The Roof Deck – Preparation for Underlayment

The roof deck is the roofing material layer between the primary structural components (trusses & joists) and either insulated layers or weatherproofing layers in a typical roof system. Usually the roof deck acts as a unifying structural diaphragm by tying all the structural components together. Roof deck in residential application is most commonly plywood or OSB sheathing.

Before installing roofing underlayment the deck should always be clean, dry, and moisture free. Be sure to remove all protrusions from the deck area and ensure the deck has no voids, damaged or unsupported areas.

Debris Removal

Most debris can removed with the use of a broom, air hose or electric blower.  This is especially important in a re-roof project where much debris is generated from removing the previous roofing materials. In a new roof project, a raw roof deck or synthetic underlayment left exposed to the elements for a period of time can accumulate debris on the surface.

Examples of debris can be: road dust, pollenlawn mower discharge, leaves, branches, seeds, pine needles, sand, dirt, sea salt, etc.

Safety Precautions on a Roof Deck:

  • Good safety practices should be followed on steep slope roofs, such as use of tie-offs, toe boards, ladders and/or safety ropes and personal body harnesses.
  • If asphalt based shingles have been placed or stacked on the roof deck, you have an increased chance of loose granules on the roof deck. These granules can make the deck very slippery.
  • Respect and adhere to any cautionary statements printed on the product label, installation instructions and/or printed on the product.
  • If an air hose and pneumatic nailer is to be used make sure to wear safety goggles and a mouth & nose mask.
  • Slip resistance may vary with surface conditions from; debris that accumulates, weather, footwear and roof pitch.
  • Depending on roof pitch and surface conditions, blocking may be required to support materials on the roof and is good safety practice.
  • Remember to seal the fastener holes that secured the blocking after they have been removed.

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