SuperFOIL SF19+ for London Lofts, Terraces and Extensions: A Practical Guide

London's roofs are rarely simple. A Victorian or Edwardian terrace often has a steep main roof, a lower back addition, a flat-roofed rear extension and perhaps a loft that someone converted decades ago. Each of those needs a different insulation answer. This guide looks at where SuperFOIL SF19+ multifoil insulation fits on typical London jobs, where it doesn't, and what the rules say in England.

For the full technical background (layers, R-values, certification and fixing rules) read our complete SuperFOIL SF19+ guide. This article is the London-specific version.

Quick answer

• SF19+ is a light, flexible 11-layer multifoil roll (45mm nominal). It suits rafter-level and flat-roof jobs on awkward, uneven London structures, where a roll is easier to handle than rigid board.
• It relies on air gaps either side to perform, and those gaps take up depth. Where headroom is very tight, PIR board usually gets more insulation into less space.
• If you have plenty of depth, or a plain cold loft, mineral wool or PIR board is usually the better and simpler choice.
• Loft conversions need Building Regulations approval, and may need planning permission, a party wall agreement or both.
• We deliver to England only, and rolls are light enough to carry up a typical terrace staircase.

Why London homes are a special case

Older homes make up a large share of England's housing. The government's English Housing Survey (2024 figures) reports that 20% of owner-occupied homes and 32% of privately rented homes in England were built before 1919. Those figures are national, not London-only, but anyone who has worked on London terraces will recognise the pattern: solid brick walls, shallow rafters, chimney breasts, and tight access.

Those features make every insulation choice a trade-off between performance, depth and handling. A roll is easy to carry up a narrow staircase and can be cut around awkward timbers. Rigid board gets more resistance from less thickness but is harder to scribe around uneven rafters. Which wins depends on your roof.

Loft rooms and rafter-level insulation

A converted loft in a terrace is mostly rafters, dormer cheeks, dwarf walls and sloping ceilings. Fitting SF19+ under the rafters works as follows, per the manufacturer's installation guide:

• Overlap neighbouring rolls by at least 50mm and tape every joint, edge and penetration.
• Staple at intervals of no more than 300mm, then fix counter-battens at no more than 600mm centres.
• Keep an air gap on both sides of the foil. The air gaps are what let the reflective layers work.
• Maintain existing roof ventilation, and consider the ventilation requirements of Part F.
• Check for asbestos before disturbing old materials, and check the roof, gutters and rainwater goods first.

Dormer cheeks, dwarf walls and awkward corners are where the roll's flexibility helps, because it can be cut and folded around timbers. Roof windows and penetrations need care: they must be fully surrounded, taped and battened as the guide describes.

One practical point for terraces: SuperFOIL cannot be walked on. Fit it from below, or do not leave it exposed where someone might step.

Flues, chimneys and fire

London terraces often have chimney breasts and old flues running through the roof space. SF19+ has a low fire classification (Class F on its declaration of performance, and Class E as a complete wall system under its Kiwa Agrément), so it needs care. The Kiwa certificate says the wall system should be separated from heat-producing chimneys, ductwork and flue pipes, should not touch heat sources above 80°C, and should be covered by a plasterboard lining with taped joints. Apply the same caution to a roof. If your loft conversion involves protected escape routes, speak to your Building Control body about fire requirements before you buy materials.

Building regulations for London loft work

These points apply across England, including London.

• Loft conversions. Converting a loft is a change to the energy status of the space, so the existing roof elements need to meet the limits in Approved Document L (Table 4.3 in the current edition). The improved roof U-value there is 0.16 W/m²K.
• Headroom. Approved Document L accepts a lesser standard where meeting the target would limit headroom. The depth of insulation plus any air gap should be at least the depth of the rafters, using the best-performing option you can fit. Your Building Control body decides what is acceptable.
• New elements. New or rebuilt roof and wall areas, such as a rear dormer or an extension, are held to tighter limits (Table 4.2). SF19+ alone is unlikely to reach them, so it is normally one layer in a build-up.
• Edition. A new edition of Approved Document L takes effect on 24 March 2027, with transitional arrangements. Check which edition applies to your project's application date.

Our building regulations guide explains the wider rules.

Planning and party walls

The Planning Portal says many loft conversions are permitted development, with volume limits of 40 cubic metres for a terraced house and 50 for other houses. Permitted development does not apply on designated land such as conservation areas and National Parks, and building regulations approval is required for any loft conversion. If you work on or near a shared wall, the Party Wall etc. Act 1996 may require you to serve notice on neighbours. Check both before you start. Listed buildings need listed building consent, and Historic England recommends breathable materials for traditional roofs and walls, which is a different brief from a foil-faced roll.

Flat roofs on rear extensions

Flat roofs are common on London rear and side extensions. SuperFOIL publishes an over-joist installation guide for flat roofs, using firrings and battens to keep the required airspaces. Where insulation is split above and below the joists (a hybrid roof), SuperFOIL warns of interstitial condensation risk and advises contacting its technical support before you proceed. Its technical support also lists U-value calculations and condensation risk analysis, which are worth using on any flat roof you want to get right first time.

Where PIR or mineral wool is better

• Cold lofts with open joists. Mineral wool at depth is simple and cost-effective. See our loft insulation thickness guide.
• Solid brick walls inside. PIR-backed plasterboard is usually easier to specify, as our insulated plasterboard guide shows. SF19+ has Kiwa certification as an internal wall system, but with conditions on moisture and fitting.
• Very tight headroom. SF19+ only reaches its published roof figure with air spaces on both sides. If every millimetre of headroom matters, foil-faced PIR between and under the rafters usually delivers more for the depth.
• Noise. Foil does little for airborne sound. If a party wall or floor needs acoustic work, wool or a specialist system is the right tool.

Our wool vs PIR vs foil comparison sets these out side by side. You can also size a job with our insulation calculator.

Frequently asked questions

Can I insulate a London loft room with SF19+ alone?

Possibly for a modest upgrade, but a conversion that needs Building Regulations approval will be judged on its U-value calculation. Ask your Building Control body, and use a calculation for the full build-up, including plasterboard and air gaps.

Is SF19+ suitable for a Victorian roof?

It can be fitted under the rafters of a conventional slate or tile roof if the roof is sound and ventilated. Listed buildings and conservation areas need extra care and consent.

Will the rolls fit up a narrow staircase?

The 1.2m x 10m roll weighs about 10kg and the 1.5m x 10m about 13kg, so they are easy to carry. Check the delivery driver can reach your property.

Do you deliver to London?

We deliver to England only, including London. See our delivery information.

Order SuperFOIL SF19+

Order SF19+ in 1.2m x 10m or 1.5m x 10m rolls, or browse the whole SuperFOIL multifoil collection. Current trade prices are shown on each product page. We deliver to England only (see delivery information). Call us on 03330 908479 (Mon–Thu 8am–5pm, Fri 8am–12pm), email sales@insulationwarehousedirect.co.uk, or order online.

Sources: English Housing Survey 2024 to 2025: profile of households and dwellings; Approved Document L (Conservation of fuel and power); Planning Portal: loft conversions; Party Wall etc. Act 1996 guidance; Historic England: risks of energy efficiency interventions; SuperFOIL SF19+ product page; SuperFOIL under rafter installation guide; flat roof over joist guide.