Roof R Value Code

The international codes i codes are the widely accepted comprehensive set of model codes used in the us and abroad to help ensure the engineering of safe sustainable affordable and resilient structures.

Roof r value code.

Code official finds proposed design is satisfactory and complies. Building and energy codes almost always specify a required minimum r value for exterior walls and roof assemblies with above deck insulation so the minimum required r value in your local jurisdiction is something that you need to take into account when planning a building project. These energy code r value requirements change from state to state and even city to city. Both codes provide specific instructions for re roofing projects and both are clear that replacements must comply with insulation r value requirements if the roof system is part of the building thermal envelope and contains insulation entirely above the deck.

For example two inches of extruded polystyrene with an r value of 11 has an rsi of 1 93721. These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation. To convert rsi to r value multiply the rsi by 5 67826. The international code council icc is a non profit organization dedicated to developing model codes and standards used in the design build and compliance process.

For roofing replacements it is necessary to look at the ibc. Roof replacements shall comply with section c402 1 3 c402 1 4 c402 1 5 or c407 where the existing roof assembly is part of the building thermal envelope and contains insulation entirely above the roof deck. The higher the r value the better the thermal performance of the insulation. R value based method of section c402 1 3 u c and f factor based method of section c402 1 4.

Average wall and roof u factor 0 200 in climate zones. 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. Insulation level are specified by r value. 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.

R value is a measure of insulation s ability to resist heat traveling through it. Existing buildings requirements are sprinkled throughout the i codes. 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. Depending on where you live and the part of your home you re insulating walls crawlspace attic etc you ll need a different r value.

Typical recommendations for exterior walls are r 13 to r 23 while r 30 r 38 and r 49 are common for ceilings and attic spaces.