Tin Foil Hat


Someone once suggested I should get a tin foil hat. I did them one better – a tin foil roof. Now not only can the aliens not suck me into their space ships but the government can’t read my mind with their spy satellites!

Seriously though, the foil-bubble-bubble-foil (FBBF) insulation, Reflectix in this case, does a great job of insulating and reflecting heat back into the house. This is our first layer for the roof insulation. It also acts as a vapor barrier so it goes inside the insulation in our climate. This is the same material we put on the outside of our mobile chicken hoop house several years ago.

How Heat is lost from the buildings

  • Conduction – Put one hand on a piece of stone at room temperature and your other other hand on a piece of wood at room temperature. The wood will feel warmer because it doesn’t conduct the heat away from your hand as fast. Conduction is expressed as the U-value. The R-value of a material is the inverse of the U-value and expresses the resistance to the movement of heat. Conduction heat loss is best handled by insulations like fiberglass batts, the pink foam board we used, etc. Even better would be a vacuum – a thermos bottle. Concrete has a R-value of around 1 to 2 per eight inch thick block. That’s not very good. Pink foam insulation has a R-value of 5 per inch.
  • Radiation – Earth radiates heat back into space on a clear night. When we have cloud cover we lose less heat and the ground stays warmer. Similarly, the naked roof of the house has been radiating heat. The metal in the FBBF is almost a 100% efficient mirror, reflecting the heat back down to the house.
  • Convection – heat moving through a fluid medium such as air, water, etc. To stop this loss you want to tightly seal your house. The old phrase is that most houses have a cumulative hole in them big enough for a cat to walk through. I think our old farm house could have passed a cougar before I started tightening it up! In our tiny cottage the pink foam, the spray foam and the FBBF all work to stop convection heat losses by stopping the flow of air. Of course, you do want some fresh air to breath, for combustion in the woodstove, etc so if you seal up the cracks you need to provide other controlled sources of air. More on that another day.

  • That is what the house looked like in the morning before we began adding the reflective insulation hood. The pink insulation is all up and the scaffolding is down. In the foreground is a stack of the insulation books for the roof that we made of half inch pink foam and zip ties.

    Unfortunately they don’t offer Reflectix in 20′ x 24′ sheets like we needed, at least not that I was able to find locally. The roll in front of Holly there is 4′ x 50′.


    To make a sheet big enough for the house we duct taped six 20′ long sheets together to run up over the concrete barrel vault arch of our tiny cottage. Duct tape is amazing stuff. Rather than deal with the 10′ long extras we saved those three for another project. This makes the roof cap stronger and I’ll have other things I need it for down the road.

    We did the taping against a long board, applying a length of tape to both sides of the foil and butting it carefully. At the ends of the joint I gave it a little extra reinforcing by wrapping the tape over to the other side.

    I had first considered doing the taping together up on the roof because getting the large single piece of foil up over the roof seemed daunting. In the end we went with taping on the boards on the ground as shown here. That still leaves the problem of how to get that big unwieldy 24′ x 20′ sheet up over the roof without the wind stealing it!


    To do this we rolled it up and then unrolled it over the house. Sounds simple but there is a trick – somehow three people had to get it unrolled onto the roof without any staging, scaffolding and only one ladder…


    I attached a long rope to the 1/3rd points along the edge of the foil with packing tape. In the photo above Will is standing off to the right holding the center point of the rope so we could find the ‘handle’. We got a little breeze right then and for a moment it looked like we might have a kite. Will then took the rope to the opposite side, to my left in the photo, laying the rope on the foil. We rolled the foil up so the rope was rolled into the roll of foil. After properly positioning the foil on the west side of the house I climbed up on top and simply pulled the rope causing the roll of foil to climb up the house, over the roof and down the other side. This worked beautifully! it is always fun when a wild idea turns out perfectly.


    Because I needed to still have a ladder up on the roof I needed some way for the foil, which projects past the ends of the house, to go past the ladder. I also didn’t want the wind catching the foil and blowing it away. The solution to both problems was to simply cut flaps into the ends of the foil back to within six inches of the arches of the roof. This allowed the roll to pass by the ladder leaning on the peak of the roof without bunching up. Any wind just flips the flaps around without lifting the house’s tin foil cap. I then climbed up and tucked the flap under the ladder – Levo Ladderati!

    Additionally, while the sheet was on the ground I marked the ends of the roof for the North-South axis as well as the center line of the foil to make it easier to position. This was very helpful.


    Once the roll of Reflectix was over the other side we tied it down and began doing serious securing of the foil to the roof. We began by slitting the foil so it could drop down over the extending rebar (left for next year) and then duct taped the slits securely shut. We also temporarily attached the foil with duct tape all around the eves.

    The next step was to attach a 14′ long 2×4 to the edge of the foil and then screw another to that, sandwiching the foil between the two long boards. You can see this along the roof edge in the photo at the top. These act as weights holding the foil down tight. More to come on that.

    Lastly we added temporary ropes over the roof to ward off any kite like activity in tonight’s wind. Tomorrow we’ll pickup from there.

    Just as we finished up it started spitting hail. The timing couldn’t have been better.

    Outdoors: 40°F/20°F Sunny, Partly Cloudy, Frozen Rain in Evening
    Farm House: 57°F/50°F two log fire
    Tiny Cottage: 50°F/39°F

    About Walter Jeffries

    Tinker, Tailor...
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    4 Responses to Tin Foil Hat

    1. Anonymous says:

      Once again you’ve amazed me with your ingenuity. DH and I hope to build a small dwelling soon and are following your progress with great interest. Thanks for sharing.

    2. Andrea says:

      I fear for your sanity in such a small space. Your talking a 1/10 the size of a normal house and for five people + all your dogs? I couldnt do it. I need privacy to get away.

    3. We spend a great deal of time outdoors and are also used to our indoors space being fairly small. In our existing farm house we shut of much of it in the winter so that it is easier to heat. Our core space is about 1,000 sq-ft, so four times the size of the tiny cottage and it is a very open core space.

      Also, the tiny cottage’s 252 sq-ft doesn’t take into account the kids’ loft where their bed is, the utility attic and the fact that everything is custom designed for much better usage of space. That last bit makes a big difference.

      Time will tell! :)

    4. Oh, and I meant to mention, the dogs don’t spend much time indoors even in our existing house. They are working dogs and prefer to be outside most of the time. They do come in for visits but in the winter they consider the interior of our house way too hot. Perhaps they would be driven stir crazy in such a small space!

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