When I can see the insulation installation during a pre-drywall inspection, I am able to speak with my clients about this question: when is R-13 insulation NOT R-13 insulation?
Basically when it's compacted too tightly, it leaves gaps, is smashed inward beside studs or slips down inside the wall.
But start at the beginning.
The number associated with R-value is insulation's ability to RESIST heat transfer. Hence the R. More fully stated, R-value is Resistance Value.
Heat seeks cold. Heat moves toward cold. Insulation is an attempt to prevent heat from passing through the thermal barrier it provides.
Your thermos prevents the heat in liquids from getting out, or cooling. Your cooler at the beach prevents heat from getting in and warming your drinks or food.
Heat will transfer to cold until two substances, gas or liquid or solid, reach a thermal equilibrium.
Convection is the physics of the transfer of heat (gas or liquid) with the warmer moving toward the cooler. This can happen anywhere, even inside your walls. When heat and cool interact, moving with each other, the process is called a convective loop.
So, when is R-13 insulation NOT R-13 insulation? When it is installed such that it creates a convective loop. When air can circulate about such a loop happens. Physics.
R-13 insulation is about 5" thick, but can be squished into a 2x4 wall, or to 3.25" without much reduction in R-value.
But any more than that, like to 2" or less, reduces its R-value to 6.6.
Around the window to the left the insulation was smashed in to a depth of less than 2".
This was very consistent through the house, with many windows, and doors, showing such an installation.
It creates a long, convective loop up and down the windows.
While it seems like a small space, added up this can be a real energy waster. It represents poor installation.
Obviously, when the edges of insulation are squished or stapled in beside the studs, and all over the house, and the vapor retarder (the paper) is not touching the insulation, there will be convective looping.
When this is all over the house, added up, this can be a real energy waster. It represents poor installation.
See the little flap of paper? That is intended by the manufacturer to fit over the stud, and be stapled to the stud.
This way the insulation comes to the edge of the studs on the side and completely fills the void. A filled void means less convective looping.
And, of course, gaps are mere silliness. There should never be gaps. Can you say convective loop boys and girls?
There is a huge misunderstanding of the paper flaps on the sides of insulation. I have had builders' reps call me before to say they have never heard about them prior to reading my report. Really?
Go to any DIY site, or insulation manufacturer site, and the flaps are explained clearly.
Additionally, there are new batt insulation out which has "Stapling Optional," or some similar phrase, printed on the vapor retarder.
It is thought that such insulation is so sticky or whatever that gravity and weight will not affect it, and it doesn't need to be stapled to the studs.
However, I have thermal image after thermal image, house after house, where, on a one-year warranty inspection, the insulation is shown to have slipped down the wall.
I can't invent this stuff. And builders seem to want to argue the point. One representative, no doubt thoroughly trained in thermal image science, said that not only was I wrong, but I needed a new thermal camera.
My recommendation: insulation should be a one-time installation. Properly done it should provide a proper thermal barrier for the life of the home. It can always be added to in attics, for example. Standards change. But well done insulation should be permanently well done. And improperly done insulation, where convective loops are created, is permanently improperly done. Physics.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560