Green Roof Thermal Conductivity

A frequently cited benefit of green roofs is the thermal insulating effect of the growing medium but no u value calculation convention recognises it.

Green roof thermal conductivity.

The thermal conductivity value for dry sand is 0 27 w mk ashrae 1967. Also the thermal conductivity of roof layers is assumed to be k 1 0 72 for cement plastering layer k 2 1 1 for rc roof slab k 3 0 533 for cement and sand base screed to fall layer k 4 0 033 for waterproof layer k 5 1 580 for soil substrate layer 40 moisture content and k 6 0 533 for turfing layer as a vegetation cover at the top of the green roof. A steady state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. In contrast during the.

The thermal conductivity for soil was only used on the acob roof analysis since the uppermost sensor used on the green roof analysis 2bn was sitting in 1 5 inches of soil above the surface of the ceiling. Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost. Traditional roof green roof n sensible et r q q q substrate 0 where r n net radiation q sensible sensible heat flux due to convection q et latent heat flux due to convection q substrate roof conductive heat flux through roof n sensible r q q roof 0 energy balance. Whereas in the case of buildings with.

Performance of growing media for green roofs a multi year laboratory testing campaign was carried out on 8 samples which aimed to define the thermal resistance reference values of growing media as a function of density and water content. Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates. The best net heat flux gains for vegetated green roofs were 4 7 w m 2 for the sand roof and 7 8 w m 2 for the silt clay roof. Commonly the layers of a green roof from the top down consist of surface vegetation substrate filter water retaining mat drainage root barrier and a waterproofing membrane that all sit atop the structural support.

Moderate or no insulation a green roof acts as a thermal barrier. Winter thermal benefits achieved from a green roof system depend on vegetation type and material properties of the layers including thickness physical structure and thermal conductivity. Winter is minor in the case of a well insulated roof.