I have a log timber cottage from the early 1800s, and this summer the major renovation will take place. Currently, there is a floor on a gravel bank in the largest part of the house, with beams directly on the ground, and coal slag filled all the way up to the floor planks.
In one of the rooms, I previously excavated and made a traditional ventilated joist system with insulation and a false bottom, but it doesn't work very well. It was hard to get thickness on it without raising the floor, and almost impossible to avoid drafts along the edges where the foundation stones protrude. Additionally, the floors are so low that the top of the floor planks is only a few centimeters above the sill, which means that most of the joist system hangs below the actual wall. Hardly an optimal solution.
So, I have been thinking about what to do instead. I considered excavating and casting an insulated slab, but I think the slab would make it difficult to get the floor warm quickly when visiting in the winter.
My second idea, which I would appreciate some comments on, is to excavate properly, perhaps lay 50 mm of washed macadam, new joists on concrete blocks and secured to the walls, and then fill up to the top of the joists with leca balls 12-20K, which are capillary breaking at 75 mm. The total layer of leca balls might be around 200-300 mm.
Comments on this or other ideas would be greatly appreciated.
In one of the rooms, I previously excavated and made a traditional ventilated joist system with insulation and a false bottom, but it doesn't work very well. It was hard to get thickness on it without raising the floor, and almost impossible to avoid drafts along the edges where the foundation stones protrude. Additionally, the floors are so low that the top of the floor planks is only a few centimeters above the sill, which means that most of the joist system hangs below the actual wall. Hardly an optimal solution.
So, I have been thinking about what to do instead. I considered excavating and casting an insulated slab, but I think the slab would make it difficult to get the floor warm quickly when visiting in the winter.
My second idea, which I would appreciate some comments on, is to excavate properly, perhaps lay 50 mm of washed macadam, new joists on concrete blocks and secured to the walls, and then fill up to the top of the joists with leca balls 12-20K, which are capillary breaking at 75 mm. The total layer of leca balls might be around 200-300 mm.
Comments on this or other ideas would be greatly appreciated.
Excavating and filling with lecakulor is something the previous owners of our cottage did, but unfortunately, I don't know any details. I've never really noticed if the floor is cold in the winter, which should be a good sign. It's very damp in the ground around it as it's on a slope with a stream at one end, a field above, and forest beyond the field. It does feel a bit damp sometimes when you get there, but not too bad, and no specific smell, so I think the foundation is doing quite well thanks to what they did (?).
I don't know if I'm particularly suited to comment on the construction otherwise...isn't a moisture barrier needed, plastic, I mean?
I don't know if I'm particularly suited to comment on the construction otherwise...isn't a moisture barrier needed, plastic, I mean?
Idea number two sounds interesting, but there won't be any ventilation down there. Isn't there a risk that ground moisture will travel up through the gravel and lecakulor and end up in the floor planks?
I think like Bonnier that perhaps some diffusion-tight plastic is needed at the bottom against the ground.
I think like Bonnier that perhaps some diffusion-tight plastic is needed at the bottom against the ground.
Thanks for the answer, Bonnier, it sounds quite hopeful.
Whether or not plastic is needed is not entirely uncomplicated. On one hand, the plastic would definitely reduce moisture migration up through the floor, but on the other hand, the moisture level under the house would increase, and there is a risk of higher moisture load where the plastic ends, that is, towards the walls. And you don't want that... It seems safer to let moisture rise spread out over the entire floor, so to speak.
And considering that the old floor has managed without a capillary-breaking layer for almost 200 years, I don't think moisture would be a big problem. Moreover, there will likely be some ventilation in the lecaskikt through the dry-stone foundation, I suspect.
Whether or not plastic is needed is not entirely uncomplicated. On one hand, the plastic would definitely reduce moisture migration up through the floor, but on the other hand, the moisture level under the house would increase, and there is a risk of higher moisture load where the plastic ends, that is, towards the walls. And you don't want that... It seems safer to let moisture rise spread out over the entire floor, so to speak.
And considering that the old floor has managed without a capillary-breaking layer for almost 200 years, I don't think moisture would be a big problem. Moreover, there will likely be some ventilation in the lecaskikt through the dry-stone foundation, I suspect.
There is an old link:
http://www.byggahus.se/forum/grund-markarbeten/13024-grund-med-lecakulor.html#post156098
I will look for some information, maybe I'll get back in a couple of days, but a clay layer on the inside of the foundation wall (if it's already considered sealed) or filling the joist cassettes with an internal layer of clay were foolproof ways to reduce drafts.
But a culturally correct drainage on the outside perhaps to support the foundation might be tempting?
One could make external foundation insulation to reduce moisture ingress if it slopes towards the house. I've read about it in some books. You use, if I'm not mistaken, an excavated slope from the house, maybe 1:10, a meter or so out from the house. Insulate (bark should be excellent) and place about 10cm of clay on top as sealing, but make sure to have about 30cm to the sill if possible (externally).
