SuperFOIL SF19+ for Midlands Homes: 1930s Semis, Garages and Timber Floors

Midlands towns have a familiar mix of housing: older terraces near the centre, 1930s semi-detached houses in the suburbs, and post-war estates beyond them. Plenty of those homes now have a garage that could be a room, a loft that could be a bedroom, or a ground floor that feels cold underfoot. This guide covers where SuperFOIL SF19+ multifoil insulation helps on those jobs, and where another product is the better choice.

If you want the full technical story on the product first, read our complete SuperFOIL SF19+ guide.

Quick answer

• SF19+ fits well in three Midlands-style jobs: suspended timber ground floors, garage and outbuilding conversions, and rooms in a roof.
• For an ordinary open loft, mineral wool at depth is simpler and usually better value.
• For cavity walls, filling the cavity is the normal route. SF19+ is not a cavity-fill product.
• Garage and loft conversions are a change to the energy status of the space, so Building Regulations apply.
• We deliver to England only, including the East and West Midlands.

The homes you are actually working on

England's housing stock is old, and the Midlands is no exception. According to the English Housing Survey (2024 figures), 16% of owner-occupied homes in England were built between 1945 and 1964, and 29% of social rented homes were built in that same period. Interwar semis sit alongside them. Those are national figures rather than Midlands ones, but they describe the kind of house you will meet on most streets here: brick, often with a cavity wall, a pitched tiled roof, and a timber or concrete ground floor depending on the age.

That variety matters, because the right insulation depends on the construction. Before buying anything, find out what you have. A 1930s semi may have a suspended timber floor, but a post-war house or an extension may have solid concrete. Some post-war homes were built using non-traditional methods, so check your property's construction before you drill into walls or fix to a frame.

Suspended timber floors in 1930s semis

A suspended timber floor is one of the most useful places for SF19+ in this housing type. SuperFOIL lists SF19+ as a recommended product for suspended timber floors, and for solid floors where battens are used. The manufacturer's floor installation guide sets out how it goes in:

• If you are adding other insulation, such as mineral wool, fit that between the joists first, then fit the SF19+ roughly halfway between the top of the joists and the top of that insulation, as the manufacturer's guide describes.
• If you are not adding other insulation, leave about a 50mm cavity above the SF19+ for the best performance.
• Lap the roll up the wall edges, overlap rolls by around 100mm, and tape every joint and penetration with SuperFOIL multifoil tape.
• Secure it with SuperFOIL spacers, staples or battens, then refit the floorboards.

The published floor R-value for SF19+ is 4.29 m²K/W with two air spaces. That figure only applies if the air gaps are built in. Keep any underfloor ventilation clear, and fix any damp problem before you insulate. Our suspended timber floor insulation guide covers the alternative of fitting PIR boards between the joists.

Garage conversions

Turning an integral garage into a room is one of the most common projects on 1930s and post-war semis. Approved Document L treats it as a change to the energy status of the space, because a previously unheated space becomes part of the heated home. Existing walls, roof and floor need to meet the limits for existing elements in Table 4.3, and any new or replaced elements, such as a rebuilt front wall where the door was, must meet the tighter limits in Table 4.2 (0.18 W/m²K for a wall). New windows and doors have to meet their own standards as well.

In practice that means SF19+ will usually be one layer in a build-up, not the whole answer. It can work on:

• sloping or flat garage roofs, fitted below the rafters or joists with air gaps;
• walls, if the structure is dry, since the Kiwa Agrément for the wall system expects walls free from damp and mould;
• the floor, with battens, or by fitting SuperFOIL's SFUF underlay for a solid floor.

A concrete garage floor usually needs a damp-proof membrane and often rigid board or a specified floor build-up. See our flooring insulation boards if you want a rigid option. Your Building Control body will want to see the proposed construction and calculations.

Detached garages, sheds and workshops

Many Midlands homes have a detached garage in the back garden, now used as a workshop, gym, studio or hobby room. These are exactly the "three surfaces at small scale" jobs where a light roll is quick to fit. Because these buildings are often unheated for much of the year, condensation is the main risk, so plan ventilation as well as insulation. Our shed and garage insulation guide covers the wider job.

Rooms in the roof

Semi-detached houses are popular loft conversion candidates. The Planning Portal gives a volume allowance of 50 cubic metres for a detached or semi-detached house under permitted development, with conditions and exclusions, and building regulations approval is needed regardless. Hip-to-gable and rear dormer conversions are common on semis. The rafters and dormer cheeks in the finished room are where SF19+ can be fitted under the rafters using the manufacturer's method (50mm overlaps, staples at no more than 300mm, counter-battens at no more than 600mm centres, air gaps either side, and existing ventilation maintained). The first fix needs a check for asbestos and sound roof coverings.

Where PIR or mineral wool is the better answer

• Open, accessible lofts. Mineral wool at 270mm is the standard approach. See our loft insulation thickness guide.
• Cavity walls. If a survey says your cavity is suitable, cavity wall insulation is the normal route and is installed from outside, by a specialist.
• Internal solid walls. PIR-backed plasterboard, from our insulated plasterboard range, gives a predictable U-value from one board.
• Tight spaces. Where there is not enough room for air gaps, PIR is more efficient per millimetre.

The wool vs PIR vs foil guide compares them side by side, and the insulation calculator helps you work out quantities.

A note on the regulations

The current Approved Document L guidance for existing dwellings (2021 edition with 2023 amendments) applies to work now, but a new edition takes effect on 24 March 2027 with transitional arrangements. If your job straddles that date, ask Building Control which edition applies.

Frequently asked questions

Can SF19+ go under a ground floor in a 1930s semi?

If the floor is a ventilated suspended timber floor in good condition, yes. SuperFOIL recommends SF19+ for suspended timber floors. Keep airbricks clear and check for damp first.

Is SF19+ enough for a garage conversion?

Usually not on its own. A garage conversion has to meet the limits in Approved Document L, which are set as U-values. Treat SF19+ as one part of a calculated build-up and check it with Building Control.

Which roll width should I choose?

Choose the width that gives the fewest joins on your surface. We sell 1.2m x 10m and 1.5m x 10m rolls.

Do you deliver to the Midlands?

We deliver to England only, which includes the East and West Midlands. See our delivery information.

Order SuperFOIL SF19+

Browse the whole SuperFOIL multifoil collection or go straight to the 1.2m or 1.5m rolls above. 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; SuperFOIL SF19+ product page; SuperFOIL floor installation guide; SuperFOIL under rafter installation guide; Kiwa BDA Agrément BAW-24-342-S-A-UK.