Double Glazing in South Africa

Start with the sealed unit

What are double glazed windows?

The separated panes and cavity reduce heat transfer compared with an otherwise comparable single pane. Low-emissivity coatings, the fill and the edge construction can improve thermal performance further. The completed window also includes its frame, opening parts and seals.

Two panes alone do not tell you how well a window performs. A sealed glass unit can still sit in a poorly performing frame or an opening with air leakage. Specify and compare the complete window, then check how it will be installed.

Treat it as a complete window

Glass and frame choices that matter

Start with the room and the problem. A cold bedroom, a sun-exposed living room and a room facing traffic may need different glass combinations, even in the same house. Give the supplier that brief before comparing options.

Choose the glass combination as well as the frame

• Low-e glass: a low-emissivity coating manages radiant heat transfer. Different coatings have different solar and daylight characteristics.
• Air or gas fill: ask what the quoted unit contains and which performance figures apply to it.
• Spacer and seals: include the edge construction in the specification and warranty discussion.
• Acoustic, safety or security requirements: describe these separately. The number of panes is not a complete specification for them.

For double glazed aluminium windows, ask explicitly about the frame’s thermal break. For any frame, also check handles, hardware, opening clearances, cleaning access and the finish you will need to maintain.

Compare the same measures

How to compare double-glazing performance

Ask for whole-window U-value and SHGC information for the quoted size and configuration, with the glass and frame identified. In South African aluminium systems, tools such as U-Solve evaluate those whole-window properties; a glass-only brochure is not the same comparison.

A low U-value helps limit heat transfer driven by the indoor–outdoor temperature difference. SHGC addresses sunlight entering as heat. Select them together with your local climate, orientation and shading rather than choosing the lowest number in every column. Include daylight and ventilation needs in the discussion.

Air leakage is a separate issue. Ask how the opening sections seal and how the frame-to-wall joint will be finished. For the broader meaning of thermal transmittance, read the U-value guide.

A window upgrade can improve comfort, but it does not guarantee a fixed electricity saving. The result depends on the existing windows, other heat-loss paths and how the home is heated or cooled. Compare the project with other existing-home insulation priorities before committing the budget.

Price the same finished job

Double glazed window prices in South Africa

A useful price needs a window schedule and a defined installation scope. Size, opening style, frame system, glass combination, access and finishing can all change the quotation. A price per square metre alone leaves important differences unresolved.

Include these details in every quotation

• Each opening: measured dimensions, quantity, opening direction and any fixed panels.
• The window system: frame profile, finish, glazing build-up and relevant performance information.
• Removal and access: old-window disposal, scaffolding or other access arrangements where needed.
• Installation and making good: perimeter joints, weatherproofing, plaster, paint, trims and any sill work.
• Commercial details: VAT, delivery, lead time, payment stages, warranties and exclusions.

For a renovation, ask whether repairing the existing frame or fitting a suitable replacement glazing unit is feasible before pricing a full replacement. Compare quotes on the same scope, then assess the difference against the problem you want to solve.

Assess what can be retained

Can existing windows be converted to double glazing?

Sometimes, but a thicker or heavier unit cannot simply be assumed to fit an existing frame. A glazing specialist needs to assess the available rebate, frame condition, support, hardware, drainage and the proposed glazing system.

1. Replace the glazing unit in a suitable frame. Ask the supplier to confirm compatibility and the resulting whole-window performance.
2. Replace the complete window. Consider this when the frame, operation or weatherproofing also needs upgrading.
3. Assess secondary glazing. A separate additional internal pane or panel is a different arrangement from a factory-sealed IGU. Discuss opening access, cleaning and moisture details.

Ask who takes responsibility for measurement, compatibility and the finished installation. A retrofit proposal should say what remains, what changes and which components the warranty covers.

If the budget or construction does not suit replacement, use the window-insulation guide to compare draught sealing, coverings and other improvements. Those options have their own roles; they do not turn every existing pane into the equivalent of a specified double-glazed window.

Set realistic expectations

Will double glazing reduce noise and condensation?

Noise: specify the sound problem

An acoustic glazing combination may use different pane thicknesses or a laminated pane. Tell the supplier whether the issue is traffic, voices or another source, and request appropriate tested information. A thermal U-value does not measure sound reduction; no single noise-reduction percentage applies to every double-glazed window.

Also assess gaps and other sound paths around the room. A well-specified pane will not address every route through which noise enters.

Condensation: identify which surface is wet

• Room-side glass: improved thermal performance can reduce cold-surface condensation, but indoor humidity and ventilation still matter.
• Between the panes: misting in the sealed cavity indicates a unit/seal problem. Ask the glazing supplier to inspect it and check the warranty.
• Outside surface: condensation can occur on efficient glazing in suitable weather conditions; it is different from moisture trapped inside the sealed unit.

Locate the moisture before deciding on a repair. Read the moisture-control guide for household humidity and condensation questions. Double glazing is not a substitute for resolving the source of excess moisture.

Make the specification reviewable

Before you order new windows

1. Write down the goal for each room. Separate winter comfort, sun control, noise, operation and appearance.
2. Confirm the survey and window schedule. Record opening sizes, frame choices, ventilation needs and access.
3. Compare evidence. Match the quoted glass and frame to whole-window thermal figures and any relevant acoustic information.
4. Agree the installation details. Identify responsibility for fixing, sealing, drainage, making good and checks at handover.
5. Keep the records. Retain the specification, invoice, care instructions and written warranty covering the unit, frame, hardware and installation as applicable.

For a new build or an alteration, have the responsible project professional confirm the applicable glazing, safety and energy requirements. Read the SANS 10400-XA introduction for energy-efficiency context; this guide does not establish a compliance specification for your windows.

At handover, check operation, visible damage, the agreed finish and the documentation. Follow the supplier’s cleaning and maintenance instructions, and keep drainage paths intended by the window system clear.

Common questions

Choosing windows with confidence