How to tell whether to repair or replace

Every part of a house is a surface on a structure

Deck boards on joists. Siding on sheathing. A finished floor on a subfloor. In each pair the half you can see fails first and matters least. Surfaces wear from use. Structure does not wear from use at all: it fails from water, from movement, or from carrying what it was never built to carry, and none of that reaches the surface until late.

The screwdriver test, done properly

A long flat blade screwdriver, or an awl, settles more questions about a house than anything else you own, because it measures whether the wood still has fiber in it. Sound wood is springy and pushes back. Rot has eaten that fiber out, so the wood takes the tip and keeps taking it.

Push straight in with ordinary thumb pressure, the kind you would use on a doorbell. Sound wood lets the tip bite a fraction and stops, and levering the blade sideways lifts a long splinter you have to tear free. Rotted wood swallows the tip under that same pressure, and what comes out breaks short and crumbles. Splinter length is the reading that does not lie. Color is not, because wet framing goes dark and stays strong.

Two things fool people. Silvered fuzz on old exposed lumber is sunlight weathering, and a fingernail scratches through it to sound wood. And paint bridges: a board looks flawless while the wood under it has nothing left, because the film spans what is gone. Your eye reads the coating. The screwdriver reads the wood. Where to push:

• End grain and joints first, then the faces you cannot see. A cut end wicks water in along the grain, and what gets into a lap joint does not dry back out. Shaded sides and the back of a post stay wet longest.
• A grid, not a spot, every few inches along a run. One push at the edge of a soft area finds sound wood and misleads you.
• Then chase the boundary. Where the tip sinks, work outward until it stops and mark that line. It is the real size of the job, usually wider than the stain that sent you there.

What you notice, and the order it turns up in

Damage gets noticed in a fairly fixed order, and that order runs backward to how much each item matters. A mark on a wall is the earliest thing a house says and the easiest to put off. Movement under load is the structure speaking for itself, and by then the call has been made for you. Probe at the mark rather than waiting for the movement.

• A mark. A stain, a dark streak, a white powdery bloom, or paint failing in one patch while the wall around it holds.
• A fastener that spins. A screw that turns and never tightens has lost the wood it was gripping, the first word from structure rather than surface.
• A joint that was tight and is now open. A trim miter, a caulk line splitting in the same place each year, a board easing off the wall.
• A musty smell, meaning something has been wet long enough to grow, usually where nobody looks.
• Give underfoot, then movement under load: a rail that shifts at its post, a stair that flexes, a deck that sways.

Where the line falls on real jobs

Wood does not rot without a reason, and neither answer touches it. A new fascia board under a gutter that still runs over resets the clock, so overflowing gutters and damp under a house are worth settling first.

The rule holds everywhere. Fix the surface where the structure is sound, fix the structure where it is not, and never lay new surface over failed structure.

• Deck boards versus deck frame. Boards are consumable, the frame is not. A splintered gray deck on sound joists and posts carries a new surface fine. Soft joist ends, an unflashed ledger or buried post bases, and the boards are the least of it.
• A door versus its frame. Most doors that stick or will not latch are fine, and the fault is the hinge or the opening, which is why a new door hung in the same out of true frame ends up getting planed too.
• Siding sections versus a full run. A few damaged boards on a healthy wall get cut out. What pushes it to the whole run is a profile no longer made, or damage running further behind the wall than the face shows.
• Patching drywall versus re-boarding. Holes, cracks and popped tape are patches. Board gone soft from water is not, because nothing is left for compound to hold.
• New flooring versus what is under it. A flat, dry, solid subfloor makes the covering a free choice, and softness under it gets repaired first.

When replacing wins even though the structure is sound

Three things move a sound assembly into the replace column, and none is about damage.

• Access is the cost. Second story soffit and fascia, anything that needs scaffolding, anything under a finished floor. Reaching it is paid for once whether you fix one board or the run.
• The material is no longer made and the repair sits where you look at it every day. A back elevation nobody sees is a different question.
• The same repair keeps coming back. That is not a repair problem. Something is still moving or still getting wet.

Run the test yourself

The diagnosis is entirely a homeowner job. A screwdriver, a flashlight and twenty minutes tell you which layer failed, and when we look at a job that could go either way the probe is the first thing we do. Saying what you found, soft for two feet either side of the back step and hard past that, beats any account of how it looks.

Plenty of the repairs are yours once the probe says the structure is sound. A soft deck board out with a drill and a saw, a short length of exterior trim, a drywall patch, a caulk joint recut. A door that sticks is usually the hinge rather than the door, and that is a screwdriver job.

Get somebody out when the probe finds soft wood at a joist, beam, post base or ledger, when a deck or stair moves under you, when a ceiling sags rather than only stains, or when you cannot find the water. Anything behind a cover plate is its own trade at any job size, and not part of this work.

So which is it

The two ways of getting this wrong do not cost the same. Replace what only needed a repair and you have spent money you did not need to. Repair what needed replacing and you pay twice.

Now, if the failed layer is structure and something depends on it. Deck framing, stair stringers, guardrail posts, floor joists, anything holding weight over your head. Also now if water is still getting in, because that never improves on its own.

Soon, if the structure is sound but the surface has stopped protecting it. Open joints in exterior trim, bare wood where paint has failed, a lifted siding board.

It can wait, genuinely, if the damage is cosmetic and everything under it is dry and solid. A gray deck on a sound frame, faded paint, a scuffed door. What decides it is not how bad it looks. It is where the screwdriver stops.

Questions that come with this one