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 a 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.