Green Roof R Value

Green roofs save energy compared to uninsulated roofs or poorly insulated roofs or even better black poorly insulated roofs.

Green roof r value.

R value minke et al. For example a code may require that skylights have only an r 5. Let s imagine a roof that should have an r 30 value. 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.

A green roof may improve property values and marketability especially in urban areas with little green space. They provide shade to the top of a building evapotranspiration. For example if you have a type of insulation that has an r value of r 5 per inch of thickness you will need a depth of 6 inches of this insulation installed in your attic to reach r 30 if you live in zones 2 or 3. For a very good introductory overview article on r value see r values over at the website of.

1982 wong 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. Green roofs can have lower energy cost than conventional roofs and sometimes compete well against white roofing effects are more pronounced for lodging buildings. These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation.

R value of about 2 5 ft f btu. 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. In other words go above r 20 and make green roof decisions for other reasons than energy. Codes may specify a smaller r value for these components compared to the rest of the roof.

2003 evapotranspiration schmidt 2003 berghage et al. 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. Determining insulation r value accuracy. Plants need water to grow so the green roof is designed to retain some degree of moisture.

Here s a handy r value table that covers most types of roof coverings building insulation and a few other materials. R value of various materials. Neglected thermal storage moisture dependent performance and. Green roofs reduce the temperature of the building and the surrounding air in multiple ways.

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. 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.