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Physical Properties and Compliance with UK Building Regulations
 
The following technical information is also available for download as a PDF file here.

Stabilised rammed earth (SRE) can successfully be used to conform to the Building Regulations (2000) for England and Wales as an acceptable alternative form of low-rise masonry construction in public and residential buildings. Recommendations for how this can be achieved are given through the case study by the Planning Department of Chesterfield Borough Council (ref: Hall, Damms & Djerbib, 2004).
Regulation 7 - Materials and Workmanship
At present there are no officially recognised codes of practice for rammed earth construction in the United Kingdom. The fitness of SRE materials is currently established under:
a) Tests and calculations, and
b ) Past experience


Suitability and classification of soil materials is established in accordance with:
  • BS 1377-2: 1990 - Soils for Civil Engineering Purposes - Part 2: Classification Tests, British Standards Institute, London

  • BS 1377-4: 1990 - Soils for Civil Engineering Purposes - Part 4: Compaction Related Tests, British Standards Institute, London
  • .

    A series of 100mm SRE cube samples are produced in a laboratory using the prescribed mix design in accordance with the guidelines prescribed in:
  • Hall M and Djerbib Y, 2004b, "Rammed Earth Sample Production: Context, Recommendations and Consistency", Construction and Building Materials, 18 [4] pp.281-286. N.B. Based upon BS 1881 for concrete materials
  • .

    The curing shrinkage and estimated construction tolerances are calculated based upon:
  • BS EN 772-16: 2000 Methods of Test for Masonry Units - Part 16: Determination of Dimensions, British Standards Institute, London
  • .

    Cube samples are tested for compressive strength in accordance with the guidelines prescribed in:
  • Hall M and Djerbib Y, 2004b, "Rammed Earth Sample Production: Context, Recommendations and Consistency", Construction and Building Materials, 18 [4] pp.281-286. NB Based upon BS 1881 for concrete materials.

    Cube samples can also be tested for other physical properties depending upon the application, e.g. moisture absorption, acoustic, thermal etc.
  • Approved Document A - Structural Stability
    For the purpose of assessment under Part A (structural stability) of the Building Regulations, SRE walls can simply be treated as a high density mass walling element.

    Test Specimens
    All SRE test specimens are characterised and produced as 100mm cube samples using the methodologies proposed by Hall M & Djerbib Y, 2004, "Rammed Earth Sample Production: Context, Recommendations and Consistency",Construction and Building Materials, 18 [4] pp.281-286.

    Compressive strength
    Minimum characteristic unconfined compressive strength (f 'cu) = ≥ 3.5 N/mm2 Typical range of f 'cu =3.5 N/mm2 to 12 N/mm2.
    N.B. The f 'cu can be increased by altering the soil grading, the cement content, the ramming and the curing procedures.

    Density
    Typical dry density (ρd) = 2000 to 2100 kg/m3 (at 98% of Proctor compaction) Tested in accordance with BS 1377-4: 1990 - Soils for Civil Engineering Purposes - Part 4: Compaction Related Tests.

    Fixing capacity
    300mm Hilti C10 epoxy holds 2,000kg pull, Amdel Report No. M1034/87.

    For further details of compliance please refer to:
  • Hall M, Damms P & Djerbib Y, 2004, "Stabilised Rammed Earth (SRE) and the Building Regulations (2000): Part A Structural Stability", Building Engineer, 79 [6] pp. 18-21
  • .
    Approved Document B - Fire Safety
    SRE is classified as a "non-combustible material".
    Fire resistance rating = 4 hours.
  • Tests performed by CSIRO Report No. 1839.
  • Approved Document C4 - Resistance to Weather and Ground Moisture
    SRE walls are constructed using standard practices for DPC & DPM installation

    Experimental testing has revealed that SRE easily conforms to the Building Regulations in this country;
  • Hall M & Djerbib Y, 2004, "Moisture Ingress in Rammed Earth: Part 2 The Effect of Particle-Size Distribution on the Absorption of Static Pressure-Driven Water", Construction and Building Materials


  • Water Absorption Properties
    Pressure-driven moisture absorption:
    Initial surface absorption after 10 min (6% cement content) = 1.90 to 9.95 ml/m2 sec
    Capillary absorption:
    Typical Sorptivity (S) value = 0.251 to 1.631 mm min-0.5
    Initial rate of suction (6% cement content) = 0.29 to 1.47 kg/m2 min (Compare with conventional materials using graph below)


    Graph: adapted from Hall M & Djerbib Y, 2005, "Moisture ingress in rammed earth: Part 3 - Sorptivity, surface receptiveness and surface inflow velocity", Construction and Building Materials.
    Durability Properties
    Durability of SRE materials is determined using the 'accelerated erosion test' (AET) in accordance with
  • Standards New Zealand, 1998, NZS 4298: 1998 Materials and Workmanship for Earth Buildings, Wellington, New Zealand
  • AET value for SRE = 0.0 mm/min

  • Tests performed by Materials Consultants Aust. Pty. Ltd. Report No. 202/87

    Please note: Unstabilised rammed earth walls may not be compliant under Building Regulations. Both Regulation 7 and Approved Document C categorically state that external masonry walls on a building must:
  • Not be damaged by rain or snow
  • Resist the passage of rain (or snow) to the inside of the building
  • Not transmit moisture due to rain (or snow) to another part of the building that might be damaged
  • Approved Document E - Resistance to the Passage of Sound
    In order to demonstrate compliance "laboratory values for new internal walls and floors within: dwelling-houses, flats and rooms for residential purposes, whether purpose-built or formed by material change of use" must have a minimum Rw of 40 dB (Rw = weighted sound reduction index)

    Example: an SRE wall; Assuming a wall thickness of 300mm the typical Rw of the wall = 58.3 dB
    Approved Document L1 - Conservation of Fuel and Power in Dwellings
    SRE buildings can be assessed either using the target U-value method, the Carbon Index method or the elemental method. The walls can be constructed in 3 different Part L-compliant configurations:
    1. Solid SRE wall with external insulated cladding + render
    2. Solid SRE wall with internal dry lining
    3. Cavity SRE wall with solid-foam cavity insulation

    Example:
    For a cavity SRE wall with 175mm SRE inner & outer leaves incorporating polyisocyanurate solid cavity insulation and stainless steel wall ties;
    Calculated U-value = 0.335 W/m2 K (for 50mm thick insulation)
    Or, = 0.245 W/m2 K (for 75mm thick insulation)

    SRE walls also have very high thermal capacitance (i.e. "thermal mass")
    Typical value for a 300mm wall = 1673 KL/m3K
    Approximate thermal time lag = 6 - 8 hours


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