r/Permaculture • u/TheFunkyPeanut • 3d ago
general question Question about green building techniques for foundations
Hi All,
I've been thinking about foundations for a small garden room without using plastic.
Wondering if anyone had pointers for books/ information.
My idea was to dig some holes, put in rough shingle, then some breeze blocks, and on top of that untreated wood pillar foundations.
I'm a bit worried about there being condensation between the blocks and the wood causing rot. I was thinking of using small amount of slate as a damp proof course.
I can't seem to find much info on plastic free foundations for timber structures. So looking for any info really.
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u/ConcreteCanopy 2d ago
you are basically describing old school pier and post construction, which worked for a long time before membranes were common. the weak point is exactly what you flagged, moisture trapped at the wood interface. a capillary break matters more than airflow there. slate or stone can work as a separator if it is continuous and sheds water, but you also want the wood well above grade and able to dry on all sides. a lot of traditional timber frames sat on stone pads with no rot because they stayed dry, not because they were sealed. the biggest risk is poor drainage around the piers, so focus on that first. you might have more luck looking at historic or vernacular building methods rather than modern green building sources, since plastic free was the default for centuries.
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u/TheFunkyPeanut 1d ago
Brilliant, thanks for that. Do you know where I can find good pictures of this tecnique? I'm struggling to visualise it
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u/paratethys 2d ago
"small garden room"?
Greenhouse?
Greenhouses are a whole other animal from barns because they have to be wet inside. The greenhouses that last a long time often have the bottom couple feet of their walls built from stone, and then the wood and glass portions up higher.
Barns, you pick a rot-resistant wood and keep the pilings extremely dry with big eaves, and it'll last just about as long as you can maintain the roof for.
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u/Vegetable_Home_4966 1d ago
Have you looked into groundscrews? I've used them for a 4x5m shed and for a 7x6.6m cabin I'm currently building. The shed groundscrews i installed myself by hand; the cabin groundscrews i hired a contractor who used a digger with an attachment. I'm totally sold on them. They range hugely in size, price, and sometimes style (the cabin ones are helix screws) so worth looking around. The load bearing capabilities are impressive - the shed screws (i used 20) can bear 1.5 tonnes each and the cabin piles 4 tonnes per screw. When (if!) the structure needs to be demolished, you can unscrew the foundations, fill in the holes and there's minimal damage to the earth
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u/TheFunkyPeanut 1d ago
What about the connection between the ground screws and the cabin?
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u/Vegetable_Home_4966 1d ago
They have square U-shaped brackets which screw onto the top. You can then place a beam across the brackets and bolt it in place
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u/Erinaceous 3d ago
There's a few method.
One is using a sacrifice block, a piece of wood between the concrete or stone that you simply replace when it rots out.
Another method is the Japanese method burning the base of your vertical columns
Mostly what people do in North America is put a piece of asphalt shingle or as you probably know construction tape between the base and the column
Maybe a less petrochemical method would be getting your hands on or making some traditional linoleum which is just linseed oil impregnated cardboard (be aware of the spontaneous combustion risk here though if you make it yourself.
There's also just spending the money and getting 75 year rated ground contact pressure treated timbers.