Case study kindly provided courtesy of WoodforGood
Once again WoodforGood has shared a fascinating case study, this time regarding the use of cross-laminated timber (CLT) in a commercial mixed-use project in sunny San Francisco, California, completed in 2021. Good to see that these projects are becoming more common in North America, makes one wonder what we could do with modern timber construction methods here in South Africa.
San Francisco welcomes its first completed CLT building this year. Designed by Perkins&Will, 1 De Haro is a commercial mixed-use project that combines light manufacturing with Class A office space.
Construction began in 2019 on the 130 000 sg ft four-story building and the building’s core and shell was completed in 2021.
Mixed use brings manufacturers and office workers together
Built on the site of a former gravel company, 1 De Haro is set to breathe new life into a derelict triangle of land.
It aims to increase economic diversity in the area, by bringing together small manufacturing and creative businesses with office workers, in the heart of a residential neighbourhood complete with shops, restaurants and other amenities.
The first of its kind brings a host of benefits
1 De Haro will be San Francisco’s first multi-story CLT building to utilise a fully mass timber structure. Relatively new in North America, this construction method was chosen for a number of reasons:
- Firstly, timber’s ability to sequester carbon means the building has lower embodied carbon than a steel or concrete equivalent.
- Secondly, mass timber is precision-engineered in the factory and can be manufactured to millimetre accuracy. This creates a high-performance material that can be delivered to the exact requirements of an architect’s plans.
- Also, building with CLT reduces structure erection time by as much as 25%, with panels and beams delivered to site by the manufacturers in the correct order for assembly.
Celebrating the warmth of wood
The building is wrapped in an elegant glass curtain wall, with the windows naturally lighting the space while also offering a view inside. Meanwhile, by leaving the wooden ceilings and beams exposed inside, building occupiers will benefit from timber’s biophilic properties, which have been shown to improve both mental wellbeing and physical health. The natural material also connects to the building’s purpose of supporting local craftspeople and manufacturers.
Use of timber
1 De Haro is a hybrid structure built primarily with a combination of CLT and glulam (glue-laminated timber).
Due to the nature of the soil in the area, deep piles were required to anchor the building securely, with the overall number of piles increasing with the weight of the building. The mass timber framing system was calculated at 30% less than the weight of a comparable concrete system, which meant that significantly fewer piles were required. Perkins&Will completed schematic designs in both timber and concrete and steel, so that an accurate comparison could be made.
A concrete slab was laid to meet the building code’s requirements for light industrial use. And as the building code at the time didn’t address the impact of seismic factors on buildings constructed with mass timber alone, steel BRB (buckling-restrained brace) frames were used alongside glulam beams and columns to transfer the lateral loads.
The upper floors were constructed with a CLT slab and glulam beam and post structure, with wood-to-wood connections. This means the building will also be flexible to meet future tenants’ needs as the internal layout can be easily reconfigured as required.
The CLT floors were topped with a concrete topping slab and acoustic mat to dampen the sound from the solid surfaces.
Mass timber buildings on the rise in California
Engineered timber construction methods that have been established in Canada and Europe for many years are now becoming increasingly common in North America as states start to adopt the new building code standards.
On 1st July, the 2021 California Building Code came into force, paving the way for more mass timber buildings in the state. Allowing buildings up to 18 stories to be built from engineered wood, California is set to benefit from the renewability, carbon sequestering and faster production process afforded by this construction method.
You can view the full lifecycle analysis and embodied carbon figures of the building in this pdf.