the property rather than relying on a standard double glazed unit for every situation.

​

​

Can Double Glazing Reduce Outside Noise?

 

Double glazing can reduce the amount of external sound entering a home, particularly when replacing single glazing or old windows with gaps around the frames. Closed, properly sealed windows are considerably more effective than open or poorly fitting windows because sound can travel readily through air gaps. Government guidance identifies windows, doors and ventilation openings as common weak points in a building’s resistance to outside noise.

​

However, standard thermal double glazing is primarily designed to reduce heat loss. It may improve comfort and provide some double glazing sound reduction, but it is not necessarily the most effective specification for a property exposed to heavy traffic, railway or aircraft noise.

​

Where noise reduction is an important objective, the glazing and complete window should be selected specifically for acoustic performance.

​

​

Are Double Glazed Windows Soundproof?

 

No ordinary domestic window can normally be described as completely soundproof.

​

When homeowners search for double glazed windows soundproof solutions, they are usually looking for a substantial reduction in intrusive noise rather than complete silence. Some sound may continue to enter through walls, roofs, doors, ventilation openings and other parts of the building even after the windows have been upgraded.

​

A realistic objective is to reduce the disturbance sufficiently to make conversations, television, relaxation and sleep more comfortable.

​

The degree of improvement will depend on:

​

• The existing windows

• The noise source

• The frequencies produced by that noise

• Window size and position

• Glass specification

• Frame and seal quality

• Ventilation openings

• Installation details

• The construction of the surrounding walls and roof

​

An installer should avoid promising that new windows will eliminate all external noise.

​

​

How Does Noise Enter Through Windows?

 

Sound can enter through both the glazing and the surrounding construction.

​

Potential routes include:

​

• Glass vibrating in response to sound

• Gaps around opening sections

• Worn or compressed window seals

• Poorly sealed frame perimeters

• Loose glazing units

• Trickle ventilators

• Air vents

• Thin window panels

• Poorly fitted external doors

• Open windows

​

Replacing the glass alone may therefore provide limited improvement if the frames remain draughty or the sound is entering through another weak point.

​

Historic England notes that draught-proofing can also help reduce noise because it closes the gaps through which air and sound can pass.

​

​

Standard Double Glazing Versus Acoustic Double Glazing

 

A standard double glazed unit commonly uses two similar panes separated by a sealed cavity. This can reduce outside noise compared with basic single glazing, particularly when the complete window closes tightly.

​

Acoustic glazing is designed more specifically to control sound transmission. It may use:

​

• Thicker glass

• Panes of different thicknesses

• Acoustic laminated glass

• A carefully selected cavity

• A combination of laminated and standard glass

• Higher-performance frames and seals

​

Pilkington advises that glass sound insulation can be improved by increasing pane thickness, incorporating laminated glass and increasing the distance between panes. Its technical guidance also explains that using panes of different thicknesses can help reduce resonance effects.

​

The best solution will depend on the noise source and the construction of the window.

​

​

Acoustic Laminated Glass

 

Acoustic laminated glass consists of layers of glass bonded around a specialist sound-control interlayer.

​

The interlayer helps absorb sound energy and reduce vibration through the pane. Acoustic laminated glass can be used as part of a double glazed unit, allowing the window to provide both thermal insulation and improved acoustic performance.

​

Glass manufacturers identify acoustic laminated glass as one of the most effective glazing options for higher levels of sound insulation.

​

It may be particularly useful for homes affected by:

​

• Busy roads

• Railways

• Aircraft

• Night-time street activity

• Commercial premises

• Schools or playgrounds

• Regular delivery or service vehicles

​

The glass should still be installed within a suitable frame with effective seals. High-performance glass will not compensate for significant air leakage around the window.

​

​

Why Different Glass Thicknesses Can Help

 

Two identical panes can respond similarly to particular sound frequencies. Using panes of different thicknesses can alter the way each pane vibrates and improve the unit’s performance across a wider range of frequencies.

​

For example, an acoustic unit might combine a thicker laminated pane with a different-thickness inner pane rather than using two identical pieces of standard glass.

​

This is why the number of panes alone does not determine performance. A properly designed double glazed unit can sometimes perform better acoustically than a poorly specified triple glazed unit. Pilkington advises that triple glazing is not automatically better for noise reduction and that the glass combination must be selected carefully.

​

​

The Gap Between the Panes

 

The separation between glazed layers affects acoustic performance.

​

Within a sealed double glazed unit, the cavity is limited by the window frame and the thermal specification. Increasing the distance between separate window layers can provide further benefits, which is one reason well-designed secondary glazing can be highly effective.

​

A wider gap should not simply be requested without considering the complete unit. Glass thickness, frame capacity, weight, thermal performance and manufacturer testing must all be taken into account.

​

​

Window Frames and Seals

 

Effective double glazed windows sound reduction requires a frame that closes tightly and remains stable.

​

Important features include:

​

• Continuous weather seals

• Correctly adjusted hinges

• Secure multi-point locking

• Suitable compression around opening sections

• Properly glazed sealed units

• Correct frame fixing

• Effective sealing around the opening

• Good-quality perimeter finishing

​

A window that is slightly misaligned may leave a small gap that allows a disproportionate amount of sound to enter.

​

Opening windows should be checked after installation to confirm that handles, hinges and locks pull the sash firmly against the seals without requiring excessive force.

​

​

Installation Quality

 

Even a well-specified acoustic window can underperform if it is badly installed.

​

The window must be accurately measured, adequately supported and securely fixed. Gaps between the frame and surrounding wall should be properly filled and sealed rather than concealed behind trims.

