Insulation Added to Area House – Savings Ensue

The following is a guest post by Area Husband:

Last October we added insulation to our house, and ever since I’ve been wondering whether it was worth it. Sure it is more comfortable and less drafty at night, but will it result in a significant energy savings?

A bit of background: our house was built in 1925, and as best as we can tell the original house lacked insulation. A later owner added attic insulation, but by the time we moved in the loose fill that constituted the insulation was rated at an R-4. The Department of Energy recommends attic insulation to R-49 in our area, so we were off by about an order of magnitude.

Our first floor has a brick exterior and lathe and plaster in the interior, so no room for insulation. Our second floor has sloped ceilings and knee walls and a lot of dead air space between the interior and exterior. And then there is the poorly-insulated attic.

Fast forward. We used cellulose to insulate the attic to R-49, the second floor knee and gabled walls to about an R-20 and the crawlspace to R-30. The first floor walls are not insulated and have an R-value of less than 5. So insulation should help somewhat, but most of the heat is probably still leaking out the first floor.

Now to the heart of the matter—how much energy are we saving? To get at this question, you might compare our current energy usage to last year’s for an equivalent month. Since we use natural gas, the appropriate comparison would be use cubic feet per month. It would provide a reasonable approximation, but I think we can do better. One year will be colder than the other, thereby skewing the results.

So maybe we could compute an average monthly temperature for December 2007 and December 2008 and do a comparison that way? It makes more sense, but we face the tyranny of averages. For example, a month might have an average of 35F because most of the days were near 40 but there were a few days near zero, or most days were near 35. For heating a house, it matters. So I think we can still do better. I ended up computing the number of heating degree days per hundred cubic feet of natural gas consumed for a given winter month. Higher values indicate greater energy efficiency, because we are able to use the same amount of energy (100 cubic feet) for an increased home heating demand. (http://en.wikipedia.org/wiki/Heating_degree_day)

Returning to the central question: did the insulation project result in a significant energy savings? The data indicate a 28% energy efficiency gain.

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Since I neglected to post this last fall, here are some photos of our insulation project:


"before" photo of un-insulated storage area behind knee wall


I furred out the rafters to add room for blown in insulation


Then I added sheet rock late into the night before the insulation pros arrived


The other knee walls (without storage closets) had holes cut through them. The insulation pro's son crawled through the holes to place a lining behind the walls to hold the correct thickness of blown-in insulation in place.


The cellulose was blown in through nifty holes cut into the walls (thus providing additional motivation to *someday* replace the ugly wallpaper).


And for a couple awkward "shed roof" areas, it was blown in through the downstairs ceiling.


here are the bales of cellulose being fed into a hopper. (We used about twice the number of bales that you can see here!)


...and up to the second floor where we needed it. :)


Oh, and lastly we took out the weird GIANT roof vent (that was non-functional as it was perpetually blocked by squirrel nests) and had three normal sized vents put in to ventilate our newly insulated attic.