Solar Glazing

Solar glazing is becoming more and more popular in today's energy-conscious culture. The South-facing facade is a big commodity nowadays and everyone seems to want it, whether it's for a traditional or modern design, new build or extension.

Architects, designers and self-builders alike are installing these large, glazed screens which haven't been available until fairly recently, at least not at the scale they are being produced today. This size of glazing is far from the standard folding patio doors!

The reason for their popularity is quite intuitive - who wouldn't dream of opening up a whole side of their house to bring the outdoors in and to flood their living room with an abundance of natural light and warm sunshine?

The latter is often known as passive solar gain and although great in the winter when you are getting lots of free heating but not so great in the summer when the amount of heat can become hard to control. In a heavy masonry construction (and therefore high thermal mass), this heat can be stored in the walls and floor, acting like a radiator to seep the heat back into the living spaces long after the sun goes down. Many houses built in the 70's and 80's were designed to self-heat with this principle but unfortunately they only ever seemed to work in hotter climates, not so much in our cloudy, rainy Britain!

These large glazed windows created uncomfortable heat in the summer and allowed a lot of heat to escape in winter so offered little stability in terms of a stable temperature throughout the seasons. In other instances, the UV light from the sun when exposed to wooden floors, furniture and fabrics, fades colours and sometimes even causes floor adhesives in some floor types to break down. It's obvious why the amount of sunlight entering a house needs to be controlled!

Building Regulations today addresses the issue, referred to as 'limiting the effects of solar gain in summer;. The regulations themselves refer to another document, SAP Appendix P, which includes methods for calculating solar gain, and indicates some of the solutions we can use to minimise some of the less welcome effects.

1. Contrary to popular belief, a West-facing facade (towards the setting sun) is a better orientation to place your solar glazing as you will receive some of the heating effects in winter (although not as powerful as South facing in winter) but less of the uncomfortable over-heating in summer.
2. A roof overhang can create an element of shading that provides the correct amount of shading from the high sun in the summer, but allows in the low winter sun.
3. The obvious post-fit solution is blinds and curtains, which can be fitted internally or externally to control the amount of light. The downside of curtains is of course that they don't always fit aesthetically with the large glazed screens. Blinds are a good light control solution but can obviously be expensive when installed across a whole wall of glazing.
4. In warmer climates, people have used shutters for hundreds of years to keep the sun out as well as to ventilate rooms (when shutters are closed but windows are open). Whilst regular shutters won't work with large glazing systems, it's worth noting that a good ventilation system will help to regulate the heat gathered by the glazing system.
5. Special glazing products already exist and are being developed further, for example Pilkington's Suncool and St Gobain's Cool-Lite, which work to reduce solar gain by reducing solar transmittance whilst maintaining low-emissivity in order to meet today's low U value standards. These technologies are modern-day answers to glass tinting but the glass remains clear!

Regardless of these solutions, we should be vigilant against the interiors we choose to place in front of glazed windows. Avoid wooden floors that aren't UV stable (such as cork and lino) or brightly coloured furniture in sensitive materials (such as silk). Choose pale colours where fade won't be as noticeable, keep artwork away from direct sunlight and make sure rugs are rotated frequently (at least they will fade evenly). Most importantly, check the UV resistance of your furniture and fittings! It's all worth it for that added natural light.

Resources: Homebuilding and Renovating