6 Royal Parade

Project: 

Restoration and Retrofit of orginal Georgian and Victorian windows in a conversion project from office to domestic. 

Client: 

Spa Town Properties Ltd. 

The Challenge: 

Upgrading the thermal performance of Georgian sash windows, retaining the delicate glazing bars of the six over six fenestration while maintaining the historic aesthetic. Maintaining or reinstating a sense of historic glass on the front façade. The client was not keen on a secondary glazing route and so we decided on a high performance glazing retrofit once we had detailed additional reinforcement and decided on the capacity of the sashes and glazing bar profiles. Since we were effectively at least doubling, possibly trippling, the glass weight of the window sashes with two pieces of 4mm glass replacing a single piece of glass at varying thicknesses, some as thin as 2mm.  We had to come up with a satisfactory metal reinforcement solution for the mid rails of the top sashes since they did not have the later horn reinforcement of later sindow sashes. We were worried that the traditional dove tailed open tenon joint of the georgian sashes would not be robust enough for prolonged use and the material taken from the glazing bars would render them too slender to reliably relieve that weight from those stress points. 

The Solution: 

Using our specialized workshop facilities, we stripped all paint and putty and extracted all glass. We then dismantled all sashes, adjusted their rebates to accommodate the new glazing and repaired all rotten aspects with reclaimed pitch pine. We specified a discrete metal strapping solution with stainless steel screws which were rebated into the lower corners of the sashes and then capped with a sympathetic piece of timber. We glazed the sashes with individual slim-line IGUs which were krypton-filled with kiln-distorted glass. The larger windows are possibly the largest kiln-distorted glass units in the country requiring an oversized kiln and custom glass sheet size. These units have a centre pain U-value of 1.4. We were really happy with our commitment to historically sympathetic materials and discreet retrofit solutions. Harrogate conservation officers were happy with our material choices and methodology which meant a swift and pain free process to get approval and onto site for our client.  Painted in Linseed oil paint from Brouns & Co and sealed with oakum and burnt sand mastic, the windows now stand proud overlooking the Pumphouse.