A converted loft is the hardest room in the house to insulate well. It has sloping ceilings, low stud walls, a gable, a flat ceiling and dead space behind the walls, and every one of those meets another at an awkward junction. The SWIP Room in Roof (RIR) system is designed to treat all of them as one envelope. Stay Warm Insulation installs it as a SWIP approved installer, and this guide explains how it works, in SWIP's own terms.
What is SWIP Room in Roof insulation?
SWIP describe RIR as an insulated dry lining solution for room in roof applications in new and existing buildings. The core component is the SWIP RIR Insulation Board:
- 50mm of Unilin Thin-R PIR insulation, which carries its own BBA certificate (23/6997)
- bonded to 12.5mm Knauf Wallboard plasterboard, giving a 62.5mm board ready to finish
The board is the part you see, but the system is more than one board. SWIP's specification brings together the RIR board, SWIP EcoBatt mineral wool, the SWIP internal wall insulation system for solid walls, SWIP vapour control membranes and loft roll, so each part of the room gets the treatment that suits it.
If your loft walls are solid masonry rather than timber, the relevant system for those walls is SWIP internal wall insulation.
The six parts of a room in roof
SWIP's design guide sets out the thermal envelope of a room in roof as six elements. Getting a warm room means treating all of them, because heat leaves through whichever one is left out:
- Gable end, the solid end wall
- Dormer window, including the dormer cheeks and the head
- Sloping ceiling, following the rafters
- Stud wall, the low wall at the side of the room
- Residual loft space, the dead space behind the stud walls
- Flat ceiling, at the top of the room
Most loft rooms that stay cold after being "insulated" have had one or two of these done well and the junctions between them ignored.
Stud walls: two methods
The low timber stud walls at the side of a loft room can be treated in one of two ways, and SWIP's guide sets out both. Which one suits depends on whether you can reach behind the wall.
From the room side. The 62.5mm RIR board is fixed through the existing plasterboard into the existing timbers, with 100mm fixings at 300mm centres. Nothing has to be stripped out, although the wall comes into the room by the thickness of the board.
From behind, in the residual loft space. Where there is access to the back of the studs, 95mm SWIP EcoBatt mineral wool is friction fitted between the rear of the timber studs and held with SWIP green netting. The room itself is not touched at all, which makes this the natural choice where there are fitted wardrobes or a finished bathroom on the room side.
Gable ends and party walls
Gable ends are solid walls, so they are not treated with the RIR board. SWIP specify their internal wall insulation system, at 95mm or 65mm, for the solid elements of the heat loss perimeter, including gable ends.
Party walls only need insulating if the space on the other side is unheated. If your neighbour's side is a heated room, the wall is not classed as a heat loss wall and does not need treatment beyond restricting cold bridging at its edges.
Ceilings and the residual loft
The sloping ceilings take the 62.5mm RIR board, fixed through the existing plasterboard into the rafters in the same way as the stud walls.
For the residual loft space and the flat ceiling, SWIP recommend loft roll laid to a minimum of 270mm from above. Where there is no way to get above a flat ceiling, it can be insulated from the warm side with the 62.5mm RIR board instead.
That residual loft floor is easy to forget. Once the stud wall is insulated, the space behind it is cold, and its floor sits over the ceiling of the room below.
Ventilation and moisture
SWIP put this plainly: without proper ventilation, a property can suffer condensation after a room in roof is insulated, so ventilation has to be maintained or improved.
- Crossflow. Air should be able to travel up one side of a sloping ceiling, across the loft at the top and back down the other side. Where a ceiling is vaulted and there is no crossflow between the two slopes, extra ventilation has to be provided.
- Clear eaves. Eaves ventilation must be cleared of any old insulation blocking the airflow, leaving at least a 50mm air gap.
More on why this matters, and what happens when it is skipped, in our guide to ventilation after insulating.
Tight spots, flues and downlights
Limited space. Around dormer and roof windows there is often no room for the full board at the heads, cills and jambs. SWIP's answer is their 27mm or 12.5mm insulated reveal boards, which keep those areas insulated and reduce cold bridging rather than leaving them bare. Our guide to window reveals and sills explains why that edge matters so much.
Flues and mechanical vents. Any balanced flue or mechanical vent in use has its terminal or cowl removed and a suitable metal or PVC sleeve fitted, so it projects beyond the new surface. This has to be done by a qualified person.
