Glass and Glazing

“What type of glass / glazing units can my property have?”

This is one of our most frequently asked questions. There are a few things to consider when looking at glazing options and possible restrictions based on for your property.

Unit Thickness
Glass Make up
Unit Sightlines
Astragals Types

The Unit Thickness is determined by the turn out size of the glazing check in the glazing frame. This is calculated by deducting the profile mould, glazing tape and glazing bead sizes from the overall frame thickness. On our Sash and Case windows, the overall sash thickness is 50mmm - The maximum standard double glazed unit is thickness is 20mm and 14mm for heritage double glazing because the profile mould is deeper to be more in keeping with a single glazed profile mould.

Glass Make up is determined by two main components - the glass thickness and the cavity size and spacer bar options (usually increments of 2mm) The glass make up is usually noted as;

Inner pane thickness and type / Cavity thickness / Outer pane thickness and type

6.4mm Laminate Safety Glass / 6mm Black Spacer Bar / 4mm Toughened Safety Glass

The Unit Sightline is the border/depth of seal that secures the two pieces of glass together to form a glazed unit. Standard Double Glazing typically has a 12mm sightline and is glazed into a 16mm glass check, whereas Slim Heritage Double Glazing has been designed with a Slim Sightline of around 7mm so can be glazed into a smaller glass check.

Astragals Types are typically the thin piece of decorative moulds that divide up a larger glazing area into smaller panes. This can be accomplished in two ways;

Solid Astragals - The traditional method which mainly applies to Single Glazing, Slim Heritage Double Glazing and Fineo Glass. Traditionally used in period and Category listed buildings

Plant on astragals - which are used alongside Back-to-Back Spacer bar grids incorporated inside standard double glazed units. This method replicates the overall final appearance of traditional astragal. Typically permitted in modern and conservation properties.

The information below in a general guide and you should always reviewing your local councils guidelines before making the decision to changing any glass types.

Double Glazed Unit Diagram

24mm Solid Ogee Astragal

Slim Heritage Double Glazing Unit

24mm Solid Ogee Astragal /

Fineo Glazing Unit

GLAZING OPTIONS

Single Glazing -

No longer as popular as it used to be but however still a common glazing method. A vast variety of single glazed patterned or obscure glass are available.
Slight Line -

N.A
Our Most Common Make Up's -

4mm Float

4mm Tough
Comments;

Typically only older properties have single glazing as double glazing is more thermal efficient and offers better acoustic values.
Suitable for;

- Historical or Period

- Category Listed Properties

- Conservation
Manufacturers Guarantee -

N.A
Astragal Type -

19mm - 21 Solid / Through Astragals - Ogee Mould

Edinburgh, Lambs Tongue, Gothic Arch also available
Glazing Methods;

- Traditional Putty Option or

- Dry Glazing System with Angled Timber Glazing Beads
Standard Double Glazing -

Standard double glazing offers an excellent balance between energy efficiency and cost. Incorporating a range of design styles, safety glass, acoustic glass and spacer bar options.
Slight Line -

12mm
Our Most Common Make Up's -

4mm Float / 12mm Cavity / 4mm Float Lowe and Argon

4mm Tough / 12mm Cavity / 4mm Tough Lowe and Argon

4mm Tough / 12mm Cavity / 6.4mm Laminate Lowe and Argon
Typical Centre Pane U-Value -

4/12/4 with Lowe and Argon Gas: 1.4
Astragal Type -

21mm Back to Back Spacer with Plant On Astragals

46mm Solid Astragals
Suitable for -

- A clear choice for conservation properties

- Other property types that do not hold a listed property status
Manufacturers Guarantee -

5 + Years from date of suppliers invoice
Astragal Type -

21mm Back to Back Spacer with Plant On Astragals

46mm Solid Astragals
Glazing Methods -

Dry Glazing System with Angled Timber Glazing Beads
Heritage Double Glazing -

Heritage double glazing offers a much needed option for more energy efficient glazing in listed properties. Incorporating a range of design styles, safety glass, acoustic glass.
Slight Line -

7-8mm
Our Most Common Make Up's -

4mm Float / 4mm Cavity / 4mm Float Lowe and Argon

4mm Tough / 6mm Cavity / 4mm Tough Lowe and Argon

4mm Tough / 4mm Cavity / 6.4mm Laminate Lowe and Argon
Typical Centre Pane U-Value -

