Bay Window Repair in Dunedin – Mullions, Corner Posts & Structural Reglazing

A bay is exposed on three faces instead of one, which means three times the weather and a set of corner joints that have had to stay sealed for a century. On a Roslyn or Maori Hill villa the bay usually faces the street and takes the brunt of it, which is why bays rot before the rest of the joinery does.

Corner joints are where bays leak

The vertical joints between the front pane and the returns are the weak point. Original detailing relied on paint and putty, and after decades of movement the joint opens. Water then runs down inside the mullion and comes out at the sill or into the wall below.

We open the joint, cut out the failed material, treat any soft timber and reseal. Sealing over the top of a joint without opening it traps water inside the mullion.

Sagging heads and settled bays

Some bays are cantilevered and not supported from below, and after a hundred years the head can sag enough to bind the sashes. That is a structural question rather than a glazing one, and we will say so.

What we can do is diagnose whether a sticking bay sash is the frame settling or simply the hardware and paint, which is far more often the case.

Double glazing a bay

Bays are excellent candidates for retrofitted double glazing because they are large, single glazed and face the weather. Each sash is machined for the unit and rebeaded, and the original glazing bars stay in place.

Weight is the thing to check. A large bay sash with a double glazed unit in it is considerably heavier, so cords, weights or stays get upgraded at the same time.

Bays, and why they fail first

Three faces of weather

A bay is exposed on three elevations instead of one and relies on vertical corner joints staying sealed for a century. When they open, water runs down inside the mullion and appears somewhere else entirely, often in the wall below rather than at the sill.

That is why a bay can look sound from outside while the framing behind it is wet.

Opening a joint properly

The failed sealant has to come out, the timber behind has to be checked and treated, and the joint has to be reformed before anything is resealed.

Running a bead over the top of a failed joint traps water inside the mullion where it cannot dry, and it is the most common bad repair we are called out to undo on a bay.

How Window and Glass Repair Dunedin diagnoses and repairs in Dunedin

Guessing at a cause is how people pay twice. Window and Glass Repair Dunedin finds the fault before quoting the fix, which sometimes means saying the problem is not the window at all.

1. Inspect the opening as one system

   Frame, sashes, hardware, seals and drainage all get checked together, because a fault in any of them presents identically from inside. Looking only at the obvious part is how the wrong repair gets sold.

2. Separate condensation from water ingress

   In a Dunedin winter this is the single most common diagnostic question. Water on the inside face of the glass, pooling on the sill, worse in the morning and worse in bedrooms, is almost always condensation. Water appearing after rain and tracking from the head is not.

3. Water test where ingress is real

   Controlled water on one zone at a time from the bottom up, with somebody watching inside. It takes an hour and it is the only reliable way to find an entry point rather than resealing everything and hoping.

4. Check the drainage before condemning a seal

   Aluminium frames let water in by design and drain it back out through weep holes in the sill. Blocked weeps present exactly like a failed gasket. Clearing them costs almost nothing, so it gets ruled out first.

5. Report the cause in writing

   You get told what failed, why, and whether it will recur. Where the cause is a head flashing, the cladding above or the way the room is ventilated, Window and Glass Repair Dunedin says so rather than quoting glazing work that cannot fix it.

6. Quote repair against replacement

   Where both are genuine options they go on the same quote with the reasoning. Most windows Window and Glass Repair Dunedin is called to do not need replacing, and you should be able to see the gap between the two numbers yourself.

7. Test again before leaving

   Every sash opened, closed, locked and checked for even seal compression. On a leak repair the opening is water tested a second time to confirm the fix.

Why bay window repair in Dunedin is its own problem

The housing stock and the climate here combine in a way that produces faults you do not see in warmer cities.

Old joinery that has already moved

A house that has stood since the 1890s has settled, and the openings have gone out of square with it. A sash that will not latch is very often a dropped or racked opening rather than a failed lock, and adjusting is far cheaper than replacing.

Student and rental housing gets harder use

A large share of the older stock is tenanted, which means more cycles on the hardware and more forced sashes. MBIE inspected fifty three Dunedin student rentals in May and June 2026, which gives some sense of how much attention this housing is getting.

