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Out of Africa

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The cool, white Modernism of The Manser Practice's Umoja House, a diplomatic office in Dar es Salaam, Tanzania, is a fitting response to the city and its climate

Umoja House is a shared office, a 'co-location' of diplomatic missions from several countries. It is a rarity for diplomats to have the diplomacy to work side by side, but the UK's Foreign and Commonwealth Office (FCO) has orchestrated the process of colocating the UK's High Commission and the Department For International Development (DFID), plus the European Union and the embassies of Germany and the Netherlands. This grouping has been the client body for the project and has now become joint building manager.

Dar es Salaam is a poor city in a poor country, a city where even the assiduous Mr Pevsner would have been hard pressed to chart an architectural context to which a new building might respond. There are mostly basic concrete-framed, post-war buildings, with the quality rising sometimes in the diplomatic area, plus some rendering and tiled pitched roofs. If the new European presence appears assertive in its scale and gleaming whiteness, Manser's international Modernism works here. Its regionalism comes from its response to climate.

Located just 7infinity south of the equator, the high temperatures typical of this latitude are greatly modified by the coastal location.

Maximum temperatures rarely rise above the low 30degreesCs, and the lowest midday temperatures are in the mid-20degreesCs. The drawback of the coast is oppressive humidity, often more than 90 per cent (there is also occasional intense rainfall). Some who have worked around the tropics find these Tanzanian conditions less bearable than, say, the dry heat of the Gulf, where temperatures can be up to 20degreesC higher.

Manser's early climate-responsive design concept for the building was a doughnut on pilotis, with an oversailing roof. Thus relatively shallow office space around a central void would lead to convection, with air drawn in at ground level, flowing up the void and out at the roof perimeter. It could have powered some natural cross-ventilation to offices, a back-up if there were to be a system failure in what has always been planned as an air-conditioned building. That concern about system failure looks less significant now, with good technology installed and forward plans in place for building maintenance (see Project management box).

Reality caught up with the doughnut.

Each mission had a separate, relatively fixed floor area requirement not easy to massage into this shape. Manser's response has been to create two parallel blocks of office space either side of an atrium, each block deep enough for double-banked cellular accommodation. The atrium is bridged at either end, allowing each mission to occupy a single floor with only one secure entrance from the rest of the building. In Manser's earlier concept, the floorplates ran from the endstop of the solid west wall eastward for different lengths, so meeting the different area needs.

Now all the floorplates are of the same length, with different enclosed areas as required, leaving the rest of the floorplates as varyingsized open terraces. These terraces could be enclosed as office space in the future.

The other main problem of a doughnut is its lack of orientation. In the final design, orientation has become a very formative influence on the building. On a tight site, the building is skewed as far as possible toward getting its principal facades facing north and south. With the east-west sunpath almost overhead at this latitude, the facades to north and south get near-complete solar shading from the oversailing roof and fixed louvres set a metre out. To the west, the stepped-plan solid wall provides complete protection. To the east, offices running to the ends of floorplates are louvred, but terraces are unprotected. The deeply overhung end to the atrium is open-walled but meshscreened, admitting very little direct sunlight in the early morning.

While these reality checks have made the layout more conventional, an essence of doughnut remains. The five mission floors still stand on pilotis around the central void of the atrium under an oversailing, wavy concrete roof. At ground level there is a ring of 'pods' - separate concrete walled and roofed structures - for consular entry, conference room, plant, etc. Above and around these pods are steel mesh screens allowing air (but not livestock) into the base of the atrium. The corners of the pods are rounded with the intent of improving air flow. The overall air flow is a balance, between stack effect and coastal winds. The mesh east wall admits more winds, but reduces the 'purity' of the doughnut stack effect. (This mesh also admits rain occasionally. ) These rounded wall corners have been used as motifs elsewhere on the site, along with curving concrete roofs, for singlestorey structures, notably the visa section building at the front of the site (shared by the UK, Germany and the Netherlands), for the porte cochère outside the consular entrance, and for another plant pod on the site edge.

When I visited Umoja House in midDecember, a joint missions Christmas party was being set up in the atrium. In this nonair-conditioned space, the oppressiveness of the outdoor climate was greatly reduced by shade, air movement and the thermal mass of the building (concrete with an exterior layer of insulated render). The environment was well tempered. And psychologically, white feels cooler. It still takes a bit of acclimatisation, but then the midnight temperature that day was 27infinityC. Warm for the time of year.

The surrounding office spaces, not much shown in photographs for security reasons, are generally double-banked along spine corridors. Only the DFID has gone for much open-plan space, as it has in the UK. Total occupancy is about 250. Offices are plasterwalled, with acoustic render ceilings, and with oak floors in shared areas. Only corridors (or the centreline of open-plan areas) have drop-ceilings for chilled air supply.

