Design Your Own Wall For A Wood House

One of the main discussion topics between builders and architects and construction engineers is: insulation, heating, humidity and ventilation. Especially in panel walls there is the problem that high insulation values create humidity in the walls, unless special techniques are applied to stop humidity to enter the walls.

Let’s design a very basic wall: gypsum on the inside, then mineral wool/glass-wool, then pine on the outside. Nobody builds like this, but let’s do it as an experiment. We want the wall to be very well insulated so we put 20 centimeters insulation between the gypsum on the inside and the pine on the outside. Here’s what the wall looks like:

Temperature and Humidity 01

Inside the wall are projected two curves: a black line with the temperature (view the Celcius scale on the left) and a blue line with the dew point, i.e. the temperature at which the humidity condensates.

As long as the black line is higher than the blue line: no problem. But as soon as the black line meets the blue line there is a big big problem: condensation. Meaning: fungus, rot, and badness. We don’t want the black line meeting the blue line. What to do?

One option is to add a ventilation opening between the insulation and the outside pine, effectively ventilating any condensate away.

Temperature and humidity 2This option will work, but there is a risk: one small ventilation hiccup, and the moisture is back. If the mineral wool sags or expands, and blocks the ventilation, we are back at square one. What to do? Maybe add OSB boards on the outside of the ventilation, so that the mineral wool can not sag? Let’s try…

Bingo, this works. And this is how panel houses are build in general.

Temperature and humidity 3

Want to design your own wall, and find out how it handles humidity? Go to this website http://www.u-value.net and try for yourself. Here is the link to the last wall on this page.

One final note. In the above example we used mineral wool as an insulation material. Especially in hotter climates, such as the south of France, that is not a good idea. In the summer you will have a very uncomfortable house. Want to understand why? Click here.