Planning to replace the facade on an old cottage from 1931. The walls are made of vertical tongue and groove planks, 70 mm thick. The interior wall is covered with some type of paper, Tretex, and wallpaper. On the outside, there's just a windbreak paper, and then the outer panel is nailed directly into the plank wall, which is in good condition.
My first thought is to do the same. Tear off the paper, put up new, and then nail the panel directly into the planks and let it go down a couple of centimeters on the foundation below the sill. After some thought, it strikes me that I would be perforating the paper everywhere. Also, the facade wouldn't be ventilated.
What would you do? Proceed as before "since it's worked for almost 100 years" or add a nail batten in between? The major disadvantage I see is that the roof overhang would decrease by 3 cm all around the cottage, and it's not large as it is today...
My first thought is to do the same. Tear off the paper, put up new, and then nail the panel directly into the planks and let it go down a couple of centimeters on the foundation below the sill. After some thought, it strikes me that I would be perforating the paper everywhere. Also, the facade wouldn't be ventilated.
What would you do? Proceed as before "since it's worked for almost 100 years" or add a nail batten in between? The major disadvantage I see is that the roof overhang would decrease by 3 cm all around the cottage, and it's not large as it is today...
Don't complicate it. If it has worked for almost 100 years, it has.
To elaborate: It's when you start adding insulation to old houses that you need to think about these kinds of questions. If you are just replacing with the same thing, and everything else looks healthy, then at least I think it's unnecessary to start changing the actual "construction philosophy."
Older houses were built to "breathe," while today's houses are built like plastic bags but with ventilation and other air circulation designed for that purpose. (Between these two, there was a period when houses were built like hermetically sealed tin cans, in the late 70s to early 80s.) These two construction methods differ fundamentally in underlying philosophy, and if you start changing one according to the other's philosophy or vice versa, I argue that sooner or later you will encounter problems.
However, not everyone agrees with this; time will tell who is right.
To elaborate: It's when you start adding insulation to old houses that you need to think about these kinds of questions. If you are just replacing with the same thing, and everything else looks healthy, then at least I think it's unnecessary to start changing the actual "construction philosophy."
Older houses were built to "breathe," while today's houses are built like plastic bags but with ventilation and other air circulation designed for that purpose. (Between these two, there was a period when houses were built like hermetically sealed tin cans, in the late 70s to early 80s.) These two construction methods differ fundamentally in underlying philosophy, and if you start changing one according to the other's philosophy or vice versa, I argue that sooner or later you will encounter problems.
However, not everyone agrees with this; time will tell who is right.
Once received an explanation.
The crucial factor is where the dew point is located, the point where heat meets cold and condenses.
In old houses with thin, poorly insulated, solid walls, the dew point is located outside the facade.
If you make the wall thicker, you move the dew point inside the wall, then you need a vapor barrier on the inside and an air gap on the outside to ventilate the panel.
If you create an air gap on an existing wall, the dew point can end up right in the gap; if condensation occurs there, the facade will rot from the back.
The crucial factor is where the dew point is located, the point where heat meets cold and condenses.
In old houses with thin, poorly insulated, solid walls, the dew point is located outside the facade.
If you make the wall thicker, you move the dew point inside the wall, then you need a vapor barrier on the inside and an air gap on the outside to ventilate the panel.
If you create an air gap on an existing wall, the dew point can end up right in the gap; if condensation occurs there, the facade will rot from the back.
Exactly, that's the next level in the courseIsakare said:
The theory behind a ventilated facade is to ventilate moisture that penetrates during driving rain. It certainly doesn't hurt to put a new wind barrier on the plank wall and then a horizontal nail batten to enable this. The wall also becomes more airtight in this way.
The main reason for introducing an air gap in modern construction is the use of modern airtight paints that trap moisture in the panel because it cannot dry out quickly enough either inwardly or outwardly. Use traditional paints such as slurry paint, tar paint, or linseed oil paint, and it works fine.
As falkn points out, it can also facilitate drying if moisture penetrates, as well as limit the ability of penetrating moisture to dampen the wall/insulation. Modern construction is infinitely more delicate and sensitive than old constructions. Log houses' walls had no protective facades but handled rain by themselves.
Moreover, the dew point can never be outside the wall. It is always inside the wall. How far into the wall it is depends on the conditions.
So, as ricebridge first mentions, do not change a winning concept unless there are good reasons.
As falkn points out, it can also facilitate drying if moisture penetrates, as well as limit the ability of penetrating moisture to dampen the wall/insulation. Modern construction is infinitely more delicate and sensitive than old constructions. Log houses' walls had no protective facades but handled rain by themselves.
Moreover, the dew point can never be outside the wall. It is always inside the wall. How far into the wall it is depends on the conditions.
So, as ricebridge first mentions, do not change a winning concept unless there are good reasons.