Bifold door glass options

Double vs triple glazing

The default for UK bifold installations is double glazing — two panes of glass with a 16mm or 20mm argon-filled gap between them. This achieves U-values of around 1.2 W/m²K with a low-E coating, which is excellent.

Triple glazing adds a third pane and a second gas-filled gap, taking the U-value down to around 0.7 W/m²K. The catch: triple glazing is significantly heavier (around 50% more), more expensive (+£500–£800 per door set), and the marginal improvement is small in real-world terms.

Specify triple glazing if: Passivhaus certification, very exposed/cold location (Scottish Highlands, North Sea coast), or local regulatory requirements demand it. Otherwise, well-specified double glazing is sufficient.

Low-E coatings (always specify)

Low-emissivity (low-E) coatings are microscopically thin metal oxide layers applied to one of the internal surfaces of the glass. They reflect long-wavelength infrared (heat) back into the room while letting short-wavelength solar radiation through.

Effect: a low-E double-glazed unit performs roughly as well as standard triple glazing without the weight, cost or sightline penalty. Every modern bifold should have low-E coating as standard — if a quote doesn't specify it, ask.

Solar control glass

Solar control glass has an additional coating designed to reflect solar heat (not just trap room heat). This prevents summer overheating in south-facing installations.

Specify if: south-facing bifolds, especially in extensions with limited shade or ventilation. The "garden room becomes a greenhouse in summer" problem is almost entirely a solar control glass problem.

Two approaches: online coatings (applied during manufacture, robust, slightly tinted appearance) and off-line coatings (sputtered on later, more selective spectral filtering, can look almost clear). Quality systems offer either.

Acoustic glass

Acoustic (or laminated) glass uses a PVB (polyvinyl butyral) interlayer between two glass panes, dampening sound transmission. Reduces noise by 5–10 dB compared to standard double glazing.

Specify if: the property faces a busy road, railway line, airport flight path, or has significant outdoor noise (commercial premises, busy pubs nearby). The cost adder is modest — typically £150–£300 per door set.

Note: any laminated glass is also more secure than toughened — harder to break through, even after the outer pane is broken — so acoustic glass doubles as a security upgrade.

Privacy glass

Several options for installations where you need to block visibility while keeping light:

• Obscure glass: textured rolling on one surface during manufacture. Permanent, range of patterns from "subtle" to "opaque". Used in bathrooms historically but works for any privacy-conscious installation.
• Frosted glass: similar effect via acid-etching or sandblasting. Often custom patterns (logos, designs).
• Switchable glass (PDLC — polymer dispersed liquid crystal): clear when electric current is applied, opaque when off. Expensive (£800+ per panel) but spectacular. Used in high-end installations where privacy is intermittent.
• Reflective glass: mirror-finish externally during daylight, transparent at night unless internal lights are on. Niche use.

Self-cleaning glass

Pilkington Activ is the established self-cleaning glass — a thin coating that uses UV light to break down organic dirt (the photocatalytic effect), then water (rain) sheets it off rather than beading.

Specify if: upper-floor bifolds where cleaning access is awkward, large installations where regular cleaning is impractical, coastal locations with salt deposits. Cost adder: roughly £100–£200 per door set.

Limitations: it's not magic — heavy dirt, fingerprints, water spots from hard water still need physical cleaning. But maintenance interval extends from monthly to roughly quarterly in typical conditions.

Safety glass — when it's required

UK Building Regulations (Part K) require safety glass in any glazed area where impact is likely. For bifold doors:

• Any pane below 800mm from finished floor level → must be safety glass
• Any pane within 300mm of a doorway, regardless of height → must be safety glass
• In practice: every pane in every bifold door panel must be safety glass

Two safety glass types: toughened (heat-treated, breaks into small blunt pieces) and laminated (PVB interlayer holds pieces together if broken). For external doors at risk of attempted forced entry, laminated is more secure.

U-value targets to know

• 1.6 W/m²K — minimum for Building Regulations Part L compliance (replacement doors)
• 1.4 W/m²K — typical aluminium bifold with quality double glazing + low-E
• 1.2 W/m²K — high-spec double glazing with argon fill + warm-edge spacers
• 0.8 W/m²K — triple glazing with krypton fill (Passivhaus-grade)
• 0.6 W/m²K — premium triple-glazed with quad coating + krypton (rare in bifolds)

What we'd typically specify

For a standard residential bifold installation in the UK Midlands:

• Double-glazed sealed units, 28mm overall thickness
• 4mm outer toughened + 20mm argon gap + 4mm inner toughened
• Low-E coating on surface 3 (internal-facing inner pane)
• Warm-edge spacer (not aluminium)
• Low-iron clear glass (no green tint)

This gives U-value around 1.2 W/m²K, excellent acoustic performance, full Part K compliance, and clear (not tinted) glass. Adds about £200–£400 above bottom-spec double glazing — worth it for the quality difference.