Green Roof Thermal Conductivity

Winter is minor in the case of a well insulated roof.

Green roof thermal conductivity.

A steady state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. Moderate or no insulation a green roof acts as a thermal barrier. The thermal conductivity value for dry sand is 0 27 w mk ashrae 1967. A frequently cited benefit of green roofs is the thermal insulating effect of the growing medium but no u value calculation convention recognises it.

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. 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. 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. 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.

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

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. 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. Whereas in the case of buildings with.