Roofglaze News

Designing with rooflights to save energy and enhance internal environments

By Ray Paddick, Technical Manager, Roofglaze Limited

The benefits of introducing natural daylight into buildings are clear. Daylight has many advantages over artificial light – not least the fact that it is a completely free, unlimited natural resource. It is also well documented that daylight provides a beneficial effect to building occupants in terms of health and wellbeing.

It is therefore unsurprising that daylight is playing an increasingly important role in contemporary building design.

With the huge variety of modern rooflight types available, designs can be optimised to provide specific characteristics to suit diverse requirements. The need to save energy and reduce emissions is high on most building specifiers’ lists and in this respect.

Design with rooflights to save energy

There has previously been a widely held view that whilst rooflights are an excellent way of bringing the many benefits of natural light into a building, their poorer insulation value allowed more heat to escape, increasing the running costs of the building. Recent research* has confirmed this view is no longer accurate, as modern rooflight design has resulted in significant gains in insulation value in recent years.

Considerable energy savings can be achieved by bringing daylight into a building through rooflights and windows and utilising natural light with automatic controls that dim, or switch off, artificial lighting during the day.

Design parameters for the building, such as temperature set point, hours of occupancy and internal gains, can all alter the effect that rooflight area can have on the total energy requirements of heating, cooling and artificial lighting systems.The savings in total energy costs and carbon footprint therefore vary from building to building, but are usually found to be positive as rooflight area increases.

Thermal insulation values

The thermal insulation performance of rooflights is expressed as a ‘U-value’. This is the measurement of heat transmission through a material or assembly of materials. The U- value of a material is a gauge on how well heat passes through the material: lower the U value, the greater the resistance to heat transfer and therefore the better the insulating value. The U-value is widely used throughout the building and construction industry to specify assemblies of components which provide a suitable insulation and energy efficiency value. U-Value is expressed in units of W/m² K and relates to the amount of heat lost in watts (W) per square metre. Basically if a rooflight has a U-Value of 1 W/m² K, for every degree of temperature difference between the inside and outside surface there would be 1 Watt of heat energy flowing through each meter squared of its surface. Rooflights with U-values of or below 1.4 W/m² K can generally be accepted to be among the most highly thermally efficient of today’s rooflights and will provide a positive contribution to building energy efficiency and building regulations compliance.

Design with rooflights for better internal environments

For those of us living in temperate Northern climates, the beneficial effect of sunlight is easy to recognise: a couple of sunny days seem to lift everyone’s spirits. There is a growing body of evidence to suggest that buildings enjoying high levels of natural light are literally more successful than those more reliant on artificial light. In all environments the eye and brain functions respond better to natural light, so people perform better. Natural daylight promotes a sense of wellbeing amongst building occupants and rooflights achieve this without the potential distractions created by views through vertical windows. Where vertical windows do not exist, rooflights provide occupants with beneficial ‘daylight contact’.

Other factors to consider

In addition to improving light levels and reducing dependency on artificial lighting, rooflights can impact on buildings in other ways – all of which need to be considered at the specification stage.

• Solar heat gain and glare
• If heat build-up is not desirable, a number of ‘solar control’ glazing options exist, allowing natural light to be introduced without excessive heat build-up. These include translucent and tinted solar control glazing options, or translucent Nanogel^®-filled multiwall polycarbonate.
• Acoustic insulation
• Large rooflight areas can have a significant impact on the acoustic properties of a room or space. Acoustic properties of rooflight materials should always be considered. New materials such as Nanogel-filled polycarbonate can provide excellent acoustic properties.
• Aesthetics

There is a huge choice of rooflight designs available, covering applications from simple roof windows and monopitch rooflights through to bespoke-designed self-supporting glazed structures. Suffice to say, whatever the building type, there are rooflights available that will not only meet practical requirements, but also enhance both internal and external appearances. Even the humble flat roof dome type modular rooflight has undergone a transformation, with sleek new designs featuring flat glass glazing elements.

For further information about designing with rooflights, visit www.roofglaze.co.uk, orwww.narm.org.uk.

• Designing with rooflights - supporting the guidance in ADL2A & ADL2B (2010)
• This document contains findings of research undertaken by De Montfort University into the effects of rooflighting on energy consumption and CO₂ emissions. It can be downloaded free at www.narm.org.uk