Roof Batt Insulation R Value

When determining how much insulation you need don t guesstimate calculate.

Roof batt insulation r value.

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 r value is r 3 5 to r 3 6 per inch so filling a 2 4 cavity yields about an r 13. R3 r18 r21 total roof r value. The higher the r value the greater the insulation performance.

When it comes to choosing the right installation for your home it is not the thickness of the product or the type of material that counts but the r value. The percentage increase increase increase original number 100. 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. Add insulation to attic.

Step 1 determine the r values of all the materials you have used and then add them together. The r value is a measure of the insulation batt s resistance to heat flow also known as thermal resistance. 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. 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.

Minimum insulation r value requirements non residential above roof deck. It has a lower r value per inch than closed cell foam and is vapor permeable. The stud wall plus the insulation has an r value of 16 5 11 16. R value per inch ft f hr btu rsi per millimeter k m w r value for typical installed thickness not per inch source.

See the department of energy s doe ranges for recommended levels of insulation below. The greater the r value the greater the resistance to heat transfer and the greater the insulating effect and subsequent energy savings. Know exactly how much you need with our project calculators. R value measures how well certain building insulation materials can resist heat.

National roofing contractors association. Closed cell spray foam 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. R value of roofing materials and building insulation.

As a benchmark one inch of solid wood has an r value of 1. Recommended insulation levels for retrofitting existing wood framed buildings. Existing 3 4 inches of insulation. 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.