Rated R Value For 2x8 Roof Joist

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.

Rated r value for 2x8 roof joist.

For example us r10 si r 1 76. Add r3 1 for each inch of new cellulose you blow in 1. Sheetrock only has a r value or about 0 5. When determining how much insulation you need don t guesstimate calculate.

These are all us r values. Most common r value upgrades. This is very important in situations where your code requires an r 21 for the wall but you only have a 2 4 stud because closed cell spray foam is the only way you would achieve the required r value to meet code. Solid panel insulation has amazing r values.

Insulation rated on its ability to reduce thermal transfer or r value comes in rolls and batts that fit between joists. What r value do i need. That means if you used foam it green closed cell which is r 7 per inch it s r value for a 3 5 deep wall cavity would be r 24 5. Know exactly how much you need with our project calculators.

Thanks 01 03 2008 05 37 pm 8. 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. Also i believe the overlooked benefit of covering the studs and creating a solid barrier with very few areas for air penetration can be well worth the cost. The thicker the insulation the higher the r value.

4 5 rigid will work in rafters as small as 2x6 and will get an r 30 and some change rating. With 1 2 wood structural panels with exterior glue applied at right angles to top of joist or top chord of trusses with 8d nails. Add blown in cellulose to attic. 2 x 8 f d joists 16 o c 1 layer 3 4 bead board ceiling span 17 18 live load 40 lbs.

In my brand you get an r 31 in a 2x8 at 2 5 pounds per cubic foot. Substrate roof floor ceiling time assembly ff file no. Install it then have mark get out his caulking gun and seal all the corners. If you are starting with an un insulated space it is very important to read the section below titled estimating r values for un insulated spaces note.

2009 ibc from table 720 1 3 minimum protection for floor and roof systems the floor construction of item 21 1 1 is wood joists wood i joists floor trusses and flat or pitched roof trusses spaced a maximum 24 o c. To convert to si r values multiply by 0 176. I believe 8 1 4 is the thickness on an r 30. Are your rafters rough.