Expert: John Henry Architect - 8/26/2008

Question
I live in the far north of Pakistan which is called northern Areas, is very cold almost for 8 months. I want to build a new  house. I am tired of old non-energy efficient house. I have been surfing the net for a few weeks for information on this topic. Fortunately I found this site. So if you answer my following questions that will be a great help to me. What kind of house i.e cement block, cob or mud block is suitable there? Insulation is not available. I want to build the walls with cement blocks with one layer cob inner side vapor barrier is not available and want to use normal plastic sheets for this. Is it wise to use plastic sheets between cement block layer and cob. Pleas give me advice on the following:
1. Cob, or traditional mud block which one is better?
2. In case I want to use cement blocks then I will make two layer wall outer cement inner traditional block or cob. Is this useful?
3. Again I think if I use plastic sheets as vapor barrier then I will use it between cement block and cob, What do you advice on this?
4. What if I use 2 slim layers of cement blocks and leave a gape between two and fill it with traditional blocks or cob and use of plastic in between for leak proof
5. The ticker the wall the more the R-value, is this correct thinking?
Note : the plot is totally dry and no risk of humidity, the soil is sandy. It has a south facing hillock and I can use passive solar energy easily.

Answer
Dear Sir,
The best insulating material has air molecules trapped in some kind of binder, as cellulose surrounds air pockets in wood or synthetic bubbles in styrofoam.  A thick earthen wall is the next best, but cold radiates inward as does heat so the thicker the better.  Cob or mud, in the straw and other plant binders, has an insulating factor but not nearly as great as wood or styrofoam for example.  Concrete block is a poor material for inherent insulation as it radiates heat and cold inward; the worst is a solid stone wall.  However if you have earthquakes then block is structurally more stable.  I would not try to put a sheet of plastic behind the cob as the latter will not adhere properly.  It would work better against the concrete block, with perhaps ties to hold the cob in place.  The thicker the earthen veneer the better.  Adding cob in the middle of two courses of concrete block is a good method of insulation.  Adding the vapor barrier on the inside would help keep the interior drier.
If you can find styrofoam, I would glue it to the inside of the block, about two or three inches, then affix gypsum board over that.  In cold winter temperatures, all windows would help ward off the low temperatures if wooden shutters were added.  Create a shaded porch over south facing windows, have the largest band of windows on the south, so that as the sun drops in the winter the sun can radiate into the house, then close the shutters over the windows.  Also, your roof is important in retaining heat.  Wood is best, but if you can build a thatch roof then you will be able to retain interior heat.