When installing wood flooring in an area prone to gathering moisture, such as a basement or bathroom, it is important to place a moisture barrier down first. The barrier will protect the porous flooring from damage due to moisture absorption. While there are several products designed specifically for this use, some installers choose roofing felt as their barrier.
Also known as tarpaper, roofing felt is a protective barrier most often used between the wooden roof of a home and the shingles or other roofing material. Weatherproof tarpaper adds extra protection in the event shingles are blown off in a storm. Most often it's made of fiberglass fleece soaked in bitumen, which gives the material its waterproof qualities. In addition to fiberglass, two other variations are made from polyester and recycled rags. In all cases, a waterproofing agent is added to make the material moisture proof.
Flooring Moisture Barrier
Most flooring manufacturers recommend a moisture barrier laid for flooring being installed on the ground (slab) floor or a finished basement. While there are several products manufactured specifically for this purpose, some installers choose to use roofing felt when installing wood floors due to its lesser cost and excellent moisture protection. An added benefit when laying wood floors over plywood is the absorption of vibration by the felt, which results in a reduction of noise.
Concerns about roofing felt stem from the bituminous impregnating agents (tar and asphaltic bitumen) and whether fumes from the felt may rise into rooms. A vapor barrier such as kraft paper will trap any such fumes, but may not be necessary depending on the flooring material. Wooden floors will act as a vapor barrier and are often laid directly on top of the felt. Roofing felt is not considered toxic and is not listed as a carcinogen. Under normal use, the product is considered stable and nonreactive.
No longer used in the manufacture of roofing felt, asbestos can still be found in old (pre-1990) rolls of the material. Originally used for its fire-resistance and ability to strengthen the cloth, asbestos once made up 15 percent of the material. Asbestos was phased out of production in the 1980s. If you plan to use roofing felt, be sure to buy new material from a reputable source such as a home building center. Never reuse old felt.
Due to its manufacture with petroleum products, roofing felt is flammable. No open flames or smoking should be near the product during installation. Once secured between the sub-floor and the newly laid floor, the material will be secure from open flames and will be no more of a fire threat than when used on the roof of a building.