Room in Roof Insulation
Up to 25% of the heat in your home can be lost through the roof, so if you use your loft as a living space, or plan to convert the loft space into a room, then it is important to insulate between the rafters in the ceiling and the timbers in any stud walls in the roof space to help keep your energy bills low.
Room in roof insulation will keep the room warmer in the winter and cooler in the summer when the sun shines directly onto the roof.
Installing room in roof insulation can be disruptive, so is best planned at a time when other work is being done in the roof space or the roof.
If there is an existing room in the roof, then any boards already attached to the rafters will have to be removed prior to the installation.
Installation
Room in roof insulation insulates the spaces between the rafters and roof tiles, and between the studwork in the side walls
Typically, extruded polymer sheets are placed to fit tightly between the rafters and sealed with expanding foam or aluminium tape so there is no air flow between the room and the unheated roof.
There should be a 50mm gap between the top of the insulation and the underside of the roof tiles to allow ventilation, preventing the buildup of moisture and rot.
In some cases, the rafters may not be deep enough to accommodate enough insulation to meet current building standards. In this case, reflective aluminium sheets called multifoil can be attached to the underside of the rafters to increase the insulation value with minimal additional thickness. In some cases, the ceiling height may have to be reduced so that extra insulation can be fitted between the rafters and plasterboard ceiling.
If the roof is being replaced, then battens can be attached to the upper side of the rafters to provide more space for insulation without reducing the ceiling height in the room
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Semi rigid batts of mineral wool can also be used in the same way as polymer sheets. Mineral wool is typically cheaper than polymer boards but it has lower insulating values. In most roofs, the rafters will lack the depth to accommodate enough mineral wool to meet current building regulations without a significant reduction in ceiling height
Room in roof insulation is different from typical loft insulation that uses mineral wool rolled between and over the rafters in your loft space
If using mineral wool, it is recommended to install a vapour control layer on the underside of the rafters and the inside of any stud walls to keep the mineral wool in place, prevent heat loss from draughts and prevent condensation building up in the mineral wool Damp mineral wool reduces its insulating properties
Costs and savings
Costs for room in roof insulation will vary, depending upon the size of the loft, but for typicalsized lofts the price is typically around £1,500 to £2,700 and could save you several hundred pounds a year depending on house type and heating system.
Spray foam insulation
Some companies offer to spray insulating foam directly under the roof tiles and between the rafters
Most building professionals do not recommend this because it can trap moisture in the rafters and joists, which can then cause them to rot. Trapped moisture will also attract wood-boring pests.
The presence of spray foam insulation can affect the ability to get a mortgage on a property and once it’s applied it is a very difficult and costly job to remove it. If sprayed directly onto the underside of roofing tiles, those tiles can't then be reused should the roof need repairing in the future
