how insulation works

I have recently rediscovered the “Preservation in Mississippi” blog and am trying to read it when i get a chance. This morning I delving into the concrete block construction fad in Vicksburg (this relates to studying for my test tomorrow i swear) and was curious as to why they claimed to provide excellent insulation. Some readers were curious too and one guy had an answer:

“The blocks used for the cap of the low wall show some playfulness with the block machine. The manufacture used a form for the short side of the block that was half the size of the block they were making. This gave it a half rockface, half smooth finish to the block.

“[The concrete block construction] claims are 100% valid. The continuous dead air space they refer to in the article is a pretty good insulator since dead air does not transfer temperatures. With modern insulation like fiberglass bats or spray foam (gasp, boo, hiss) its not the product insulating the structure but the dead air space the insulating material tries to create. Like Malvaney said air infiltrating the space will negate the value of a cavity.

“Well maintained this method of construction is fairly efficient. Although temperature transfer through walls is pretty low on the list of concerns. Walls are fourth on the list behind roof, floor, & openings(doors and windows).”

Dead air space provides insulation?! This was something I didn’t know but it makes sense of course. The “loft” of your sleeping bag or comforter keeps you warm (and when you loose that loft cause you washed it, you’re not warm anymore). I sought to verify this with a trip to howstuffworks and learned that the purpose of insulation is to retard the transfer of heat and since air is poor conductor of heat it is probably the most basic, effective, and accessible form of insulator. This would also explain [to me] why all these new thermal fabrics and such are so full of “technology” because they have to get around the most basic rules of insulation.


not exactly related, but this is a picture of the very uninsulated (and drafty) attic of Sunshine. You can imagine how all that hot hot air in the summer transfers DOWN into the house!

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