Sash Window Replacement in Heritage-heritage-heritage-listed buildings

Original sash windows are character-defining for many heritage-heritage-listed buildings. Replacement (rather than repair) is usually refused; modern slim double glazing options have changed what's possible — but consent is still required.

The consent baseline

All alterations to windows in heritage-heritage-listed buildings require Provincial Heritage Resources Authority (PHRA) permit — including draught-proofing, secondary glazing, paint colour changes, and frame replacement. Replacing original timber sashes with uPVC is almost always refused.

Repair-first principle

Conservation officers expect:

Repair of damaged parts (splice in new timber, replace cords/weights)
Like-for-like restoration of severely decayed elements
Re-instatement of original glazing bars where lost
Linseed oil paint and traditional putty

Performance upgrades within consent

Draughtproofing

Discreet brush seals routed into the meeting rails. Significantly improves comfort with minimal visual impact.

Slim double glazing

Vacuum-insulated glass units down to 8mm overall thickness fit within existing sashes. Acceptable to many heritage officer (PHRA)s for non-prominent locations.

Secondary glazing

Inner pane behind original window. Significantly improves thermal and acoustic performance. Often accepted as reversible solution.

Insulated shutters

Internal shutters with insulated panels. Heritage-appropriate, removable.

When replacement is permitted

Where original windows have been replaced (with sympathetic copies)
Where decay is beyond economic repair
To restore lost windows (with evidence of original design)

Replacement must match original profile exactly — slim glazing bars, correct meeting rail dimensions, proper horns.

Costs

Sash overhaul and draughtproofing: R12,000–R30,000 per window
Slim double glazing retrofit: R18,000–R44,000 per window
Secondary glazing: R8,000–R24,000 per window
Like-for-like replacement timber sash: R36,000–R90,000

MCFAR works with heritage joiners and conservation specialists.

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Frequently Asked Questions

Will heritage officers accept uPVC sashes?

Almost never on heritage-heritage-listed buildings. Conservation areas: sometimes for rear elevations only.

Can I install double glazing in my Georgian house?

Slim double glazing within the original timber sash is increasingly accepted. Always seek consent first.