Approved Document L of the Building Regulations covers the conservation of fuel and power for England and Wales. The document is divided into 4 separate categories as follows:
- L1 A – Conservation of fuel & power in new dwellings (eg, new build houses & flats).
- L1B – Conservation of fuel & power in existing dwellings (eg, extensions & conservatories).
- L2A – Conservation of fuel & power in new buildings other than dwellings (eg, new build constructions other than dwellings, including new non
dwelling extension greater than 100m² and more than 25% of the gross floor area).
- L2B - Conservation of fuel & power in existing buildings other than dwellings (eg, consequential improvement works to buildings other than
Dwellings, including new non dwelling extension less than 100m² and less than 25% of the gross floor area)
Each document provides guidance concerning the desired thermal requirements for building elements for each of the four different building uses. The thermal targets for flat roofs under the four categories are as follows:
- L1 A = 0.18 W/m²K
- L1B = 0.18 W/m²K
- L2A = 0.18 W/m²K
- L2B = 0.18 W/m²K
Where existing flat roofs are to be retained and upgraded, no further thermal insulation is required so long as the U-Value to the existing roof is less than 0.35 W’m²K. Stand alone buildings with an area less than 50m² that are not dwellings are exempt from the approved document requirements.
Building Regulations for Scotland are covered under separate legislation within Technical Handbooks. The handbooks are split into domestic and non-domestic documents, however Section 6 in both relates to thermal requirements. Under Section 6, the target U-Values for new build constructions are as follows:
Domestic = 0.18 W/m²K
Non-domestic = 0.15 W/m²K
For clarification of your thermal requirements, please don’t hesitate to contact Icopal Technical Service Department.
The design of falls is covered by BS 6229:2003 Flat roofs with continuously supported coverings. Code of practice, BS 8217:2005 Reinforced bitumen membranes for roofing. Code of practice and NHBC Standards. For definition purposes BS 6229 defines a flat roof as “having a pitch less than 10° to the horizontal”.
New flat exposed waterproofing roofs should be designed to have adequate finished falls and to drain efficiently. Typically the creation of a pitch or slope can be achieved either in the deck or by using tapered insulation. Where the use of tapered insulation is preferred, table 6 in BS 6229 states that roofs should be designed to a 1:40 fall, with the expectation of achieving an actual 1:80 finished fall reducing the potential impact of future deflection.