Let s look at an r 19 batt in a 2x6 cavity step 1.
Compressed attic insulation.
When it s time to re roof adding 2 of roofing polyiso or a 2 5 polyiso nailbase panel would be sufficient to beat code minimum performance on a u factor basis due to the r11 thermal break over the rafters.
To make a niche i want to compress the insulation quite a bit down to only 1 5 or 1 75 inches.
Simple thermal analysis reveals that if you have 5 missing insulation in an attic bare sheetrock you ll have a slightly more than a 54 drop in r value.
There was no plywood up there plus it looks like the insulation is not uniformly compressed.
Yes the compressed r value can be estimated using the following method.
These thermal defects undermine the r value of your attic insulation.
I believe it is r 19.
See install batt and roll insulation for details.
Batt and roll insulation and loose fill sometimes known as blown in insulation.
You can mix the type and material of insulation too.
Insulation loses its effectiveness when it is constantly being compressed by being walked on or having boxes stored on it loses its insulation ability.
Grab a tape measure and a flashlight to see what kind of insulation you already have in the attic and how deep it is.
The floor insulation can simply be left in place if you re now heating the attic.
Insulation ratings can be improved by adding more layers of insulation.
R value simply means resistance to heat flow.
This lowers the insulation s r value.
When compressed to less than its labeled thickness glass fi ber insulation will experience a reduction in r value.
There is a path down the center of the attic that has the top 6 inches of insulation above the joists that appears to have been compressed by either some one crawling across the attic or laying a piece of plywood across the joists.
I have a question for you regarding what you wrote.
You can compress fiberglass insulation as much as you want i am trying to make a shower niche on a 2x6 exterior wall in which fiberglass insulation already exists.
Make sure your home is properly insulated in all these locations.
For every x the insulation material is compressed the r value decreases by approximately one half of that percentage or x compressed.
Pull up and dispose of any material that s compressed water stained or moldy it s useless.
The ideal attic insulation r value is different than the ideal wall insulation r value.
Achieving greater r values in attics.
The chart below indicates the compressed r value of standard building insulation products when installed in framing cavities with a depth that is less than the labeled thickness of the insulation.
Over the years fiberglass batt insulation gradually collapses and deteriorates.
Batt and roll insulation works well between joist and stud spaces or if you have a wide open space or a crawlspace.
Subtract the cavity depth from the thickness of the batt in inches.
Then use the numbers in the chart at right to estimate its r value.
