The Sacred Heart Cathedral was consecrated in the year 2015 after a successful completion of construction and commissioning. It can hold up to 1500 people at the same time making it the second largest cathedral in Kenya.
The cathedral is owned by the Roman Catholic Diocese of Kericho. It was constructed by a project team comprising of both international and local firms with Esteel Construction Ltd Kenya as the main contractor. The architectural team comprised of John McAslan and partners of the United Kingdom and Triad Architects of Kenya. The quantity surveyor, Barker and Barton, is a local firm.
EAMS of Kenya handled electrical and mechanical works. Structural engineering works was handled by Arup of the United Kingdom and Botswana and Eng Plan of Kenya. The furniture design and entrance doors were done by Studio Propilis of Kenya. John Clark, Glasspainter of Germany did stained glass and artworks, he had local artists as well in his team. These were Florence Wangui who was responsible for the bronze relief panels on the entrance doors and the “Stations of the Cross” glass panels and Githaka Karuri and his team were responsible for the “Creation” mosaic.
The cathedral has since bagged three awards, in 2017 the Civic Trust, which organises Europe’s longest-established built environment awards for projects that provide cultural, social, economic or environmental benefit, presented Special Awards to the Kericho Cathedral team. In addition, the project was a winner in the Surface Design Awards for the lighting design, and received the Judges Special Award at the British Construction Industry Awards in 2016.
The building is approximately 1,375 square meters, and up to 25m high, tapering down to 10m at the entrance. The ceiling of concrete arched frames is interspersed with timber ribs and the inclined roof is clad with locally-made clay tiles. Its base is clad in the most durable of local stones: Nairobi Blue Stone. The project team ensured that most of the materials used in its construction were made by local craftsmen, it’s only when the materials were not locally available that it will be sourced elsewhere.
One of the main challenges during its construction was the location. Kericho town lies within a seismic and volcanically-active zone of the East African Rift System. That informs the careful engineering that has developed the structure such that it will be strong in the event of an earthquake in this highly-seismic zone. A seismic hazard desk study was carried out by Arup, therefore, to establish seismic design criteria appropriate to the Kericho site. The Arup team regarded this as essential because the Cathedral will be a building of cultural significance, with a design life of 100 years; during which time an earthquake may well occur.
The international and local teams worked well together to harness best practice in seismic engineering, structural design, natural ventilation, acoustics and lighting, while at the same time respecting the local environment and the needs of the church and community. The quality is notable, with local teams demonstrating outstanding skill in delivering a structure larger and more complex than they would usually work on, to an exceptionally high standard.
Structural and Civil engineering
Arup provided civil, structural, building physics, acoustics and lighting consultancy to develop the design of the building, and then supported Kenyan engineering firms to complete and deliver the building through to completion, with specific inputs to the fair-faced concrete construction, and acoustics and lighting commissioning.
Various structural options were considered during concept design stage. The design team decided to adopt a simpler geometry. They settled on the simplest of structural forms: a Vierendeel truss.
Concrete was also settled on as the material of choice because it could be produced in batches on site and the most common building material in the region, so supply chain, and design and construction expertise were already in place.
Stability is provided through different mechanisms in the two primary directions. Laterally, the concrete frames are inherently stiff because of the triangular form above the column head level. Forces are therefore delivered to the column heads, where a large bending moment is developed to prevent the column rotating when subjected to those forces. This moment could be carried at ground level but would have resulted in substantial substructure works and columns that were at their widest at ground level. The adopted solution, therefore, was to carry the moments at the column heads, leading to columns that are widest at the top and are doing relatively little structural work below ground. Longitudinally, the roof carries stability forces to the column heads, where they are transferred into a concrete slab which, in turn, transfers them to the external wall line.
The roof frames need to be joined in such a way that sufficient stiffness is developed. In non-seismic regions, this direction is usually less critical because the lateral loads due to wind load are relatively small. In a seismic region, such as this one, the dominant lateral load is related to the total weight of the building, so is equal in both directions. The structural form in this direction was therefore more challenging to resolve than might otherwise have been the case.
