Every now and then we have a client that wants us to build a house and then in the process use product this or that for the purpose of finising the roof, or insulating the walls, or whatever. Usually product “this or that” is supposed to somehow lower the maintenance cost of the new house. For instance: composite materials for covering outside walls.
Alternatives For Wall Cladding And Roof Tiling
Many years ago products based on asbestos were popular for roof tiling and wall cladding. We all know how that one ended, and today it is very difficult to get rid of the stuff without hiring guys in white astronaut suits. In The Netherland we recently had a client who almost landed himself in jail for a weekend when he tried to get rid of 1 m2 of asbestos flooring from his old house, without hiring the astronaut-brigade. We all had to laugh about his story, but still it is a serious environmental offense.
Anybody that is in the process of designing and building a new house runs into this discussion: should we build with a damp-open construction, with damp-open walls and roof, or not? Because opinions differ, and the debate is heated, amoung architects and building engineers. One is more energy-efficient, but the other is more ecological… etcetera…
We build two types of wooden houses: traditional log houses, and panel houses. Both have pros and cons, today we want to discuss the traditional log house.
How We Build Energy Efficient Log House
First we build a wall from solid laminated logs, 80-200 millimeter thick, then we add insulation on the outside and finally we cover the outside with decoration planks, usually from larch. The building process is as follows:
Previously we wrote about a house that we built in Belgium. This house had double outside log walls (2 x 8 centimeter massive wood) with 20 centimeters cellullose between the walls.
The advantage of this construction was the damp-open construction (no plastic foils anywhere in the walls) plus the enormous thermal capacity of the walls. In the evening the walls warm the house, during summer daytime they cool the house.
And there is yet another advantage of cellulose: the fire rating. If impregnated with fire retardant material, cellulose will not burn. Look at the video below where different insulation materials are compared. It is not a scientific test, but it gives a good impression of what happens in case of fire. Want to know the winner without going through the whole video? Skip to 14m:30s.
We try to avoid polyethylenes and polystyrenes, whether extruded or expanded, as much as we can. It has zero thermal mass, it burns and often with a lot of black smoke, it turns into chemical waste.
Instead we use Rockwool, cellulose, sometimes wood fibre (not tested in the video above). But the poly-stuff we avoid.
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:
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?
Building energy efficient houses is all about R-values: higher R-values mean lower energy-loss, and lower energy bills. Simple. Or maybe not. Maybe it is a little more complicated than that. Maybe there is more in play than just R-values.
In Belgium we just finished a traditional double wall log house. Traditional as in: traditional looks, and traditional techniques. We used as the insulation material between the log walls, instead of the more common rock wool or glass wool.
The advantage of is that it absorbs humidity, and can act as a buffer for humidity, just like wood. It breathes, just like wood, and it stores humidity, just like wood. It creates an enormous thermal mass.