Is your insulation doing what you think it is doing?

I do not want to tackle the huge ugly topic of whether fiberglass insulation should be used at all–as it frequently is in attics.

For today, I just want to talk about one obvious issue with fiberglass insulation that prevents it from performing as expected.

The short version of what is wrong with fiberglass insulation is that it is not an air barrier, therefor, if it is not encapsulated and air sealed on all six sides its performance suffers. In an attic, at most, only five sides is likely to be sealed leaving the entire top not sealed.

This post is about the sides, which can and must be air sealed. The vented sides are typically not adequately air sealed, especially along the eaves. Insulation baffles, designed to keep insulation out of the lower roof venting and to allow for air flow into the attic, rarely gets adequately sealed.

Soffit vent that allows air flow into the attic

Because the baffle/top plate connection is not air sealed, and because fiberglass insulation represents very little resistance to air flow, air pushes its way into the attic right through the insulation. As it does this, it either cools the ceiling in the area, or warms the ceiling in the area depending on the season and/or side of the house.

In the winter and/or the north side of the home, the air will tend to make the ceiling cooler in the area of the vent. In the summer, especially on the sun side, the air will tend to warm the ceiling in the area of the vent. This will increase both heating and cooling loads of the home.

This next picture shows what that area looks like at the interior ceiling with Infrared camera on the South side of the home. Warm air is moving through the insulation and warming the ceiling.

In the same house on the North side we can see how the ceiling area near the vent, as indicated by infrared camera, is “cooler.” In the actual picture we can see the fungal growth present because this vent happens to be in the area of the bathroom. The moisture in the bathroom condenses on the cooler surface creating a perfect environment for mold growth.

The only real repair for this condition is to pull back the insulation and properly air seal the gaps where the insulation baffle and the house framing meet.

Spray foams are good for sealing the areas where the baffle makes contact with the framing as indicated in the circle in the picture above. Of course, in a perfect world, we would not use fiberglass insulation at all, and instead use types of insulation that are much better at stopping the flow of air. Cellulose fiber insulation can do a much better job at this.


Charles Buell, Real Estate Inspections in Seattle

Why does that black ring on my ceiling keep coming back?

It was hard to not notice the five o’clock shadow around the light fixture.  My buyer had not noticed it, and when I brought it to their attention I asked them if they knew what it was.  They in turn asked me if I knew what the discoloration meant.

Why is there a black ring around the can light?

Why is there a black ring around the can light?

I said, “sure I know what it means.”  I had already pulled my ITID (the one absolutely essential home inspection tool) out of my bag of tricks and used it successfully.   “ITID” means: Internal Thermal Imaging Device  (you know the cheap version of those fancy expensive thermal imaging cameras that one can buy from FLIR or Fluke). Because I have such a device, I knew what the dark area was from.  One of the strengths of my ITID is that I get to run through other possible causes of the marks–like maybe the area had been patched or painted in relation to the installation of the light fixture.

But after ruling out those possibilities, I concluded that perhaps when they installed the fixture they never re-installed the insulation around the fixture.

It sure looked like “ghosting” typical of an uninsulated ceiling areas.  Because the black area is “cooler” than the surrounding surface.  Cooler surfaces will collect any dust that circulates by it in the air.

To back up what my ITID saw, I merely had to check for missing insulation in the attic.

The insulation baffle around the light visible in the attic

The insulation baffle around the light visible in the attic

Well just like the expensive devices, my ITID while correct–did not tell me the “entire” story.

There was missing insulation all right–but it was missing because of the insulation baffle around the light fixture.  This is an older fixture that is not rated to be buried in insulation–like what would be required in modern construction.

My recommendation was to replace the old X-Rated ( the “X” stands for extra heat loss) can-light with an IC-Rated can-light.  The “IC” stands for “Insulation Contact” and comes stamped on any can-light that is rated to be buried in insulation.

As you can see from the ghosting around the can-light in the first picture–if you have several of these in your insulated ceiling, it can add up to a very large area of under insulated ceiling.

Without the black staining around the can-light there would likely have been no reason, in the context of a Standard Home Inspection, to scan the area with a thermal imaging device–but the defect would still have presented itself when inspecting the attic.  Whenever there are can-lites in insulated ceilings it is a good idea to bring out what ever tools are at your disposal to get a clearer picture of what is going on.

When the ice damns form, that is not the time to find out.

By Charles Buell, Real Estate Inspections in Seattle

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