhesive underlays are typically vapor barriers that require proper ventilation of the roof system. Without adequate ventilation, condensation can form and damage the internal structure. Elements such as roof or soffit vents must be installed to ensure airflow and properly vent the roof.
  • Adhesion is the key – Make sure that the roof substrate is clean, dry and free of wax, dirt or debris. Dust and dirt impair the adhesive properties of the self-adhesive membrane. Weathered surfaces require the use of a primer prior to installation to keep the surface clean and smooth. Contact the underlay manufacturer for a list of approved primers.
  • Flash penetrations – Always flash around roof penetrations such as ventilation slots, chimneys and other protrusions. Often times, when a roof is leaking, it is around these penetrations because they were not properly flashed. You can often use the mat yourself as a flashing material or buy special roof flashing tapes.
  • Eliminate gaps – Do not use the underlay to bridge gaps in the roof substrate. Always use a flashing membrane or roofing tape to seal the gap, then attach the underlay.
  • Seals and seals – Sealing compounds that contain plasticizers can react disadvantageously to the adhesive system of the underlay, which can cause the mastic to liquefy. It is the installer’s responsibility to ensure that the pad is compatible with any product that he comes into contact with.
  • Overlaps – Always start at the eaves and work your way towards the ridge to make sure the water flows over all the rounds of the sides, which are typically 3 inches on most self-adhesive products. Finals are usually recommended with a 6-inch overlap.
  • exert pressure – Applying sufficient pressure with a large pressure of 80 pounds or a hand roller over the entire surface with special attention to areas of overlap is crucial in establishing a firm bond with the roofing sub-floor.
  • Foot traction – Most underlays have some sort of traction surface, be it granules, embossed pattern or chemically treated traction enhancement. Make sure the membrane you are using provides excellent foot traction even in humid environments to ensure safety.
  • Waterproofing roof terraces – A growing trend in building codes and with some contractors is to seal the plywood and OSB roofing panels with a 40 mil 4 inch flashing membrane. Follow the manufacturer’s installation instructions carefully to ensure water flows over the laps to prevent water from entering.
  • Split release liner – Self-adhesive pads that come with a split-release liner make installation easier. Most underlays are at least 36 inches wide and the split sharing makes the product easier to handle and is especially beneficial when flashing roof valleys.

MFM branded contentMake sure that the self-adhesive roofing underlay around the usual roof fixings is self-sealing to prevent future leaks.

Peace of mind

The most important aspect of self-adhesive substrates is that, when installed correctly, they can give the roofer a feel and significantly reduce the number of recalls to repair a leaky roof. Information is available from the manufacturer in the form of technical data sheets, installation instructions, installation videos, and other sources such as social media and YouTube.

If you do your research before the job, you have a much better chance of future referrals from satisfied customers.

Comments are closed.