Insulating at ceiling level

Energy Efficiency and Historic Buildings
Insulating pitched roofs at ceiling level- cold roofs

This guidance note provides advice on the principles, risks, materials and methods for insulating pitched roofs at ceiling level. When insulation is placed at this position the roof is often referred to as a ‘cold roof’.

Insulating the top floor ceiling is one of the easiest and cheapest means of improving the energy efficiency of buildings. Such work can be carried out successfully in older buildings if approached with care. Even very thick layers of insulation will not cause problems if installed carefully with materials that are compatible with the existing construction.

Energy is lost through ceilings in two ways: by heat passing through the thin fabric of the ceilings, and by warm air escaping though cracks and gaps in the ceiling around pipes, fittings etc. Both are equally important.

Adding insulation to a loft is relatively straightforward but it is a good idea to wear gloves and a breathing mask when working in a loft. Insulation can be bought from a builder’s merchant or DIY store. Insulation made from natural materials like sheep’s wool or recycled materials like cotton or newspapers that can further increase the ‘green’ credentials of the roof can be sourced from more specialist suppliers.

Rolls or batts of insulation can be laid between the ceiling joists. A second layer of insulation can be laid over the top of the joists and at right angles to them to increase the benefit. Make sure that insulation is tight fitting. Gaps between the insulation and adjoining building elements, such as ceiling joists, can allow draughts that reduce the thermal benefits of the insulation, whilst also causing cold spots (thermal bridges) prone to damp and mould growth.

It is very important that ventilation of the loft is maintained. Blocking the ventilation to make the loft space warmer will not significantly increase the warmth in the rooms below, but will risk creating problems of condensation. Take care not to block eaves vents with insulation or to wrap up electrical wiring that might overheat. Water pipes have the opposite concern. Insulating the ceiling will make the loft space colder in winter, increasing the risk of frost damage to pipes above the insulation. Make sure that all water pipes both warm and cold are insulated.