Each window also has a fan coil unit beneath it. Air conditioning is provided centrally, although controlled per floor. It runs for working hours; there is enough thermal inertia only to require it to be switched on a couple of hours before work starts.

Each mission has generally fitted out its own space, some with a little help from the FCO. Partitioning could be removed or relocated at other mullions by negotiating around air inlet spacings and runs of light fittings.

There are plentiful windows, although for security they are heavy-framed and bottomhung, opening only about 100mm at the top (another factor that would limit attempts at cross-ventilation). It is a paradox in this intensely lit country that the necessarily extensive solar shading creates a significant uniformity of interior daylighting. Artificial lights are often on. However, at Umoja House, views out are not blocked by the external brises soleil. And, impressively, views into the atrium are alive with light. The quality of light in the atrium is a real bonus. It comes from many directions - from around the ground level pods, through the mesh slots in the stepped-plan west wall, from the open east end of the atrium, from the roof perimeter, and from slowly roving 'spotlights' of intense sunlight shining through fixed circular skylights in the atrium roof. It is a neat piece of architectural animation.

It is an unfortunate necessity that this space will be enjoyed by only a small community. But if some visitors are inspired by its lessons of regional design, it will have been the more worthwhile.

Project management It is several years since the High Commission acquired this site, initially for its own use. A limited competition was held in 1995/96. Security upgrading delayed the project for most of a year following the August 1998 bombing of the US embassy in Nairobi, in neighbouring Kenya, and also in Dar es Salaam. Some four years of international meetings in Croydon and on the Continent run by Mike Kelly of the FCO brought the project to its current completion date, via many revisions of layout designs.

For construction, each main UK-based consultant had a local counterpart which attended site meetings and gave day-to-day approvals, but did not perform a full executive consultant role. Any significant design changes were made in the UK and issued as variations by the local project manager, David Lawson. Tight control has been kept on changes, contributing to the delivery of the project both on time and on budget.

Lawson wrote into contracts that production documents should be delivered within 90 days of engagement, to get the component procurement process flowing in a build period of 19 months. While some items were procured locally, such as concrete, timber and paving, much came from Europe and South Africa. Added to this, Lawson wanted some of the systems running early, especially the air conditioning, which ran from February 2002.Not only was this part of pre-commissioning, it also provided improved conditions for finishing trades such as painters, and provided humidity control for the oak flooring, which was delivered to site in air-conditioned containers. The timber has not moved noticeably since.

This was part of a more general approach over the last few months of the project, of snagging-as-you-go, so that the project could be handed over in running order by the time the project managers left, around now.

Some £1 million of cost cutting was required on an overall £16 million project budget (including site purchase). For example, cheaper marble was sourced from Spain, and a different German insulated render system used. Local sourcing was increased, such as local concrete pavers in place of Yorkshire setts. And the timber car shading for the main car park was changed to a proprietary canvas system on galvanised tubular framing.

It was normal to use local labour, although foreign suppliers offering product warranties often sent their own supervisor/trainers. Norwegian general contractor Noremco has been in Tanzania for about 20 years; it completed some two million site man-hours without a reportable accident. Assistant project manager George Lilley says that it was the best-organised site he has encountered and that the quality of workmanship is as good as you would find in Europe. (And it is. ) Lawson and Lilley have planned for the running of the building.

One of the two chillers could provide a workable, though reduced cooling regime, and there are back-up generators and a water supply from a borehole. A significant stock of spares is held, and contracts have been let for the delivery of other spares at short notice; the materials palette is not extensive. Maintenance contracts exist, including the cleaning of this pristine building sited in a notably dusty environment. Skilled people are in place to run the building, and a joint management committee of the missions - which each paid for the building and now its running in proportion to their areas of use - is responsible for managing upkeep generally, although each mission maintains its own space. Lawson and Lilley leave in hope.

Environment and structure The challenge for the structural and services engineering design of the project was to create a secure building, built to European standards in one of the poorest countries in the world with little local industry and with an extremely aggressive climate.

Defence against the climate pervaded all aspects of the design. The building is orientated on an east-west axis to minimise solar gain with a solid concrete west wall to protect against the afternoon low altitude sun. Brises soleil used on the other facades are designed to prevent all but the early morning sun from reaching the facades themselves. The inspiration for the solar concrete shell roof structure came from the local architecture. Covering the two wings of the building and the courtyard, it is designed both to absorb the sun's energy and to act as a climate modifier to the internal facades and to the open courtyard. Modelling this design concept was carried out inhouse using TAS software, which verified that the courtyard would remain environmentally acceptable, relying on the prevailing sea breezes to reinforce the stack air movement.

