Damp-open is one of the current hot topics in the construction industry, and you as a consumer will likely hear about it. But what is it exactly? What does it mean for your house and your energy bill. Not always very clear, so we will try to explain.
Disclaimer: we prefer damp-open, so now you know already where we stand in this discussion.
Air tight and damp tight
Damp tight is often confused with air tight, but these things are not the same. Air tight means your house does not leak any air. No draught. Air tight is always good because who wants to sit in the draught. Old houses sometimes are not air tight and there is draught everywhere. No problem if you don’t care about a little draught and a higher energy bill. And really, a little draught might even be good: fresh air, less humidity, not always a bad thing. But you can always open the windows for a little fresh air and in general you don’t want draught. Your house should be air tight.
Also, nowadays air tightness is a requirements in the building codes of almost every country. In some countries such as France and Lithuania the government even checks your house for air leaks when you’re done building. Too many leaks and you get a penalty. The norm in most EU-countries is 0,6 m3/h.m² at a pressure difference of 50 Pascal.
The rationale behind all this is actually quite simple. leaking air contains energy, Joules, and air leaks mean energy leaks. So again: air tight is better.
But what about damp tight, what is that? Well, even if a house is completely air tight, then still damp (H2O is gas form) can leak through the walls and roof to the outside world. It depends on the wall construction. A wall with a plastic shield or foil can be fully damp tight, so no damp leaks to the outside. Our walls do not have such a shield or foil, our walls are damp open or at least partially damp open, so damp can leak out.
For leaking damp there is the exact same argument as for leaking air. Leaking damp contains energy, and if a lot of damp leaks out, you loose a lot of energy. For that reason all modern utility buildings such as airports, hospitals, offices and schools are damp tight, they have a shield or foil in the walls and roof. The idea being: if you don’t loose damp, you don’t loose energy.
Of course that is correct, but if your building or house is air tight AND damp tight it will get very uncomfortable in no-time. The humidity from cooking, showering and from your body has to go somewhere. So the damp tight people have a solution for that: air conditioning. They suck all the air in the building to a central heat recuperator, and before air is blown out of the building the last Joule is take out, and this energy is used to pre-heat the incoming air.
This requires big air vents and pipes everywhere in the house and you can see these pipes in every utility building, immediately above the ceiling. If you’re unlucky they make noise. Of course with such a system with a central outlet and intake of air, you should keep the windows closed and usually these modern building have non-openable windows.
Now on paper and in theory this all works very well, and actually in practice it also works, and these modern buildings can be very energy efficient. But for us it still doesn’t feel good. For an airport maybe it is ok, but a damp tight house feels unnatural. Like living in a plastic bag.
Why we prefer damp open
We prefer damp open because we think all these air conditioning installations and tubes all over the house with CO2 sensors, filters, computers and what not make for a very complicated solution. We think it is overkill for a normal house. And, these systems are not cheap, and they need maintenance. An airport has a dedicated maintenance department with schedules and regular checks and all that stuff, but in your house even replacing filters every three months will go wrong after a while. The result is a uncomfortable house.
Luckily you can get much the same result with much simpler techniques. What we do is we build a wall that is damp open, and stores the energy in the wall itself. So when damp migrates through the wall to the outside world, it cools down and warms the wall, storing enery in the wall. At night this energy is returned to the house. Much simpler, and it works. We will admit, not as energy efficient as the airport solution, but we can easily meet the latest EU-requirements, at lower cost, and it will keep working without a maintenance schedule, hissing tubes, heat pumps, sensors and filters.
A++-klasse and Passiv-Haus
With our techniques we can easily build houses at A+++ class level or at Passic Haus specifications, but without all the complications of a full air condition system. Better for your mortgage.
And then again there is this final point that we must come back to: a damp open house is just more comfortable. Easier to build, less noise, no big metal pipes through the house, no air filters, no nothing. Just a simple house, based on pure nature. And very very energy efficient.