Fuel burning appliances. If there is one in the room in roof, a competent person has to confirm its ventilation is sufficient before and after the work. SWIP state that works must not proceed until that is signed off.
Downlighters. Recessed lights are sealed in a way that keeps the insulation and airtightness continuous without compromising the safe use of the fitting.
Building Regulations targets
Room in roof insulation is notifiable work under the Building Regulations. SWIP's specification quotes the Approved Document L1B figures the work is designed against:
| Element | Threshold | Improvement target |
|---|---|---|
| Roof | 0.35 W/m²K | 0.16 to 0.18 W/m²K |
| Walls, including dormer cheeks and gable ends | 0.70 W/m²K | 0.30 W/m²K |
The improvement targets apply where they are technically attainable. Because the achieved figure depends on what the board is fixed to, we calculate it for the specific property rather than quoting one number for every loft.
When it is not suitable
A room in roof is surveyed before anything is specified, and SWIP list the circumstances where installation should not go ahead without remedial work first, including:
- damp or mould on the rafters and joists
- signs of condensation on surfaces in the cold loft space
- damp plasterboard or rotten timber
- holes in the roofing felt, or water getting in
- unsuitable existing electrical cables
- bats or other protected species in the roof space
It also has to genuinely be a room in roof. Under the RdSAP conventions SWIP refer to, the room must be reached by a permanent fixed staircase, and the common wall has to be under 1.8m high for at least half its length. Otherwise it counts as a separate storey. For the wider picture on converted lofts, including when re-roofing first is the better route, see room in roof and rafter insulation.
What SWIP Room in Roof insulation costs
These figures come from our own priced work rather than industry averages:
| Scope | From our quote book |
|---|---|
| SWIP RIR board, per square metre | £130 to £150, most often £140 |
| Whole room in roof or rafter project | £3,000 to £7,500 |
Where a project lands depends on the roof area, how many of the six elements are being treated, how much preparation and making good is needed, and details like dormers, flues and fitted furniture. Every quote is fixed and itemised, so you can see exactly what each element costs.
If you have a cold loft room and want to know what it would take, get a free, fixed, itemised quote.
SWIP Room in Roof insulation FAQs
What is SWIP Room in Roof insulation?
SWIP RIR is an insulated dry lining system for converted lofts and rooms in the roof. Its main component is the SWIP RIR Insulation Board: 50mm of Unilin Thin-R PIR insulation bonded to 12.5mm Knauf plasterboard, 62.5mm in total. It is fixed to the sloping ceilings and stud walls of the room, and used alongside SWIP mineral wool, SWIP internal wall insulation for any solid walls, and loft roll for the residual loft space, so the whole room is wrapped rather than one surface at a time.
Does the existing plasterboard have to be stripped out?
Not usually. SWIP specify the 62.5mm board to be mechanically fixed through the existing plasterboard into the existing timber rafters and studs, using 100mm fixings at no more than 300mm centres. That keeps disruption down. The exception is where the existing build up is not sound, is damp, or has no ventilation path behind it, which is why the survey comes first.
What U-value does SWIP RIR achieve?
There is no single figure, because the result depends on the construction it is fixed to, the rafter depth and what is already there. SWIP publish no fixed U-value for the RIR board for that reason. The targets it is designed against come from Approved Document L1B, quoted in SWIP’s own specification: for the roof, a threshold of 0.35 W/m²K with an improvement target of 0.16 to 0.18; for walls including dormer cheeks and gable ends, a threshold of 0.70 with a target of 0.30. We calculate the figure for your property rather than quoting a generic one.
Does a room in roof need a ventilation gap?
Yes. SWIP are explicit that ventilation must be maintained or improved. Eaves ventilation has to be cleared of any old insulation blocking the airflow, leaving at least a 50mm air gap, and air needs to be able to travel up one slope, across the loft at the top and down the other side. Where a ceiling is vaulted and there is no crossflow, extra ventilation has to be added.
How much does SWIP Room in Roof insulation cost?
On our own priced SWIP RIR work the board lines have run from £130 to £150 per square metre, with £140 the most common rate. Whole room in roof and rafter projects with us typically come to £3,000 to £7,500, depending on the roof area, how much of the room is treated and how much preparation is needed. Every quote is fixed and itemised after a free survey.