Timber Window Sash Replacement in Wellington

It is the middle option almost nobody is offered, and in a city with thousands of villas and bungalows still carrying their original single glazed sashes it should be the default answer far more often than it is. Full joinery replacement means cutting out the frame, disturbing the cladding and losing the original proportions. A new sash costs a fraction of that and nobody on the street can tell it happened.

When a sash is genuinely past repairing

We repair sashes far more often than we replace them, so this page exists for the cases where repair is no longer honest.

Rot through the full section

Scarfing works where sound timber remains either side of the damage. Once a bottom rail is soft through its whole thickness, or two rails and a stile have gone, there is not enough left to key new timber into.

Failed joints

Sashes are mortice and tenon jointed. When the glue has failed and the joints have opened, the sash racks out of square and no amount of filler holds it. That shows as a sash you can flex by hand at the corner.

Too thin for a sealed unit

Some early sashes are simply not deep enough in the rebate to carry a double glazed unit even after machining. Where the owner wants double glazing, a new sash built to the same external profile but a deeper rebate is the way to get it.

Matching what is already there

A replacement sash is worth nothing if it reads as new from the footpath. Four details carry the match.

The external profile of the rails and stiles, including any moulding. The glazing bar layout and thickness, which is what your eye actually reads at a distance. The glass line, meaning how far the pane sits back from the face. And the timber, which we specify for stability and paint holding rather than for cost. We take the old sash as the pattern wherever enough of it survives.

Double glazing a new sash

This is the main reason people choose replacement over repair. A new sash can be built with a deeper rebate from the start, which means a sealed unit goes in without machining away timber that was never designed to lose it.

Weight is the thing to plan for. A double glazed sash is roughly twice the weight of the single glazed one it replaces, so the cast iron weights get changed or added to and the cords are upgraded. Done at the same time it costs almost nothing. Done afterwards it is a second visit.

Making a sash that matches

Taking the old one as the pattern

Wherever enough of the original survives we use it as the pattern rather than working from measurements. Profiles from the villa era are not standard and a modern approximation reads as wrong even when the dimensions are right.

Four details carry the match: the external profile, the glazing bar layout and thickness, the glass line, and the timber species.

Building it for a sealed unit from the start

If double glazing is on the plan, the new sash gets a deeper rebate built in rather than machined out later. That keeps the section strong and means no timber is lost that was never meant to go.

The weights and cords get upgraded in the same visit for the extra load, which costs almost nothing while everything is already apart.

Timber Sash Replacement at a glance

What is replaced

The sash only, in the existing frame

What stays

Box frame, pulleys, weights, architraves, linings and cladding

Matching

External profile, glazing bar layout, glass line and timber species

Glazing

Single glazed with putty, or a deeper rebate for a sealed unit

Balance

Weights changed or added and cords upgraded for a double glazed sash

Lead time

Two to four weeks, with temporary glazing while the sash is off