Tar paper for my roof. Do I need it or is it a waste of money?
Yes, it should be installed as part of a new roofing system. Not doing so is risky and the benefits of installing this inexpensive roof component easily out weigh any cost savings if omitted.
Tar paper, sometimes referred to as roofing felt or underlayment, is a heavy duty paper or fiberglass mat impregnated with tar or asphalt. For residential roofing, tar paper comes in a few different classifications, previously classified by weight and sold in rolls by length or area covered. Common residential tar paper is sold as #15 or #30. A roll of #15 tar paper covers approximately 400 square feet of roof area and #30 will cove about half or 200 square feet of roof area.
In years past, tar paper was classified by weight. 15# (lb) and 30# (lb) rolls were considerably thicker and heavier than the currently available product. The standard #15 tar paper is quite thin and should only be used as a temporary covering and usually only under inexpensive 3 tab shingles. #30 felt should be used for heavier dimensional shingles, wood shingles and shakes, and sometimes under slate and tile roofing.
Reasons for installing tar paper as part of a new roof
Temporary protection from sudden rain storms.
- During roof installation, tar paper is quickly installed and is temporary protection is the roofers are not able to completely cover a roof before the end of the day, or before a sudden rain storm. If shingles are blown off or damaged during a storm, a layer of tar paper will temporarily keep much of the rain out of your house until repairs can be made.
Ease of old shingle removal.
- A layer of tar paper will prevent the asphalt shingles from sticking to the roof sheathing. Particularly useful to the next home owner who is removing the original and installing a new roof. Removing shingles stuck to the roof deck is time consuming and costly.
Added protection from wind blown rain.
- In high wind areas it is often possible for water to be forced under shingles and into the roof deck and attic.
Shingle installation guide
- Tar paper and most underlayments come with guide lines marked horizontally on the rolls. These guide lines are helpful as quick reference marks to keep the shingles running straight across the roof.
The only reason not to install tar paper is to save money. But the small extra expense is easily offset by the benefits.
- Tar paper, and most other underlayments, should be installed over the ice and water shield and the eave drip edge. On the rake or edges of the roof, the paper should be installed under the edge drip edge. This allows water that is blown under the rake shingles to run onto the felt paper, under the shingles, and eventually out and over the eave drip edge.
- If the tar paper gets wet and buckles before the shingles are installed, allow the paper to dry and flatten before proceeding with the roofing. A little bit of light rain or drizzle while the shingles are being installed is usually not a problem. The tar paper will dry shortly as the water evaporates through the shingles.
- Thin #15 underlayment should not be expected to keep a roof dry for any length of time. #30 is a bit heavier and will last, if properly nailed with roofing nails, cap nails or “tin tags”, for a few weeks depending on the weather. Some synthetic underlayments are estimated to last six months with proper nailing.