Crittall Secondary Glazing
Crittall and other slim steel-frame windows are architecturally defining — and thermally and acoustically poor. Secondary glazing keeps every original sightline intact and adds the performance the frame can't.
Why Crittall needs a room-side answer
Original Crittall frames are a 20 mm steel section holding a single 4 mm pane. There is no cavity to fill and no meaningful thermal break, so replacement double-glazed units either look wrong (heavier sightline) or lose the character entirely. Room-side secondary glazing leaves the steel frame visually unchanged from the pavement and outside.
Our Crittall specification
Slim-line aluminium hinged casement or horizontal slider set behind the original, with a 100 mm cavity for acoustic work or 50–75 mm for thermal-only. Powder-coated to match the interior reveal — most owners choose matte black to echo the Crittall frame.
- Hinged casement mirrors the original opening
- 6.4 mm laminated acoustic glass standard
- 50–200 mm cavity depending on target
- Matte-black RAL 9005 to match Crittall
Listed and conservation Crittall
Post-war Crittall installations in mid-century houses are increasingly locally listed. Room-side secondary glazing typically clears without formal consent because nothing changes on the elevation. We supply the survey pack a heritage officer will want to see.
Where it works
Mid-century semis and detached, converted warehouses and mills, 1920s–50s commercial fronts, garden-room extensions. We have installed on all of the above across Sheffield, Leeds and further afield.
Frequently asked questions
Replacement slim-DGU Crittall exists but the sightline thickens and the cost is 4–6× a room-side secondary install. On listed or characterful buildings we always recommend keeping the original and going secondary.
Ready for a free, no-obligation quote?
South Yorkshire's specialists in secondary glazing — survey, measure, manufacture and install.