Green Roof R Value

Neglected thermal storage moisture dependent performance and.

Green roof r value.

R value of various materials. For example a code may require that skylights have only an r 5. These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation. In other words go above r 20 and make green roof decisions for other reasons than energy.

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. You should of course see the manufacturer provided technical data sheet for the r value of specific products. They provide shade to the top of a building evapotranspiration. Green roofs reduce the temperature of the building and the surrounding air in multiple ways.

2003 evapotranspiration schmidt 2003 berghage et al. Green roofs can have lower energy cost than conventional roofs and sometimes compete well against white roofing effects are more pronounced for lodging buildings. 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. Skylights and roof hatches are another component of roof thermal performance.

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. 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. 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. Codes may specify a smaller r value for these components compared to the rest of the roof. 1982 wong et al. A green roof may improve property values and marketability especially in urban areas with little green space.

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. Here s a handy r value table that covers most types of roof coverings building insulation and a few other materials. Once you have more than r 20 in a roof assembly that is you meet the code things pretty much don t matter. 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. Let s imagine a roof that should have an r 30 value.