Slim-line · 12–14mm · Conservation-compliant
Double glazed sash windows in Edinburgh are achievable without replacing the original sash. A 12–14mm argon-filled slim-line unit fits into the existing 19mm glazing rebate, drops the centre-pane U-value from around 5.8 down to 1.2 W/m²K, and from the street the window looks unchanged. It's the upgrade that delivers most of what a full replacement does, at around half the price, while keeping every piece of original timber.
Argon-filled slim-line units that fit inside the original sash — modern performance, original character. Call 0800 193 1505 or request a fixed-price survey.
A slim-line double-glazed unit is two panes of 3mm or 4mm glass separated by a 5–8mm warm-edge spacer filled with argon gas. Total thickness is 12–14mm — slim enough to fit the 19mm glazing rebate of an original Edinburgh sash. The outer pane is laminated or restoration glass; the inner pane is low-e coated. Sealed perimeter; 10-year fogging warranty. We dismount the sash, route the rebate, fit the unit and re-bed in linseed putty.
Original single-glazed sash: centre-pane U-value around 5.8 W/m²K. Slim-line double-glazed: 1.2 W/m²K. Acoustic improvement: 28–32 dB Rw (depending on glass spec) versus around 18 dB single-glazed. Condensation on the inside pane in winter — virtually gone. Heat loss through the window — cut by 75–80%. The remaining cold spots come from draught around the perimeter, which is why we always combine slim-line with brush-pile draught-proofing in the same visit.
Slim-line slot-in units are accepted by Edinburgh case officers as a like-for-like upgrade on most Category B and C listed buildings and across the city's conservation areas, particularly when the outer pane is hand-blown restoration glass. We handle the Listed Building Consent application or conservation prior approval as part of the job, with no separate fee.
Slim-line glazing fixes heat loss through the glass. It doesn't fix a snapped cord, a rotten cill, a worn meeting rail or a perimeter draught — those need separate repair and draught-proofing work, which we always include in the same quote so the visit pays for itself once.
Cold front-facing tenement rooms in Marchmont, Bruntsfield, Polwarth, the Grange, Morningside, New Town and Stockbridge. Listed Georgian and Victorian terraces where the case officer will not approve replacement. Properties where the owner wants the original sash and ironmongery kept intact. It's the most-specified sash window upgrade we deliver across central Edinburgh.
| Item | Price | Notes |
|---|---|---|
| Slim-line 12mm unit, standard restoration outer glass | £395 per sash | |
| Slim-line 14mm unit, hand-blown outer pane (listed buildings) | £545 per sash | |
| Add brush-pile draught-proofing while sashes are out | £165 per window | |
| Listed Building Consent handling | Included |
Listed-building paperwork sorted for us, original sashes saved, and the front room is no longer a wind tunnel. Brilliant from quote to completion.
James & Catriona R., Stockbridge EH3 — Sash & case restoration + secondary glazing · 5/5 ·
Quietest the house has ever been. Bay windows look stunning, and the survey caught a lintel issue two other firms missed.
Rachel B., Trinity EH5 — Triple glazing — full house · 5/5 ·