By Gareth Griffiths 📷Gareth Griffiths, Wolf+Wolf and Afrimat
A global first, 84 Harrington Street is officially the world’s tallest building constructed using hempcrete blocks and hemp building materials, say the owners, designer and materials provider. This makeover and partial rebuild of an existing building boasts one of the most expansive uses of hemp-based building block material in South Africa.
I was fortunate enough to be taken for an extensive tour of the building site, courtesy of project architect, ‘Wolf’ Wolf of Wolf+Wolf Architects, Cape Town. Wolf has considerable experience in designing buildings with hemp, from as early as the build of Tony Budden’s first ‘Hemp House’ overlooking the valley and beach in Noordhoek, Cape Town. Budden is a founder and active director of the developers of the new building, the Hemporium.
According to Hemporium and Afrimat Hemp, “84 Harrington Street is setting the benchmark for how to build a safe, carbon-neutral, multi-story building using hemp blocks and hemp systems.”
Hemp construction considered the gold standard for CO₂ reduction
There is a massive increase in the global demand for bio-based construction which is driven by the need for the reduction of CO₂ emissions. Hemp construction is considered the gold standard for CO₂ reduction in buildings.
Previously, hemp houses built in South Africa made use of hempcrete, but not as bricks. For a project of 84 Harrington’s scale, this was not feasible, and inspiration was taken from hemp blocks developed in Europe. The creation of hemp blocks is a viable way to commercialize hemp in the construction industry.
Wolf says that the hemp blocks specified were 110mm x 190mm x 390mm in size, comparable to a standard building block. Previously, ‘Hempcrete’, such as used at the Noordhoek Hemp House and elsewhere, was imported but now it is locally produced. Wolf is such a strong advocate of the material that he used it in the construction of his own studio, located in Cape Town’s environmentally sensitive heritage district, the Bo-Kaap.
The project, built on an existing brownfields site, involved the preservation of certain aspects of the legacy building on that site, notably the facade and some of the existing five floors. To this was added seven additional floors using conventional reinforced concrete (RC) framing technology. Thermally Activated Building Systems (TABS) were added to the new RC members, with chillers at roof garden level, to introduce a measure of natural passive climate control. This is expected to be highly successful, in addition to the use of hemp interior walling, which helps keep a comfortable climate indoors. The designers are confident that the results of this intervention will mean that only the restaurant, office and retail spaces will require HVAC.
There is a chemical molecular-level affinity between hemp and lime , which lends the properties needed by the product to become a mainstream construction material. This means that it provides a strong internal walling material with better acoustic and insulation properties than conventional gypsum-board. The internal walls are cavity walls and services can run inside the cavity as per standard practice.
Plastering is done using airplast, which is smoothly plastered and left exposed, therefore able to maximise CO2 absorption.