Thursday, 14 August 2008

Insulate Your Ground Floor Properly - A Few Points to Know and Understand

There are several different types of ground floor:

1. Solid Concrete ground supported floor.

2. Suspended Concrete Slab floor.

3. Suspended Timber Joist floor

Each method uses a different type of construction material but each method has one thing in common. They all need to be insulated. The depth of insulation required depends on several things. The type of method used, the materials involved and the size and shape of the house.

A good rule of thumb is that the greater the perimeter length the greater the need to ensure a good depth of insulation. In a timber joist suspended floor you can use a flexible insulation roll such as rock wool. The depth to which you lay the roll will depend on both of the conditions stated above. The insulation is placed between the joists and suspended there by use of netting that supports the insulation.

Placing insulation to a depth of 300mm is normal but it is best to get some advice from a SAP ratings company who will be able to work out the best design for your needs.

In a solid or suspended floor where the insulation supports the concrete floor only rigid plastic boards that have a high compressive strength are suitable for use, Kingspan, Celotex and Springvale are a couple of market leaders in this area.

Options include but are not limited to polyurethane, foamed glass, expanded polystyrene and extruded polystyrene. The boards should be moisture resistant and if placed below the DPM (not a normal practice) should also be unaffected by ground contaminants.

Please note that while it is possible to place a floor screed over these boards and that these floors can be reinforced with steel bars, the insulation itself is not a structural material and they do not act as a structural material.

No matter, which floor detail you decide to use, you should aim to achieve a U-value of at least 0.15 W/m2K. This is a lower value than that required by the building regulations but in the interest of getting the best value from your home, you should aim at the best possible value that you can achieve rather than accepting the bare minimum.

One thing to remember is this: no matter which floor design you choose you will need to place a edging of insulation around the entire perimeter of your house. This edging needs to be at least 50mm thick to be effective and must extend from the bottom of the horizontal insulation to above the top of your floor. Once your floor has been finished you can trim it off as required.

The only exception to this is of course the suspended timber floor, which already has the insulation the depth of the floor.

Remember this is going to be your home. Make the best of it.

Ed Gordon is a Self-Build Consultant who specialises in timber frame and Energy Efficiency. His main aim to help you in reducing the construction Carbon Footprint of your new property while keeping your costs as low as possible. For more information go to

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