With all this rain in January homeowners are calling us saying “I wish I had a rain coat for my roof” On some of the roof repair service calls we are going out on, the repair specialists are finding that the roof has no underlayment of any kind. In the photo the moisture has turned to frost in this homeowners attic.

Roofing underlayment also know as a vapour barrier provides a vital second layer of protection on top of the roof deck or sheathing to help keep moisture out. It is also a necessary condition for roofing manufacturers’ warranties.

Underlayments fall under three basic categories: felts, synthetics, and self-adhering ice-and-water barriers.

Asphalt-Saturated Felt- is know as builder’s felt or felt paper, and has been covering roofs for 50 plus years. Although inexpensive and fairly easy to install, felt paper can be susceptible to tearing, especially in hot temperatures, and makes for a slippery surface to walk on while installing the roof covering. Asphalt felt also tends to trap moisture within the roofing system since it does not breathe well.

Synthetic Underlayment-are marketed as wrinkle-free, tear resistant, and safer for workers to walk on during installation.
They are waterproof, but they also allow moisture to pass out of the system. As a result, synthetic underlayments are mold resistant. They are lighter weight than felt papers, are lighter in color for a cooler roof, and are typically sold in greater widths and lengths. This translates into labor and time savings for roofing contractors.

Self-Adhering Underlayments were initially used primarily in geographical areas where the temperature is below 0 for 30 days or greater where ice damming threatens roof integrity. These self-adhering ice-and-water barriers were installed mainly in the valleys and low slope areas of roofs where ice damming tends to occur. An ice-and-water barrier is significantly thicker than felt or synthetic underlayments, is seamless, provides top-rate water protection, and requires no fasteners for installation. When an ice-and-water barrier is used in a roofing system, it is applied as a first layer, with the felt paper or synthetic underlayment applied on top, across the entire roof deck. These self-adhering underlayments are designed to seal up around any nails or staples used to install the felt paper, synthetic underlayment, or roof shingles.

If your roof does not have underlayment of any kind your roof will do several things.
• Water can leak into any unsealed flashing, underneath unsealed fasteners, or underneath loose shingles and will travel until it finds seams in your roof deck.
• The water will then travel directly into your attic, into your insulation and then eventually into your ceiling and walls.
• The roof sheathing can become moist which eventually causes mould and wood rot.
The choice of roofing underlayments depends on several factors. Manufacturers’ specifications, local building codes, the slope of the roof and the environment in which your home is found are determinants for choosing the correct materials.