This project in Howard Street, Kew, is special even by Sealasash standards. The home is of real heritage significance – it was once the residence of Sir Robert Menzies – and the brief was clear: dramatically improve comfort and performance without disturbing the character that makes the house so important.
Our solution was to retain the original timber windows and upgrade them with vacuum-insulated double glazing by Panasonic, combined with a full Sealasash core service and detailed repair work to extend their life for decades to come.
The Brief – Keep the Character, Upgrade the Performance
Across the home, there are 10 double-hung timber windows, each with arched top sashes and colonial bars. The client wanted:
- Better thermal performance and comfort
- Improved noise control
- Minimal visual change to the façade and interior
- A solution that respects the original joinery and heritage fabric
To achieve this, we specified:
Targeted timber repairs and sill replacements to address existing damage
Vacuum insulated glass by Panasonic (Glavenir) (6.1 mm annealed) to all sashes
A core service to restore smooth, reliable operation of the double hung windows
Detailed draught and acoustic sealing
Targeted timber repairs and sill replacements to address existing rot.
Working With Arches and Colonial Bars
The arched top sashes and colonial bars are a defining feature of the house. The client was clear that these elements must be retained.
On this project we will:
- Keep all existing colonial bar layouts so the windows look the same before and after the upgrade
- Carry out minor repairs to internal bars where needed
- Install new external bars to suit the new vacuum glass and maintain the original sightlines
- Create four unique arch templates to accurately reproduce each arch profile for the new glass
This templating work is critical with vacuum glass – each unit must be manufactured to exact dimensions, and any variation in the arch shape needs to be captured before production.ow has a complete thermal and acoustic envelope without altering its original look.
Core Service, Draught Sealing and Bottom Sash Design
All 10 windows will receive a full Sealasash core service, including:
- New staff bead and parting bead
- White brush and acoustic seals fitted to control draughts and airborne noise
- Adjustment and servicing to ensure the bottom sashes move smoothly and close tightly
One particular challenge on this house is the existing extended deep fixed staff bead at the bottom of the windows, which creates a pocket for the bottom sash to close into. This detail offers good potential for sealing, but it needed to be handled carefully.
All the new timber we supplied is sustainable & white primed to suit.
Repairing and Preserving the Original Timber
The brief includes substantial repair work to stabilise and extend the life of the original joinery:
- W3 – Living room:
- Major rot in the sill
- Sections to be cut out and replaced
- Repairs under parting beads and to the underside of the sill
- Four other windows:
- Major sill repairs under the parting beads and in the centre of the sills
- All 10 windows:
- Joint repairs to strengthen frame and sash junctions
These repairs are carried out using high-quality matching timbers and proven repair methods, so the windows retain their original profiles while gaining a new lease on life. See the before and after photo of W3 below.
Outcome for a Heritage Home in Kew
The completed Howard Street project delivered
- Vacuum-insulated performance from Panasonic’s Glavenir glass, significantly improving thermal comfort and reducing heat loss through the original timber windows
- Better acoustic comfort, helped by the combination of vacuum glass and acoustic brush seals
- Restored and strengthened timber windows, with sills and joints repaired rather than replaced!
- Unchanged character, with arched sashes, colonial bars and the overall façade reading exactly as it always has
For a home with the history of Sir Robert Menzies’ former residence, this balance is crucial: the building retains its original face to the street, but quietly gains the comfort, performance and longevity expected of a modern high-end home.
For more on how glass performance transforms efficiency, see our guide to understanding window performance.
