Determining insulation r value accuracy.
Green roof r value.
1982 wong 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.
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.
R value of various materials.
2003 evapotranspiration schmidt 2003 berghage et al.
Codes may specify a smaller r value for these components compared to the rest of the roof.
These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation.
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.
You should of course see the manufacturer provided technical data sheet for the r value of specific products.
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.
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.
For example a code may require that skylights have only an r 5.
Skylights and roof hatches are another component of roof thermal performance.
R value of about 2 5 ft f btu.
Completely dry growing media the dirt of the green roof so to speak has a minimal r value typically about 0 5 inch.
A green roof may improve property values and marketability especially in urban areas with little green space.
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.
They provide shade to the top of a building evapotranspiration.
Neglected thermal storage moisture dependent performance and.
R value minke et al.
In other words go above r 20 and make green roof decisions for other reasons than energy.
Once you have more than r 20 in a roof assembly that is you meet the code things pretty much don t matter.
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.
Here s a handy r value table that covers most types of roof coverings building insulation and a few other materials.
Green roofs save energy compared to uninsulated roofs or poorly insulated roofs or even better black poorly insulated roofs.
