Green Roof R Value

Determining insulation r value accuracy.

Green roof r value.

Every construction design architect engineer a e knows a material s r value is an important factor when specifying insulation products with many regulations requiring minimum values for wall ceiling and roof assemblies. R value of about 2 5 ft f btu. These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation. You should of course see the manufacturer provided technical data sheet for the r value of specific products.

In other words go above r 20 and make green roof decisions for other reasons than energy. A green roof may improve property values and marketability especially in urban areas with little green space. Completely dry growing media the dirt of the green roof so to speak has a minimal r value typically about 0 5 inch. R value minke et al.

R value of various materials. Let s imagine a roof that should have an r 30 value. For a very good introductory overview article on r value see r values over at the website of. Green roofs can have lower energy cost than conventional roofs and sometimes compete well against white roofing effects are more pronounced for lodging buildings.

They provide shade to the top of a building evapotranspiration. Back in june 2012 i stated that green roofs should not be considered as dedicated insulation layers and thus should not be counted as part of a roof s total assembly r value. Increased r value a measure of the resistance of a material to heat flow of the roofing system along with reduced temperatures on the roof lessen hvac loads resulting in energy cost savings. The plants in a green roof absorb water through their roots and then use surrounding heat from the air to evaporate the water while some roofs can reach temperatures of up to 90 f in the summertime these two features can allow.

Green roofs save energy compared to uninsulated roofs or poorly insulated roofs or even better black poorly insulated roofs. Plants need water to grow so the green roof is designed to retain some degree of moisture. 1982 wong et al. For example a code may require that skylights have only an r 5.

Codes may specify a smaller r value for these components compared to the rest of the roof. Skylights and roof hatches are another component of roof thermal performance. Green roofs reduce the temperature of the building and the surrounding air in multiple ways. Neglected thermal storage moisture dependent performance and.

2003 evapotranspiration schmidt 2003 berghage et al. Once you have more than r 20 in a roof assembly that is you meet the code things pretty much don t matter.