SuperFOIL insulation in Cardiff homes is the answer when traditional loft insulation is not practical. Instead of laying a deep blanket of mineral wool across the loft floor, multifoil is fixed to the underside of the roof, between or across the rafters. That keeps the whole roof space warmer and leaves the floor free for storage, boarding or a room.
We supply and fit SuperFOIL multifoil, such as SF19, in lofts, room-in-roof bedrooms, low-pitched roofs and outbuildings across Cardiff and South Wales. Every job starts with a free survey, because how well multifoil works depends almost entirely on how it is fitted.
What multifoil insulation is
Multifoil is a thin, flexible roll made from layers of reflective foil separated by wadding. It works in a different way from mineral wool. Wool slows heat down by trapping still air in a thick layer. Multifoil combines its own insulating layers with reflective surfaces that face sealed air gaps either side of it, so it relies on those air gaps being formed and kept intact.
Because it is a continuous foil sheet with taped joints, SuperFOIL describes its SF19+ product as also acting as a vapour control layer and a radiant barrier as well as an insulator. That makes the detailing of joins and edges important: a well-taped installation behaves very differently from a loose one.
We do not quote headline performance figures on this page. The real-world result depends on the roof build-up, the air gaps and what else is in the roof, so we explain the options for your specific roof at the survey.
Who multifoil insulation suits
Standard mineral wool loft insulation on the floor is still the best value choice for a plain, unused cold loft. Multifoil earns its place when that does not fit how you use the space:
- Lofts used for storage or as a hobby space. Insulating the roof keeps the space warmer and leaves the floor clear to board.
- Room-in-roof bedrooms. Many Cardiff terraces and semis have attic rooms with sloping ceilings and little space behind them. Thin insulation is often the only thing that fits.
- Low-pitched roofs. Where there is not enough height to walk about in, or to fit 270mm of wool on the floor and still get to the eaves, multifoil takes up far less room.
- Garages, workshops and garden rooms. Uninsulated roofs on outbuildings are cold in winter and roasting in summer. Multifoil under the roof makes them far more usable.
- Combined jobs. Some homeowners want multifoil on the rafters and wool on the parts of the floor that are not boarded. We can do both in one visit.
If you are trying to decide between the two, our guide to SuperFOIL vs mineral wool sets out the trade-offs honestly.
Signs multifoil might be the right choice
- You want to keep using the loft for storage and do not want it freezing cold up there.
- Your attic room is cold in winter and too hot in summer.
- The roof slope is so shallow that laying deep wool would block the eaves.
- Your garage or outbuilding roof has no insulation at all.
- Condensation drips from the underside of an outbuilding roof in cold weather.
How we fit SuperFOIL properly
Between the rafters or over them
Multifoil can be fitted between the rafters, across their underside, or in a combination of both. Fitting it across the underside covers the timbers in one continuous sheet and cuts the heat lost through the wood itself. Fitting between the rafters keeps more headroom. We choose the method based on your roof depth, how much space you need and what will be finished over it.
Air gaps
The air gaps either side of the foil are what make multifoil work. We fix timber battens to hold it in position and form those gaps rather than stapling the foil tight against the roof felt or a plasterboard ceiling. Squashing it flat against another surface defeats the point.
Taping every joint
Each run of multifoil is overlapped at the joins and sealed with foil tape, and the edges are taped or sealed where they meet walls and timbers. Gaps let warm, damp air through to the cold roof, which wastes heat and can lead to condensation. Taping is slow, fiddly work, and it is where cheap installs cut corners.
Ventilation
The roof still needs to breathe. Older roofs with traditional bitumen felt need a ventilated gap kept between the felt and the insulation. We check the roof covering, the eaves and any existing vents at the survey and design the installation around them. If there is already mould on the underside of the roof, that needs sorting first: see loft mould treatment.
What affects the cost
SuperFOIL installation starts from £800. What moves the price:
- Roof area. Multifoil is priced by the area of roof covered, not the floor area, so steep roofs use more.
- Fitting method. Between and over rafters, with battens, takes more material and time than a single layer.
- Access. Tight, low roofs and attic rooms with stud walls are slower to work in.
- Finishing. If you want the foil boarded over or the space finished, that is extra.
- Combined work. Adding wool to the floor, boarding or a new loft ladder in the same visit.
What happens on the day
We protect the landing and stairs, set up lighting and bring the rolls and battens up through the hatch. If old insulation or debris needs clearing from the rafters first, we do that, then fix the battens, cut and fit the multifoil, and tape every join and edge.
We check that ventilation routes stay open at the eaves and around any vents before we finish. A typical loft or garage roof takes one to two days depending on size and access. When we are done we clean up and walk you through what has been fitted, including the details that will be hidden later.
Aftercare and what to expect
- Do not puncture the foil. If you hang shelves or run cables, fix them to the battens and re-tape any cuts with foil tape.
- Expect the space to feel different. The loft will be noticeably warmer in winter and cooler on hot days than a bare roof.
- Keep the vents clear. Do not block eaves or tile vents with stored items.
- Converting later? A full loft conversion needs Building Regulations approval, and the insulation spec will be set by that design. Tell us and we will work with it.
We cover Cardiff and the surrounding towns. Have a look at the areas we work in, or call 0800 229 4668 to arrange a free survey.