top of page

​

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:

​

  1. Survey & advice — measure sashes/boxes, assess timber condition, confirm feasibility and discuss consents.

  2. Design & specification — glazing build-ups, sightlines, putty/bead profiles, safety glass and finishes for sign-off.

  3. Consent support — drawings/specs for planning/listed building applications where required.

  4. Workshop & installation — precise rebating, unit fitment, sealing; re-cording/re-balancing for smooth travel.

  5. 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​

​

bottom of page