The panel under your shingles is the part of the roof most homeowners never ask about, and it is the part that decides whether the nails hold. On a tear-off, the crew sees the sheathing for the first time, and whatever the spec said about it either gets followed or gets argued about on a ladder. Before you sign, the roof spec should name the panel type, its thickness, its span rating, and how it is fastened.
Material and spec
Two panel types show up on St. Louis roofs most often: oriented strand board, usually called OSB, and plywood. Both can carry asphalt shingles when they are the right thickness and span rating for the rafter spacing underneath. OSB is the common choice for a reroof on a house built in the last few decades. Plywood is common on older work and on jobs where the crew or the homeowner prefers it. Neither is wrong by itself. The spec has to say which one goes on, because a quote that says only "new decking as needed" leaves the choice to whoever is holding the saw that day.
Thickness and span rating are the two numbers to read. Panel stamps show a span rating such as 24/16, which describes the rafter spacing the panel is rated to cover. Rafters at 24 inches on center are the common case in older St. Louis County houses, and a panel rated for that spacing should be named on the spec. Thickness usually runs from 7/16 inch to 5/8 inch for residential roofs, and a thicker panel gives the nail more to hold. Ask for the thickness in the spec, not just the material name.
Edge support matters on the same sheets. Where two panels meet between rafters, the edges need support, either from blocking or from metal edge clips. Without support, the panel edges can move, and the shingles over the joint can show ripples. The spec should say whether clips are included, and whether they are part of the decking line or a separate item.
Fasteners are the next line. The roofing nail that holds shingles also runs through the sheathing, so the nail length has to clear the panel and reach solid wood. Nail type and spacing follow the shingle maker's instructions and the code the permit desk enforces. Ask the roofer to write the nail spacing into the scope. The point is that the spacing belongs in writing, the same as the shingle line. Keys installs Atlas and Malarkey shingles, and each maker publishes its own nailing instructions, so the spec should refer to them by name.
Old decking has its own check. Water that has leaked for years softens the edge of a panel, swells it, and sometimes leaves a dark stain that marks where the panel has been wet and dried more than once. A sound panel can be left in place, but a swollen or delaminated panel should be replaced. The spec should say how damaged sheets are identified, who marks them, and whether the homeowner approves each replacement before it happens.
What it costs
Decking is usually priced in one of two ways. Some quotes carry a sheet count inside the base roof price, with a unit rate for each extra sheet that the crew finds rotted once the old shingles are off. Other quotes leave the decking out entirely and bill it by the sheet on the day. Neither approach is unusual, but the difference matters. A homeowner who sees the base price and does not see the unit rate can end up paying a number nobody discussed.
Ask for the replacement rate in writing per sheet, with the panel type and thickness stated. A line that says "replacement at cost" is not a rate. If the spec calls for OSB and the crew installs plywood, the rate may be different, and the homeowner should know which panel the rate covers. Ask whether the rate includes the blocking or edge clips. Those can add labor and material that the sheet price alone does not show.
The sheet count is also an estimate. A roofer can count the sheets that look soft from the attic before the tear-off, but the real count often comes after the shingles are off. The spec should say who counts the sheets once the deck is exposed, and whether the crew photographs each damaged sheet before replacing it. Photos give the homeowner a record of what was replaced and why.
Do not let the decking conversation slide into the shingle line. Panel cost and shingle cost are separate. A quote can look close on shingles and still differ by several sheets of decking that one bid counted and the other did not.
What to ask
Put these questions to every roofer before you pick a date.
- Which panel type goes on, OSB or plywood, and what is its span rating?
- What is the panel thickness in inches, and does it match the rafter spacing in my attic?
- Are edge clips or blocking included in the roof price?
- What nail type and spacing will the crew use, and where is it written?
- What is the price per replacement sheet, in writing, with the panel type stated?
- Who counts the damaged sheets once the shingles are off, and will the crew photograph each one?
- Will you ask me to approve each extra sheet before it goes on, or will the crew replace it as part of the job?
Ask the roofer to show you the decking they plan to use. A sample from a supplier is enough, and the stamp on the panel will show the span rating and thickness. If the roofer cannot tell you the panel type, that answer is part of the bid.
A roofer who answers these questions in writing gives you a spec you can compare to another bid. A roofer who does not answer them has left the decking to the day of the work, and that is the point where the price can change. You can call the Keys office at (314) 220-2333 and ask these same questions before you schedule anything.