Roof Batt Insulation R Value

The r value is a measure of the insulation batt s resistance to heat flow also known as thermal resistance.

Roof batt insulation r value.

The higher the r value the greater the insulation performance. Existing 3 4 inches of insulation. Built up roof membrane gravel surfaced membrane and gravel only 0 33. 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.

Step 1 determine the r values of all the materials you have used and then add them together. R value per inch ft f hr btu rsi per millimeter k m w r value for typical installed thickness not per inch source. 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 4 r 25 5 r 25 state only mt montana 2012 iecc 6 r 30. For example a 2 by 4 inch stud wall has an r value of 5 and a layer of 3 inch batt insulation has an r value of 11.

The greater the r value the greater the resistance to heat transfer and the greater the insulating effect and subsequent energy savings. As a benchmark one inch of solid wood has an r value of 1. R3 r18 r21 total roof r value. Closed cell spray foam has a far better r value per inch than other less effective insulations like cellulose fiberglass or even open cell foam.

R value measures how well certain building insulation materials can resist heat. Recommended insulation levels for retrofitting existing wood framed buildings. The increase r21 r3 exactly 18 the value by which you are increasing the r value. Closed cell spray foam insulation.

The stud wall plus the insulation has an r value of 16 5 11 16. Add insulation to attic. R value of roofing materials and building insulation. In comparison an inch of blown fiberglass insulation has an r value of 3 1 3 4 and an inch of blown cellulose in an attic has an r value of 3 2 3 7 along with knowing the r value of a particular insulation it is also important to calculate the r value of a total system.

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. National roofing contractors association. When determining how much insulation you need don t guesstimate calculate. It has a lower r value per inch than closed cell foam and is vapor permeable.

See the department of energy s doe ranges for recommended levels of insulation below. The percentage increase increase increase original number 100. I calculate insulation resistance to heat loss or r percentage improvement always as relative to the original number. The r value is r 3 5 to r 3 6 per inch so filling a 2 4 cavity yields about an r 13.