Slimline Double Glazing for Sash Windows in London
Enjoy warmer, quieter rooms while preserving period character. Our slimline double glazed units fit sympathetically into timber sash windows, combining a traditional putty-fronted look with modern performance. We work across London homes in Conservation Areas and provide clear advice where listed building consent is needed.
Fast quote: 020 7609 3012 · info@sashrestorationlondon.com
What is slimline double glazing?
“Slimline” (or “heritage”) sealed units are thinner than standard double glazing and use low-E glass with argon or krypton gas to improve insulation while keeping narrow sight-lines. Typical overall unit thicknesses are around 11–16 mm with warm-edge spacers and a putty-fronted finish to match original aesthetics.
When it’s suitable (and when it isn’t):
-
Period & Conservation Areas: Often acceptable on a case-by-case basis when appearance and detailing are preserved. We prepare drawings/specs to support applications where required.
-
Listed buildings: Consent is usually required and outcomes vary by authority and building significance. Where double glazing isn’t approved, draught-proofing and secondary glazing are proven alternatives that retain original fabric.
We’ll confirm feasibility at survey and advise on the most conservation-friendly route for your home.
Benefits you’ll notice:
-
Warmth & comfort: low-E coatings and gas-filled cavities reduce heat loss versus single glazing.
-
Quieter rooms: well-sealed units and tuned clearances help soften traffic noise.
-
Authentic look: slim sightlines, traditional putty lines and matched glazing bars preserve the period aesthetic.
-
Reduced draughts: glazing upgrades combined with discreet sealing to cut air leakage.
Options & specification:
-
Glazing build-ups: low-E toughened/laminated where required; warm-edge spacers; argon or krypton gas. Manufacturer-stated centre-of-glass Ug values for slim heritage units typically range from ~2.6–1.2 W/m²K depending on thickness and gas fill. Whole-window performance varies by frame and installation.
-
Appearance: putty-fronted or bead finish; low-iron glass for clarity; crown/cylinder effect options to mimic historic waviness.
-
Joinery: careful rebating to accept slim units; re-cording/re-balancing sashes for added glass weight; reinforcement where needed.
-
Sealing: discreet brush seals and tuned clearances reduce rattles and light bleed.
-
Compliance: safety glass to critical locations; documented install, care and warranty.
Risks & considerations (we manage these for you):
-
Added weight: we re-cord and balance sashes or specify spring balances to maintain smooth operation.
-
Moisture & drainage: correct bedding/putty, ventilation and paint systems are essential for longevity.
-
Glazing bar geometry: very slim bars may need careful design or double-rebate solutions to maintain sightlines.
-
Planning/listed consent: required in many cases—alternatives like secondary glazing can be more readily approved while delivering strong thermal and acoustic gains.
Our process:
-
Survey & advice — measure sashes/boxes, assess timber condition, confirm feasibility and discuss consents.
-
Design & specification — glazing build-ups, sightlines, putty/bead profiles, safety glass and finishes for sign-off.
-
Consent support — drawings/specs for planning/listed building applications where required.
-
Workshop & installation — precise rebating, unit fitment, sealing; re-cording/re-balancing for smooth travel.
-
Finishing & handover — paint touch-in, operation checks and written care/warranty.
Lead times & pricing:
Typical lead time is 3–6 weeks from sign-off. Pricing depends on sash sizes, glazing build-up, joinery adjustments and any consent drawings. We provide a fixed, itemised quotation after survey.
Frequently asked questions:
Will it look like my original single glazing?
Yes—slim units are designed to keep narrow sight-lines and traditional putty lines so the upgrade is visually discreet.
What performance can I expect?
Manufacturer-quoted centre-of-glass Ug values for slim units typically range from ~2.6–1.2 W/m²K depending on thickness and gas fill; whole-window ratings vary with frame condition and installation quality.
Do I need permission?
In Conservation Areas it’s often case-by-case; in listed buildings, consent is usually required. Where double glazing isn’t approved, secondary glazing and draught-proofing are strongly supported conservation measures.
Is there a guarantee?
Yes—your quotation will state unit warranty and workmanship cover. Care guidance is provided at handover.
Related services:
Service areas:
Greater London including Islington, Camden, Hackney, Westminster, Kensington & Chelsea, Haringey and nearby Hertfordshire.
Get a quote:
Tell us about your property, sash sizes and any planning constraints. Contact us at: 02076093012