4/6/4 with Lowe and Argon Gas: 1.2

4/6/4 with Lowe and Krypton Gas: 1.0
Comments -

Currently the most economical double glazing option for listed properties but not the most impressive in regards to noise pollution or heat retention.
Suitable for -

- Historical or Period

- Category Listed Properties

- Other property types
Manufacturers Guarantee -

5 Years from date of suppliers invoice
Astragal Type -

23mm Solid / Through Astragals - Ogee Mould

Traditional widths of Ogee, Edinburgh, Lambs Tongue, Gothic Arch also available
Glazing Methods -

- Traditional Putty Option or

- Dry Glazing System with Angled Timber Glazing Beads
Fineo -

With the performance levels close to triple glazing but with the profile of thick single glazing a boasting an extensive guarantee. Fineos vacuum glass is certainly the most technologic advanced and is worth considering if it fits within your projects budget.
Our Most Common Make Up's -

4mm Float / 4mm Float

Lowe and Argon

4mm Tough / 4mm Tough

Lowe and Argon
Slight Line -

8mm
Typical Centre Pane U-Value -

Comments -

Boasting a Quieter, Warmer and Greener Enviroment
Suitable for;

- Historical or Period

- Category Listed Properties

- Conservation Properties

- Modern Properties
Astragal Type -

23mm Solid / Through Astragals - Ogee Mould

Edinburgh, Lambs Tongue, Gothic Arch also available

Plant On Astragals can also be used
Glazing Methods;

- Traditional Putty Option or

- Dry Glazing System with Angled Timber Glazing Beads
Manufacturers Guarantee -

15 Years from date of suppliers invoice
Supplier Website:

https://www.energlaze.co.uk/

DECORTIVE GLASS - SUPPLIER INFO

Pilkington is on of the leading glass manufacturers in the world and set the industry standard for alot of glass products such as obscure or textured glass.

Pilkingtons Optifloat, Canterbury and Stippolyte are our clients most popular choice of obscure glass but they offer a variety of designs.

(please note some design my not be available in the uk)

https://www.pilkington.com/en-gb/uk/householders/decorative-glazing
Barron Glass specialises in the manufacture of Etched Glass Designs and other decorative glass for traditional & contemporary spaces

https://www.barronglass.co.uk

Available as cut to size (sheet size 1120 x 2140 mm). Thicknesses: standard 4mm and safety glass (5 mm or 7mm laminate - we do not recommend that our glass be toughened). All patterns also available in a fully opaque version suitable for locations where complete privacy is required (laminate only).
Forsyth Glazing: Being Scotland’s leading and largest specialist in providing decoration on glass we can accommodate the majority of designs presented to us. We can apply the following:

Lead & Coloured Film

Bevels

Brilliant Cut Lines

Sandblast Designs

https://www.forsythglazing.co.uk/decorative-glass-quote-request/

SAFETY GLASS

Toughened Glass -

The glass is heated to very high temperatures (around 600–700°C) and then rapidly cooled, this make it much more resistant to impacts, bending, and thermal stress compared to regular (annealed) glass. When it fails, it breaks into small, blunt chunks instead of dangerous sharp shards—this is why it’s considered a safety glass.
Toughened Glass -

4-5 times stronger than standard annealed glass
Comments -

- Historical or Period

- Category Listed Properties

- Conservation
Laminate Glass -

Laminated glass is primarily used to address safety and security concerns. It consists of a minimum of two layers of glass bonded together with a thin PVB interlayer. This construction gives laminated glass its key advantage: even when cracked—whether through accidental impact or repeated manual attack—the glass remains intact rather than shattering. This helps delay forced entry and reduces the risk of injury.

For this reason, we always recommend the use of laminated glass in skylights, roof lanterns, and cupolas, where it prevents broken glass from falling from above and enhances overall safety
Common Thicknesses -

6.4mm Standard

8.8mm Standard

6.8mm Acoustic
Glazing Methods;

Dry Glazing System with Angled Timber Glazing Beads
Comments -

Can be used in most single, double and triple glazed applications
Fire Glass Scotland

There are many manufactures, types and thickness of fire glass that all come with different ratings regarding Integrity and Integrity & Installation. Fire Glass Scotland is a leading importer and supplier of fire glass in Scotland with excellent technical support.

https://www.fireglassuk.com

Solid 24mm Ogee Astragals

Heritage Double Glazed

4mm Toughened / 6 Cavity / 4mm Toughened - Low'e and Krypton Glas