How thick should roof felt be?

To understand why synthetic subflooring could replace roofing felt, you need to know what roofing felt is. Roofing felt is essentially a polyester or fiberglass fleece soaked in some waterproofing agent. It is available in two thicknesses, 15 pounds and 30 pounds. Those numbers are a reference to the amount of 100 square feet of paper it weighed in the early days of use.

The actual weight per square foot these days is actually less than what the label says, but 15 pounds. Roofing felt usually comes in 36-inch wide rolls. Organic felt is an underlayment and moisture barrier between the main roof (e.g. asphalt shingles) and the roof covering.

Continue reading in ROOFING BEST PRACTICES or select a topic from the closely related articles below, or view the full ARTICLE INDEX. The valleys should be lined with a full width of roofing felt (or bituminous membrane) tight inside the valley so that there is no slack. The conclusion of the BSC report is an argument in favor of installing a waterproof moisture barrier under roof shingles, perhaps instead of traditional, permeable roofing felt. In cold or temperate climates, this does not present a problem because the combination of intense wetting due to rain or rain is combined with solar heating at high outdoor temperatures, say the authors, who continue to argue that the bent roof shingles observed in the morning (caused by moisture that migrates back into upstairs).

from the roof terrace) relax during the day. When applying roofing felt, pay special attention to areas that receive the most water, including roof hips, ridges and areas around adjacent walls. If you were to ask a room full of roofing contractors to tell you what the best roofing felt is, each contractor would respond by giving you the weight of the felt rather than the brand, since weight matters more than the brand. The best weight for roofing felt is the 30-pound product, as it provides a thicker, stronger base for roofers that won't break, especially on steep roofs where footfall is critical.

In other words, in just over a decade, the subfloor under the roof surface may begin to deteriorate. Air flow resistance reduces the penetration of windblown water from the outside and the penetration of moist air from inside a roof. So what is this synthetic base, how is it different from roofing felt and why are builders making the switch?.

Kenneth Sowden
Kenneth Sowden

Professional Handyman turned Roofer. Avid internet practitioner. I have gelled my love for roofing and the internet and started this blog to help other around the world.

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