Spaced decking is a roof deck built from boards laid with gaps between them, while solid decking is a continuous surface of plywood or oriented strand board (OSB). Asphalt shingle manufacturers generally call for a solid, flat, nail-holding surface under their products, which is why a roof with spaced decking usually needs the gaps closed with sheet material (an overlay or a replacement) before new shingles go on.
Plenty of older Oklahoma homes were built with gapped boards, and plenty of homeowners first learn about it when an estimate changes after the old roof comes off. This page explains the two deck types, how they behave differently, the common ways to bring a spaced deck up to a solid one, and what to ask. Parts of it describe our own practice, labeled as such. Rules differ by manufacturer, city and county, so confirm anything specific with the shingle manufacturer's current instructions and your building department. We do not list prices.
Key takeaways
- Spaced decking (also called plank or skip sheathing in some places) uses boards with gaps. It was commonly paired with wood shakes, which dry out better with air moving around them.
- Solid decking is a continuous layer of plywood or OSB. It is what most shingle instructions assume.
- Shingles on gapped boards can have fastening and support problems. A solid layer fixes both.
- The two common fixes are an overlay (new sheets fastened over the old boards) and a replacement (old boards removed and new sheets installed). Each has trade-offs.
- Our crews' practice on many older homes with spaced decking is to overlay OSB. That is our practice, not a universal rule, and the right answer depends on what the old deck looks like once it is exposed.
- The deck can only be judged properly after tear-off. That is why a redeck line often appears on estimates as a contingency.
What is spaced decking?
Spaced decking is a roof deck made of boards, often one-by lumber, fastened across the rafters with deliberate gaps between them. Builders used it for a simple reason: the original roof covering was often wood shakes or shingles, and those last longer when air can move underneath them and help them dry.
When the roof is later changed to asphalt shingles, the gaps become a problem. Shingles are made to be nailed to a continuous surface. A nail that lands in a gap has nothing to hold, the shingle layers can sag between boards, and the roof can show waves and low spots. Older boards may also be warped, cupped, cracked, rotted or full of old nail holes from previous roofs.
Plank decking can also mean tight boards laid edge to edge. That is closer to solid in coverage but still behaves differently from sheet decking, because boards swell, shrink and warp individually and have joints that move.
What is solid decking?
Solid decking is the modern default. Sheets of plywood or OSB are fastened to the rafters, making a flat surface across the entire roof. The sheets are typically spaced very slightly at the edges so they can expand, which is by design and is not the same thing as spaced decking.
A solid deck gives shingles a continuous nailing surface, helps support the roof during construction and gives the underlayment a flat place to lie. Our short comparison of OSB vs plywood decking covers the two sheet materials, and our explainer on what a redeck is covers the process.
How do spaced and solid decking compare?
The table describes general tendencies. Every roof is different, and manufacturer instructions govern.
| Topic | Spaced or plank decking | Solid decking (plywood or OSB) |
|---|---|---|
| What it is | Boards with gaps (or edge-to-edge planks) | Continuous sheets across the roof |
| Typical age of home | Often older homes, originally built for wood roofing | Newer homes, and older homes that have been redecked |
| Fit with asphalt shingles | Generally not a suitable surface without added sheet material | The standard assumption in shingle instructions |
| Nail holding | Only where the nail hits a board | Across the whole surface |
| Airflow beneath roofing | Air can move through the gaps | Sealed surface; attic ventilation does the work |
| Flatness | Can be uneven, warped or cupped | Flat and consistent when installed correctly |
| Hidden problems | Rot, gaps, old fastener holes, patches in mixed materials | Moisture damage, delamination or edge swell if wet over time |
| Fix when upgrading | Overlay with sheets or replace | Replace damaged sheets only |
| Effort and disruption | Higher: extra material and labor | Lower, unless there is damage |
| Inspection | Difficult to judge until the old roof is off | Often easier to judge, but still best checked after tear-off |
What are the options for a spaced deck?
There are three realistic paths. Our crews look at the deck before choosing.
1. Overlay with sheet material. New sheets (our practice is OSB) are fastened over the old boards, creating a solid, flat surface without removing the old deck. This is a common solution on older Oklahoma homes with sound but gapped boards. The old boards stay in place and act as a base layer.
2. Remove the old boards and install new sheets. This is a full redeck. It is typically chosen when the old boards are rotted, badly damaged or otherwise unsuitable to leave in place, or when a particular detail calls for it.
3. Repair only the damaged areas. If most of the deck is sound solid sheeting and only some areas are damaged, individual sheets are replaced. This does not apply to a deck that is spaced throughout.
An overlay adds a layer of thickness. That changes some details: the length of nails or fasteners, how the roof meets the edge metal and walls, how flashing sits and how rake and eave details finish. A good crew accounts for this and the estimate should say what is included. Whether an overlay is acceptable for a given roof is a question for the manufacturer's instructions, the local code and a roofer who has seen your deck.
Why do our crews overlay OSB on spaced decking?
This is our practice, drawn from the experience of the owner of Total Roof Protection OKC, who says that Oklahoma is where he first encountered spaced decking in quantity, after starting in a part of the country where plywood was the norm. He describes OSB overlaid on top of the current wood decking as the approach on jobs where the old deck is sound enough to keep. He also notes that when an old roof comes off, the old deck can show hundreds of holes from years of fasteners.
The reasoning, in plain terms:
- A continuous surface helps shingles get fastened properly. The overlay gives nails somewhere to hold.
