Secondary Glazing for Listed Buildings

Why it is the accepted option

Listing protects the whole building, inside and out, and the windows are usually among the most significant surviving features. Replacement units and slim double glazing both involve altering or removing historic joinery and glass, which is why applications for them are so often refused. Secondary glazing adds a separate independent window on the room side, leaves the original untouched, and can be taken out again leaving only fixing holes in later plaster. That reversibility is the whole argument.

Consent, in general terms

Listed building consent is required for works affecting the special interest of a listed building. Many authorities take the view that a well designed, reversible secondary glazing installation fixed into later linings does not require consent, while others ask for an application, particularly where the frame lands on historic joinery, where the window is decorative, or where the property is Grade I or II*. Conservation area status alone does not usually control internal work. The final answer belongs to your local conservation officer, and Historic England publishes the national guidance behind their decisions.

• Ask the conservation officer before ordering
• Grade I and II* usually warrant an application
• Reversibility is the point most often assessed
• We supply drawings and specifications free of charge

What conservation officers typically look for

In practice the same handful of things come up: how slim the frames are and whether they read against the primary glazing bars, whether the unit is set back into the reveal so it is invisible from the street, what it is fixed to, whether the finish is a recessive colour rather than bright white, whether the original window can still be opened and maintained, and whether the installation can be removed without damage. Meeting those points is a design decision made at survey, not an afterthought.

How we keep it reversible

Fixings go into later linings, plaster or the architrave wherever the reveal allows, never into historic glazing bars or sash boxes. We use mechanical fixings rather than adhesive systems, record fixing positions, and use a low modulus sealant that removes cleanly. Nothing is cut back, nothing is planted onto original joinery, and the panel sizes are set so the frames align with existing horizontal lines in the window.

• Fixings into later linings, not historic fabric
• Mechanical fixings, no bonded systems
• Sight lines aligned to existing glazing bars
• Recessive RAL finishes and heritage colours

Protecting fragile original glass

Cylinder blown, crown and hand drawn glass cannot be replaced like for like, and leaded and stained panels are vulnerable to impact, wind load and thermal shock. A room side pane shelters the historic glass from all three and reduces the temperature swing across it. On decorative windows we frequently specify a fixed or lift out panel with the slimmest available sight line so nothing competes visually with the original.

What to submit if consent is needed

Applications go through quickly when the paperwork is complete: a location plan, photographs of each affected window inside and out, a section drawing showing the frame position within the reveal and the fixing points, the product specification including frame profile, finish and glass, and a short heritage statement explaining reversibility and the lack of harm to fabric. We prepare the drawings and specification at no cost for any window we have surveyed.