Plank Decking on Older Houses, and When It Gets Replaced

October 2026

Boards first, sheets later

Before plywood and OSB were the normal thing to put on a roof, houses got decked with boards. Long planks of solid lumber, nailed across the rafters one after another, with the roofing laid right on top. A lot of the older homes around the Salt Lake valley still have them, including plenty of the bungalows in and around South Salt Lake, and you usually cannot tell from the street.

Plank decking is not a problem by itself. Some of it is sound, dense old lumber that will outlast the next three roofs. Some of it is a patchwork of split boards and soft spots. The trick is knowing which kind you have, and deciding what to do about it while the roof is open and the boards are right there to look at.

Why some of those boards have gaps

If you look up in an older attic and see daylight lines between the boards, you may be looking at skip sheathing. Wood shake roofs were often laid on boards spaced apart on purpose, so the shakes could breathe and dry out from underneath. When those houses later got asphalt shingles, the spaced boards sometimes stayed.

Asphalt shingles need a solid surface under every inch. Laid over gaps, a shingle sags into the space, a nail can land on nothing at all, and the roof shows every line of the boards underneath it after a few hot summers. Any roof going over skip sheathing needs a solid layer added first, and that is not optional.

How plank decking ages

Solid boards behave differently from sheet goods, and the ways they wear out are worth knowing if you own one of these houses.

Cupping and shrinking

A wide board dries out unevenly over the decades and curls along its width, so the edges lift a little and the middle sinks. The boards also shrink, and the gaps between them open up. Across a whole slope that adds up to a deck with a slight washboard feel underfoot, and a new shingle laid directly on it will show every ridge.

Knots, splits and old nail holes

Knots dry out and drop out, leaving round holes straight through the deck. Boards split along their length where they were nailed near the ends. And after two or three roofs have been nailed down and torn off, some boards are so full of old holes that a new nail just slides into one of them and holds nothing.

Soft where the water sat

Plank decking rots where any deck rots, around the old leak points, and the roof deck repair page for South Salt Lake covers where we find it. What is different on boards is how far it spreads. A sheet of plywood rots in a patch. A plank carries water along its length, so a soft spot by a vent can run the whole width of a rafter bay along one board while the boards above and below it stay hard.

What those boards carry in April

Deck condition matters more here than in a mild climate because of what sits on top of it. Late season snow in this valley is wet and heavy, far heavier than the dry powder that falls in midwinter, and an older roof can end up holding a real load for days at a time. Every soft board and every nail that no longer grips is a weak point under that weight.

When we walk an older plank roof, we pay attention to how it feels between the rafters. A slope that gives noticeably, or a ridge line that has started to sag, tells us to look harder at both the boards and the framing under them. Sometimes the fix is decking. Occasionally it is a conversation about the rafters, and it is better to have that one before the job than halfway through it.

Two old roofs on top of the boards

A lot of older houses in the valley got a second layer of shingles nailed straight over the first one at some point, and a few have three. Every layer was nailed through the ones below into the same boards, so a plank under a three-layer roof can have more holes in it than wood. All that weight has been sitting on the deck for years, too.

We take every layer off down to the boards. It is the only way to see what the planks look like, and a new roof nailed through two old ones into tired boards has very little to hold on to. The tear-off on these houses takes longer and fills more of the trailer, which is worth knowing before the day comes.

Sheeting over the gaps changes the attic air

Skip sheathing let the attic breathe through every gap. Once those gaps are covered with a solid layer, the attic loses that air movement, and it needs real intake and exhaust vents to replace it. Without them, warm, damp air from the house sits under the new deck in winter and condenses on the cold underside of it.

So when we sheet over spaced boards, we look at the ventilation in the same visit: soffit intake at the eaves, and exhaust at or near the ridge. Our roof ventilation page covers how we balance the two. It costs far less to add vents while the roof is open than to chase frost in the attic the first winter after.

Once the old roof is off and every board is in view, the choices for the deck itself are laid out on the South Salt Lake deck page. If the planks are good, they stay.

What a new layer changes at the edges

Sheeting over planks raises the roof surface by the thickness of the new panels. That sounds minor, and in the middle of a slope it is. At the edges it matters. The drip edge has to sit right against the new surface and still kick water past the fascia, the rake trim has to cover the added thickness, and the step flashing along any wall gets reset to the new height.

Fasteners matter too. Nails for the new sheets need to be long enough to go through the panel and well into the planks or the rafters below. Short nails into old, dry boards will back out over a few winters. We plan all of that before the job starts, because it is a lot easier to have the right trim on the truck than to find out at four in the afternoon.

Spotting plank decking from your own attic

You can usually tell what you have from inside. Plywood and OSB show as big sheets with a stamp printed on them and seams every four or eight feet. Planks show as long boards running sideways across the rafters, each one six to ten inches wide, often with the saw marks still on them. If you see daylight lines between the boards, you have skip sheathing. When the whole deck is past saving, that becomes deck replacement, usually alongside a full roof replacement.

If your house is older and you are not sure what is under your shingles, call (801) 382-8898 and have us take a look from the attic, or send us a note through the contact page and we will set up a time.

Questions about plank decking

Is plank decking a bad thing to have?

No. Good old lumber can be as strong as anything sold today. The concern is condition: gaps, cupping, splits and soft spots. A plank deck in good shape gets new roofing right on top of it. One in rough shape gets boards replaced or a layer of sheets added first.

Why does my attic get so dusty when you tear off the roof?

Plank decking has a seam every few inches, and grit from the old shingles falls straight through those seams into the attic. Cover or remove anything stored up there before the job, and expect some dust to settle for a day or two afterward.

Can you just put plywood over everything to be safe?

We can, and on a gapped or cupped deck it is the right move. On sound planks it adds weight and work without much benefit, so we show you the boards first and you decide.

Will adding sheathing make my roof look different?

From the street, no. The added thickness is a fraction of an inch and the new drip edge and trim cover it. What you will notice is a flatter roof surface, since the new shingles are lying on something smooth instead of following the boards.

How do I know how much decking you replaced?

We photograph the bad boards and sheets before they come out and keep a count as we go. We show you the pictures and the count before anything closes up, so there is no question about what was done under the shingles.

Old houses deserve a careful deck

The deck is the part of a roof you only get to see once in a long while, on the day the old shingles come off. On a plank house it is worth slowing down for.

If you are planning a new roof on an older house, leave a note on the contact page with roughly when the house was built, and ask us to look from the attic before anything gets ordered.