Roofing felt is a layer of tar paper installed beneath the shingles to provide a backup waterproof membrane in case of leakage. Felt, otherwise known as underpayment, is required when asphalt shingles are installed as a first layer of roofing or when they are applied over wood shingles or a built-up roof.
Roofing felt (similar to tar paper) is the base material used to make roof shingles and roll roofing. Typical uses of felt paper are as an underlay(ment) (sarking) beneath other building materials, particularly roofing and siding materials, and is one type of membrane used in asphalt built up roofing (BUR) systems.
Sizes & Roof Felt Types
There are two different types of roofing felt, #15 and #30. The only difference between the two are the strength. #30 is stronger, meaning that throughout the roof building process, the material is less likely to tear and also creates a much safer working environment for the builders unlike #15. The way to decide which one to buy is mainly dependent on how long you reckon the job will take. If you are planning for the roof to take around three weeks to complete, then you are better off buying #30 as it will be stronger to survive through the weather. However, if you are not planning for the job to take as long then #15 will be best since it won’t be open to the weather as long, plus any moisture in the house once the roof is complete, will be able to pass through the roofing felt better which is what we want so that the house can get a better air circulation.
Roofing felt is a type of insulation that is used to prevent the entry of moisture. A heavy downpour or storms can destroy tiles. Many times, repairs do not take place for several weeks. During this period, roofing felt acts as a barrier and keeps the place from filling with water.
Fire Protection – Systems are available that satisfy even the most stringent fire regulations. Class A protection can be achieved (in accordance to BS 476) with relative ease.
Elastomeric – Most modern felts are designed to be elastomeric, meaning they can move with your building. Settlement cracks will be comfortably bridged without compromising the waterproofing.
Insulant Compatible – Built up felt systems are compatible with all the modern insulants including EPS, XPS, Phenolic, Foamglass and even the ecologically friendly wool and straw based systems.
Design Compatible – The lightweight and resilient properties of built-up felt systems means that they can be adopted in almost any flat roof design – Submerged, Green, inverted and warm roofs are all possible.