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Digital Subscriptions > Build It > July 2018 > How to insulate foundations

How to insulate foundations

Good energy performance starts from the ground up. Tim Doherty reveals what you need to know to get this part of your project right
This illustration from Viking House shows its Passive House Budget Build package, which includes a highly-insulated foundation designed to achieve a U-value of 0.10 W/m2K

When we think of foundations, most of us probably imagine straightforward strip or trench fill versions – where the concrete and blockwork footings are positioned only beneath the external and internal loadbearing walls. But if you’re thinking about your insulation strategy, you also need to factor in the ground floor type you’re using.

For instance, groundbearing slabs must have their own foundation of suitably compacted hardcore and sand blindings. Meanwhile, suspended floors – whether timber or concrete – are directly supported by the house’s external walls and foundations. So everything becomes part of the same thermal element.

Performance standards

Nearly all houses built before 1980 have cold ground floors. No thought was given to heat loss through the supporting soil or, worse still, active draughts are present through gaps in suspended structures.

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About Build It

Looking for ideas and practical advice to help you create a tailor-made home that suits your lifestyle perfectly? The July issue of Build It has you covered. Here's a sneak peek at what's inside: - Self-build secrets: 10 things you need to know before you build - How to get planning permission for your extension - PVCu windows: are they the right choice for your project? - The best ways to insulate foundations - Going off-grid: options for heating & electrics - Budgeting basics: how to get an accurate estimate for your build ...and more!