​

Particular attention may be required around:

​

• Uneven masonry

• Bay windows

• Older timber subframes

• Stone surrounds

• Window heads and sills

• Structural openings that have been altered

• Existing air vents

​

Ask whether the quoted acoustic performance applies only to the glass or to the complete tested window system. The finished installation is only as effective as its weakest component.

​

​

Trickle Vents and Ventilation

 

Acoustic performance is greatest when windows are closed, but homes still require adequate ventilation.

​

Replacement windows in England must satisfy Building Regulations requirements relating to ventilation as well as thermal performance, safety and means of escape. Background or trickle ventilators may be needed depending on the existing ventilation arrangements and the rooms being served.

​

A standard ventilator creates an intentional air path and can therefore affect the overall sound insulation of the window. In properties exposed to high outside noise, acoustic ventilators or an alternative ventilation strategy may need to be considered.

​

Do not remove or block required ventilation solely to reduce noise. Condensation, humidity and indoor air quality should be considered alongside acoustic comfort.

​

​

Secondary Glazing for Noise Reduction

 

Secondary glazing involves installing another glazed frame on the room side of the existing window.

​

Because the secondary panel can be separated from the original window by a considerably larger space than the cavity within standard double glazing, it can provide strong acoustic benefits when properly designed and sealed.

​

Historic England describes secondary glazing as highly effective at reducing noise and notes that it allows original windows to be retained.

​

Secondary glazing can be particularly useful where:

​

• Original timber windows should be preserved

• The building is listed

• The property is in a conservation area

• External window replacement is restricted

• Existing windows remain repairable

• A larger separation between glazed layers is required

• Road or aircraft noise is severe

​

The existing window should normally be repaired and draught-proofed as part of the installation. Large gaps or poorly closing original sashes can reduce the overall benefit.

​

​

Repairing Existing Windows

 

Complete window replacement is not always necessary.

​

Older windows may be improved by:

​

• Repairing damaged frames

• Adjusting opening sections

• Replacing worn hinges

• Renewing window seals

• Repairing catches and locks

• Sealing gaps around the frame

• Draught-proofing sliding sashes

• Replacing unsuitable glass

• Adding secondary glazing

​

Repair and secondary glazing may be especially appropriate for traditional timber windows that contribute to the appearance of a period property.

​

A specialist should inspect the windows before recommending replacement, particularly where the frames remain structurally sound.

​

​

Reducing Noise Through Doors

 

External doors can also allow substantial noise into a property.

​

A lightweight, poorly sealed door may reduce the benefit gained from upgrading nearby windows. Check:

​

• Seals around the door leaf

• The threshold

• Letter plates

• Keyholes

• Glazed panels

• Side lights and fanlights

• Frame-to-wall junctions

• Door alignment

​

Where a front door faces a busy street, a well-sealed replacement door or an enclosed entrance lobby may improve overall comfort.

​

​

Choosing Windows for Different Noise Sources

 

Different noise sources have different acoustic characteristics. Traffic, voices, aircraft and machinery do not all produce the same frequency range.

​

This means that a window advertised with a single acoustic figure may not perform equally well against every type of sound.

​

Ask the supplier for the tested performance of the complete proposed unit. Common ratings include:

​

• Rw: a weighted sound-reduction figure

• Rw + Ctr: a rating adjusted to give greater relevance to lower-frequency sources such as road traffic

​

These figures should be supported by product test information rather than an unsupported sales claim. Pilkington recommends selecting glazing for the particular noise profile and requesting test data where acoustic performance is important.

​

​

Should You Replace Every Window?

 

It may be possible to prioritise the rooms and elevations most affected by noise.

​

Typical priorities include:

​

• Main bedrooms

• Children’s bedrooms

• Front living rooms

• Home offices

• Windows directly facing a road or railway

• Upper floors exposed above boundary walls

• Rooms used during the noisiest periods

​

However, replacing only one window may provide disappointing results if noise continues to enter through an adjoining window, door or ventilation opening.

​

A room-by-room assessment can identify the principal sound paths before work begins.

​

​

Conservation Areas and Listed Buildings

 

Properties in conservation areas or listed buildings may be subject to restrictions on window replacement.

​

Secondary glazing, draught-proofing and repair may provide effective noise reduction while preserving the external appearance of original windows.

​

Listed building consent may be required where historic windows or internal features will be altered. Planning permission may also be needed where the replacement changes the external appearance or permitted development rights are restricted.

​

Establish the consent requirements before ordering acoustic windows or removing original frames.

​

​

Questions to Ask a Window Installer

 

Before accepting a quotation, ask:

​

• Is the glass specifically designed for acoustic performance?

• What are the glass thicknesses?

• Does the unit contain acoustic laminated glass?

• What tested sound-reduction rating is available?

• Does the rating relate to the glass or the complete window?

• Is the specification suitable for the particular noise source?

• How will the frame perimeter be sealed?

• Are acoustic ventilation options available?

• Would secondary glazing provide better results?

• Which guarantees and compliance certificates will be provided?

​

The quotation should clearly describe the glass build-up, frame system, opening style and ventilation arrangement.

​

​

Find Trusted Acoustic Window Installers

 

Successful double glazing sound proofing is based on careful assessment and appropriate specification rather than simply choosing the thickest or most expensive window.

​

APN Double Glazing can connect homeowners with experienced local installers for acoustic double glazing, laminated glass, replacement windows, improved window seals and secondary glazing.

​

Get in touch for expert advice and a free, no-obligation quote to help reduce outside noise in your home.

​

​