Buildings that include visual comfort in the design brief ensure a high degree of health, wellbeing and productivity for its’ occupants. A wide range of research studies shows that factors such as outdoor views, natural daylight and direct sunlight can have real psychological benefits.
In addition, as natural daylight is maximised in buildings, reliance on electricity is minimised, thereby reducing the negative impact on the environment.
The MULTI COMFORT design concept recognises these benefits, and visual comfort is one of four comfort factors included in any Multi comfort design. Visual comfort was a key element considered in the design and construction of Bartholomew Barn, the first MULTI COMFORT building in the UK. Waverley worked with the architect and contractor to ensure the choice of window blinds aided the visual comfort design.
Bartholomew Barn project brief
The new-build Bartholomew Barn at King’s Hawford Junior School in Banbury is a multi-purpose hall that is used for a wide range of education activities including music, drama and sport. There is a variety of different requirements in terms of visual comfort.
Maximising daylight was a very much part of the design brief on this environmentally sensitive project. Another key objective was to ensure a high degree of visual comfort to positively impact the student’s ability to learn and a teacher’s ability to teach.
Challenges for achieving visual comfort
This project brief presented some challenges: the requirement for natural daylight differs with different activities and working environments. For example, direct sunlight and reflective surfaces such as desks can cause repetitive eye strain, whilst the substantial room darkening is required if interactive whiteboards are used. However, blocking out natural daylight and relying on electric lighting not only increases a building’s in-use environmental impact but also blocks views to the outside world, creating a less stimulating environment and thus impacting negatively on the occupant’s health and well-being.
Solutions to control daylight levels
Skylight windows were included in the design to allow high levels of natural daylight to flood into the property.
Bartholomew Barn has two rows of skylight windows on the north elevation that provide an even light into the main teaching space whilst the third row of roof light windows on the north elevation gives natural daylight to the student changing rooms, without compromising privacy. Four fully glazed doors with glazed panels above are spaced evenly along the south elevation to provide useful winter solar heat and light, as well as uninhibited views of the outside. This combination of light sources has the effect of providing a holistic visual connection with the outside world.
The choice of a solar shading solution that could easily control the levels of natural daylight was key. This would allow occupants to change the levels of visual comfort required for the many different activities for which the barn is used.
Waverley installed electric dim-out blinds to the roof light windows to provide total light exclusion during theatrical performances for example.
For the office windows on the east elevation, glare control is ensured by the external canopy roof, which protects the glazing from high summer sun without impeding the view.
Specification considerations for window blinds
The amount of visible light transmitted by window blind fabrics is an often overlooked factor when specifying window blinds.
BREEAM guidelines stipulate that Visible Light Transmission data (Tv%) should not exceed 10% to provide visual comfort. Through-vision is another important consideration when choosing a window blind fabric. Typically the amount of through-vision reduces as the Tv % reduces i.e the reduction of light transmittance means a reduction in how much you can see through the fabric to maintain a view of the outside world. A Tv factor of 3% is widely regarded as the optimum light transmission level that also allows a view through.
Blind fabrics with silver foil type backing such as Verosol Silverscreen provide superior shading performance with a greater openness factor. This is because the metal backing dramatically reduces the amount of light diffused through the fabric yarns.
To find out more about performance data for solar shading fabrics read our blog.
Waverley have a RIBA approved CPD that explains how to use solar shading to improve the environmental credentials of your building. Book a CPD here.