Exterior trim replacement cost

Replacing exterior trim costs $8 to $25 a linear foot installed, typically around $14. A house with 300 linear feet of trim therefore runs $2,400 to $7,500. It is the first thing on a house to rot and the last thing anyone budgets for.

Trim is what stops water at every edge: around windows and doors, at corners, along the rakes and eaves, and at the bottom of the wall. When it fails it does so at the end grain, which is always at the bottom of a vertical piece and always where nobody looks.

What it costs

PVC is usually the right answer

For exterior trim on a painted house, cellular PVC has become the default among people who do this for a living, and the reasoning is simple: it does not rot, it does not absorb water, insects do not eat it, and it holds paint indefinitely.

It costs 30 to 60% more than pine and it eliminates the single failure mode that makes trim a recurring expense.

Where it is not right: on a stained or natural wood house, where it will always look like plastic. And it moves noticeably with temperature, so long runs need proper expansion gaps and the right fasteners, which an installer who has not used it before gets wrong.

Fiber cement trim is the other durable option, and it suits a fiber cement clad house because the movement and the appearance match.

Aluminium wrapping over existing wood is the cheapest approach and it is a trap. It hides the wood rather than replacing it, and any water that gets behind the aluminium cannot dry. Houses wrapped in the 1990s frequently have completely rotten trim inside intact-looking metal.

Where it rots, and why

Bottom end grain, every time. Wood wicks water up through cut ends, and the bottom of a corner board or a casing leg sits closest to the splash zone.

Behind sealant at the top. Sealant fails, water gets in behind, and there is nowhere for it to go.

Where trim meets a roof with no kick-out flashing.

Under a window with no sill pan or no drip edge, so water runs back under the sill and into the casing.

Anywhere it touches or is close to the ground. Trim should stop at least six inches above grade and above a roof surface.

A repair that replaces the rotten piece without addressing which of those caused it buys about four years.

Repair or replace the run

Splicing in a new section of trim is legitimate and costs $150 to $500 per repair. It makes sense where one leg of a casing has gone and the rest is sound.

Replace the whole run when more than a third of it is soft, when the paint is failing along its length, or when you are painting the house anyway. Painting over trim that is about to be replaced is money spent twice, and the painter will usually tell you so.

Frequently asked questions

How do I know if trim is rotten?

Push a screwdriver into it, hard, at the bottom of each vertical piece and at the mitres. Sound wood resists. Soft wood takes the tip with almost no pressure, often under paint that looks perfect.

Can trim be repaired with filler?

Epoxy wood consolidant and filler is a genuine repair for a small area of soft wood in an otherwise sound piece, and it is what restoration carpenters use on historic trim. It costs $50 to $200 a repair and it is not the answer for a length that has gone through.

Should trim be primed on all sides?

Yes, including every cut end, before it goes on. This is the single biggest factor in how long wood trim lasts and it is skipped constantly because it slows the job down.

Is aluminium wrapping ever a good idea?

On sound trim, done meticulously with proper drainage at the bottom, it works and it eliminates painting. Done ordinarily, it traps water. Given the failure rate, PVC replacement is the better money.

Does trim need to be replaced when re-siding?

Not necessarily, and it is by far the cheapest time to do it. Once the siding is on, replacing a corner board means cutting siding. Decide before the siding goes up.