What does a roof deck look like?
Short answer. A roof deck is the flat wooden layer nailed to the rafters or trusses that the underlayment and shingles sit on. In most Georgia homes it is 4 by 8 foot sheets of OSB, which looks like pressed wood chips, or plywood, which shows layered wood veneers; older homes may have rows of solid wood planks instead.
From the attic
Look up between the rafters and you are seeing the underside of the deck. You will notice:
- OSB: large sheets made of wood strands pressed together in a random pattern, often stamped with grade marks. Some OSB has a shiny foil face, which is a radiant barrier meant to cut attic heat.
- Plywood: sheets with a smoother wood grain face. At the edges you can see the thin layers glued together.
- Plank decking: boards about 6 or 8 inches wide running across the rafters, common in homes built before plywood took over. Some older roofs have gaps between boards, called skip sheathing, from the days of wood shakes.
- Small metal clips: H shaped clips between sheets, midway between rafters, that support panel edges.
During a tear-off
Once the old shingles and underlayment are stripped, the deck is exposed from above. Healthy decking is firm, flat and dry. Problem spots look dark, stained or delaminated, feel soft underfoot, or show nail holes that will not hold. Crews cut those sections out and replace them before new underlayment goes down.
What a problem deck looks like from inside
- Dark water stains around nails or along panel seams.
- Black or white fuzzy growth, a sign of poor ventilation.
- Sheets that bow down between rafters.
- Daylight showing where there should be none.
Read OSB vs plywood roof decking and roof anatomy explained for how the deck fits into the whole roof.