Charles Buell Consulting LLC - Consulting on Building Science and Forensics in the Seattle Area (Formerly Charles Buell Inspections INC)

August 3, 2024 by Charles Buell

Infrared and Air Movement

I find this infrared anomaly super fascinating.

There were cavities above all my window headers that never got insulated when I insulated the house 20+ years ago. What they looked like, and where they were located, became evident when I remodeled my bathroom recently.

I decided to drill one-inch holes all around under the soffits and insulate them. This required bringing my antiquated, rusted-out, insulation blowing machined back to life for one last job. A little duct-tape and it got us through the job–sad to see it at the dump.

This IR image shows where insulation was missing, with the sun hitting that side of the house in the evening . The second picture was taken in the morning, and you could see that the cool night air was pushing through the hole making a cold spot on the back side of the interior wall.

I never would have thought that air in that cavity could find a path to the interior of the house though lath and plaster. It was confirmed with the tissue paper over the hole, as did a smoke test.

It must be quite a tortured path for air movement. I think this accounts for the difficulty of air sealing old houses and evidenced by poor blower door tests.

The negative pressure was created by a big fan (on high) in a window on the opposite side of the house, that was being used to cool down the house over-night.

More fun with IR.

Charles Buell Consulting LLC

May 31, 2024 by Charles Buell

How Can There Be Frost On My Roof In Late May?

May 31st, my morning walk.

It was 43°F, dew point 41°F, and humidity 94%. I was very surprised to see night sky frost on my neighbor’s house roof. I have been keeping track of earliest and latest night-sky-frost for several years. My data for latest frost has been stuck on May 20th for several years.

Night sky radiational frost — Frost on areas of a vaulted roof

As the nights get shorter it becomes more and more difficult for there to be enough time for daytime heat build-up in an attic to cool enough for frost to form. One can easily see this effect in the way roofs with attics as opposed to vaulted roofs (or unheated roofs) support frost development.

Take the following picture for example.

Notice how there is frost build-up on the left side (vaulted side) and no build-up on the right side (attic area). The overhang also shows frost. So these are the colder areas where the night sky could suppress the roof surface temperature enough for frost to form. The attic side has so much more volume to cool down and the short nights do not provide enough time.

Here is some more frost from this morning’s walk, This is a little detached storage shed that is more or less open on one side and obviously not heated. It is a place I can always count on seeing frost when conditions are “marginal.”

There is also something else that has to happen for night sky frost to form as late as May 31st. The day prior has to have been cloudy. So a very cloudy day followed by a very clear night with high enough humidity, temperatures that reach the dew point, and low enough ambient temperature, will allow some areas to form frost.

Here is a link to learn more about Night Sky Radiational Cooling.

Charles Buell, Charles Buell Consulting LLC

January 5, 2023 by Charles Buell

On Guard

One of the arguably most silly IRC codes, is the code for guards on decks/porches etc.

The code (R312.1) does not require them on drop-offs under 30 inches (as long as grade does not slope to more than that within 36″ of the drop-off). I am pretty sure if someone was to fall off a deck 29 inches above the ground, even with a rose bush to break their fall, they could die or be seriously injured or at least spill their beer.

I personally recommend guards be installed at any deck/porch/floor surface that is more than anyone would expect to step off of. In other words, ideally 7-3/4 as defined by the maximum riser height in the code.

When one steps off a surface in the dark, wouldn’t it be nice if one could “expect” to stop in that distance?

In my area, lots of people apparently agree with me as lots of times I will see guards where none are required, like in the following picture.

The City of Seattle made a code clarification that guards, when installed in areas where not required, must meet the same installation requirements of locations that do require them. This requirement results in guards that look like the following picture, and to me, it makes a lot of sense.

Guard around a low raised area on both side of the entryway

These guard requirements include the height of the guard, the size of openings and their ability to resist lateral forces. Strangulation issues for small children can exist with improper guards whether the deck is one foot of the ground or 30+ inches off the ground.

By Charles Buell, Real Estate Inspections in Seattle

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