Kew Gardens Passivhaus Learning Centre

RBG Kew commissioned a masterplan exercise in 2017 to highlight development opportunities and a site hierarchy for future building developments. The new Learning Centre formed a part of that masterplan and highlighted the need for 7 formal teaching spaces for students of all ages, office space for the Kew Learning team, gallery space for exhibits and learning materials and space for learning in external and sheltered external areas.

The building also forms a key element of the Kew Gardens Strategy for Change, which has recently commited their sites to becoming carbon positive by 2030. As such, the brief for this first building required Passivhaus performance (which now aims at Passivhaus Plus), BREEAM Outstanding and Whole Life Zero Carbon, with the embodied carbon of the building's materials and construction, as well as carbon in use, being paid back by the energy the building will create in a 75 year service life period with as few offsite offsets as possible.

These concept layouts set out how the spaces could be laid out on site to deliver the flow intent within the constraints so the surrounding gardens. In each option, the learning spaces surround a shared learning hub, which is accessed from a gallery space surrounding a seminar room. The intent with the gallery is to remove any areas of circulation by widening zones to enable a learning function from the whole floor area. The intent for a ‘beacon’ to be provided to highlight the nucleus of the learning centre is also explored, which focuses on the seminar space in the centre of the plan which also served as a visual anchor for the main entrance to the Learning Centre.

In order to prevent damage to the surrounding tree root structure network, the building footprint has been limited to the footprint of the previous building and only extends beyond this point where the root protection zones cease. The proposed building will use the existing slab of the redundant building as the substrate for its ground floor insulated raft to save embodied carbon. This prevents any impact on the tree root network and also provides the best possible thermal bridge-free foundation detail, with the building structure effectively floating above the cold ground.

The visual impact on the gardens has been reduced by limiting the areas of two storey development to the far side of the site when viewed from the gardens, with the roof pitched at a shallow 9 degrees and clad with sedum to the lower level and PV cells to the higher area. The intent here is to merge the building in with planting at low levels and reflections of the sky at upper levels, to blend the building in to its surroundings.

The materials used for the building structure and facade are based upon a review of embodied carbon, with external cladding provide from Kew Gardens trees, rammed earth walls, timber frame structure and 90% recycle content brick cladding. The insulation used for the building will be grown from mycelium and bound with waste products to form a fully bio-derived and compostable solution.

The new learning centre will have a heating demand of less than 13w/sqm, with full ventilation and heat recovery provided for the highly efficient, high comfort teaching spaces. The energy used by the building will come from a variety of sources, with PV solar arrays combining with air source heat pumps to provide the small amounts of additional heating required over and above that provided by the passive solar gains designed into the window size and orientation. Heat recovery from waste water, electrolytic energy from sewage streams and heat recovery from areas of composting in the external grounds planting areas will also be employed as visible learning exercises.