A Few Good Pointers for Installing Self-Adhering Roofing Underlayments

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

MFM Peel & Seal - Roof Vent Flashing
Properly flash all roof penetrations to create a waterproof barrier against the elements at these critical leak points.

Self-adhering or “self-stick” roofing underlayments have been around for more than 30 years protecting building structures from moisture damage caused by wind-driven rain, ice dams or failure of the finished roofing surface.

A number of insurance companies and code bodies have begun requiring contractors to cover the entire roof with a self-adhering underlayment to protect the home’s interior from any unnecessary water damage. One reason for the change has been that mechanically attached roofing felts and newer synthetic underlayments cannot provide the same level of protection should water or moisture penetrate the roofing system. Another reason is that self-adhered underlayments protect the structure before, during and after the installation of the roofing system.

- Sponsor -
MFM Roof Deck Tape
Sealing the plywood and OSB roof deck panels is an excellent way to provide your customer with additional waterproofing protection before, during and after the underlayment is installed.

Blown off shingles, ice dams or seam leaks on metal roofing systems allow water to get beneath the finished roof system. Self-adhered underlayments offer secondary water protection for the entire roof in the event of a roofing breach. Most of these self-adhered underlayments are also self-sealing around roofing fasteners to maintain a waterproof barrier. It’s no wonder that today, there are more self-adhered products available than single-ply and built-up membranes combined.

Although self-adhered underlayments are easy to install, there are several Installation keys that should be followed closely to provide maximum performance once the product is installed:

  • Building Codes – know all applicable building codes, as well as the manufacturer’s recommended installation instructions, prior to the installation of any roofing underlayment. There are often minimum installation temperatures, roof pitch restrictions and exposure ratings on self-adhered underlayments to ensure that the product is installed as intended.
  • Product Approvals – self-adhered underlayments can be certified or comply with industry standards to ensure their performance on the jobsite. Issuing bodies such as the International Code Council (ICC), Miami-Dade County, and Florida Building Code and provide documentation of a product’s intended use and limitations. Always check to see if your roofing project requires a code-approved underlayment.
  • Ventilation – self-adhered underlayment are typically vapor barriers requiring proper ventilation of the roof system. Without proper ventilation, condensation can form causing damage to the interior structure. Items such as roof or soffit vents will need to be installed ensuring the flow of air to properly vent the roof.
  • Adhesion is the Key – ensure that the roofing substrate is clean, dry, and free of waxes, dirt or debris. Dust and dirt will impair the adhesive properties of the self-adhered membrane. Weathered surfaces require the use of a primer prior to installation to provide a clean and smooth surface. Contact the underlayment manufacturer for their list of approved primers.
  • Flash Penetrations – always flash around roof penetrations such as vents, chimneys and other protrusions. Many times when a roof leaks, it is around these penetrations because they were not properly flashed. You can often use the underlayment itself as a flashing material or purchase specialized roof flashing tapes.
  • Eliminate Gaps – do not use the underlayment to bridge gaps in the roofing substrate. Always use a flashing membrane or roofing tape to seal the gap, then install the underlayment.
  • Caulks and Sealants – caulks and sealants that contain plasticizers may react adversely to the adhesive system of the underlayment, which may cause the mastic to liquefy. It is the responsibility of the installer to ensure that the underlayment is compatible with any product it will come in contact with.
  • Overlaps – always start at the eave and work up towards the ridge to ensure that water will flow over all side laps, which are normally 3″ on most self-adhered products. End laps are typically recommended to have an overlap of 6”.
  • Apply Pressure – applying sufficient pressure with a large 80 lb. push or hand roller over the entire surface, paying special attention to any overlap areas, is critical in establishing solid adherence to the roofing substrate.
  • Foot Traction – most underlayments have some type of traction top surface whether it be granules, embossed pattern or chemically-treated traction enhancement. Make sure that the membrane you are using provides excellent foot traction, even in wet environments, to ensure safety.
  • Sealing Roof Deck Panels – a growing trend in building codes and amongst some contractors, is to seal the plywood and OSB roof deck panels with a 40-mil, 4” wide flashing membrane. Follow the manufacturer’s installation instructions closely to ensure that water flows over the laps to prevent water penetration.
  • Split Release Liner – self-adhered underlayments that come with a split release liner offer easier installation. Most underlayments are at least 36” wide and the split release allows for easier handling of the product and is especially beneficial when flashing roof valleys.
MFM branded content
Make sure that the self-adhered roofing underlayment is self-sealing around common roofing fasteners to avoid future leaks.

Peace of Mind

The most important aspect of self-adhering underlayments is that when installed correctly, they can provide the roofing contractor with piece-of-mind and greatly reduce the number of call-backs to fix a leaking roof. Information is readily available from the manufacture in the form of technical data sheets, installation instructions, installation videos and other sources such as social media and YouTube.

By properly informing yourself prior to the job, you stand a much greater chance of future referrals from pleased customers.

Stay Updated

Get our email newsletter with LBM industry trends, data, new products, and best practices.