d12 thin double glazing

HD12: 12mm Thin Double Glazing

At just 12mm thick, D12 offers an ultra-slim solution for replacement windows on period properties. Popular with many planning authorities, Histoglass Thin Double Glazing is ideal even for listed buildings.

D12 offers superb aesthetics, astonishing durability, and significant acoustic and thermal insulation properties compared to standard single glazing. It meets all 6 parts of the BS EN 1279 standard, and is covered by a 7-year manufacturer’s warranty. Read more about the benefits of Histoglass Thin Double Glazing.

Thermal Insulation

Histoglass HD12 replacement double glazing will cut energy loss by around 67% when compared to single glazing:

Ug (W/m2K)
Histoglass HD12 1.5
Single glazing 5.8


Technical information

Inner pane: 3mm Low-E float
Cavity/spacer bar 6mm (gas-filled)
Outer pane 3mm
Ug 1.5 (W/m2K)
Weight 15kg/m2.

Review our technical documents relating to Thin Double Glazing. Please note that having your glass toughened will slightly increase thickness and may, therefore, not be 12mm overall anymore and become HD12/13.


Maximum pane sizes

Square 1100x1100mm
Rectangular 700x1400mm
Note that the maximum size for any pane made from cylinder glass is 800x800mm.


Glass types

  • The inner (interior) pane is always float glass with a low-emissivity coating.
  • The outer (exterior) pane can be chosen from float glass or any of our historic glass types
  • Both inner and outer panes can be specified as toughened and laminated glass, depending on the glass type.
  • Toughened glass is always 4mm thick, so it will affect your unit’s thickness.

Rebate depths

  • On new frames, the ideal rebate is 21mm and the width of the glazing bar should be 24mm
  • See HD12’s optimal dimensions
  • For clearance, we recommend 1.5mm on all 4 sides (so 3mm in both the width and height)
  • Create an additional seal by allowing the paint to overlap onto the glass by 1-2mm.


Specification & installation

  • To maintain our 7-year warranty, we supply Kawo Elastokitt bedding compound with all our glazing orders. Whilst this can also be used as a putty finish, we recommend linseed putty / glazing bead to achieve a more traditional look and feel.
  • Within the thin double glazing units, the aluminium spacer bar is supplied as standard in either black or white. However, to match your window frames, we can supply other RAL colours on request for an additional charge.


HD12 still not suitable?

For technical and planning reasons, some windows just can’t be fitted with Histoglass Thin Double Glazing. That’s the time to consider our MONO single-glazing system.  MONO delivers substantial thermal and acoustic insulation benefits, and comes in a range of period glass types to suit your period property.