Yesterday, I posted about my test of the two insulation options I’ve been considering. So I also decided to compare those results to the insulating properties of thatch roofing we have around the land. The sheds that we built for the pond circulation pumps have a polycarbonate roof covered in about 2 layers of loose thatch:

I measured the temperature of the roof under the thatch at 36.5C

This is compared to 56.3C on the nearby polycarbonate parking area roof that doesn’t have any cover:

Comparing this to the shaded side of the pump shed, we get an ambient temperature of 35.4:

So the thatch seems to insulate quite well. The insulated roof is only about 1C warmer than ambient while the uninsulated polycarbonate roof is about 20C hotter.

What is the lesson drawn from all of this? That pretty much any kind of insulation of any of these types will block almost all of the heat flow down from a hot roof.

With that said, I was pretty surprised that the thin (decorative) layer of thatch we put on the pump sheds did such a good job of insulating. It was comparable to the products sold as actual insulation in this test. I guess it isn’t too much of a surprise since it is a relatively light color (so it reflects some of the light out) and since it is above the roof, most of the heat it absorbs is likely to blow away in the ambient breeze rather than radiate downwards through the layers and finally through the polycarbonate.

Aesthetically, Praew and I both like the look of the thatch. It has a rustic look that fits well with the wooden houses that we are building. And the thatch on top of polycarbonate is actually the lightest (in terms of weight) of all of the roof options we have. For the floating house, reducing the weight of the roof itself will also reduce the weight of the roof support structure. Together, this ought to greatly lower the CG, which might help with stability. (Remember, it is a floating house, so stability is important. I don’t want my house to capsize.)

The biggest downside of thatch is that it is very flammable. Since our neighbors are quite fond of burning things, it isn’t so hard to imagine that a stray ember might ignite our roof. So we have begun looking into synthetic thatch as an alternative. A quick internet search shows that there are some places in town that sell it. The pictures look nice, so we will try to get some samples to see what the real thing is like. But at least they claim to be much better in terms of fire resistance and have the added benefit of lasting 25+ years. (Thatch needs maintenance every year or two.)