Loft conversions not only add another room to a property but they can also help to reduce energy bills and achieve a better EPC rating: a welcome bonus. However, the effective use of insulation has a massive impact on all of this – so here’s a short guide to help you get the best results.
To insulate a pitched roof for a loft conversion, there are two main methods that we would recommend:
Cold roofs - existing roofs and shared roofs
For houses with shared roofs and where the roof covering is not being replaced, we suggest insulating between and under the rafters. This means putting a layer of insulation between the rafters, followed by a second layer (usually insulated plasterboard) fixed beneath the rafters, which helps to reduce heat loss (thermal bridging).
This construction method is called a cold roof, as the rafters are not part of the warm insulated part of the structure. When adding the insulation between the rafters there should be a 50mm ventilation gap above the insulation, between the insulation and the sarking felt. The insulation should be level with the bottom of the rafters, with the insulated plasterboard then fixed underneath this.
Dwarf walls
In smaller lofts, floor joists are often used to support the sloping rafters with a dwarf, timber stud wall, usually approximately 1m to 1.5m high. They should also be insulated with a framing board between the timber studs and on the floor behind the dwarf wall, from the wall up to the edge of the roof. Insulated plasterboard may also be fitted to the inner face of the wall. This insulation approach will help to provide a continuous layer of insulation around the space, preventing unnecessary heat loss.
Warm roofs - re-roofing a detached property
Less common – but sometimes required. In this case, the best method would be to insulate ‘between and over.’ This involves fixing insulation between and above the rafters. This is called a warm roof, as the majority of the insulation is above the timbers of the roof.
One advantage of this is that it gives more headroom within the loft conversion. Remember that this method is only suitable when all the roofing is being completely removed as it requires access above the rafters.
What insulation is going to give me the best results?
To achieve the required level of insulation without having to reduce the headroom or floor space, it’s important that you choose an insulation product that gives the best possible U-value for the minimum thickness. Polyisocyanurate (PIR) insulation remains a popular choice, as it is amongst the most thermally efficient insulation on the market. For example, Eco-Versal, our 5 in 1 insulation board, has a thermal conductivity of 0.022 W/mK across all thicknesses.
And finally, before you go…
To easily identify what thickness of EcoTherm Insulation product you need to meet your project's U-value requirements, please visit our simple to use U-value calculator tool.