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Insulating concrete forms

Insulated concrete forms by Logix

There are several systems on the market which allow you to cast concrete using clip together poystyrene forms. The two leafs of insulation are connected together by plastic ties and the units are clipped together and then filled with concrete, usually by pumping, so the whole process is very fast. Reinforcing bar can be inserted in the concrete though this is seldom necessary for domestic work. The concrete can be vibrated. It is also possible to create curves. There is a variety of external finishes possible including render, timber and sheet cladding and brick and stone slips. Internal lining is necessary with concrete render, plasterboard or clay based boards.

First the bad news. Both concrete and expanded poystyrene are high in embodied energy  and they both have associated pollution during manufacture. However in terms of the embodied energy  needed to provide thermal mass, concrete is one of the better choices.

Insulation values

Having said that, there can be some excellent in-use energy saving benefits to this type of system provided the external layer of insulation is substantially increased. As they are supplied, the inner and outer leaf of insulation are usually each about 70mm thick with the concrete layer being about 125mm although these dimensions can be varied.

It seems that the manufacturers have still not generally caught up with the sort of insulation required for Passivhaus standard so the occasional examples in the UK where this has been attempted have relied on adding extra EP insulation to the outer skin to bring the total up to about 300mm. Concrete can be foamed to increase its insulation value but with resulting loss of strength. The thermal mass of the concrete can help retain heat and contribute to decrement delay. However the calculation of the effects of decrement delay are complex and require expert advice.

Other advantages

The fact that concrete is poured into the wall means that there is a continuous air-tight layer so there should be no problems with air tightness, in the walls themselves at least. Concrete is a good sound insulator and has excellent fire resistance. The combination of clip together formwork and poured concrete tends to significantly reduce waste and offcuts on site.

An interesting example of ICF walls are the three recently completed houses at Chewton Mendip

Building regulations

Structure

The Building Regulations part A covers the structure of a building. This Approved Document goes into a lot of detail for traditional masonry buildings but almost none for timber frame, steel frame, earth building SIPs etc. For these you will need to consult a structural engineer (while SIPs structures are usually handled by the manufacturer)

Fire safety

With most forms of construction there will be implications concerning fire safety. These are covered in the Building Regulations and you can see examples of how to conform with these in Part B (Fire Safety)

Site preparation and resistance to contaminants

This section,  Part C, covers site remediation along with protection from nasties which might affect the construction and occupants such as damp, rain, radon etc. There is an abridged version of the Approved Document specially for houses.

 

 

2 comments to Insulating concrete forms

  • Nathan Evans

    I have a specialist company building ICF house structures in the south west of England, we use the Nudura brand of ICF, as we believe it to be the best most cost efficient product on the market.
    And we are taking booking for projects next year.

  • Andre Sellers

    Hi i am looking for a supplier of ICFs can you recomend any please i have used them in house building in Australia.

    many thanks Andre

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