Sash Window Painting on Belsize Avenue: Restoration Case Study

Belsize Avenue is one of the grandest residential streets in Belsize Park, lined with imposing Victorian terraces built in the 1870s and 1880s. The original timber sash windows on these NW3 properties are an essential part of their character, but after 140 years of London weather, many need careful restoration and repainting. This case study documents a recent project on Belsize Avenue where we restored and painted 18 sash windows across the front and rear of a four-storey terraced house.

The Initial Assessment

When we first inspected the property on Belsize Avenue, the sash windows had not been properly maintained for over 20 years. Multiple layers of cracked and peeling paint covered the frames and sashes. Several lower sashes had rotten timber at the bottom rails where water had pooled. Sash cords had broken on many windows, leaving them inoperable or propped open with wooden blocks. The original crown glass had survived in most upper sashes, but several panes in the lower sashes had cracked.

Despite these issues, the windows were fundamentally sound. The frames were made from dense-grain pine that, apart from the localised rot, remained structurally solid. Restoration was clearly the right approach — replacement with modern units would have required planning permission, cost significantly more, and diminished the character of this handsome Belsize Park terrace.

The Restoration Process

Each window was restored individually over two days. Day one involved removing the sashes, stripping all old paint using infrared heat, cutting out rotten timber and splicing in new matching sections, and replacing broken sash cords. We used pre-stretched sash cord and cleaned the original cast-iron weights before rehung them. Any cracked glass was replaced with period-appropriate horticultural glass that closely matches the slight waviness of original Victorian glass.

Day two was dedicated to priming, undercoating, and applying two finish coats using Dulux Weathershield Exterior Satin in Brilliant White. This product offers excellent adhesion to timber, resists cracking and peeling, and maintains its colour well despite UV exposure. Each sash was painted before refitting, ensuring every edge and rebate was fully sealed against moisture ingress.

Draught-Proofing and Performance

As part of the restoration, we fitted Sealmaster draught-proofing to every window. Brush strips were installed in the sash channels, and compression seals were fitted to the meeting rails and the top and bottom of each sash. The homeowner reported a noticeable improvement in comfort and a reduction in heating costs following the work.

Results and Costs

The complete restoration of 18 sash windows on this Belsize Avenue property took three weeks and cost £9,800 including all materials, scaffold hire for the front elevation, and draught-proofing. The homeowner was delighted with the result — the windows looked as good as new, operated smoothly, and were properly sealed against draughts for the first time in decades.

If your Belsize Park property needs sash window restoration and painting, call us on 020 3874 2670. We provide free window assessments and can advise on the most effective approach for your NW3 home.