Why the need for new regulations ?

A major part of the UK ’ s commitment to meeting its targets for carbon reduction is being driven by a tightening of the Building Regulations surrounding energy efficiency standards for homes .

The Ministry of Housing , Communities and Local Government ( MHCLG ) argues that by making our buildings more energy efficient and embracing smart technologies , we can cut energy bills , reduce demand for energy , and boost economic growth while meeting our targets for carbon reduction and maintaining healthy environments . As such it has introduced ‘ The Future Homes Standard ’ to ensure all new homes achieve a 30 % improvement in energy efficiency standards by 2025 .

The new Building Regulations aimed at achieving these targets will comprise five new Approved Documents , which will come into effect in June 2022 .

Manufacturers , architects , specifiers and customers looking to install rooflights and roof windows will be most interested in uplifts to the Approved Document L , Conservation of fuel and power Vol 1 : Dwellings . ^{[ 1 ]}

What do the new regulations state ?

For rooflights , skylights and roof windows ( of which the definition is crucially important ), the relevant consideration is the thermal transmittance . This is measured as a U-value in units of W / m ² K , which stands for Watts /

meter square Kelvin . The lower the U-value the more efficient the construction is at keeping heat flow through the structure to a minimum .

The new regulations deem the worst acceptable U-values to be 2.2W /( m ² K ) for rooflights and 1.6 W ( m ² K ) for roof windows .

Rooflights v roof windows – what ’ s the difference ?

To correctly assess whether an element meets the new limiting U-value figure , the U-value must be calculated for the element in the appropriate plane – either

horizontal or vertical . Now this makes a big difference , as testing the same product in either a horizontal or vertical position will make a significant difference to the resulting U-value figure . With the vertical position providing a much lower ( better ) U-value figure .

This is where the definition of the terms and roof window prove crucial in determining how they should be tested and what the relevant U-value should be for each .

According to the Approved Document the following definitions apply :

Rooflight : A glazed unit installed out of plane with the surface of the roof on a kerb or upstand . Also sometimes referred to as a skylight . Roof window : A window installed in the same orientation as , and in plane with , the surrounding roof .

Therefore , while we might refer to our product as a rooflight or skylight , the official terminology for a conservation rooflight , which is designed to sit flush within a roof line , should be a roof window .

According to the approved document , the U-values for roof

windows should be calculated based on a vertical position . For rooflights , U-values should be calculated based on a horizontal position .

Further guidance in the Building Research Establishment ’ s BR 443 ^{[ 2 ]} tells us that U-values for roof windows and rooflights are usually quoted for the in the vertical plane . This allows comparison of different products that could be used at different inclinations . However , for the purposes for calculating heat losses from buildings , U-values should relate to the plane of the component as installed in the building .