This should reduce the moisture addition to the foundation...
http://www.byggahus.se/forum/grund-markarbeten/13024-grund-med-lecakulor.html#post156098
I will look for some information, maybe I'll get back in a couple of days, but a clay layer on the inside of the foundation wall (if it's already considered sealed) or filling the joist cassettes with an internal layer of clay were foolproof ways to reduce drafts.
But a culturally correct drainage on the outside perhaps to support the foundation might be tempting?
One could make external foundation insulation to reduce moisture ingress if it slopes towards the house. I've read about it in some books. You use, if I'm not mistaken, an excavated slope from the house, maybe 1:10, a meter or so out from the house. Insulate (bark should be excellent) and place about 10cm of clay on top as sealing, but make sure to have about 30cm to the sill if possible (externally).
This should reduce the moisture addition to the foundation...
jon_h said:
Anders_Roslagen: I had managed to miss that thread, thanks. And thank you for the tip about the drainage, something to think about.
Torpanders, I'm afraid I have even worse conditions than you. In my case, the floor only goes up 1-3 cm on the sill beam. How do you mean I should ensure there is no draft between the sill and the foundation stones? The foundation in my case is incredibly poorly executed, mostly just some stone chips thrown between the cornerstones. And the cornerstones are also poorly executed, have sunk down quite a bit. It'll be a matter of wedging up with new stones when I replace the sills.
Torpanders, I'm afraid I have even worse conditions than you. In my case, the floor only goes up 1-3 cm on the sill beam. How do you mean I should ensure there is no draft between the sill and the foundation stones? The foundation in my case is incredibly poorly executed, mostly just some stone chips thrown between the cornerstones. And the cornerstones are also poorly executed, have sunk down quite a bit. It'll be a matter of wedging up with new stones when I replace the sills.
Ok what does it look like on the outside?jon_h said:
Do you have room to lower the sill i.e., one more timber course downwards if you're going to lift the house anyway and work on it?
Can you sacrifice some of the ceiling height?
You have to make the most of what's available; every cm is indeed valuable to reduce the thermal bridge.
If you can get up to 10 cm, you should manage with that, considering the thermal bridge is protected on the inside of the house.
My foundation consists of natural stone with 60-120 cm diameter sealed with small stones mixed with old clay/manure/moss, etc.?
So it is draft-free... i.e., seals up against the sill.
I don't think I can reasonably add more wood at the bottom than the construction already has (or will have). The ground is already so high, so it would require extensive excavation to lower it enough without having the ground slope towards the house. The house itself is difficult to raise, it's mostly in two of the corners that it will be lifted perhaps 50-100 mm to restore what's sunk and rotted away. Then there will be issues with the chimney stack if I lift more.
And I can hardly sacrifice the ceiling height, the roof is between 185 and 210 cm as it is today. And I'm 199..
And I can hardly sacrifice the ceiling height, the roof is between 185 and 210 cm as it is today. And I'm 199..
Ok, then I don't know... check with a professional who specializes in building conservation, maybe they have the solution?jon_h said:I don't think that I can reasonably add more timber at the bottom than the construction has (or will have). The ground is already so high, so it would require extensive excavation to lower it enough without the ground sloping toward the house. The house itself is difficult to raise; it's mostly in two of the corners that it will be lifted maybe 50-100 mm to restore what has sunk and rotted away. Then there will be trouble with the chimney stack if I lift it more.
And the ceiling height I can hardly sacrifice; the ceiling is between 185 and 210 cm as it is today. And I'm 199..
199 tall and 185 in ceiling.. oh dear
I'm 190 and have 210.. a whole universe then!
The alternative could be to excavate and insulate the ground (geotex/crushed stone/foam/PE-foil) on top of which you build your wooden floor (framed or floating). This essentially becomes a variant of the modern insulated crawl space. For it to work, details are important; the PE-foil must extend under the sill and be carefully placed against the chimney and similar structures. It may also be appropriate to place a sheet metal with a drip edge (more traditionally it would be clay and birch bark) at the bottom of the sill to divert water away from the sill/plastic.
What you achieve is essentially decoupling the foundation from the rest of the house.
Regarding lecakulor, they are not COMPLETELY capillary-breaking in practice.
What you achieve is essentially decoupling the foundation from the rest of the house.
Regarding lecakulor, they are not COMPLETELY capillary-breaking in practice.
A sensible suggestion, but it is precisely the connection of the plastic that is difficult to get right. Especially against the partition walls, which more or less rest on stone all the way.
Leca 12-20K is supposed to have a capillary rise height of 75 mm as I understand it.
Leca 12-20K is supposed to have a capillary rise height of 75 mm as I understand it.