Roof System R Values

No statewide mandated r values phoenix 2012 iecc yuma 2009 iecc tucson 2012 iecc flagstaff 2009 iecc 2 r 20 2 r 20 2 r 20 5 r 20 state only ar arkansas.

Roof system r values.

For example a window that is r 2 in the i p system is about rsi 0 35 since 2 5 68 0 35. For example ashrae 90 1 2016 references ashrae 169 climate data for building design standards iecc 2018 however did not adopt the new ashrae. To convert rsi to r value multiply the rsi by 5 67826. The r value is a measure of the insulation batt s resistance to heat flow also known as thermal resistance.

For example two inches of extruded polystyrene with an r value of 11 has an rsi of 1 93721. Always check with your local code authority. State applicable energy ashrae zone minimum r value state local ms mississippi ashrae 90 1 2010 2 r 20 3 r 20 state local mo missouri 2012 iecc. R values expressed in i p units are approximately 5 68 times as large as r values expressed in si units.

Non residential above roof deck. In countries where the si system is generally in use the r values will also normally be given in si units. Iecc and ashrae 90 1 require similar minimum r values for insulation but they differ significantly in their approach to providing those values. Add the results for all the materials together to get the total r value for the roof assembly.

The greater the r value the greater the resistance to heat transfer and the greater the insulating effect and subsequent energy savings. For facilities with low slope roofs understanding that difference is crucial. To calculate the total r value of a roof assembly find the total thickness in inches of each type of insulating material within the system. Please note that the r values for roof membranes shingles tiles air films and roof deck materials might or might not be permitted by your local code to be included when total roof assembly r value is being calculated for the purpose of satisfying energy code requirements.

Cool roof design shall follow the requirements in chapter 1 cool roofs. To calculate the r value of a roof system your contractor will take into account the underlayment coverboards adhesives insulation and even the membrane. The average r value for some common roof materials include. When it comes to choosing the right installation for your home it is not the thickness of the product.

Consider that when cool roofing is used with insulation r values greater than 24 the cool roof surface has little if no influence on the energy performance of the building.