The emotion then becomes technique, becomes technology, when we enter the scale of detail, therefore the attention to detail: the detail is the center of the projectwith millimetric precision, the size, the unit of measurement of a wooden project of the detail is the millimeter, so we must reason and design in millimeters, this is the unit of measurement, precisely because the smallest scale is the scale that makes us draw, design and think about wood in the correct way.
Every slat, every board must be thought out and designed from the very first conception of the project. The detail is aimed at the correct construction of the building, that is, at the correct installation, it is aimed at the durability of the building. We must be proud and happy when the wooden building lasts beyond our life, therefore more than a hundred years, and it will be so, if we have it designed correctly.
The ground attack is the sum, it is the detail of detailsthe prince of the details of a wooden building because it is from the ground, from under the ground, that the building starts and the ancients teach.
Let’s see in this guide article, extracted from Wooden Construction Manual by Paolo De Martin (published by May Publisher), what are the errors related to the poor installation of wooden walls and what are the main ones design measures to be adopted in the study of the ground attack.
Mistakes to avoid
If we are faced with serious errorsas in the Fig.1the unfortunate installation of wooden wallsyou immediately realize what are the gross errors in assembling these walls in impossible situations. There is no rational ground connection, the sheath is interrupted immediately, the installation of the hardware and metal joints is completely incorrect, there is no curb, the slab is without a minimum level planarity, there is water inside the construction site, it is a swimming pool, a tub. Here, all this it has nothing to do with with the world of wooden constructions.
The ancients taught us that a light element should be placed on top of a heavy element, that an element that is sensitive to water should be placed on top of an element that resists water. They are basic rules of construction.
The wooden boards are laid, to be dried, on a cobblestone, and so also the farmers of the Alpine valleys, when they cut the wood for the use of biomass in their wood stoves, lay it to dry on a cobblestone. It is a millenary tradition that we must always keep in mind when designing a wooden building.
I will never stop repeating that the detachment of the wood from the ground and from any humid area is the fundamental rule. It is a fundamental rule because it removes the risk, it significantly reduces the risk of rotting and therefore of the durability of the system.
The ground attack must be an attack away from the ground.
Even today, even modern-day shepherds know that even a simple hut must be placed on an element that is far from the ground. This is a very rudimentary construction, but this is the right principle, we must always design with this principle in mind.
The design must be done according to the location and the terrain
Now let’s get into the more technical part of the details. The ground attack must be in function of place and terrain. In fig.4 a schematic drawing of a ground attack is presented, which allows us to understand the thicknesses of the various materials, and this is the first design step to take.
We have a reinforced concrete slab 20 cm, we have to insulate it because we want to build a very efficient building, without thermal bridges, I don’t say passive because otherwise we would need 25-30 cm of insulation.
We place 25 cm of insulatinga cellular glass, an XPS, or an expanded grey polystyrene, because we are towards the cellars, towards the ground, so it must be an insulator that has humidity resistance characteristics.
Then we need at least 10 cm of lightweight screed or quartz sandwhich is more expensive, or a mixed cellular concrete, therefore a minimum dry screed of 10 cm, 15 cm would be better, but we keep it to a minimum.
Then we clearly need aimpact sound insulation and that’s another 3-4 cm. We need a laying screed of at least 6 cm, inside which, if we want, we can lay a radiant heating system, and then we need to add another four centimetres, probably, but with the prefabricated plasterboard panels with the pipes inside we can also stay on 6 cm.
Then we need 2 cm of flooring. We have reached the minimum of 36 cm. Let’s say that, in reality, this measurement It can very easily reach up to 40-45 cm. So, in fact we have a 40 cm package, almost half a meter that is above our attic. Compared to the external level, therefore, we have a plus 40 cm, and this becomes a problem because leaving the levels like this, we need three steps to go out into the garden. And this is one of the issues to be addressed and resolved, even with different solutions.
Let’s say we fill the ground outside, we fill what I call the risk zone, to bring everything to zero level we fill it with soil, and this is very wrong, because we have already seen that you cannot put soil next to wood. If I fill the difference in height with soil, it will happen that my lower wooden stringer, or the X-Lam panel, will be at minus 40 cm, so we would be assembling a wall even below the ground level. This is not possible.
Project strategies to adopt
So, the first solution, keeping the 40 cm package, is to work with external layout and project dimensions. We need to raise the wall, so I have to simultaneously work with the ground elevations on the outside and raise my wooden wall that is close to the ground.
There horizontal sheathing of the atticwhich is essential, must then continue vertically near the wall and also towards the ground, just as the insulation must also continue below the level of the existing ground.
Condensation may form on the surface because there is a colder spot, because the insole is cold, because the ground is cold, so theInsulation towards the lower part is certainly highly recommended and can solve the problem.
We have 36 cm of height difference. The ground level is higher than the lower wooden stringer. The wall is therefore too low and so we must work simultaneously on the project of the levels and the external arrangement and raise the level of the wall as much as possible. Obviously respecting the national and international rules and regulations, therefore architectural barriers, fire prevention, etc.
So in conclusion, the project strategies to be adopted are:
- plan the external layout first;
- check the surrounding land levels;
- decide on materials for the exterior;
- adapt the project to the ground attack and not vice versa, respecting the priorities of the wood.
To learn more, continue reading from the volume
Photo:iStock.com/jnnault
