Eco property
Eco property house on stilts

Do Eco Properties Need a Foundation Slab?


The dream of eco properties is to create a space that’s not only suitable, healthy, and safe for living in, but is also in tune with its natural surroundings. How those buildings are made, and what they’re made from, then, becomes a crucially important part of the whole project. But defining one building material as “eco friendly” and another as “not eco friendly” quickly creates lots of unclear lines in the sand.

Essentially, no, eco properties don’t necessarily need a foundation slab – but just because there are alternatives, doesn’t necessarily mean that they’re better than a foundation slab. The immediate environment of the building, local weather conditions, as well as local building regulations impact significantly which type of foundation is most suitable for an eco property.

Let’s look at what needs to be considered when settling on a foundation type.

Immediate environment

The most significant factor for deciding on a foundation type is the immediate environment that the building will be situated in. How much you need to protect against water, for example, will vary hugely between a hot, arid, environment (such as central North America) and a humid one (such as the UK).

If you plonk a shed in a desert, it’s unlikely to get moisture rot on its base in decades, but a shed base in an English field is unlikely to last more than a few years.

But humidity & precipitation isn’t the only consideration. Another significant factor is how rocky the ground is. The stonier the ground is, the harder it is to excavate a space in which to pour a foundation slab. That said, you tend to get less ground movement with stonier ground – so a slab may not be necessary anyway!

Eco property house with stilts
What sort of permanence is intended?

A concrete foundation is an undoubtedly permanent thing – while it’s technically possible to dig out the concrete, doing so is so much work that in practice it means that it’s like to stay there forever. As such, planning officers tend to have much tighter controls about when and where a concrete foundation is permitted. Not only from a permanence perspective, but because replacing the soil with impermeable concrete dramatically affects how much rainwater is absorbed by the ground.

If the eco property in question is intended to be ecologically friendly and as permanent as possible, then a foundation slab (with a suitable void) is a great option if it’s approved by the local planning authority. If a concrete slab isn’t approved, however, all is not lost. You can still make a sturdy foundation with well-built and well-designed footings. Most old buildings relied on footings and are still going strong!

Failing that you can actually build above-ground footings. One of the most beautiful ways is to create a part-concrete footing with a large rock on top, and then scribe posts onto that rock.

This process, completely without concrete or modern tools, is quite calmingly presented in this video:

Eco property living roof
Is the property going to be earth-integrated?

In climates that necessitate more protection from weather, integrating buildings into the ground helps to maintain a regular temperature. A common way to do this while still letting light in is to either build a house into a hill, or to bank soil around it to create an artificial hill once it’s been built.

Both of these methods, when properly built, create a great deal of weatherproofing, but require the structure to hold up a lot more weight than usual above-ground houses. In these cases, a solid foundation slab with a good void is almost always your best bet.

Isn’t concrete not eco friendly?

The production of concrete is responsible for a significant amount of emissions, but you can argue that the production of most things causes emissions. The important thing is to calculate whether those emissions will be offset by the longevity of a structure. 

A concrete structure might cause some emissions at the point of manufacture, but (based on some ancient Roman concrete structures) it’ll also be inert and in place for, theoretically, thousands of years.

Need to talk about foundation slabs?

The best way to pour a foundation slab is over a compressible void former. And if you’re building an eco property, it makes sense to choose a void former that’s eco friendly. Our Clayboard is just the thing!

Let’s talk about how to make your eco house a forever home.

25 February 2022

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