- Leaving sound boards in place can be practical. It avoids the cost and time of pulling a whole deck when the boards are in good shape. We do not publish prices; ask for the difference on your estimate.
- The overlay can flatten out minor waves. A flat surface helps shingles lie flat.
It is not always the right answer. If the old boards are soft, rotted or structurally compromised, covering them does not make them sound. Our crews decide after tear-off, when the boards can actually be seen and checked. That is our practice, not a rule for every house, and a different roofer may recommend a different approach. If you are comparing bids, ask each roofer which approach they use and why.
What happens when the deck is a surprise?
An estimate written before tear-off is a best reading of the roof. The deck is under the shingles and underlayment, and no one can fully see it until the old roof is off. That is why decking often shows up as a per-sheet or per-section line on an estimate, with the actual count known only after the old material is removed. Our guide to why a roof estimate changes goes through the typical items. Whether any of it is paid by an insurance policy is a matter for your policy; read yours and ask your agent.
Ask before you sign:
- Is a redeck line on the estimate, and how is it priced (per sheet, per section)?
- What triggers it, and who decides?
- Will I be shown photos of what was found?
- What approach is used for spaced decking, and why?
What does the underlayment have to do with it?
The deck and the underlayment work together. A clean, solid deck gives the underlayment a flat place to lie, and old underlayment layers hide the deck's condition. Our crews' practice is to remove old underlayment so the deck can be seen; we explain that in our comparison of synthetic underlayment and felt. On a spaced deck, the sheet overlay goes down first, then the underlayment, and then the shingles, according to the manufacturer's instructions.
Does solid decking change attic ventilation?
It can. On a roof that originally breathed through gaps, closing the deck with sheets changes how air moves. A roof with a solid deck relies on the attic's intake and exhaust ventilation to keep air circulating. That is one reason crews look at soffits, ridge and other vents at the same time as the deck. Requirements for ventilation vary by city and county; ask your building department or roofer. The shingle manufacturer's instructions also address ventilation.
Which option fits your roof and budget: spaced decking vs solid decking?
Homeowners rarely choose the deck type from scratch, but you do have decisions to make when you have spaced decking.
- Find out what you have. A roofer can often tell from the attic by looking at the underside of the deck, with no need to climb on the roof. Look from inside; do not walk the roof.
- Ask the manufacturer's rule. What do the shingle instructions require under their shingles?
- Ask for the plan for spaced decking in writing. Overlay, replace or repair, and how the roofer will decide.
- Ask about the details that thickness changes. Fasteners, edge metal, flashing, vents and transitions.
- Ask what happens if the deck is worse than it looks. The contingency should be stated in advance.
- Compare itemized, written bids. A bid that says "decking as needed" with no description is hard to compare.
What mistakes do homeowners make with decking?
- Assuming shingles can go on spaced boards. Manufacturer instructions generally assume solid decking.
- Treating a redeck line as a scam. It is a legitimate contingency, but it should be documented and explained.
- Not asking how the deck will be judged. Ask for photos, or ask to see it.
- Assuming an overlay fixes a rotten deck. If boards are structurally compromised, covering them is not the same as repairing them.
- Forgetting the details an overlay changes. Edges, flashing and fasteners need attention.
- Mixing up spaced decking and normal sheet gaps. Small expansion gaps between sheets are normal; large gaps between boards are not.
- Taking a blog post as final. Check the manufacturer's current instructions and local requirements.
Frequently asked questions
What is spaced decking on a roof? Boards laid with gaps between them, often on older homes originally built for wood shakes. The gaps let air move under the roofing. They are generally not suitable as the nailing surface for asphalt shingles without added sheet material.
Can you put shingles over spaced decking? Manufacturers generally assume a solid deck under their shingles, so spaced decking usually needs to be covered with sheets or replaced first. Check the instructions for your shingle and ask your roofer.
What is the difference between plank decking and spaced decking? Plank decking is boards, which may be tight or gapped. Spaced decking specifically has deliberate gaps. Both behave differently from sheet decking because boards move and warp individually.
Is OSB over spaced decking acceptable? It is our practice on many older homes where the old boards are sound enough to keep. Whether it is acceptable for your roof depends on the manufacturer's instructions, local code and the condition of the deck. Confirm with your roofer and building department.
Should the old boards be removed instead? Sometimes. If the boards are rotted, badly damaged or otherwise unsuitable, removal and replacement is the better path. A roofer should decide after tear-off, when the boards are visible.
How do I know if I have spaced decking? Often it can be seen from the attic as boards with visible gaps between them on the underside of the roof. A roofer can confirm. Please do not climb up to check.
Does a redeck change my estimate? Often it can, because the deck is not fully visible until tear-off. Ask how decking is handled on the estimate, how it is priced and how you will be shown what was found.
Will insurance pay for a redeck? Policies differ. Read yours, ask your agent, and do not assume either way.
Does solid decking affect attic ventilation? It can change how a roof breathes, so ventilation is checked at the same time. Ask your roofer to describe the intake and exhaust plan.
Want to know what is under your shingles?
We can look at your deck from the attic, explain what we see, describe how we would handle it and put the decking approach and the contingency terms on an itemized written estimate. An inspection tells you about the roof; it does not predict or replace your insurer's decision, and we will not tell you otherwise. Call Total Roof Protection OKC at 405-415-5841, or see our roofing services.