An asphalt roofing felt made of a specially formulated organic sheet which has been fully saturated with waterproofing asphalt. This product is strong, flexible and impervious to water penetration, but will allow water vapor to pass through the restricted rate. Preconditioned to help it lay flat and remain stable after installation on a roof deck. Guidelines are provided every 2? across the sheet to aid the roofer in keeping asphalt shingles aligned.