Go back to article: A sustainable storage solution for the Science Museum Group

Hempcrete Museum Store design and construction

Having selected the building material, the museum appointed contractors whose approach supported the intent to produce a low cost, low-energy and sustainable storage building. The building design was modelled with Integrated Environmental Solutions (IES) software using environmental data from the hangar interior and the site, and the known thermal efficiency and hygroscopic performance of hempcrete in order to produce a reduced air handling system. In fact, the software did not accurately simulate the hygroscopic behaviour of the hempcrete and a numerical procedure was therefore developed to adjust the parameters of simulated temperature and humidity to bring them closer to results from laboratory tests. This resulted in the design of a heating and ventilation system with no active control of humidity and no active cooling mechanism, but with expectations of meeting an RH level of 50±5 per cent most of the time (Jankovic, 2012) by relying on the passive buffering performance of the hempcrete walls and on seasonal ambient humidity levels.

A steel-framed three-storey, six-room repository, providing 980m2 of storage space, was planned, taking full advantage of the height within the hangar.

Figure 14

Architects line drawing plan of a storage hangar

Architectural plans for a steel-framed, three-storey, six-room repository, providing 980m2 of storage space

Ceiling height on each level was dictated by the needs of the collections and the rafters of the hangar; the ground level ceiling had to be high enough for the tallest of the horse-drawn carriages, which reduced the height of the other two levels to just under average ceiling heights (225 cm). Cross-laminated timbers, formed from spruce panels bonded together perpendicularly to one another, would give the floors and ceilings high structural strength, excellent dimensional stability and vapour permeability (Sutton et al, 2011) The panel sections would be inserted into the steel framework, speeding up construction time and eliminating site waste. Before the steel framework was erected, the original hangar floor had to be removed and a new floor poured with deeper foundations for the support columns as a high floor load had been specified for the archival storerooms.

Because the storage repository was being built inside a hangar which would mitigate wind chill and some temperature extremes, the focus was on thermal inertia and humidity control rather than temperature regulation. The contractor fitted a prefabricated cladding system, Hemclad®, coupled with Hemcrete® in timber framed panels, over the primary steel frame structure. While the cladding system normally had a thickness of 120mm and included a hemp fibre quilt for thermal insulation, the system was modified to eliminate the fibre quilt and increase panel thickness to 200mm to augment moisture and thermal buffering capacities.

Hemcrete® is a proprietary blend of lime-based binder and prepared hemp shiv, mixed with water to form a slurry for casting or spraying. Hemcrete® panels are factory produced, force-dried and available in bespoke sizes. The panels meet current British Standard fire resistance tests for building materials. Pre-cast panels are intended for year-round construction and where time on site is restricted. While hemp-lime mix can be produced wet on site and either cast inside a framework or sprayed against a lining board, as there was a tight deadline due to the storage needs of the collections, construction of the store had to take place over the winter months and pre-cast panels were the only construction choice.

Figure 15

Colour photograph of workers precasting hempcrete panels for use in the storage building

Pre-casting panels for the Museum store

To reduce any potential dust emanating from the uncoated hempcrete panels and for fire protection, the inner face of each Hemcrete® panel was lined with a thin vapour-permeable unpainted magnesium silicate board (Multi-Pro)[3], even though it was likely that this would reduce the buffering capability of the hemp-lime. The outer face of the building was covered with a vapour permeable membrane, wood fibreboard and rodent-proof wire mesh with an added layer of Multi-Pro board against collision damage at floor level.

Figure 16

Colour photograph of the precast panels showing white magnesium silicate material on the upper surface

Pre-cast panels in D2; magnesium silicate board (white) on upper face

Figure 17

A set of two colour photographs showing Colour photograph showing installation of the precast panels on the steel storage structure

Installation of the hemp-lime panels on the steel structure

Access to each of the larger object storage rooms is through both steel roller shutter doors and personnel doors; each storage room also has a fire exit. Free-standing stair access, balconies and railings were installed front and back and an object-only lift installed at one front right corner. Reach truck access is through gates in the safety railings.

Figure 18

Colour photograph showing transportation of objects to upper storeys of the structure using a forklift truck

Access to upper floor using forklift and pallet bay

Figure 19

Colour photograph showing construction of storage hangar and installation of the M and E system

Installation of M&E system on the exterior of HMS

Component DOI: http://dx.doi.org/10.15180/150405/010