Double glazing
The term 'glazing' refers to the glass component of a building's façade or internal surfaces.
Historically, the external windows of buildings were generally single glazed, consisting of just one layer of glass, however, a substantial amount of heat is lost through single glazing, and it also transmits a significant amount of noise, so mulit-layerd glazing systems were developed such as double glazing and triple glazing.
Double glazing comprises two layers of glass separated by a spacer bar (also known as a profile); a continuous hollow frame typically made of aluminium or a low heat-conductive material. 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. This space is filled with air or with a gas such as argon, which improves the thermal properties of the window. Larger cavities may be provided to achieve greater sound reduction.
A desiccant in the spacer bar absorbs any residual moisture within the cavity, preventing internal misting as a result of condensation.
U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are used to measure how effective elements of a buildings fabric are as insulators. That is, how effective they are at preventing heat from transmitting between the inside and the outside of a building. Typically, the U-value of single glazing is around 4.8 to 5.8 W/m²K, whilst double glazing is around 1.2 to 3.7 W/m²K. NB Triple can achieve a U-value below 1 W/m²K.
Thermal performance is affected by the quality of the installation, the inclusion of thermal breaks in the frame, suitable weather seals, the gas used to fill the units, and the type of glass used. Low-e glass has a coating added to one or more of its surfaces to reduce its emissivity so that it reflects, rather than absorbs, a higher proportion of long-wave infra-red radiation..
The sound reduction achieved by single glazing (6 mm thick) is typically around 27 dB, whilst double glazing (100 mm air space) is around 42 dB.
The sound reduction achieved by double glazing is affected by:
- Good installation to ensure airtightness
- Sound absorbent linings to the reveals within the air space.
- The weight of glass used – the heavier the glass, the better the sound insulation.
- The size of air space between layers - up to 300 mm.
[edit] Related articles on Designing Buildings Wiki
- Air tightness in buildings.
- BFRC window rating scheme.
- Choosing the correct glazed facade heating system.
- Conservation rooflights.
- Domestic windows.
- Double glazing v triple glazing.
- Glass.
- Glazing.
- Low-E glass.
- Sash windows.
- Secondary glazing.
- Thermal conduction in buildings.
- Triple glazing.
- Types of window.
- U-values.
- Window.
Featured articles and news
Introducing or next Guest Editor Arun Baybars
Practising architect and design panel review member.
Quick summary by size, shape, test, material, use or bonding.
Types of rapidly renewable content
From forestry to agricultural crops and their by-products.
Terraced houses and the public realm
The discernible difference between the public realm of detached housing and of terraced housing.
Put digitalisation and sustainability at the core of curricula
Project management educators are urged.
Looking back at the influence of climate events
From a designer and writer: 'There are limits to growth but no limits to development'.
Terms, histories, theories and practice.
Biophilic design and natural light
Letting in the light and natural elements into spaces.
APM Programme Management Conference 2024
Strategies for Success.
Residential takes the reins as contract awards even out
Contracts down, but remain above the last quarter of 2023.
Celebrating Eid and the largest mud-brick building.
Barry Kingscote claims prestigious CIOB CMYA Award.
The British Mosque: an architectural and social history
The story of some 1,500 mosques or more in Britain.
Heat pump refrigerants, efficiencies and impacts
R12 to R1270 what are the differences?
Global heat pump market in 2023
Challenging times with positive but modest outlook.
Beyond the infrastructure pipeline
Opportunities and chokepoints.
Comments