What failing roof decking looks like from inside and out
From the yard, bad decking shows up as a wavy or sagging slope, often in a regular pattern between rafters. In the attic, look for dark stains, white fuzzy growth on the underside of the sheets, or nail tips rusted orange. OSB that's been wet for a long time swells at the edges and flakes apart in layers. Plywood tends to delaminate, with the plies separating like a peeling book cover.
Walking the roof tells us more. A soft spot gives underfoot like a trampoline, and that's usually a sheet that lost its strength to a slow leak at a pipe boot, a valley or an old skylight. When a stain is still spreading, tracking down the active leak comes first. We mark suspect sheets with paint during the inspection so you see the likely count before tear-off.
Why many older San Antonio homes have plank decking
Homes built before plywood became common, including many in neighborhoods like Monte Vista and Alamo Heights, often have 1x6 or 1x8 board decking. Those boards are usually dense old lumber and can still be in decent shape after decades. The issue is the gaps between them, which can be wide enough that roofing nails miss wood and shingles sag along the joints over time.
When plank decking is sound but gappy, shingle makers commonly call for an overlay of 7/16 or 1/2 inch sheathing across the roof before shingles go on. When individual boards are rotted or split, we cut them out and replace them with matching lumber or plywood shimmed to the same height. We'll show you which approach your roof needs and why, with photos of the boards themselves.
Do you have to replace all the decking during a reroof?
Usually not. Most tear-offs reveal a handful of bad sheets, typically around penetrations, valleys and the lower edge where water backs up from clogged gutters. Replacing the whole deck makes sense only when damage is widespread, when the existing sheathing is too thin to hold fasteners, or when plank gaps call for an overlay. Paying for a full deck you don't need is money better spent on ventilation.
Ask any roofer how decking will be priced before you sign. A per-sheet price written into a full roof replacement agreement protects you from a vague change order once the old roof is off. We photograph every sheet we replace, before and after, and the count on your invoice matches the photos you receive.
How attic heat and moisture wear out sheathing
Summer attic temperatures in San Antonio commonly pass 140 to 150 degrees, and the decking sits at the hottest point of that space. Heat alone doesn't rot wood, but it dries and shrinks sheathing so nails loosen over the years. The real damage comes when warm, humid air gets trapped and condenses on the underside of the deck during cool nights in winter and early spring.
Poorly balanced intake and exhaust vents are a common cause. If we see mildew across a whole slope rather than at one leak point, we look at the soffits and ridge before laying new sheets. Fixing the balance between soffit and ridge vents keeps new decking from failing the same way. Bathroom fans that dump straight into the attic are another culprit we check.
Plywood or OSB: which panel we install and why
Both are accepted roof sheathing, and both last when they're kept dry and fastened correctly. Plywood shrugs off brief wetting a little better and holds nails well near its edges. OSB is very consistent in thickness, and it's what you'll find on most newer tract homes around the city. We generally match what's already on your roof so new sheets sit flush with the old ones.
Whatever the panel, the details matter more than the brand. Sheets should break over rafters, keep a small expansion gap at the edges, and be nailed on the schedule the code and the roofing maker call for. Clips between rafters help on wider spacing. If you're adding a radiant barrier during the reroof, foil-faced radiant barrier sheathing can go in wherever we replace sheets.
