Rotten Window Sill Repair in Dunedin – Sills, Cills & Bottom Rails Scarfed in New Timber

Timber windows here rot from the bottom up and always for the same reason. The paint film cracks, rain gets behind it, and the end grain in the sill soaks it up and holds it through a cold damp winter. South and west elevations go first. The head and stiles of the same window are usually still perfect old growth rimu.

Finding the full extent before quoting

Rot spreads further than it looks. Paint holds a shell over timber that has gone soft behind it, so a patch that appears to be 100mm across is often twice that. We probe with an awl along the whole sill and up the jambs before we quote, so the price does not move once we open it up.

Scarf repair instead of filler

Two part filler over soft timber is a cosmetic fix that lasts a season or two. It is harder than the wood around it, so it works loose as the timber moves, and it seals moisture in behind itself.

A scarf repair cuts a clean angled joint back into sound timber and lets in a new piece of seasoned wood, glued with an exterior adhesive and pinned. Shaped and primed, it disappears under paint and lasts as long as the rest of the window.

Stopping it happening again

The repair only holds if the water stops getting in. That means end grain sealed before priming, a proper drip groove under the sill nose so water cannot track back, and paint maintained instead of left until it cracks.

On exposed southerly elevations we will usually recommend recutting the drip groove if it has been painted solid, which is a very common cause of repeat rot.

Making sure it does not come back

The drip groove

Under the nose of a timber sill there is a groove that makes water drop off rather than track back underneath. Decades of repainting fill it, and once it is bridged every drop of water runs back into the joint between sill and frame.

We recut it as part of every sill repair. It is a five minute job and it is the single most common reason a sill that was repaired properly rots again in the same place.

Sealing end grain before priming

Timber takes on water through its end grain many times faster than through its face. A scarf repair creates fresh end grain at both ends of the new piece.

Those faces get sealed before the piece goes in, then the whole repair is primed. Skipping that step is invisible on the day and obvious in three winters.

How Window and Glass Repair Dunedin approaches rotten window sill repair in Dunedin

Dunedin has more original timber joinery still in service than any other New Zealand city. Most of it is repairable and the method is what decides whether the repair lasts.

1. Establish what is actually sound

   Window and Glass Repair Dunedin probes the timber to find where decay stops, which is almost always further than it looks from the paint line. That defines the extent of the work before a price is given rather than after.

2. Take the sash out where possible

   Bench work gives better access, a cleaner joint and the chance to deal with everything at once. The opening is secured while the sash is away rather than left open to a Dunedin winter.

3. Cut back and scarf in matched heartwood

   Decayed timber is cut back to sound material and new heartwood spliced in with a long scarf joint, glued and fixed. Window and Glass Repair Dunedin does not fill rotten timber, because filler bridges the problem instead of removing it and it reappears at the edge of the repair within a few years.

4. Free the moving parts

   A century of paint in the staff bead, the parting bead and the rebates is the most common reason a sash will not move. Stripping those surfaces back returns windows that have been painted shut for decades.

5. Replace cords, weights and pulleys as a set

   On a double hung sash the counterbalance is a system. Window and Glass Repair Dunedin replaces the cord with waxed cotton of the correct diameter for the pulley and rebalances the weights to the actual mass of the repaired sash, which changes if it has been reglazed.

6. Draught proof while it is apart

   Brush seals in the stiles and at the meeting rail go in during the same visit. Done separately it costs a second dismantling, and on a frosty Dunedin morning the meeting rail is the biggest single draught path in the house.

7. Reglaze, prime and reinstate

   New putty or beads, and bare repaired timber primed the same day even where the finish coat is somebody else's scope. One wet week on unprimed end grain undoes the work.

Why rotten window sill repair matters more in Dunedin

This is the city where original joinery is most worth saving and most at risk.

The largest Victorian and Edwardian stock in the country

What is in these houses cannot be bought again. Original sashes carry glass with visible ripple and joinery profiles that no modern manufacturer runs, so replacing them is a permanent loss rather than an upgrade.