Frost and damp accelerate everything

Around fifty ground frost days a year, and a lot of the older stock heated intermittently. Repeated wetting and freezing at the bottom rail is what turns a small paint crack into a rotten sill within a few seasons.

South Dunedin ground is a factor

On the flat, the water table sits close to the surface and moisture frequently rises from the ground rather than condensing from the air. Window and Glass Repair Dunedin checks that before quoting glass that would not fix it.

What bay window repair costs in Dunedin

Repair pricing looks unpredictable from outside because it depends entirely on what is actually wrong. These are the bands we quote within.

Diagnosis and call out

A standard assessment covers inspecting the opening as a system and giving you a written cause. Where water ingress is suspected, a controlled water test takes about an hour and is the only reliable way to find an entry point rather than resealing everything and hoping.

Hardware and seals

The cheapest end of this trade. Stays, rollers, catches, handles and gaskets are consumables and replacing them is a fraction of what people expect. Most windows Window and Glass Repair Dunedin is called to do not need replacing and the repair typically sits well under a tenth of a new unit.

Glass and sealed units

A broken pane runs $250 to $600 in a common size. A failed double glazed unit replaced in the existing frame runs $350 to $800. In both cases the frame and hardware stay, which is why repair usually wins on a sound window.

When replacement is the honest answer

Corrosion through the section, a frame distorted by building movement, or where the reason for the job is thermal performance rather than a fault. At that point a repair is money spent on a window you will replace anyway, and Window and Glass Repair Dunedin says so.

Repair or replace: how to decide in Dunedin

Four questions that settle it, in the order worth asking them.

Is the frame itself sound

Aluminium frames usually outlive everything attached to them, and timber frames are repairable far more often than they are replaced. If the frame is sound, almost everything else is a consumable and repair is the clear answer.

Is the complaint a fault, or is it the climate

Condensation running down the inside of the glass on a frost morning is not a fault. No repair fixes it and no reglaze fixes it. Ventilation, heating and thermal performance do, which is a different job with a different budget.

What is the whole of life number

A cheap repair on a window you will replace in three years costs the money twice. A repair on a window with twenty years left is the best value work in this trade. Window and Glass Repair Dunedin puts both numbers on the same quote so the gap is visible.

Is the house being sold or tenanted

On a rental, compliance and durability change the calculation, because the window has to keep working through harder use. On a house being sold, a documented repair is often enough and a full replacement rarely returns its cost.

What makes a Dunedin bay window different

A bay is several windows joined at angles, and the junctions are where everything happens.

Corner posts and mullions carry load

On many bays the corner posts are structural and support the roof above. That changes what can be removed and it means a repair can become a building job if the post has rotted.

Multiple junctions mean multiple leak paths

Every angled joint is a place water can enter. A leaking bay usually has one specific junction at fault and finding it needs water testing rather than resealing everything.

Settlement shows up first at the bay

A bay projects from the wall and is often carried on its own small foundation. Differential settlement cracks the glass and jams the sashes before it shows anywhere else in the house.

Repairing and reglazing a Dunedin bay

Bays are worth repairing rather than replacing more often than any other window type.

Sectional repair keeps the shape

Individual sashes, sills and mullions can be repaired or replaced while the geometry stays. Replacing a whole bay means recreating the angles, the roof junction and the internal linings.

Reglazing an angled unit

Each pane in a bay is a different size and some are not rectangular. Every one is measured individually and templated where the shape is irregular.

Curtains, seats and internal work

Bays usually have a seat, a shelf or a curtain track built around them. We agree what is removed and reinstated before starting, because that is where bay jobs most often go over scope.

Bay Window Repair at a glance

Common faults

Rotten sill and mullion feet, open corner joints, sagging head

Leak repair

Joint opened, failed sealant removed, timber treated, resealed

Rot repair

Scarf repair into sound timber, profiles matched

Double glazing

Retrofit into existing sashes, hardware upgraded for weight

Character areas

Detailing matched for Roslyn and Maori Hill heritage rules