There are three basic types of underlayment used beneath roofing materials: asphalt-saturated felt; rubberized asphalt; and. non-bitumen synthetic.
Roofing underlayment is what lies between the shingles and the roof sheathing, or roof deck, which is typically either plywood or OSB. It's installed directly on the roof deck and provides a secondary layer of protection from the elements, including rain, snow, and wind.
You have the top layer that is your floor covering (Hardwood, Laminate, Vinyl, Carpet, etc.), next you have the underlayment (usually a thin layer of fiber, foam, rubber), below that you have your subfloor (plywood, OSB, concrete), and lastly you have the joists which are the foundation to your floors.
Fasteners. If the roof will not be covered with approved roof covering on the same day, ProArmor® Underlayment must be attached to the roof deck using plastic or steel cap fasteners having a minimum 1 inch diameter cap.
There are various types of roofing underlayment or underlayment materials. In the past, tar-paper was the standard, and I still occasionally come across old roofs that have it. However, today, fiberglass felt (sometimes called felt paper) and polypropylene/polyethylene are the industry standard.
#1 Synthetic Underlayment
Synthetic underlayment is made of tough materials that effectively resist water and UV rays. Its textured surface provides improved traction for roofers, making it safer to work on sloped roofs, especially in wet or icy conditions. Estimated lifespan: 20 to 35 years.
Also known as tar paper or a felt underlayment, this material offers some benefits for roof protection. But once the roof is complete, felt fails to make your home more waterproof. This is especially important for those of us living in rainy climates, such as Portland, OR, and the greater Pacific Northwest.
One of the most common types of underlayment used in residential, steep-slope applications is black, ashphalt-saturated felt paper. Felt underlayment may be made from either organic or fiberglass substrate, although the organic is much more common.
You can fasten your plywood underlayment using one of the following: galvanized, coated chisel-point staples with a 1/4" maximum crown; galvanized, coated ring shank underlayment nails with a 3/16" diameter head; or flathead wood screws treated with a moisture-resistant coating (such as galvanized or zinc).
Many roofers will tell you that staples are fine for installing the synthetic underlayment. Others will tell you that cap nails are more effective. Both options often depend on the slope of the roof itself. Cap nails are typically made of steel and feature a plastic cap to prevent roof leaks, hence their name.
That vapor barrier would go between the subfloor and the underlayment. “Combination underlayments,” as described on learn.builddirect.com, include an attached vapor barrier.
Remember, roof underlayment protects your decking if water ever gets underneath your roofing material. Without underlayment, this water eventually rots your roof decking leading to leaks, mold/mildew forming, and even structural damage.
Two layers of underlayment are required for low-slope roofs. The first course is doubled.
The most recently developed type of roof underlayment, synthetics, are made commonly from woven or spun polyethylene or polypropylene to increase durability and tear-resistance significantly compared to saturated-asphalt underlayment. This type of roof underlayment installation costs more than asphalt-saturated felt.
If your choose this route, staples are a good choice to fasten the underlayment. Staples usually have a coating which help increase the holding power.
To start laying the underlayment, position yourself at the bottom edge of the roof. Carefully lay the first strip horizontally across the roof, ensuring that it is straight and even. Allow the underlayment to overhang the eaves by about an inch; this will help direct water away from the roof and into the gutters.
Secure rows by taping them together, this will keep your underlayment in place.
Asphalt felt is the oldest and most common type of underlayment, and it typically lasts anywhere from 20 to 30 years, but in some cases it can last as little as eight. Newer synthetic or rubberized asphalt underlayments are much more durable than asphalt felt and offer better protection against water.
On new roofs, we recommend purchasing exterior grade plywood or waterproof chipboard as a suitable surface to rest on your treated timber joints. Any mortar removal or more detailed preparation should be done in advance of your felt roof project.
Homeowners looking to cut some costs question if breathable underlayment is necessary. While it's not necessary on all roofs such as high-pitched roofs, it should always be applied to the roof deck on roofs with low-slopes.
Synthetic underlayments are an excellent choice for metal roofing installations. If installed according to manufacturer recommendations, they're more durable than felt products and simpler to install. Owens Corning offers homeowners a choice of synthetic underlayments for their metal roofing system.
After all, the smallest mistake can cause the biggest mishaps for your roofing system and yourself as the homeowner. With that in mind, when replacing your roof, one of the things that you should make sure will be done is to completely remove and replace the old underlayment.
It comes in two different weights: 15- and 30-pound, with 30-pound being the more durable, heavy option. Synthetic roofing underlayment is typically made from durable polymers that are created to be water-resistant and easy to work with. Many roofing contractors prefer to use synthetic roofing underlayment over felt.