Internally, there is little alternative but to air condition the spaces. In designing this system the team was aware that the ability to maintain the equipment using local resources was perhaps the major constraint. The solution adopted is therefore simple and robust.

Minimum cooled and dehumidified fresh air is delivered constantly to all rooms through air-handling plant located in the open climatic void under the shell roof. Perimeter fan coils operating on primary chilled water provide additional cooling which can be individually adjusted.

The central chiller plant is located at ground floor level in a compound and consists of package air-cooled units. This simple concept is reinforced by the thermal mass of a concrete-framed building. The building does not require heating but the hot water supplies to kitchens and bathrooms are provided using roof-mounted solar collectors with electrical immersion heater back-up.

Electrical supplies are variable in Dar es Salaam and power outages occur regularly. The site is supplied by local high voltage to an on site substation with low voltage distribution. All electrical services are backed up by the twin diesel-generator sets located in a ground floor service pod.

Similarly, local 'potable'water services are unreliable in terms of quality and supply. The building therefore has underground water storage tanks with a 10-day capacity which can be topped up from an on-site shallow borehole. All of this potable water is treated through a packaged water treatment plant and re-filtered at the point of use.

Rainwater is stored separately and is used for irrigation and for fire fighting.For drinking, bottled water is used.

For the structure it was more economical to build it using locally sourced materials as much as possible. A concrete frame on a 6m x 7.5m grid with flat slab floor plates and reinforced concrete cores was quickly established as the obvious solution. This concept also provided thermal mass as an internal climate modifier. The local labour is skilled in the use of concrete and the workmanship on the exposed concrete elements is excellent.The robustness of the design was tested in 1998 when the security rating of the building was significantly raised following the terrorist bombings of the US embassies in Nairobi and Dar es Salaam.

This re-evaluation did not significantly change the structural system but a resistance to blast forces became a fundamental part of the design, overall and in detail.Solid concrete is used rather than block. In places reinforcing bars are 40mm in diameter.

The building is founded on the underlaying coral limestone and sands, with a water table that can reach the surface during the rainy season. To avoid the potential problems of localised 'limestone solution features' (voids where the limestone has dissolved over the centuries), a reinforced concrete raft was chosen as the foundation system. The reinforced concrete water tanks, located under the courtyard, bridge between the foundations of the two wings, their weight balancing potential uplift forces resulting from the high water table.

WEBLINKS

FCO Estate Strategy Unit www. estate. fco. gov. uk

The Manser Practice www. manser. co. uk

Norman + Dawbarn www. n-d. co. uk

Gleeds BBL www. gleedsbbl. com

Building Design Partnership www. bdp. co. uk

Cowi Tanzania Consulting Engineers & Planners www. cowi. co. tz

Warrington Fire Research www. wfrc. co. uk

Noremco www. noremco. net

CREDITS

TENDER DATE September 2000

START ON SITE DATE February 2001

CONTRACT DURATION 79 weeks

GROSS EXTERNAL FLOOR AREA 6,982m 2

CONTRACT GC/Works 1 (Edition 3) Lump Sum with Quantities

ESTIMATED FINAL CONTRACT SUM £12,495,087

CLIENT Foreign and Commonwealth Office, Estate Strategy Unit: Mike Kelly (project sponsor)

ARCHITECT (UK) The Manser Practice: Michael Manser, Jonathan Manser, Josh Berry, Barry Mullin, Marvin Farr, James Potter, Phillip Waind, Stas Louca, Matthew Woodthorpe, Helen Osbourne, Charles Stanton (TZ) Norman + Dawbarn Tanzania

PROJECT, FACILITIES MANAGER (UK) Gleeds BBL (TZ) Barker + Barton Tanzania

STRUCTURAL, SERVICES ENGINEER (UK) Building Design Partnership (TZ) Cowi Tanzania Consulting Engineers & Planners

QUANTITY SURVEYOR (UK) Baker Wilkins & Smith (TZ) QS Consultants

INTERIOR DESIGNER Bampton Lane

LANDSCAPE DESIGNER Building Design Partnership

ACOUSTIC ENGINEER BDP Acoustics

FIRE CONSULTANT Warrington Fire Research

MAIN CONTRACTOR Noremco

SUBCONTRACTORS AND SUPPLIERS furniture Paragon Business Furniture; external render Caparol (Germany); roofing membrane Sarnafil; security glazing Barlow Architectural; doors Leaderflush Doors; paints, plating Caparol (Dubai); ironmongery Yannedis; brise soleil Levolux

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