TLX Gold insulation: the over-rafter, breathable multifoil

What it is

A 2-in-1 insulating breathable membrane: a high-tensile breather membrane forms the top surface and a reflective, vapour-open underside faces a 10mm-minimum unventilated air layer below. The manufacturer states whole-product breathability figures and holds BBA certification and LABC registered detail status. Because the underside is vapour-open, no separate vapour barrier is required below the rafters in the manufacturer's build-ups — useful where an existing ceiling stays in place.

Where it fits

• Re-roofing of terraces and semis where the roof height cannot be raised: Gold is draped into the rafter space, so no counter-battens are needed.
• Where headroom matters: the manufacturer notes that counter-battening Gold over the rafters maximises internal head height when the roof can be raised.
• Shallow old rafters that cannot take deep board — Gold adds insulation at the coldest point of the roof.

Rafter depth and the build-up

Draped, the product plus its natural drape plus the 10mm minimum unventilated air layer needs roughly the top 50mm of the rafter space. Insulation between the rafters — PIR or mineral wool — goes below that, with TLX Silver under the rafters where a hybrid build-up is specified. The manufacturer gives worked examples, such as Gold over 185mm rafters with 125mm PIR between to reach 0.18 W/m²K; the figure for your roof comes from its calculation.

TLX Gold vs TLX Silver

Gold is the cold-side, breathable layer; Silver is the warm-side, airtight vapour control layer. Used together they make a manufacturer-described hybrid roof. Fitting Silver where Gold belongs — over the rafters — creates a vapour barrier on the cold side and a condensation risk the manufacturer itself warns against.

Pros

• Adds insulation from outside during a re-roof with no internal work and no headroom lost.
• Replaces the breather membrane, so no extra layer to buy or fit.
• Vapour-open: works with an existing ceiling and no separate VCL.

Limitations

• Needs the covering off — not an internal retrofit product.
• Its own resistance is modest; a target normally needs insulation between or under the rafters as well.
• The 10mm air layer beneath it must be kept; over-filling the rafter space with board defeats it.

Alternatives

A conventional breathable membrane plus internal insulation; other breathable multifoils marketed for over-rafter use (for example SuperFOIL's breathable variant and the BreatherQuilt product now under SOPREMA). Compare on the certificate, the whole-product breathability figure and the required rafter space.

Questions homeowners ask