Resurfacing a Deck on Its Existing Frame

A Sample Board in One Hand and a Screwdriver in the Other

By the time anybody in the trade gets a phone call about a deck resurface, the boards have already been chosen. There is a sample length propped against the kitchen wall, a colour with a name, and a supplier quote that covers decking and clips and quietly assumes the structure underneath is somebody else's department. Outside, the deck is fourteen summers old. Two boards by the steps have gone soft where a planter sat and the rest are doing what treated softwood does at the end of its life: holding a screw badly and passing water down into the joist below. Yet the frame in the shade underneath looks untouched. Square, dry, no soft ends, hangers full of nails. The obvious conclusion is that the expensive half of this job was paid for years ago.

That conclusion is usually right, and the way it goes wrong is specific enough to settle in an afternoon. The frame under an old deck was sized for the boards that were on it — nominal five-quarter treated softwood at whatever spacing the carpenter of the day thought reasonable, which in a great many gardens meant joists at 24 inch centres because that is what timber decking of the period would take. Composite is not that board. Most filled formulations are heavier per square foot, and each arrives with a published maximum support spacing that is a condition of its approval rather than a suggestion. A frame at 24 inches has not failed. It has simply never been asked this question.

So the job splits into two decisions taken in a fixed order. First: what spacing does the board that has been chosen require, at the angle it is going to be laid. Second: will the joists already in the ground carry the new dead load over the span they already have, at whatever spacing that first answer demands. Everything else here — the ledger, the guard, the delivery, the colour lot — waits on those two. Take them the other way round and you end up specifying a board because it is the only one that suits a frame you have not yet proved is sound.

Fourteen Years of Water Went Somewhere

Strip a metre of boards before quoting — a metre hard against the house, a metre at the outer edge, one bay in the middle — because the frame visible from the garden is the frame in the ventilated part, and the parts that rot are the parts you cannot see from there. The top edge of every joist has spent its life under a board with a gap over it, rained on through a slot and then held wet by the board's own shadow. That surface goes first and gets inspected last.

Carry an awl or a long screwdriver and use it properly. Sound treated timber resists a firm push and lifts a splinter that breaks across the grain with a snap; decayed timber takes the point six or eight millimetres with almost no resistance and lifts a fibrous sliver that tears instead. Probe the top edge at every hanger, both ends of the ledger, the joist ends sitting in the hangers, and anywhere a post, a planter or a barbecue stood for a decade. Incipient decay is a colour change and a softness long before it is a hole, and it is the stage at which a joist is still worth arguing about.

Fasteners tell you as much as the timber does. Pull one deck screw from a joist top: a screw that comes out black and pitted has been sitting in wet copper-bearing preservative for years, and the hanger nails a foot away are the same metal in the same water. Hangers get installed wrong more often than they corrode, though — roofing nails or drywall screws in the hanger holes instead of the connector manufacturer's specified nails is among the commonest defects in existing residential decks, and a torch from underneath finds it in half a minute.

The last thing to look for is the thing nobody wants to find. Where the deck meets the house, water that got behind absent or badly lapped flashing has been running into the building's rim, not the deck's. That rot is inside the wall, and it announces itself as a ledger bolt hole that has gone soft, a stain on the sheathing when the cap is pulled, or as nothing whatsoever. Find it and the resurface has stopped being a resurface, which is a conversation worth having on day one rather than on the day the boards were due.

1. Lift boards in three places at minimum: against the house, at the outer edge, and one bay mid-deck.
2. Probe the top edge of every joist you have exposed, plus both ends of the ledger and every joist end in a hanger.
3. Torch each hanger from below and check what is actually in the nail holes against the connector manufacturer's schedule.
4. Pull one deck screw and one hanger nail and read the metal for pitting and coating loss.
5. Check post bases for standing water and for end grain bearing flush on a pier top with no standoff.
6. Measure joist depth, breadth and centres at three points, and the clear span face of support to face of support.
7. Photograph everything while it is open. It is the only record of the frame that will exist for the next fifteen years.

The Board Sets the Spacing, and It Does Not Negotiate

A wood-plastic composite or plastic lumber board is a manufactured product with a tested span rating, not a piece of timber you can judge by eye and experience. ASTM D7032, the specification for establishing performance ratings for wood-plastic composite and plastic lumber deck boards, stair treads, guards and handrails, is the standard that rating is established under, and ICC-ES AC174 is the acceptance criteria an evaluation report gets issued against. What comes out the far end is a maximum support spacing belonging to one specific board in one specific orientation. Two products of identical thickness from two makers can differ by a full joist spacing, and neither of them is wrong.

That figure lives in the installation instructions, which form part of the approval rather than part of the marketing. Install outside them and the board is outside its evaluated condition, which is a code problem, and outside its warranty, which is the homeowner's problem and eventually yours. Print them and keep them on the job; the printed spacing is what an inspector will hold a tape against.

