Wales


Wales Building Regulations for Flat Roofs

 

New Dwellings

New Dwellings (Domestic Buildings) – Approved Document L1A/ADL1A

 

Approved Document L1A looks at the entire building’s performance and CO2 emissions, rather than isolating one particular element. All dwellings (domestic buildings) must be designed and built so their individual Dwelling CO2 Emissions Rate (DER) is no worse than the Target CO2 Emissions Rate (TER). The TER is based upon the performance of a defined Notional Dwelling. The Dwelling Emission Rate (DER) is calculated using a calculation methodology called SAP (Standard Assessment Procedure) 2012.

In addition to meeting the TER, there are also mandatory minimum energy efficiency standards (U-values) for the building elements (walls, floors and roofs) to achieve.

If the dwelling is built to match the Notional Dwelling criteria and better the limiting fabric U-values, it should meet the Target Emission Rate (TER). Note that other factors need to be taken into consideration including thermal bridging, ventilation, information submission (design and build values) and limiting the effects of heat gains in summer.

The area-weighted average U-value for flat roofs, taken from the Notional Dwelling specification (used to set the TER and TFEE targets), is 0.13 W/m2K

Existing Dwellings

Existing Dwellings (Domestic Buildings) – Approved Document L1B/ADL1B

 

Existing dwellings differ from new dwellings, in that they do not have to achieve a whole building Target CO2 Emissions Rate (TER, see New Dwellings). However, existing dwellings do have to meet certain target U-values for building elements (walls, floors and roofs).

The target flat roof U-value for existing dwellings or new elements are:

 

For replaced or refurbished roofs:                  0.18 W/m2K
New elements (extension/ conversion):            0.15 W/m2K

New Buildings

New Buildings other than Dwellings – Approved Document L2A/ADL2A

 

Approved Document L2A adopts a similar approach to Approved Document L1A, taking the entire building’s performance and CO2 emissions into consideration. All new buildings other than dwellings must be designed and built with their Building CO2 Emissions Rate (BER) being no worse than the Target CO2 Emissions Rate (TER).

The TER is set from a Notional Building of the same size and shape to the actual building. There are three defined Notional Buildings; heated and cooled buildings (that are side lit or unlit), and toplit buildings. The specification for each building type is summarised in ADL2A. CO2 Emissions Rates for buildings other than dwellings are calculated using the Simplified Building Energy Model (SBEM) or other approved software.

In addition to meeting the TER, a new Target Primary Energy Consumption (TPEC) rate has been introduced for new buildings other than dwellings. Put simply, this new target is aimed at two factors – energy efficiency of the fabric and its building services. The TPEC ensures these two factors are carefully considered and prevents renewable technologies being highly specified to counteract a lower performing fabric or services standards.

If the building is built to match the Notional Building specification, its BER should meet the TER. Note that other factors need to be taken into consideration including continuous building fabric insulation, air permeability, thermal bridging, performance testing and limiting the effects of heat gains in summer.

The area weighted average U-value for flat roofs, used in the Notional Building specifications for setting the TER, is 0.18 W/m2K

 

Although ADL2A is for new buildings other than dwellings, there are some exceptions if a dwelling is featured within the new building. For more details on these exceptions ADL2A should be referred to.

Special considerations are made for low energy demand buildings, modular/portable buildings, temporary buildings, industrial sites, workshops, and non-residential agricultural buildings. ADL2A should be consulted for further details.

Existing Buildings

Existing Buildings other than Dwellings – Approved Document L2B/ADL2B

 

Existing buildings do not require a Target CO2 Emissions Rate, however they do require a target U-value to meet for building elements (walls, floors and roofs). There is a new consideration for the character of the building, with buildings that are essentially domestic in character having more stringent targets to meet for extensions.

The target U-value for flat roofs on existing buildings other than dwellings are 0.15 W/m2K*** 0.18 W/m2K

 

*** Rooms for residential purposes (for example in nursing homes, student accommodation, etc.) are not dwellings, and so ADL2B will apply.

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The figures and information quoted are for guidance only.  Official Building Regulation / Standard documentation should always be consulted.

Submit your flat roof project now for a full tapered insulation scheme design and U-value calculated to Annex C