The structural design solution meant developing a vast concrete skeleton for the building, given the prominence of the concrete skeleton in the finished building, achieving a high quality, ‘as-struck’ finish was essential. The contractor, Esteel, progressed through two sample sections of the curved arch, to create their own flexible ‘kerfed’ or notched inner shutter for maximum flexibility when removing the formwork after the skeleton had gained sufficient strength.
The arches were each cast in a single days’ pour to avoid day joints, using on-site batched concrete from single-source stockpiled river sand and aggregate to achieve colour consistency. Progressive shuttering of the top surface of the arch enabled good, consistent vibration of the concrete at each stage of the continuous pour which, for the larger arches, took every minute of the equatorial 12 hours of daylight. The result was consistent, unblemished concrete, with edges so sharp that the contractor hand-chamfered the lower corners of the columns to avoid harm to the small children who regularly play in the aisles during the church services.
Natural Ventilation and Lighting
Kericho is located high in the Rift Valley where temperatures and the weather changes frequently and rapidly. With this in mind, the project team made it their business to achieve natural lighting and ventilation.
Arup carried out thermal modelling of the main space using hourly data from Nakuru which was the closest match to the monthly weather data for Kericho. The data showed that the temperature rarely drops below 10°C and rarely exceeds 32 °C and, and humidity is low.
Significant effort went into the design of the high-level vents with the architect, and the principle adopted was to lower the central roof-light strip to form a walkway with the louvre vents on each side. This arrangement avoided the need for complicated open/closing mechanisms or regular access to the vents.
Since solar gains are extremely high and thermal insulation is rarely used in Kenya, the solution was to use the architect’s vision of a clay tile roof as an outer skin, protecting a waterproof inner layer made from ubiquitous metal roofing sheets. The gap between the two layers was well ventilated to dissipate heat build-up and also to reduce impact noise from the heavy rainfall that happens most afternoons. An inner, white, plasterboard ceiling was mainly for aesthetics to provide a backdrop to the timber slats and reflect daylight, but was detailed so as not to impede airflow out through the roof.
Light sources are embedded in the building fabric: the central roof skylight runs the length of the building, widening to illuminate the altar in a shaft of light, with supplementary light coming from side windows and doors. The skylight design provides consistent ambience, despite these variations, with a diffusing glass interlayer scattering sunlight to protect the wooden fixtures and fittings inside the building and prevent the brightness acting as a distraction from services.
Both the daylighting and electric lighting work to reveal the surface qualities of the timber and concrete. The scheme is low-energy, economically sustainable, and part of the Cathedral’s character. The electric lighting is now controlled remotely from a tablet computer so that it can be switched on or off during a mass, as required, from within the congregation.
Arup worked closely with the architect during the earliest stages of the project to combine the divergent themes of: ‘family at table’ (curved seating around the altar, common in African Catholic tradition); a single, unifying volume; clarity of speech delivered from anywhere within the Cathedral; and a lively acoustic ambience to encourage participation in the service.
A sound system was essential, however, for two reasons: even the strongest voices struggle to carry past 20-25m, and the Cathedral is 50m in length; plus, the clergy wanted to be able to communicate with crowds of worshippers in the surrounding landscaped gardens when the building was full on special occasions.
As opposed to traditional churches and to protect the aesthetic simplicity in the Cathedral, the team selected smaller units that could be hidden in the building finishes. Rows of loudspeakers are located behind the slatted timber ceiling, with distributing speakers down the length of the building for even sound coverage and good speech quality. Ceiling speakers in the transepts are intentionally located near open doors to spill sound into the grounds to serve larger crowds, and additional connections are provided to extend the system to temporary external loudspeakers if required.
To keep down costs, the design was based on widely available products that could be installed by local contractors. A digital processor is provided to time-align the output of each row of loudspeakers and manage levels, and the system generally operates automatically, though it can be operated wirelessly, when required, for larger services. Though not unusual in its design or engineering, the Cathedral is exceptional in the way it has been delivered in a relatively remote region.