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Is double wall insulation necessary

from Robin TIt just occured to me that this double wall/insulation debate maybe missing the point.

a) you dont need additional insulation costs if you are not going to use ac

b) you do need protection against direct midday sun when most of the solar heat gain occurs

c) a simple shade can do a lot to reduce heat gain, will try and dig out some piccies of portakbin offices used in Saudi – they have a false auliminium roof on top of a flat roof (just like a cargo container)

d) if you make you walls thick and heavy, you increase the heat retention, which is why a shed on stilts made from corrugated sheeting actually works well!!

I would be most interested to see some comparative costs published on different wall constructionsIt just occured to me that this double wall/insulation debate maybe missing the point.

a) you dont need additional insulation costs if you are not going to use ac

b) you do need protection against direct midday sun when most of the solar heat gain occurs

c) a simple shade can do a lot to reduce heat gain, will try and dig out some piccies of portakbin offices used in Saudi – they have a false auliminium roof on top of a flat roof (just like a cargo container)

d) if you make you walls thick and heavy, you increase the heat retention, which is why a shed on stilts made from corrugated sheeting actually works well!!

I would be most interested to see some comparative costs published on different wall constructions

editor: good point. I do agree that insulated double walls are most applicable on houses with a/c but also there is a durability/quality aspect also. Shade is also important. Although I don’t have any hard evidence, the coolthaihouse is much much cooler than the rental house we were in previously. I attribute it to high ceilings and shade.

I’ve seen a demonstration at homepro of the insulated blankets commonly used below the tiles. They have an aquarium and heat lamp and show the temperature below the blanket about 10 or 20 degrees Celsius cooler.


more thoughts on insulation from Robin T I am intrigued by the debate on insulation on your site. Firstly, there are several subtle differences between trying to keep heat inside a room and keeping from entering a room. You can reflect heat not cold for example. Look at the difference in construction principles between a hot water tank (with electric immersion heater) and a refrigerator

Take the first example (and I quote from personal experience here). In the UK I installed a 50 gallon tank which used the standard 1 inch thick polyurethane insulation coating. Once it was working, I could actually feel the heat with the back of my hand coming from the insulation. I had arranged this to use off-peak electric and this came on from 12 midnight till 8am. I found that by 5 pm when I got home from working the water was only luke warm and barely sufficient for a shower. So first I wrapped kitchen foil around and then I wrapped an additional layer of 150mm thick glass fibre insulation around it completely, then covered the whole in plastic (garbage bags) all strapped together to form a complete overcoat (total cost around $20us). The result was dramatic. By 5 pm the water was still scalding and my electric bill was trivial.

If you tried the same trick with a fridge, you would not get any significant benefit. However you do get reduced running costs when a small fan is used to blow against the heat exchanger (radiator thingy) at the back of the fridge. You should never position your fridge next to a heat source (such as a gas stove). I find that the average running cost of an average 1.5m high fridge is around 200 Baht per month (5 baht per unit)

So already you can see some differences. The average fridge only has 25 – 30mm of polystyrene insulation.

In northern Europe heat is often distributed by hot water radiators. Why can we have cold water radiators down here? In theory you could but it would occupy one complete wall of an average 20m2 room (see my wet cinderblock method).

It’s all to do with temperature difference I can hear you purists pouting. Well hot water is heated to 75C and the room temp is normally 20C (diff 55C 100F). A fridge cools down to 4C whilst the usual air temp in the LOS is 33C (diff 29C 50F). An ac unit cools to 25C from 33C (ambient) (diff 8C 15F) but this is a far from complete picture here because heat may be “pouring” in from a south facing cinderblock wall.

IMHO you don’t need synthetic expensive insulation here unless you are going to use expensive air conditioning. What you do need is a sunshade to prevent the midday sun from shining directly on any house wall. If you still want insulation, what about Kapok นุ่น (noon) – very cheap often used for stuffing, particularly those Chiang Mai triangular cushions. Only snag is that it’s highly inflammable and will smoulder on like an oily rag (and should never be used for childrens’ toys). Perhaps its could be mixed with cement powder to make it less flammable, might be ok if fully contained within a wall cavity. Similarly rice husks might make a cheap insulation for a cavity wall. They must be kept dry.

I am not convinced about the cost/ benefits of a cavity wall, Perhaps this will emerge as people try different methods. I do like the 100mm high quality cinderblock

editor: there is a house around the corner from here that uses the double wall with foam insulation. It would be interesting to do an a/c test using that house vs. a normal single wall non insulated house. I believe the double wall/insulation would retain cold air significantly longer.

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