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Think you understand U-values for rooflights?

When it comes to thermal performance, specifying a quality product is crucial - but so is what you do with it

In association with
Stella contemporary flush-fitting skylight: available with single, double or triple glazing with self-clean, solar control, toughened or laminated glass, sound insulation or obscure options.
Stella contemporary flush-fitting skylight: available with single, double or triple glazing with self-clean, solar control, toughened or laminated glass, sound insulation or obscure options.

Thermal performance, crucial for modern building materials, measures heat loss via U-values (or sometimes R-values).

U-value calculations, expressed in W/m²K (Watts per metre square Kelvin), are essential early in the building strategy to predict heat loss. Lower U-values indicate better efficiency.

Both the quality of materials and the standards of workmanship and installation impact thermal performance. Poor insulation fitting can lead to higher thermal transmittance despite using good materials.

The UK’s Building Regulations Approved Document Part L sets maximum U-values for various building materials, including rooflights, ensuring energy efficiency to reduce carbon emissions and heating bills.

Accurate U-value figures are vital and should be produced using reliable software. Always request test performance reports to verify the figures.

Rooflights are tested under BS EN ISO 10077-1:2017, a standard for windows, doors and shutters, but this may not reflect their performance in different roof pitches.

Rooflight performance varies with pitch, which affects the U-value. For instance, Stella rooflights achieve a U-value of 1.5 W/m²K horizontally, improving to 1.1 W/m²K at over 60 degrees. Always ask for both figures or supporting data.

  • Stella bespoke rooflight: Select the inside frame colour to match the interior decor.
    Stella bespoke rooflight: Select the inside frame colour to match the interior decor.
  • Top performing rooflights provide extra light while maintaining a comfortable indoor temperature all year round.
    Top performing rooflights provide extra light while maintaining a comfortable indoor temperature all year round.
  • Stella Conservation Rooflights: Beautiful, flush-fitting solutions for heritage buildings.
    Stella Conservation Rooflights: Beautiful, flush-fitting solutions for heritage buildings.
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Rooflight design significantly affects thermal performance. Modern rooflights often use thermally broken aluminium and wood, resulting in good U-values but bulkier frames, reducing light entry.

Increasing glazing thickness lowers U-values but adds weight, cost and depth. Double glazing achieves a U-value of 1.0 W/m²K, while triple glazing reduces it further to 0.5 W/m²K.

For listed buildings or those in conservation areas, conservation rooflight designs should sit flush with the roofline. Using bulky modern rooflights or quad glazing for better thermal performance may harm the building's aesthetics.

Exceptions to thermal requirements exist for certain building types, such as listed buildings, conservation areas and places of worship.

Despite the need for improved testing methods, U-values are crucial in selecting rooflights and constructing energy-efficient properties. Lower U-values contribute to reduced heating costs and combat global warming so make sure you verify U-value figures for accuracy and applicability before specifying your rooflights.

For more information and technical support, visit stellarooflight.co.uk

Contact:
01794 745445
info@stellarooflight.co.uk


 

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