Loft insulation

Description
Layer of insulating material on floor of loft achieving a U-value of 0.16 W/m2K (Building Regulations).

Unit cost of installation
£325 (empty loft) £265 (top-up from 75 mm) £235 (top-up from 100 mm). These costs do not include the provision of eaves ventilation.

Bulk cost of installation
Limited scope for reductions - possibly 5%

Indicative cost and carbon saving

Maintenance
None

Lifetime
Lifetime of dwelling.

Technical suitability
Care should be taken to ensure that loft insulation does not block existing eaves ventilation. Eaves ventilation becomes more important when loft insulation is present (particularly if there is sarking felt below tiles/slates) because temperature inside loft will generally be lower leading to increased risk of condensation. In many older properties eaves ventilation is not provided deliberately and reliance is made on fortuitous ventilation. In these cases ventilation should be provided when the loft is insulated.

In some designs the rafters cut across the corner of the upper rooms to create an area of sloping ceiling. Insulation should not be packed between the rafters in this case unless provision is made to maintain eaves ventilation - rather, the sloping part of the ceiling can be insulated from within the room using an insulation board.

Air leakage around the loft hatch and light fittings should be addressed at the time the loft is insulated. In particular leakage from wet areas (e.g. bathrooms) into the loft should be minimised in order to mitigate against increased condensation in loft.

If the whole roof is being re-covered breathable sarking membranes could be used to achieve loft ventilation (assessments of suitability should be carried out in accordance with BS5250).

The insulation levels of water pipes and tanks within loft space should be checked because of an increased risk of freezing. If loft insulation completely covers joists a walkway may be needed to allow safe access to tanks etc.

Where possible electrical cables should run above the insulation layer; cables may need to be down-rated if they pass through or below the insulation layer. In cases of doubt a qualified electrician should be consulted.

Safe access to header tanks needs to be considered where joists are covered with insulation. The area below header tanks should not be insulated. Rather, the insulation layer should continue around and above tanks.

Non-technical constraints
Some lofts (for example with shallow pitch and trussed rafters) can be difficult to treat. Occupants use of the loft as storage area can be significant barrier to treatment.

Potential concerns with fuel poor
No specific issues.

Ancillary benefits
Potential DIY measure.

Trigger points for work
Repairs to roof or any other work in the loft such as re-wiring (N.B. Building Regulations Approval is required in England & Wales whenever any thermal element is renovated)

Technical Guidance Available
» GPG 171 'Domestic energy efficiency primer'
» CE104/GPG418 'Energy-efficient refurbishment of existing housing'
» CE184 - Practical refurbishment of solid-walled houses
» CE120 Energy efficient loft extensions (2005 edition)
» CE122 Energy efficient domestic extensions (2005 edition)
» National Insulation Association Ltd (NIA) 01428 654011 www.insulationassociation.org.uk
» NIA good practice guide for existing housing