A Tale of Two Roofs

The pictures below were taken within minutes of each other a day after we received a few inches of snow. They show the snow remaining on the roofs of two homes that are located just feet apart and have the same exposure to sun and wind.


The snow tells a story about the flow of energy within each home. In the first picture you can see that the snow had been melting rapidly starting at the peak of the roof. You also see a pattern in the snow tracing out the rafters due to a faster rate of melting between the rafters. In the second picture the roof was raked along the bottom but the snow toward the peak looks unchanged from the end of the snow fall. A bit of dampness on the raked part of the roof is the only indication of melt off.
The first roof clearly shows that a lot of heat is leaking through from the living areas into the space below the roof. This heats the air in the attic. Since hot air rises, the hot air in that space flows up toward the roof peak. Between the rafters that hot air is in direct contact with the underside of the roof and so transfers some of its heat easily to the snow above (heat energy naturally flows from the hotter to the colder material). The rafters provide a bit of insulation between the hot air and the snow atop the roof so the snow melts more slowly directly above the rafters producing the pattern you see in the snow.
The second roof clearly has very little heat leaking from the living area. If you observed for several more days, you would see the first roof looking bare before there are any signs of the snow melting on this roof.
In my area (southern New England) most people heat with an oil burning furnace. So, it is easy to conclude that the home under roof number one is poorly insulated, the furnace needs to run more often to maintain the temperature in the living space, so it burns more oil and the household spends more money on oil. That family is literally spending money to melt snow toward the peak of the roof.
So, the home under the second roof is using a lot less oil and saving that money. That home is my house and I do use about 1/3 fewer gallons of oil than I did before adding the insulation. That by itself is great and pays for the cost of the insulation very quickly, but I found there were other advantages beside using less oil in the winter.
I did my insulation upgrade in two steps, first I added a thick layer of cellulose insulation in the attic as a do it yourself project. The materials cost a few hundred dollars (later offset by a tax credit) from Lowes which include use of the machine that blew out the insulation. A short time later I had a contractor blow cellulose insulation into the walls. It took them less than half a day. They were able to remove a row of aluminum siding and blow the insulation in from outside. When I contacted the contractor, they arranged for a home energy audit which allowed me to get a rebate from the state for half the cost. Between rebates and tax credits the total cost was about a thousand dollars.
After each step, the first time I went back into the house I noticed that the house was quieter. I knew that insulation is sound absorbing, but I was surprised by how much. That was a nice bonus.
I got another nice surprise when the next winter time electric bill came. The bill was about 20% lower. My initial surprise gave way to feeling stupid for being surprised by that drop in electric use. After all I’m supposed to be an expert with high efficiency electric motors, and I’d read dozens of articles that pointed out that 50% of electricity used in a home is used to drive electric motors. Since the furnace and circulating pump were running much less often, I should have expected the lower electric bill.
The house also stays much cooler in the summer, so I don’t bother putting air conditioners in the windows anymore, just use fans to draw in cooler evening air. This is another nice energy savings.
When it was time for the annual furnace cleaning, I was asked if the furnace was new. It was running so much less often that it hardly needed cleaning. I only get the “annual” furnace cleaning every other year now.
The beauty of the insulation is that it doesn’t require maintenance or cleaning, there are no moving parts to wear out, it just sits there and does its job.
Sadly, most homes in the US are like the first one, they are poorly insulated so they waste heat and money. If you care about the environment or just want to save money, invest in insulation. You’ll have only one regret, the same one I have, that you didn’t do it sooner.

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