Getting Sunlight Underground

Tim Bawtree asked us to find a way to bring natural sunlight into his proposed new-build semi underground house. He met us at Grand Designs Live and so knew we produced a range of off the shelf items that ducted natural sunlight into dark spaces in buildings.

Kevin Bray our sales Director made the initial contact and visited the site of Tim's proposed new development in the regency City of Cheltenham. He returned with the almost unbelievable story of Tim's plans. Tim and his family lived in a typical Regency terraced house with a long narrow garden at the rear. His plan was to create a modern family sized house at the rear using around 2/3rds of the garden space. Access to this property would be from the rear using the existing communal access road. As the site was narrow and long, Tim's vision was to create the majority of the building underground with a two storey block above ground at one end. This end of the property was the area of our interest as it was going to house the kitchen area with two floors and around 6m between it and the sky. Tim asked us to come up with a proposal to bring natural day light into this otherwise black hole.

The three Suntile directors Kevin Bray, Tony Skuse and Anthony Harrison-Griffin worked together on creating an outline proposal to achieve this objective. As the house was being built from scratch they devised a solution that involved creating two voids as large as possible within the two story block walls allowing them to install their mirrored ducting down from the roof to the kitchen's ceiling, a distance of approx 6 metres.

With a normal Suntile installation which uses a 240mm x 240mm duct, up to 4 metres is workable, the light bounces off the mirrored ducting and intensifies on its journey. We have installed more than four metres but there is significantly less light coming out of the bottom than going in at the top. Six metres was a long way but we were determined to rise to the challenge.

The initial design was dependant on accommodating a duct size of 500mm x 1000m, we calculated that that would provide enough usable light using two drops positioned as favourably as possible.. We devised a funnel type collector that would be positioned at roof level thus increasing the amount of captured light and directing it down the duct.

Unfortunately due to various technical building difficulties, Suntile's wall void space was eroded down to a letter box shape of 150mm x 1000m. Tony had a considerable challenge in fitting as large a duct into these wall voids as possible - with the added problem of one drop having a slight bend half way down to get around a structural component. Following the ducting installation Kevin, Tony and Anthony arrived on site with their roof collectors and it soon became clear their original concept wasn't going to work. With the now reduced limited duct size something radical was going to be needed and time wasn't on their side with only a week until Tim was planning to move in.

Anthony realised that sunlight was hitting the whole roof and if there was some way to reflect that already captured light down the ducting then they had it. Anthony designed a large curved ski slope mirrored surface positioned in the same plain as the roof but at an angle of 27 degrees to the sun. This would firstly collect a large amount of sun rays and start to focus them. Then by using a series of carefully angled and positioned mirrors the rays could in theory be redirected into, ultimately, a vertical position above the letter box duct.

It's hard to describe, see the ray diagram Anthony used to prove his design and maximize the amount of light possible to pass into the letter box duct