Cost effective U-value targets for renovation works to thermal elements

Table B1 Cost effective U-value targets when undertaking renovation works to thermal elements Proposed works | Target U-value W/m2.K | Typical construction | Comments (reasonableness, practicability and cost effectiveness) Pitched roof constructions (Specification of thickness of insulation is based on lambda values (conductivity) of 0.04 W/m.K) Renewal of roof covering – no living accommodation in the roof void – existing insulation (if any) at ceiling level. No existing insulation, existing insulation less than 50 mm, in poor condition, and/or likely to be significantly disturbed or removed as part of the planned work | 0.16 | Provide 270 mm loft insulation such as mineral or cellulose fibre laid between and over the ceiling joists | Impact on boarded walkways or boarded roof spaces. Condensation risks - consider ventilation. Impact of new insulation on access to and the insulation of services. Consider combustibility of insulation (if relevant) or other fire safety risks - ref Part E Renewal of roof covering – existing insulation in good condition and will not be significantly disturbed by proposed works. Existing insulation thickness 50 mm or more but less than 100 mm | 0.16 | Top up insulation to at least 200 mm with insulation such as mineral or cellulose fibre laid between and over the ceiling joists | Impact on boarded walkways or boarded roof spaces. Condensation risks - consider ventilation. Impact of new insulation on access to and the insulation of services. Consider combustibility of insulation (if relevant) or other fire safety risks - ref Part E Renewal of the ceiling immediately below a cold loft space. Existing insulation removed as part of the works | 0.16 | Provide 270 mm loft insulation such as mineral or cellulose fibre laid between and over the ceiling joists | Impact on boarded walkways or boarded roof spaces. Condensation risks - consider ventilation. Impact of new insulation on access to and the insulation of services. Consider combustibility of insulation (if relevant) or other fire safety risks - ref Part E Renewal of roof covering – living accommodation in roof space (room-in-the-roof) | 0.18 | Cold structure – insulation between and below rafters. Warm structure – insulation between and above rafters | Condensation risks. Practical considerations in relation to the thickness of insulation involved. Consider combustibility of insulation (if relevant) or other fire safety risks - ref Part E Dormer window constructions Renewal of cladding to side walls | 0.30 | Insulation (thickness dependent on material) placed between and/or fixed to outside of wall studs. Or fully external to existing structure depending on construction | Assess condensation risk and make appropriate provision in accordance with the requirements of Part C. External fire spread and combustibility - ref Part E Renewal of roof covering – Follow guidance on improvement to pitched or flat roofs as appropriate | Assess condensation risk and make appropriate provision in accordance with the requirements of Part C