Insulating the rafter space means insulating between or below the sloping beams that are part of a sloping roof. This type of insulation creates what is called a warm roof. Insulating the Rafter space creates a well insulated loft that is not too hot in summer and not cold in winter. Insulation can be done with insulation board like celotex or more flexable with Rolls of wool like isover spacesavers we advice against the use of spray foam in most type of houses as it is often froned upon by surveyors as it can create damp problems as spray foam is non breathable.
Rafter insulation can be done from inside or outside depening on the type of roof you have. Adding insulation from the outside works great if you plan to get a new roof done. On a loft conversion where the roof is not touched adding insulation from the inside is the most common thing to do. As the entire inside space is often restructured. All our Loft conversion have insulation added inbetween the rafters, this is often done early in the process. Just after windows are installed and electric wires are laid.
There is a requirement when refurbishing a roof to have a minimum U-value of 0.18 W/m²·K. The lower a U-value or heat transfer coefficients the slower heat is able to transmit through it. The lower the U-value the better a roof is insulated. U-values are measured in watts per square metre per kelvin (W/(m²K)). OFten there is less room inbetween the rafters and higher quality insluation is needed to get to the required specs than with ceiling insulation (cold roof). 10 cm of quality insulation board should have a U-value of around 0.14 W/m²·K where 10cm of earthwool would be in the 0.24 W/m²·K range.(296 words)