BAMBOO
APPLICATIONS WITHIN CONSTRUCTION
As our assessment of sustainability within the built environment increasingly moves towards a more encompassing understanding a building's lifespan, construction materials should be thought of as more than simply an end product. Amidst the volatile volcanic landscapes and lush green jungles of Indonesia, bamboo is currently experiencing an architectural renaissance as a sustainable, economical and versatile construction material.
Drone footage © Hamish Angus McAndrew
Towards the end of 2022, I travelled to the Balinese jungles of Indonesia to take part in an intensive - and hands on - “build & design” course centred around bamboo and its use within the built environment. There I gained a technical and overarching understanding of bamboo’s application within the construction industry - everything from the propagation, cultivation, harvesting and treatment of bamboo; to the joinery and design principles involved in realising a completed bamboo structure.
Hosted by local facilitators at Bamboo U, this culminated in the live construction of a new restaurant building, being built almost entirely from bamboo. This restaurant, located at the Kul Kul Farm in Abiansemal, is believed to be the first heat-bent bamboo structural system on the island of Bali and is intended to seat up to 100 people.
Digital re-composition of my "Bamboozled" artwork created for the Royal Scottish Academy's 198th Annual Exhibition.
Cultivation & Harvest.
As a grass, bamboo grows much faster than equivalent timber species - quickly sequestering large volumes of CO2 as it increases up to 1m in height a day. Some larger species, such as Dendrocalamus asper, can reach heights of 30m and have a diameter of 20cm when mature.
Alongside this, lower nutrient demands allow bamboo to thrive in degraded land that may be unsuited for other uses and its attribute of storing water during rainy seasons, which it then gradually releases back into the soil over dry seasons, can help support surrounding flora and kick-start land after deforestation.
However, despite these alluring benefits, it is important that the growth of bamboo is correctly managed.
To avoid the monocultures we see with other farmed plant species, such as palm oil, bamboo should be cultivated as part of a wider mix of flora. This approach, called agroforestry, helps maintain diverse habitats that can support local ecosystems while also providing multiple income streams for farmers (should disease or poor yields impact one particular crop or species in a given season).
Treatment.
In the absence of a dedicated treatment facility, a simple treatment method called "vertical soak diffusion" (VSD) can be easily set up on site - allowing it to be used in remote and inaccessible places. This method involves securing harvested bamboo vertically and filling the hollow interior with a borax & boric acid solution - which flushes out the starches and sugars and replaces them with salt. This deters wood-boring insects, improves the fire resistance and reduces the bamboo's susceptibility to rot and fungus.
Heat Bending.
Flame torches were used to evenly heat individual bamboo poles one node/section at a time. This would soften the parenchyma matrix structures that bind the bamboo fibres together, generating malleability that allowed the bamboo to be gradually pushed and twisted into a new shape. The benefit of this, in theory, is that the structural potential won’t be compromised in the same way that cutting wedges would using the more commonplace method of "rup-rup" (which involves cutting narrow wedges along one side and folding the bamboo in on itself).
Heat Bent Arches.
The bending was crudely aided by wedging the bamboo between two trees to provide leverage. It was important to maintain a consistent heat across all sides of the section being targeted to prevent splitting - paying close attention to the degree of resistance that the bamboo was giving as it was being carefully pushed and twisted.
The accuracy of the curve wouldn't be overly important during this heating/softening stage. The crudely bent bamboo was then placed within a pegged out template on the ground, where it was paired up with a mirrored bent pole and pinned together where the two poles overlapped.
These arches were then paired up again, and pinned together using bamboo dowels to create the complete arches that would be used in the finished structure.
"Split" Arches.
Alongside the main arches, a series of side arches were completed with flat strips called "splits", cut from a species called Dendrocalamus strictus. To ensure enough strength, these strips were doubled up and bonded together using epoxy resin - again using a pegged out template for uniformity. The splits were clamped and tied together as the epoxy set and additionally pinned with diagonally crossing bamboo dowels to keep everything in place. The excess lengths of these dowels were chipped away using a mallet & chisel.
Sanding.
Once the epoxy had set, the ties and clamps were removed and the arches were sanded to give a flush, smooth finish (and to remove any globby bits of epoxy). After fixing a metal footing bracket to each end, these arches were then ready to be installed alongside the main heat-bent arches.
Photo by Jonathan Igharas
Assembly.
The ends of the main arches were manoeuvred into position and slotted over rebar projecting up from the foundations.
Named "elephant foot" foundations after their resemblance to an elephant's foot, these typically place a large stone atop a pile foundation to act as an interface between the concrete footing and the bamboo, with rebar tying each element together. Depending on the porosity of the stone, it not only provides a buffer from the ground, it can help to absorb moisture away from the base of the bamboo.
The elongated “elephant foot” foundations formed at the restaurant were actually adapted from a previous structure on the site.
After the arches were slotted into place, a suspended plumb weight was used to find the centre points and ensure each arch was in the correct position before proceeding further.
Gridshells.
Once satisfied that the arches were in place we began to fill out the sparse frame with gridshell saddles. This was completed using splits taken from Dendrocalumus asper. While this may appear delicate and light, these hyperbolic paraboloid forms would greatly stabilise the main arches and strengthen the overall structure.
Initially the gridshell was simply lashed together to allow a degree of flexibility, in case things needed to be adjusted as the works progressed, but they would later be pinned through at each intersection point and the ties removed once everything was fixed in place.
Bamboo Roofing.
Through a labour-intensive process, the traditional tecnique of "sirap" can be used to create pin-like bamboo shingles that are hooked onto a batten using a cut flap. The inner convex face of the bamboo is pointed upward, which helps to channel water down the roof form.
Another roofing option, called "pelupuh", involves taking the cylindrical profile of bamboo and splitting it into sections that are then flattened out using a hatchet to create flat roof tiles.
It is this roofing technique that was eventually adopted at the Kul Kul Farm restaurant.
Now complete, the Kul Kul Farm restaurant is anticipated to be open to the public in mid 2025.
Photo of completed project courtesy of Bamboo U.