Rot concentrates at the bottom rail and sill

The lowest horizontal surface takes every drop of water that gets past the glazing, and with fifty odd frost days a year it stays wet far longer than it would further north. That is why almost every timber repair here starts at the same place.

Restored timber outperforms its reputation

A properly repaired and draught proofed sash with a slim sealed unit performs far better than people expect, and it keeps the external appearance the house was designed around. The choice is rarely as stark as replace or freeze.

Heritage rules can apply

Work on a scheduled heritage building can need resource consent even where building consent is not required. Window and Glass Repair Dunedin checks the district plan schedule before quoting on anything that looks significant, rather than after.

What rotten window sill repair costs in Dunedin and how long it takes

Timber work is priced by the hour and by the extent of decay, so the honest answer involves bands rather than a single figure.

Sash repair and rebalancing

Cords, weights, pulleys, freeing painted shut sashes and rebalancing is the most common job and it sits at the lower end. It is a day or two per window depending on how much paint has to come off and whether the sash comes to the bench.

Rot repair by scarfing

Cutting back to sound heartwood and splicing in new timber is priced by the length of the repair and the number of sections. Filling would be cheaper on the day and fails within a few years, so Window and Glass Repair Dunedin does not offer it as the cheap option.

Slim sealed units in original sashes

Where the rebate can take it, retrofitting a double glazed unit into the original sash runs roughly $800 to $1,250 per window including the rebalancing the added weight requires. It keeps the external appearance completely.

Against replacement

New timber joinery on a heritage house runs $800 to $1,250 per window and more where profiles have to be matched. Restoration is usually less, and it keeps original glass and joinery that cannot be bought again.

Restoration or replacement on a Dunedin villa

The decision is more open than people assume, and these are the four things that settle it.

How much sound timber is left

If the stiles and rails are sound and the decay is confined to the bottom rail and sill, restoration is straightforward and it is the better answer. Where decay has reached the joints the calculation shifts.

Whether the house is scheduled

Work on a scheduled heritage building can require resource consent even where building consent does not apply. Where that is the case, restoration is usually the only practical route and reversible additions are preferred.

What the original glass is worth

Early float and hand drawn glass has visible ripple that modern glass does not. Once it is gone it is gone, and on a Victorian or Edwardian house it is a large part of what the windows contribute.

What performance you actually need

A restored, draught proofed sash with a slim sealed unit performs far better than its reputation. It will not match thermally broken joinery, and on a character house the gap is usually a fair trade for keeping the building intact.

Why Dunedin sills rot first

The sill is the lowest horizontal surface on the window, so every drop of water that gets past the glazing ends up there.

Standing water and failed paint

Once the paint film cracks, water gets into end grain and stays. The sill stays wet long after the rest of the joinery has dried, which is exactly the condition decay needs.

Failed glazing putty above it

Cracked putty lets water run down the inside face of the glass and straight into the rebate. Repairing the sill without replacing the putty means repairing the sill again.

Blocked or missing drainage

Timber sills are designed to shed water forward with a drip groove underneath. When that groove is bridged by paint build up, water tracks back into the frame instead.

Scarfing in new timber on a Dunedin window

This is a joinery repair rather than a filling job, and the difference shows in about three years.

Cut back to sound heartwood

Decay extends further than it looks. We cut back until the timber is sound, which sometimes means removing more than the visible damage, then splice in matched heartwood with a long scarf joint.

Why filler fails

Epoxy and filler bridge over decayed timber without removing it. It looks identical on the day and the rot continues underneath, usually reappearing at the edge of the repair.

Prime before we leave

Bare repaired timber gets primed the same day even where the finish coat is somebody else's scope. One wet week on unprimed end grain undoes the work.

Rotten Window Sill Repair at a glance

Method

Scarf repair into sound timber, glued and pinned

Timber

Seasoned exterior grade, profiled to match the original

Not used

Two part filler over soft timber as a structural repair

Detail

End grain sealed, drip groove recut where it has been painted over

Finish

Primed and ready for topcoat, or fully painted on request

Full sill

Complete sill replacement into the existing frame where needed