Roof underlayment, also called a roof vapor barrier is the layer immediately underneath the topmost roof covering material and on top of the roof deck to add extra weather protection to the roof – here is why this intermediary layer is so important for the integrity and the durability of the roof:

– Most roof types consist of individual components fastened together tightly, but even so, moisture can accumulate underneath, causing serious damage to the deeper structures, including the wood components that hold up the roof – the underlayment prevents such damage by repelling the droplets of water that form when moisture accumulates.

– Added water-resistance – the underlayment enhances the protection offered by the roof cover not only against the moisture normally present in the air, but also against larger quantities of water, such as heavy rains or snow. Roofing underlayment is made from asphalt-saturated felt, rubberized asphalt or synthetic material that does not absorb liquids, thus preventing water damage.

– Protection during roof repairs – whenever a roof is repaired, parts of it are left exposed as the repair work is progressing. If it starts raining while the topmost roof cover is being replaced, the rainwater can penetrate quickly into the attic space, causing serious water damage in just a few minutes. Roofing underlayment usually consists of large sheets that are kept in place during the replacement of shingles or tiles, protecting the attic and the roof structure until the repairs are finished. Quality roofing companies San Antonio area use underlayment in their roofing jobs.

Source: Live Site