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…
What is this all about? And what is better?
Damp-Tight And Air-Tight
Damp-Tight (as opposed to damp-open) and air-tight are two completely different things. Don’t mix them up. Air-tight means there are no air leaks. It is the same as “no draught”. No openings, no seams, no leaks, everything closed. It is as simple as that. It is difficult to oppose air-tightness. Opening all windows and freshen up the air in your house is ok, but permanent air leaks are not ok. So air-tightness is good.
But damp-tightness is a different thing. Damp-tightness means humidity can not leave your house, at least not through walls and roof. Some materials such as rubber and PVC are not just air-tight, they are also damp-tight. Other materials such as wood are still air-tight, but they are not damp-tight. Damp, or humidity, can migrate through wood and leave a wooden house.
Why Air-Tight or Damp-Tight?
Why would you want a house to be air-tight and damp-tight? Very simple: to bring down the energy bill. Warm air that leaves your house takes energy with it. Warm air with warm humidity or moisture takes even more energy with it. All warm air and warm moisture that leaves your house has to be replaced with fresh, cold air and moisture, that needs to be heated to room temperature again. There goes your energy bill…
So what some engineers do is very simple: stop the leaking of air AND humidity. Lock it all in the house, and recuperate the energy before air and humidity leaves your house. This approach results in damp-tight houses with:
- forced ventilation systems,
- complex heat recuperation systems,
- no ventilation openings, and possibly even windows that should never open.
All very nice in theory, but very artificial. You build a beautiful house on a beautiful plot of land, and then you lock it all up as if you’re living on the twelfth floor of some sky-scraper. Nothing natural about it, it is like packing your whole house in a plastic bag.
Damp-Tight, Good Idea Or Not?
By now you understand how we feel about this. We think it is nonsense. It is un-natural, illogical, non-simple, non-sensical and no good. We think air-tight is ok, although you still want to open the windows every now and then, vent it all and freshen up. But damp-tightness is never a good idea. Of course you need to make sure you avoid condensation problems in the outside walls, but other than that we can’t think of any reason to build damp-tight. Those who used to bike to school in their rubber raincoat will no doubt understand the discomfort of damp-tightness. Nothing good about it, nothing comfortable.
So as far as we are concerned we would like to get rid of all these moisture stopping membranes and PVC-foils and forced ventilation systems in a house. We prefer to build damp-open, as our ancestors have done for thousands of years.
What About The Energy Bill, Does It Go Up?
So does that imply your energy bill goes up? Actually no. The moisture that leaves your house via the wooden walls, cools down and leaves the energy in the walls. The walls themselves work as a heat battery, they store the energy and give it back to the house. Works perfect. Just a matter of using the right materials.
And at this moment we would like to say some nice words about our colleagues in the industry that build straw houses. You know, these houses build from straw bales? Unfortunately straw bale houses are still associated with hippies, gnomes and dreadlocks. Wrong! Building with straw bales has a solid theoretical foundation and is the ultimate damp-open way of building houses, and very thermo-stable. We are all in favour of straw bale houses. But alas… we build with wood, also not bad at all. And seriously better than building with polyurethane.