Single glazing v double glazing
The term 'glazing' refers to the glass components of a building's façade or internal surfaces. Historically, windows were generally single glazed, consisting of just a single layer of glass, today there are many different options for glazing. A substantial amount of heat is lost through the window, and so double and triple glazed units have been developed to provide more insulation, improving the energy efficiency of a building.
The building regulations in England and Wales require that new and replacement window units must meet certain energy efficiency requirements. Approved Document L of the building regulations classifies an external window as a 'controlled fitting', which refers to the whole unit including the frame. New and replacement windows in existing homes in England, Wales and Scotland must have a Window Energy Rating (WER) of at least band C or have a U-value of no more than 1.6 W/m²K. This is intended to reduce heat transfer, and so the requirement for heating or cooling, resulting in lower energy consumption and lower carbon emissions.
Single glazing comprises one layer of glass, bedded into the window frame. Single glazing is sometimes fixed with linseed oil putty and secured with glazing nails into the frame. Glazing beads can further secure the glass and may be screwed and glued to the frame. If the window frame is timber it must be painted or otherwise treated to avoid water ingress. Typically, single glazing can achieve a U-value of around 4.5 W/m²K. The sound reduction achieved by single glazing (6 mm thick) is typically around 27 dB
Double glazing comprises two layers of glass separated by a spacer bar and a continuous hollow frame typically made from aluminium or UPVC or some other low heat-conductive material such as timber. The spacer bar is bonded to the panes using a primary and secondary seal which creates an airtight cavity, typically with 6-20 mm between the two layers of glass. Larger cavities may be provided to achieve greater sound reduction. The space is filled with air or with a gas such as argon, which improves the thermal properties of the window. Good double glazing can achieve a U-value of around 1.2 W/m²K. The sound reduction achieved by double glazing (100 mm air space) is around 42 dB
For more information see: Single glazing and Double glazing.
Double glazing provides benefits, such as improved thermal comfort and better acoustic performance and increased security as well as reduced solar gain in the summer and a reduction in the occurrence of condensation. However, it is more expensive, heavier and may be more difficult to instal.
Single glazing might be beneficial in climates or building types that do not require heat retention, such as storage facilities.
A more economical option to replacing single glazed windows can be to instal secondary glazing. Secondary glazing involves the installation of an additional pane or panes of glass and a internal frame to existing windows. This can be used be used to improve sound insulation and to reduce heat loss and draughts through windows, or in situations where it is not permitted to change existing glazing such as listed buildings.
Secondary glazing may be suitable for:
- Listed buildings, period properties and heritage/conservation areas.
- Areas where there is traffic noise (such as hotels on main roads).
- Properties where it may be uneconomical to instal double glazing.
- Properties where it would be difficult to modify existing external windows (such as single glazed timber sash windows).
- Windows that require noise reduction, draught reduction.
[edit] Related Articles on Designing Buildings Wiki
Featured articles and news
Retrofit 25 – What's Stopping Us?
Exhibition Opens at The Building Centre.
Types of work to existing buildings
A simple circular economy wiki breakdown with further links.
A threat to the creativity that makes London special.
How can digital twins boost profitability within construction?
The smart construction dashboard, as-built data and site changes forming an accurate digital twin.
Unlocking surplus public defence land and more to speed up the delivery of housing.
The Planning and Infrastructure Bill
An outline of the bill with a mix of reactions on potential impacts from IHBC, CIEEM, CIC, ACE and EIC.
Farnborough College Unveils its Half-house for Sustainable Construction Training.
Spring Statement 2025 with reactions from industry
Confirming previously announced funding, and welfare changes amid adjusted growth forecast.
Scottish Government responds to Grenfell report
As fund for unsafe cladding assessments is launched.
CLC and BSR process map for HRB approvals
One of the initial outputs of their weekly BSR meetings.
Architects Academy at an insulation manufacturing facility
Programme of technical engagement for aspiring designers.
Building Safety Levy technical consultation response
Details of the planned levy now due in 2026.
Great British Energy install solar on school and NHS sites
200 schools and 200 NHS sites to get solar systems, as first project of the newly formed government initiative.
600 million for 60,000 more skilled construction workers
Announced by Treasury ahead of the Spring Statement.
The restoration of the novelist’s birthplace in Eastwood.
Life Critical Fire Safety External Wall System LCFS EWS
Breaking down what is meant by this now often used term.
PAC report on the Remediation of Dangerous Cladding
Recommendations on workforce, transparency, support, insurance, funding, fraud and mismanagement.
New towns, expanded settlements and housing delivery
Modular inquiry asks if new towns and expanded settlements are an effective means of delivering housing.