Project information
Eight storeys of apartments featuring cross-laminated timber panels
Completion date: 2009
Building type: Multi-storey apartment block
Location: Hackney, London
Architect: Waugh Thistleton Architects
Structural Engineer: Techniker
Timber supplier and erector: KLH UK
Timber elements: Solid wood panels for floors, roof, internal and external walls, lift and stair cores
CASE STUDY:
MURRAY GROVE, LONDON
Timelapse video showing on site constuction process.
The Architects interest in using cross-laminated timber arose from an environmental position and a desire to make CLT a more acceptable construction material, especially in tall structures.
The building comprises of 29 apartments, equally divided into private and social housing.
The cross-laminated panels were assembled using a unique structural system pioneered by KLH in Austria. The video below demonstrations how perpendicular layers of timber strips glued together to form a CLT panel.
Benefits of using CLT:
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Makes construction more sustainable.
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Lowers the energy used in construction,
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Reduces heat loss during occupation by improving insulation and airtightness
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Very easy to demolish and recycle at end of life.
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Loadbearing walls removes the need for columns and beams, therefore freeing up the internal layout.
The buildings façade is externally clad in timber, which is made up of 70% waste timber.
Exploded Axonometric
Structure
Screws and angle plates secured the joints. Stresses are generally very low throughout the structure although, at points where cross-grain pressures are high, screws were added to reinforce the timber locally. Progressive collapse is avoided by providing sufficient redundancy so that any single elements can be removed.
Construction
Had the building been constructed of conventional reinforced concrete, it would have incurred an additional 124 tonnes of carbon generated during construction. Adding this to the 188 tonnes of carbon sequestered (locked away) in the 900m3 of timber in the structure results in a total offset of some 310 tonnes of carbon. This gain, combined with the building being better insulated and more airtight than the Building Regulations demand, convinced the local planning authority to grant a dispensation from the ‘Merton’ rule that normally requires at least 10% of the energy used during occupation to be generated onsite.
The development does however include modest PV generation to power lights in common areas and the water booster pump, saving expenses that would otherwise be met by charges on occupants.
The CLT structure comfortably achieved the required fire resistance. The structural engineer allowed for charring to achieve 60-minutes fire resistance and achieved 90-minutes fire resistance by adding plasterboard.
The untreated timber relies on the building envelope for protection from damp and rot. While installation in wet weather was inconvenient, it had no effect on the panels because the system releases moisture readily as it dries.
Fixings
Cables and pipes were generally surface mounted with simple screw- fixed straps.
The plasterboard was installed on metal tophat sections. In contrast, Austrian practice takes advantage of the factory’s ability to cut chases for service runs. Hence, they would normally fix the plasterboard directly to the CLT panels.
Another encouraging conclusion is that CLT is evidently well suited to infill construction. This is because, when compared to other materials, the CLT site is less disruptive to neighbours on account of the rapid construction and quieter building activities using lightweight power tools. These tools pose a lower hazard to operatives’ health than the heavier equipment needed to drill into concrete, masonry and steel structures.
Acoustic Performance
Maintaining a high acoustic performance for the Stadthaus was an important design consideration. Acoustically, timber buildings have traditionally been classified as ‘poor’ when compared with reinforced concrete and masonry. But CLT panels:
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Have a significantly higher density than timber frame buildings.
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Provide a solid structural core on which different, independent and separating layers can be added.
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A layer principle that overcomes any sound transfer issues.
Cost
Although more expensive than an equivalent reinforced concrete frame, CLT brought significant overall savings by making a radical cut in the building programme. For example, an equivalent concrete building was estimated to take 72 weeks, whereas the CLT solution required only 49 weeks.
The CLT structure represented three days production at KLH’s factory.
Accuracy
The contractor was delighted with the +/- 5mm tolerance achieved with the timber construction, compared with the 10mm normally expected in concrete structures. The consequence of tight tolerances is the ease of fitting the structure together, its good airtightness and the ease of fixing cladding.
Floor-to floor movement due to moisture and creep is estimated to be 3mm, which gaps in finishes can tolerate.
By avoiding concrete cores, there is not the differential movement to resolve between concrete and timber that occurs with conventional timber frame.
Self-drill woodscrews installed using lightweight power drivers
Wall panel anchored to floor panel
Easy fixing of services to ceiling
Typical internal wall arrangement
Fig 10. Completed Structure
Fig 11. Exploded Axonometric
Fig 12. Site Construction Photos
Fig 13. Youtube Video Construction
Application
Although the enclosed precedents demonstrate residential applications, SIPS andCLT panels are used in other instances. They are more commonly found in residential structures because of the maximum spans achievable lend themselves to more appropriate for creating domestic spaces. Schools and other
similar structures are able to use these panels as the maximum span available from CLT (15m) still makes their use appropriate. However when attempting to
achieve larger spans necessary for offices or industrial units other structural methods become more practical due to often needing to span further.
CLT UK Production It is also worth noting that the production within the UK is currently limited, so many UK precedents have imported their panels from
Europe. Unfortunately this adds a premium to the cost, which sheds SIPS panels in a slightly more economical light when compared directly to CLT. It is being explored that the softwood necessary to produce CLT is commonly found in the UK forests, and the probable cause for no UK manufacturing is because there is still little demand for the panels in the country due to the panels being a new innovative construction method.
Construction materials