Icebox Labs Just another mad scientist.

Attic Problems (part 2)

Thermal Analysis
In January (2011) I purchased a set of 3M TL20 temperature loggers. I placed 1 outside, 1 on the ceiling of the attic, and 1 directly on the duct (under the "insulation"), and the other was DOA*. Here are a the plots from those loggers:

Figure 1: Overall Plot

Figure 1 depicts all of the raw data I collected. The black line is simply the freezing point. Since the heater turns on/off frequently, it creates a thick band of measurements, Figure 2 is a closeup:

Figure 2: Closeup

Here you can see the changes in the setpoint of our thermostat. My house has a programmable thermostat so it's turned down when we're gone, and up when we're home. The unit also tries to predict thermal properties of the house, so it'll be a certain temperature at the time you want. However, I think this feature is inaccurate and flaky. Anyway, this plot really shows how often the furnace is cycling. Figure 3 shows a plot of one-hour's worth of data:

Figure 3: 1 hour

So why did I go through the trouble of all this? 1.) Just out of curiosity, and 2.) Because I the numbers to know when I've done enough work, without having to wait for ice dams again. Once the attic is done, I'll replot these numbers to see if the difference between attic temperature and outside temperature is "close enough" so ice dams won't form, see below:

Figure 4: Difference between outside and attic temp.

On average, the attic is 26 degrees hotter than outside, but I've recorded a maximum differential of 43 degrees F. According to some thermo calculations, if 6 inches of snow covers the roof, the surface underneath the snow will be about 18 degrees hotter than the outside temperature. So, if it's 20 degrees outside, the roof surface is 38 degrees, more than enough to thaw the snow, only to refreeze at the soffits.

The magic temperature when ice dams will NOT form, is 32-18 = 14 degrees. According to my estimates, my roof surface is melting snow 36% of the time. If I can reduce the temperature differential (between outside and attic temperature) to 10-15 degrees, I'll be melting snow only 1-8% of the time. Although this is a very tall order, it will keep my roof in good shape, prevent future leaks, and prevent me from having to rake the roof all the time. This 36% number seems pretty high though, and assumes 6 inches of constant snow (unrealistic) which would imaginarily be replaced as it thaws.

Doing some more calculations, this means my average attic temperature must go down to 20 degrees, not 38 degrees. Wish me luck :)

Of course, all these calculations are based on a lot of assumptions, for this short week in January. Your mileage may vary.

Attic problems (Part 1)

My house has a lot of problems. Currently, the most urgent problem is ice damming. Thankfully, water hasn't leaked through my ceilings yet, but I'm proactive and want to fix this before it becomes a real problem.

Before I tear up my attic, let me give you a brief tour: Here is a sample view of my attic, as you can see, there is no insulation:

Since my house is on a slab foundation, all of the ductwork runs up through the attic. So, they're nice and hot up there for the winter (making icedams worse) and cold in the summer (possibly causing condensation). Fortunately, I haven't seen evidence water dripping from the ductwork.

My house was also built using the latest 1940's technology of wrapping newspaper around ducts, then "securing" it with rope tied around the ducts:

The black paper is kraft paper I believe, a lame moisture barrier in this application.

Anyway, I bought some temperature loggers to do some qualitative thermal analysis, which I'll provide later. I've a lot of work to do, but will provide updates on this project when it makes sense.

First Post

Just testing for now, but I plan on making posts on the following topics:

• Thermal analysis of my attic to solve the ice-dam problem.
• Aluminum anodization.
• Car stuff
• Cooking.
• Other project type stuff.
• Other hopefully informative things.