Solar Gain, Solar Control Film and Historic Buildings
Solar gain (or solar heat gain, SHG) in the built environment refers to the increase in thermal energy in the space or structure. Solar gain is the solar energy that can enter the building via glazed windows (and doors) and this can cause overheating in the building (Pickles 2016, 9).
Overheating can cause thermal discomfort and the inevitable health implications are due consideration; equally airflow, humidity and radiant heat are factors that impact the thermal comfort of living spaces. This heat gain can be caused by 'direct and diffuse radiant energy from the sun, entering a building or falling on a surface and being conducted or radiated to the interior' (Glossary of Environmentally Sustainable Design, 2011). Of interest, SHGC (solar heat gain coefficient) is a number between 0 and 1 and is a measure used to define the 'incident solar radiation that is admitted through glazing, both directly and by absorption and subsequently released inward' (Glossary of Environmentally Sustainable Design 2011).
The sun can overheat glass on windows and doors, cause direct solar and heat radiation, and impact on internal organic and material fabrics. Ultra Violet (UV) Light can damage paintings and furnishings (Pickles 2016, 9). The glare caused by direct solar radiation (for example, light streaming in through the windows) in today's screen-reliant world also requires consideration too.
The role of glazing in admitting external gains is significant and mitigation measures should focus on the role it plays (Historic England).
We have discussed awnings and canopies elsewhere, but what other options are there to consider when trying to manage solar gain?
Internal shading in the form of blinds, curtains and internal shutters are good options to consider. Solar control film can also limit the admittance of infrared radiation whilst allowing some visible light to pass through, and there are variants to review when making your decision. Variabilities in Solar control film include the level of reduction of daylight, reflectivity and aesthetic differences such as tints.
When considering solar control film it is worth noting that it is not a temporary solution therefore it might impact direct sunlight in the winter and it may also change the aesthetic appearance of the facade. Historic England note that Solar control films can be difficult to remove and 'would not be suitable for use on handmade or early machine-made glass' (McCaig, Pender and Pickles 2018, 34). Historic England also note that the character of the building needs to be considered in relation to any changes to the windows which might becomes tinted due to the addition of Solar control film, noting ‘any aesthetic change to a Listed Building may require listed building consent’ (Historic England). It is important to note, however, that research has found that Solar control film is 'efficient in offices that suffer from high solar gains in which orientation and window geometry are important influencing factors' (Kayani 2021).
References
Glossary of Environmentally Sustainable Design. 2011. Environment Design Guide, 1–24. Available online at <http://www.jstor.org/stable/26151899> accessed 25.6.24
Historic England. ‘Overheating in Historic Buildings’, Retrofit and Energy Efficiency in Historic Buildings. Available online at <https://historicengland.org.uk/advice/technical-advice/retrofit-and-energy-efficiency-in-historic-buildings/overheating-historic-buldings/> accessed 24.6.24
Kayani, A. 2021. 'Overheating in Historic Buildings. Historic England. Available online at < https://historicengland.org.uk/whats-new/research/back-issues/overheating-and-historic-buildings/> accessed 25.6.24
McCaig, I., Pender, R., Pickles, D. 2018. 'Energy Efficiency and Historic Buildings. How to Improve Energy Efficiency. Available online at < https://historicengland.org.uk/images-books/publications/eehb-how-to-improve-energy-efficiency/heag094-how-to-improve-energy-efficiency/> accessed 25.6.24.
Pickles, D. 2016 [2012]. 'Energy Efficiency and Historic Buildings: Secondary glazing for windows', Energy Efficiency and Historic Buildings. V1.1. Available online at < https://historicengland.org.uk/images-books/publications/eehb-secondary-glazing-windows/heag085-secondary-glazing/> accessed 25.6.24
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