Green Roof Thermal Conductivity

Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost.

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. 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. 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. Thermal conductivity varies between 0 046 0 179 w mk.

Winter is minor in the case of a well insulated roof. The thermal conductivity value for dry sand is 0 27 w mk ashrae 1967. 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. 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.

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. In contrast during the. Whereas in the case of buildings with. 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.

Many green roof soil parameters such as thermal conductivity specific heat capacity short wave reflectivity and albedo vary as a function of the moisture content. Like any ballast layer installed over the thermal insulation and water control layer neither a green roof or roof garden build up is considered to contribute any thermal performance to an inverted warm roof. Moderate or no insulation a green roof acts as a thermal barrier.