Recent project · Maryland · RooferMD, the roofing division of Mid-Atlantic Remodeling Co.
Re-decking and synthetic underlayment
Rotted and delaminated decking replaced across an entire roof before the new shingles went on. Most roofers nail over it. We don’t.
Project at a glance
| Location | Howard County, Maryland |
|---|---|
| Scope | Full tear-off, complete re-deck with new plywood, synthetic underlayment, ice-and-water shield, architectural shingles |
| Decking | 1/2-inch CDX plywood, 42 sheets |
| Roof | Architectural fiberglass shingles, Weathered Wood |
| Crew time | Three days |
| Warranty | 50-year transferable limited warranty |
Services on this job: Roof re-decking · Storm restoration · 50-year warranty
The situation
This Columbia home was built in the 1970s with 3/8-inch plywood decking, which was common then and is too thin by today’s standards. Forty years of Maryland humidity, a couple of slow leaks and an attic that was never properly ventilated had delaminated most of it. When the owners called for a roof quote, two other contractors had already told them the roof could be replaced with a few patches to the deck. Our inspector went into the attic, pushed on the plywood between the rafters, and watched it flex. From the roof, the surface felt spongy underfoot across the whole rear slope.
A roof is a system, and the deck is the part that holds the nails. Shingles nailed into delaminated plywood pull loose in the first big wind, the manufacturer will not honor the warranty, and the next leak is a matter of when. We recommended a full re-deck, showed the owners the attic photos and the spots where a thumb went through the plywood, and priced it as its own line so they could see the cost.
What we did
- Free inspection from the attic and the roof; photos of delaminated decking shared with the owners
- Old shingles and underlayment removed
- All 42 sheets of 3/8-inch decking removed and hauled away
- Rafters inspected; two sistered where the old leaks had reached the wood
- New 1/2-inch CDX plywood decking laid with H-clips, gapped 1/8 inch for expansion, nailed on a 6-inch pattern
- Synthetic underlayment over the entire deck with taped seams
- Ice-and-water shield at every eave, valley and penetration
- New drip edge, pipe boots and a continuous ridge vent
- Architectural shingles in Weathered Wood, six nails per shingle
- Magnetic nail sweep, dumpster removed, final walkthrough
How the job went
A full re-deck is the one roofing job where the house is open to the sky for a few hours, so we planned it around the forecast and staged the plywood on site so the deck could be closed the same day it was opened. The crew stripped the shingles and then the plywood in sections, starting at the ridge and working down one slope at a time. With the rafters exposed we found two that had taken water from the old leaks; we sistered new lumber to them before the new deck went on.
The new plywood went down with H-clips between the rafters so the sheets support each other, a 1/8-inch gap at every edge so the wood can expand in August without buckling, and a 6-inch nailing pattern at the edges. That nailing schedule is what makes a deck rigid enough to hold shingles through a windstorm. By the end of the first day the entire rear slope was decked and dried in with synthetic underlayment; the front slope followed on day two.
Day three was shingles, drip edge, ridge vent and cleanup. With a flat, solid deck under them, the shingles lie perfectly straight; you can see it from the street. The owners’ attic is also noticeably cooler now, because the ridge vent and cleared soffit vents finally let it breathe.
Materials and methods
The decking is 1/2-inch CDX plywood, the minimum we install and the thickness most shingle manufacturers require for their warranties. CDX has an exterior-grade glue that stands up to the humidity that destroyed the original 3/8-inch sheets. H-clips are small metal clips that lock adjacent sheets together between rafters so there is no sag at the unsupported edge.
The underlayment is synthetic, with the seams taped. Synthetic underlayment is tear-resistant, stays flat, and gives a secondary water barrier under the shingles for the life of the roof. Ice-and-water shield, a self-sealing membrane, covers the eaves, valleys and every penetration.
The shingles are an architectural fiberglass product in Weathered Wood with a Class A fire rating and a 130 mph wind rating. Six nails per shingle, starter strip at the eaves and rakes, and matching hip and ridge shingles over a vented ridge.
Why it matters for Howard County homeowners
Howard County has a lot of 1960s and 1970s housing stock in Columbia, Ellicott City and Elkridge, and a lot of it was built with 3/8-inch decking. Those roofs are now on their third or fourth set of shingles, and the deck underneath has never been replaced. If your roofer has not been in your attic, they have not inspected your roof.
The county’s humidity and the freeze-thaw winters are hard on thin plywood. Add an attic without a ridge vent, which was standard in that era, and the deck slowly cooks from underneath. A re-deck is more expensive than a re-shingle, but it is the only way to put a 50-year roof on a 50-year-old house.
Cost, insurance and what the owners paid
A full re-deck roughly doubles the labor and adds the cost of the plywood, so this job cost about 60 percent more than a straight re-shingle would have. The owners had two lower quotes that would have nailed new shingles into bad wood. Both of those roofs would have failed early and neither would have carried a valid manufacturer warranty.
Our quote broke out the decking as its own line, per sheet, so the owners knew the cost before we started. We also priced the rafter repair separately and only charged for the two rafters we actually sistered. Nothing here was an insurance claim. Financing was available.
What to expect if you hire us for a job like this
Every RooferMD roof follows the same steps, whether it is a storm claim or a planned replacement. It starts with a free inspection from the attic and the roof, with photos you keep, and an itemized quote that prices decking per sheet so the worst case is on paper before we start. We schedule around the forecast, stage the dumpster and materials the day before, and our own crew, not a subcontractor, does the work. The deck is inspected sheet by sheet during tear-off, every eave and valley gets ice-and-water shield, every shingle gets six nails, and the attic ventilation is checked and fixed because it is what decides how long the roof lasts. We sweep the yard with a magnet, walk the finished roof with you, and hand you a 50-year transferable limited warranty in writing. If the roof was storm damaged, our inspector documents the whole roof, meets the adjuster, and bills the carrier; you pay the deductible.
Questions about this kind of project
How do I know if my roof needs re-decking?
Spongy spots underfoot, visible sag between rafters from the street, daylight or dark stains in the attic, or 3/8-inch plywood on a house built before 1985. We check every roof from the attic before we quote.
Can you replace just the bad sheets?
Yes, and on most roofs that is what we do, priced per sheet. This house needed all of them.
Is the house open to the weather during a re-deck?
For a few hours per slope. We stage the plywood on site, work one slope at a time, and dry in with underlayment the same day. We schedule around the forecast.
Will the manufacturer warranty my shingles over old decking?
Most manufacturers require solid decking of at least 1/2 inch, or 7/16-inch OSB, for their warranty to apply. Shingles over delaminated 3/8-inch plywood are not covered.
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