Rated R Value For 2x8 Roof Joist

What r value do i need.

Rated r value for 2x8 roof joist.

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. Are your rafters rough. 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. 2 x 8 f d joists 16 o c 1 layer 3 4 bead board ceiling span 17 18 live load 40 lbs.

Sheetrock only has a r value or about 0 5. Add r3 1 for each inch of new cellulose you blow in 1. 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. 4 5 rigid will work in rafters as small as 2x6 and will get an r 30 and some change rating.

These are all us r values. If they are you can get cathederal ceiling batts. When determining how much insulation you need don t guesstimate calculate. In my brand you get an r 31 in a 2x8 at 2 5 pounds per cubic foot.

I believe 8 1 4 is the thickness on an r 30. R value measures how well certain building insulation materials can resist heat. For example us r10 si r 1 76. The higher the r value the greater the insulation performance.

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. Substrate roof floor ceiling time assembly ff file no. Install it then have mark get out his caulking gun and seal all the corners. The thicker the insulation the higher the r value.

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. Solid panel insulation has amazing r values. Thanks 01 03 2008 05 37 pm 8. To convert to si r values multiply by 0 176.

Know exactly how much you need with our project calculators. Most common r value upgrades. 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. 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.