The ideal attic insulation r value is different than the ideal wall insulation r value.
Compressed attic insulation.
Batt and roll insulation works well between joist and stud spaces or if you have a wide open space or a crawlspace.
Achieving greater r values in attics.
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.
What is attic insulation.
Subtract the cavity depth from the thickness of the batt in inches.
Let s look at an r 19 batt in a 2x6 cavity step 1.
I have a question for you regarding what you wrote.
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.
The floor insulation can simply be left in place if you re now heating the attic.
Insulation loses its effectiveness when it is constantly being compressed by being walked on or having boxes stored on it loses its insulation ability.
There was no plywood up there plus it looks like the insulation is not uniformly compressed.
Pull up and dispose of any material that s compressed water stained or moldy it s useless.
Grab a tape measure and a flashlight to see what kind of insulation you already have in the attic and how deep it is.
Yes the compressed r value can be estimated using the following method.
Over the years fiberglass batt insulation gradually collapses and deteriorates.
For every x the insulation material is compressed the r value decreases by approximately one half of that percentage or x compressed.
To make a niche i want to compress the insulation quite a bit down to only 1 5 or 1 75 inches.
When compressed to less than its labeled thickness glass fi ber insulation will experience a reduction in r value.
Loose fill blown in insulation is best for tight spaces or if your attic already has a layer of insulation.
There are two main types of insulation.
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.
Batt and roll insulation and loose fill sometimes known as blown in insulation.
Then use the numbers in the chart at right to estimate its r value.
These thermal defects undermine the r value of your attic insulation.
Insulation ratings can be improved by adding more layers of insulation.
I believe it is r 19.
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.
You can mix the type and material of insulation too.
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.
