Brick wins hands down
We hear a lot about the glories of prefabrication and the importance of increasing its use but, ironically, there are times when it is just too expensive - when one has to go for a hand-crafted option and work very hard to create a machine-made aesthetic.
This was the case with an office building on a business park in Leeds, where architect Philip Lees designed a building to comply with a seemingly contradictory planning brief.
The planners' guidelines stipulated that buildings should incorporate the use of both traditional and modern materials of the highest quality, and the sceptic might have come up with a design along the lines of 'something old, something new'.But in designing an office building for GMI Construction at Thorpe Park Leeds, Philip Lees hit on a solution that satisfied both requirements with one material. It opted for a terracotta panel effect, combining a traditional material with an uncompromisingly contemporary interpretation.
This was only one element in the palette of materials that the architect adopted.The two-storey building has a total floor area of 3,000m 2, arranged as two parallel wings linked by a central circulation and service core. It has a standing-seam aluminium roof and is clad in a mixture of curtain walling, composite panels and brick.
Originally the architect wanted to use terracotta tiles, but it was not to be. Alan Soaper, an associate with Philip Lees, explains: 'We wanted to achieve the modern aesthetic which we believed could only be created by using a terracotta tile cladding, but the systems we researched were massively expensive.We compared this with traditional brick and discovered that the new Desimpel modular format could achieve the same modern aesthetic at a fraction of the price.'
The practice opted to use the modular bricks, stack-bonded with narrow mortar joints, to replicate the factory-made product that it could not afford. Even more ironically, this was a far more demanding and labour-intensive form of brickwork than a conventional solution, but the price differential was still not eroded.
In fact, explains the practice's Paul Tew, the cost difference was 'enough to make the project viable'.The bricks used were of the Desimpel non-standard modular format with dimensions of 290 x 90 x 65mm. For both the architect and the contractor this was a new experience.
'We have not used stack-bonded bricks of that size before, ' Tew explains. Because the eye can detect any irregularity with stack bonding, particularly where the mortar joints are so thin, there is almost no tolerance of size variations.Therefore sorting of the bricks was essential to eliminate any that were outside the tolerance limit.
The other challenge was presented by the quantity of ties and reinforcement required.'There were double the number of wall ties and double the reinforcement, ' says Tew.
The larger number of wall ties meant 'we had to pierce the insulation twice as often'.
In addition, construction is slower than with standard brickwork and so the overall cost rises. But all these concerns were manageable, and the result - the building was finished at the end of last year - is one with which both the architect and client are delighted.
'Everybody is pleased with it, ' says Tew.'We wanted to create a mass-type arrangement rather than individual brick elements - one reason that we chose a mortar similar in colour to the brick.'That it has succeeded is reflected in a comment by Andrew Schofield, site manager for GMI Construction. 'The building has created a lot of interest and some still think we've used a terracotta tile, 'he says.
For Hanson, having achieved such an excellent result, there is still the issue of whether it can solve the paradox of on-site work being so much cheaper than factory production. It comes as no surprise that it is considering developing its own panels, clad with brick slips.
Why stack bonded brickwork?
Modern brickwork has for many years been constructed almost entirely in stretcher bond, on both domestic and commercial buildings, writes Hanson Brick's design and technical manager Paul Rogatzki.
By comparison, traditional masonry seems far more versatile, making use of numerous bonding patterns such as the well-known Flemish and English bonds. In an effort to retain the aesthetics and durability of clay masonry, architects have been looking at ways to identify with the traditional and yet produce a more radical effect.
Large-format clay tiles have provided a possible solution to this problem of escaping from tradition. On site, they are mechanically fixed back to a 'hanging'system.No mortar is necessary and the construction is fast and free from craft-related skill problems.
However, one of the system's drawbacks is the high cost.
Currently it is well established that the tile hanging is more expensive per square metre than brickwork.
One effective alternative is to build stack-bonded brickwork. The visual effect of continuous vertical and horizontal lines gives the same appearance as the tiles, which also tend to be hung in a stackbonded fashion.
Additionally, with careful design, there is an obvious benefit that the brickwork is self-supporting, in contrast to the cladding-panel effect of tile systems with their complex supporting framework.
What are the key steps in considering stack bonded masonry?
The strength of the wall is reduced by the use of continuous joints. In particular, the lateral or flexural strength - ie the resistance to wind loading - will be considerably less for a stack-bonded brickwork panel built with traditional mortar.
This problem can be resolved by increasing the frequency of wall ties per square metre.The standard spacing of 450mm vertically and 900mm horizontally should be revised. This will involve a check on the structural design.Alternatively, it may be beneficial to introduce stainless-steel structural bed-joint reinforcement.
Good-quality workmanship is important when aiming to achieve uniform, continuous joints. The type of brick selected will be most influential on this aspect.
On the Thorpe Park project, the architects have used a number of features which have provided a unique characteristic and accentuated the resemblance to modular panels.The brick type is a 290 x 90 x 65mm Rossini, a smooth red facing from Hanson's Desimpel brand in Belgium. The extended stretcher length (which is almost 50 per cent longer than the standard UK 215mm) is particularly striking in a stack-bonded arrangement.
The Rossini's smooth red texture and clean sharp rectangular appearance provided the perfect choice to achieve clean horizontal and vertical lines. Coupled with this, the walls have been built so that continuous horizontal and vertical joints divide the brickwork into panels.These joints are accentuated by the use of special shaped bricks that have a 50mm wide x 35mm recess.
These were used at the window reveals as well as at the expansion joint locations.
This effect was only achieved by the use of a high percentage of special shaped bricks. One important role for Hanson's technical support services is rationalising and simplifying the quantity and type of specials.This must take into consideration the clay characteristics, which often dictate the allowable shape and size of a product. At Thorpe Park production planning was critical to ensure that the construction programme was not hampered in any way.
It was soon apparent from the architectural detailing that the number of special shaped bricks required was considerable and that manufacturing difficulties could occur.It is not uncommon for the brickmaker to vet a set of drawings and request that the designers consider alternative, less ambitious, shapes or size.
One solution to this problem, which offers the architect a compromise, is the use of cut and bonded specials.