Screw piles instead of concrete
Why we want to build our Dansk Cottage on Ærø on screw piles instead of a conventional concrete slab.
Our plot in the village of Skovby near Søby covers around 3,300 square metres – meadow, soil, sky and a sense of space. When we started planning Dansk Cottage, one thing quickly became clear: the house should fit into this piece of nature, not bury it.
A conventional house usually stands on a concrete slab. To build one, soil is dug out, gravel is compacted and a continuous concrete surface is poured. The ground underneath is then sealed: rainwater can no longer soak away, soil life and plants lose their space, and removing such a slab later takes a great deal of effort.
That is why we are planning differently. Dansk Cottage is to stand on steel screw piles: individual piles that are screwed into the ground and carry the timber house. We are doing without a continuous concrete slab. The ground between the piles stays ground.
This brings together two things that matter to us: a modern Scandinavian timber house that feels good to be in, and a plot that keeps its character. To be honest, it is not a miracle solution – steel has an environmental footprint too. But for a timber house on a natural plot, we think it is the better fit.
A screw pile foundation consists of steel piles with a thread or helix at the lower end. A machine turns the piles into the ground like a large screw – without a large excavation and without waiting time, because no concrete has to cure.
The piles reach down into soil layers that are strong enough to bear the load. There they transfer the weight of the house into the ground through the helix and the pile shaft. Height-adjustable supports are fitted on the pile heads, and the load-bearing structure of the house rests on them – at Dansk Cottage, the prefabricated timber modules.
How deep, how many and which piles are needed is not decided by gut feeling but by the ground. That requires a soil investigation and a structural calculation. On our plot, the company Fremtidens Fundament took soil samples and screwed in test piles in October 2026 – more about that below.
These are the advantages a screw pile foundation can have over a concrete slab – depending on the ground, the house and the execution:
Instead of a poured slab, individual steel piles carry the house. No concrete is poured for the foundation itself.
There is no large excavation and no gravel bed. The piles are screwed in exactly at the support points.
Only the cross-sections of the piles touch the ground. Under and around the house, rainwater can keep soaking away.
Screw piles can in principle be unscrewed again. Steel is a material that recycles well.
Less concrete and less earth moving can reduce emissions. Whether and by how much depends on the individual case.
Important: The actual environmental impact depends on the amount of steel, how the steel is produced, transport, the type of foundation, its service life and which concrete solution it is compared with. Steel production also causes considerable CO₂ emissions. We do not yet have a life-cycle assessment for our house – so we do not quote any savings figures.
A factual overview of typical differences. In each case, the ground, the building and the planning decide.
| Criterion | Screw piles (steel) | Concrete slab |
|---|---|---|
| Material use | Individual steel piles; quantity depends on the weight of the house and the ground | Continuous slab of concrete and reinforcing steel, usually on gravel or crushed stone |
| Concrete needed | None for the foundation itself | High – the slab consists mainly of concrete |
| Earthwork | Little, only at the pile positions | Large-area excavation, compaction, sub-base |
| Soil sealing | Very small (pile cross-sections) | Complete under the slab area |
| Transport | Piles and installation rig; steel often travels long distances | Several trips for ready-mix concrete, gravel and reinforcement |
| Removal | Can in principle be unscrewed | Demolition with heavy machinery; the ground then has to be restored |
| Recycling | Steel recycles well | Crushed concrete can be processed, mostly as aggregate or hardcore |
| Corrosion protection | Required, e.g. hot-dip galvanising; depends on soil and water | Reinforcement is protected inside the concrete |
| Load-bearing capacity | Designed after soil investigation and structural calculation; load tests on site possible | Proven, spreads loads over the area; also designed by structural calculation |
| CO₂ footprint | Depends mainly on the amount of steel and how it is produced | Depends mainly on the amount of concrete and the type of cement |
Further reading: International Energy Agency on emissions from cement and steel · worldsteel (World Steel Association) on the climate impact of steel production · German Environment Agency (Umweltbundesamt) on soil sealing: in Germany, around 45 % of settlement and transport areas are sealed.
Our plot lies in the village of Skovby near Søby in the north of Ærø. It is an open natural plot with plenty of space and sky. An old potato cellar already stands on the plot.
We want to preserve this character. That is why we are planning the garden to be as natural as possible:
The foundation is one building block. Further decisions belong to it – so that it is clear what has already been done and what is still planned, the status is given for each:
Verified figures – for example on energy use or the CO₂ footprint – will only exist once the house is standing and has been measured or calculated. The house is due to be erected in January 2027, with letting from spring 2027. More about the concept on our sustainability page.
In our construction diary we explain how we decided on the screw pile foundation: Why our house stands on screws instead of concrete.
On 21 and 22 October 2026, the company Fremtidens Fundament tested the ground at several measuring points on our plot in Skovby and screwed in test piles. Photos and the site plan with the measuring points can be found in the section Soil tests on our plot.
Not automatically. A screw pile foundation needs no concrete for the foundation itself, hardly any earthwork and seals very little ground. On the other hand, it is made of steel, whose production also takes a lot of energy and causes CO₂. Which solution performs better overall depends on the amount of steel, production, transport, service life and the concrete solution it is compared with. For the soil and the plot, the intervention is usually much smaller with screw piles.
Their service life depends mainly on the corrosion protection (for example hot-dip galvanising), the wall thickness of the steel and the ground – such as moisture and salt content. Manufacturers and structural engineers design the piles for the planned service life of the building. We deliberately do not give a blanket number of years.
Yes. Light buildings such as timber houses in particular are often built on point foundations, for example screw piles. This requires suitable ground, a soil investigation and a structural calculation. The house then stands slightly raised on its supports, with air underneath.
Yes, timber houses are comparatively light and sit well on individual supports. What matters is a structure that distributes the loads cleanly onto the piles, and the number, spacing and depth of the piles according to the structural design. At Dansk Cottage, prefabricated timber modules are placed on height-adjustable supports.
In principle, yes. Screw piles can be unscrewed again with suitable equipment. The steel can then be reused or recycled, and the ground remains largely intact. How well this works in each case depends on the condition of the piles and the ground.
Because Dansk Cottage is being built on a natural plot of around 3,300 square metres whose character we want to preserve. A screw pile foundation suits our timber house made of prefabricated modules, needs no large excavation and seals hardly any ground. The soil investigation in October 2026 provided the basis for it.
Dansk Cottage is meant to become a place to breathe: a timber house in Skovby, surrounded by meadow, fruit trees and the wide sky over Ærø – and a house that takes as little as possible from the ground it stands on.
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