The laying angle is the variable that catches people out. Boards run square to the joists have a span equal to the joist spacing. Boards run at 45 degrees for a diagonal field have a span of that spacing divided by the cosine of the angle, so 16 inch centres hand each board a 22.6 inch span — very often past what the product permits. That is why makers publish a separate and tighter diagonal figure, and why a deck detailed as diagonal on the drawing needs its spacing settled before anybody prices the frame work rather than after the old boards are in the skip.

Stairs, borders and oversailing edges each carry a rule of their own. The one that surprises people is the picture-frame border, which turns the perimeter boards through 90 degrees so they run parallel to the joists and are supported by nothing at all until framing is added specifically to carry them.

Closing a Frame Down From 24 Inches

Say the answer came back needing 16 inch centres on a frame built at 24. There are four honest responses and one that looks like a response and is not. The one that is not is blocking, which runs between the joists and therefore parallel to the deck boards, sitting directly under a gap and supporting nothing. It stiffens the frame against rotation and is worth having for that, but people fit it, feel better about the deck, and have changed nothing whatever about the condition that failed.

The direct fix is more joists — a new one hung midway between each existing pair, on connector-manufacturer hangers into the ledger at one end and onto the beam at the other, at the same depth as its neighbours so the surface still comes out flat. It is a day of awkward work in a confined space with a hanger nailer, it reuses the frame you already have, and it is where most resurfaces land. Where the ledger will not take more hangers, a mid-span beam on new footings shortens the joist span instead. That fixes the joist check but leaves the board spacing exactly as it was, and the distinction is worth being clear about with a client before it appears on a quote.

The third route is a sleeper or batten grid laid over the existing joists, running the same way and doubling the support lines. It is fast, needs no hangers, and costs height — and height on a resurface is never free. Raising the walking surface reduces the guard height measured up from it, which IRC Section R312.1 governs, and it lengthens the top riser of every flight, where IRC Section R311.7.5.1 limits the difference between the largest and smallest riser to three-eighths of an inch, a tolerance a 40 mm build-up destroys at a stroke. The fourth route is the cheapest of the lot: specify a board actually rated for the spacing you already have. Several are. They are not always the board propped against the kitchen wall.

The Two Connections That Turn a Resurface Into a Rebuild

The ledger is exposed for about one week in the entire life of a deck, and this is that week. Whatever is behind it — a lag pattern copied off a previous job, a bolt into brick veneer, no flashing at all, or flashing that stops short of the ends — gets closed in again for another fifteen years the moment the new boards go down. Look now. The IRC's deck ledger connection provisions in Section R507 set out fastener types and schedules for the common cases and DCA 6 lays the same schedules out in tables; both of them assume attachment to a solid band joist, never to sheathing, never to veneer, and never through a rim that has quietly gone soft behind an unlapped flashing.

Lateral load connection is the second one, and it is the requirement most likely to have arrived after the deck was built. Current IRC editions call for specified devices tying the deck framing into the floor framing of the house to resist the deck pulling away, with the capacity and number of locations set by the adopted edition; a deck built before those provisions took effect will not have them. Whether your resurface has to add them is a question for the building department, because it is an alteration question rather than a construction one — the International Existing Building Code's alteration provisions are where that threshold sits, and the adopted edition governs. Ask before you strip, not after.

Anything new going into old treated timber has to match the metal to the preservative, and the specification that matters for hardware is ASTM A153, hot-dip galvanised after fabrication — not electroplated, not mechanically plated, and not whatever came in the box with the clips. Every new hole bored in a fifteen-year-old joist also breaks the treated shell, which under the AWPA U1 Use Category System is thinner than the label implies once the timber has weathered.

What the Next Person Will Wish You Had Left

The frame is invisible again now for another fifteen years and everything you learned about it is in your head. Write it onto something that stays with the building: the board's span rating and its printed installation instructions, the joist spacing you finished at and whether you added joists to get there, the ledger fastener schedule you found and the one you left behind, the connector part numbers, the cable system name with its evaluation report number, and the colour lot. A photograph of each, taken while the frame was open, settles warranty arguments recollection loses.

And be plain in writing about the one thing this page does not do. Every calculation here produces a demand or a quantity — the depth a joist needs, the area a stack of boards reaches, the cable an order has to contain. None of it verifies that an existing structure is adequate, because adequacy needs the load combinations, the adjustment factors belonging to a member that has been wet for fifteen years, and somebody prepared to sign. Where the frame is unknown, where the ledger goes into anything other than a sound band joist, or where the deck is high enough that a failure means an ambulance, that somebody is a structural engineer and these numbers are what you hand them.