The importance of visual comfort has been demonstrated in a wide range of research studies that show that factors such as outdoor views, natural daylight and direct sunlight can have real psychological benefits to an occupant’s health, wellbeing and productivity.
In addition, the more we make use of natural daylight the less electricity we use, thereby reducing our negative impact on the environment.
Recognising these benefits, visual comfort is one of four comfort factors that form the Multi Comfort design concept and a key element considered in the design and construction of Bartholomew Barn, the first Multi Comfort building in the UK.
Bartholomew Barn project brief
As Bartholomew Barn is a multi-purpose school that will be used for a wide range of education activities from singing lessons to drama and sport, there were a variety of different requirements in terms of visual comfort.
As can be expected in any environmentally sensitive building, the project brief involved maximising natural daylight but a key objective was also to dramatically improve visual comfort to positively impact the student’s ability to learn and a teacher’s ability to teach.
Challenges for achieving visual comfort
The project brief presented some challenges: the requirement for natural daylight has the potential to conflict with different activities and working environments. For example, direct sunlight and highly reflective surfaces such as desks can cause repetitive eye strain, whilst the use of interactive white boards require a good degree of room darkening in order to be visible. However, blocking out natural daylight and relying on artificial lighting not only increases a building’s in-use environmental impact but also inhibits a view of the outside world, impacting negatively on the occupant’s health and well-being.
Solutions to control daylight levels
Skylight windows were the first solution chosen to allow high levels of natural daylight to flood into the property.
Bartholomew Barn is generously lit by two rows of skylight windows on the north elevation to provide an even light, whilst a third row of roof light windows on the north elevation gives natural daylight to the student changing rooms, without compromising privacy. Furthermore, a series of four fully glazed doors with glazed panels above on the south elevation 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.
To control the levels of natural daylight, the choice of a solar shading solution was key to adjusting 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.
The glazing at floor level on the south elevation also has manually operated roller blinds with an opaque fabric: these blinds can be lowered to any height to provide flexible light control.
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
One key factor often overlooked during the specification of solar shading fabrics is the amount of visible light transmitted.
BREEAM guidelines stipulate that Visible Light Transmission data (Tv%) should not exceed 7% to provide visual comfort. Another consideration is the issue of through-vision. With most fabrics, 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.