Natural Building Techniques by Woolley Tom;

Author:Woolley, Tom;
Language: eng
Format: epub
Publisher: The Crowood Press

Insulation Properties of Hempcrete

As pressure increases to ensure that buildings meet with zero or net carbon standards, officialdom and the industry are moving towards so-called super-insulating materials to provide excellent thermal resistance. Claims about super-insulation are greatly exaggerated and research has revealed a massive performance gap (15) where buildings using conventional construction methods and synthetic insulations can perform up to 70 per cent worse than predicted. Hempcrete, which provides a modest U value of 0.2, is rejected by many as not providing sufficient insulation, but this is because current methods of calculating thermal performance have been designed to favour lightweight synthetic materials while ignoring thermal mass. An explanation about thermal insulation in more detail can be found in the book by Latif et al. (2019). (16)

There a number of reasons for the good thermal performance of hempcrete:

1.Thermal comfort: due to the ability of hempcrete to regulate humidity the occupants will feel more comfortable and not tempted to turn up the heat to mitigate the effects of cold walls.

2.Hempcrete maintains steady internal temperatures whatever is happening outside, which means that any additional heating is minimized to raise the temperature to an acceptable level. Cooling should not be required in hot weather.

3.Hempcrete has the enormous benefit of thermal mass while also providing a good level of insulation. Thermal mass is found in earth, concrete and masonry buildings, but without the same level of insulation.

4.To understand this means understanding the ‘decrement factor’: that is, the process by which certain materials are quicker or slower to heat up or cool down. The time lag with lightweight insulated buildings is quite short and even with super-insulated materials, heat is lost through the fabric surprisingly quickly. With hempcrete the heat loss is so slow that the building retains warmth. Research has shown that in a conventional synthetic-insulated building, internal temperatures mirror the external conditions, whereas in a hempcrete building the temperature stays almost constant. This can also be achieved in straw and earth buildings.

5.When thermal performance is calculated for building regulations using the Standard Assessment Procedure (SAP), thermal mass is barely considered, to the disadvantage of hempcrete.

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