Compressed Attic Insulation

Grab a tape measure and a flashlight to see what kind of insulation you already have in the attic and how deep it is.

Compressed attic insulation.

There was no plywood up there plus it looks like the insulation is not uniformly compressed. Then use the numbers in the chart at right to estimate its r value. Batt and roll insulation and loose fill sometimes known as blown in insulation. R value simply means resistance to heat flow.

The ideal attic insulation r value is different than the ideal wall insulation r value. See install batt and roll insulation for details. What is attic insulation. Insulation loses its effectiveness when it is constantly being compressed by being walked on or having boxes stored on it loses its insulation ability.

Let s look at an r 19 batt in a 2x6 cavity step 1. 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. Over the years fiberglass batt insulation gradually collapses and deteriorates.

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. When compressed to less than its labeled thickness glass fi ber insulation will experience a reduction in r value. The floor insulation can simply be left in place if you re now heating the attic. For every x the insulation material is compressed the r value decreases by approximately one half of that percentage or x compressed.

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. Subtract the cavity depth from the thickness of the batt in inches. These thermal defects undermine the r value of your attic insulation. I believe it is r 19.

Yes the compressed r value can be estimated using the following method. Insulation ratings can be improved by adding more layers of insulation. To make a niche i want to compress the insulation quite a bit down to only 1 5 or 1 75 inches. 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.

Loose fill blown in insulation is best for tight spaces or if your attic already has a layer of insulation. 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. Pull up and dispose of any material that s compressed water stained or moldy it s useless. Achieving greater r values in attics.

Batt and roll insulation works well between joist and stud spaces or if you have a wide open space or a crawlspace. I have a question for you regarding what you wrote.