Insulating Concrete Formwork.
Building materials over the ages have evolved as people moved from using wood, wattle and daub, to bricks, and latterly concrete Thermalite blocks. Windows were filled in with glass, single glazed at first, then double and in some instances triple glazed units where locations are particularly exposed. Roofing materials have also evolved over time, from thatch, to slate, and then clay tiles. In some instances, wood shingles have been used, and increasingly we are seeing more insulation products incorporated into their construction, as we increasingly strive to both decrease u values, and increase heat retention within our built environment.
Do you remember the days of playing with Lego? You could build models of houses, bridges, and with a few specialised shaped bricks, you could create all sorts of structures, which almost seem to defy gravity. I always thought as a child that it would be great fun if you could build a house in this way. It would be quick, easy and relatively straight forward to finish the structure. An afternoon helping a bricklayer lay concrete blocks soon gave me a quick reality check, and the hot bath at the end of the day was extremely welcome.
Last week, I came across an article in a magazine called Build it, covering the use of Insulated Concrete Formwork or ICF for short. The principal is essentially based on the Lego system. A series of high density blocks, with hollow cores are laid so as to create a wall. Once you get to a certain height, you pour concrete into the hollows, ensuring that the concrete is packed in to create a solid mass. Once the concrete has set, you can go on up with your construction. The polystyrene outer support is retained, and this in effect creates a very good level of insulation for the house.
When constructing the house, it is best to start at the corners, and then work inwards, infilling the wall with blocks. Complete blocks can either be cut using a saw, or some builders use a hot wire. Cutting would be very quick, rather like subdividing a piece of cheese. It is possible to buy specially shaped blocks, so that arches, curves, and window lintels can be created, so that in reality you have an extremely flexible build system.
Construction times are quite quick, Polysteel suggests that afirst time self builder using this system could complete the structure of 160 Sq M two story home in around a week. Work can continue in poor weather, as water tends to bounce off the polystyrene. One of the problems you might encounter is a “blow out”, which might occur if you attempt to fill too great a height of wall in one pour. Here, part of the polystyrene block may give way allowing liquid concrete to pour out. Trying to plug the gap may prove to be difficult, and there is nothing worse for putting pressure on you than the concrete lorry driver saying that he is out of time, and has to be away to deliver the next load.
Once the concrete has cured, the next part of the wall can be constructed. The manufacturer will give detailed guidance on how to use the system; apparently it takes two days training to learn how to use the system. Planning is crucial for the project to be a success. You have to know exactly where the doors and windows are going to be. Service ducts are also important, because it becomes much more difficult to create an aperture in a wall once the concrete has cured. Making alterations inside the building are also difficult once the walls have been built, because the concrete wall becomes inherently strong. On corners and at wall joints you may have to put some steel reinforcing bars in to provide additional strength, but the need for these would be determined by the manufacturer. Great care has to be taken to ensure the base of the wall is accurately level. Any mistake here will become increasingly obvious the higher you go with construction, and the mistakes are not easily rectified.
Once the walls have been completed, they have to be finished off. Obviously polystyrene is not very durable, or very attractive, particularly if the blocks have been laid during a wet period, and the site is covered with a liquid mud. Various options exist. One is to render the outside wall surface, using a traditional two coat system. Another alternative would be to use timber cladding. Quite often a mixture of both is used, and some of the end results are extremely attractive and would be extremely efficient in terms of heat retention.
When designing the house, one of the key decisions that has to be made, is to what extent do you use the ICF system? The walls it creates are extremely strong, and are quite thick. They probably are too thick for the majority of the internal walls, so a mixture of stud partition walls may be used to create the internal layout. The ICF walls would have to be used where they carry load, such as supporting the floor joists. Internally the walls are plastered as normal, and once the plastered surfaces have been painted, you would be hard pushed to tell the difference between them and a normal wall.
As a form of construction, ICF is becoming increasingly used as a method of construction, and the number of companies supplying the system is gradually increasing. Also there is an increasing range of differing sized blocks available, which will create more opportunities for varying the size and shape of the building being constructed. Building costs are also similar to Brick and Block, but you do have the advantage of time on your side, so that your contractors will be in the warm finishing the building off far quicker than you would when using a traditional build system.
If you are interested and want more information, a good contact would be the ICF Association, telephone 01403 701167, www.icfinfo.org.uk. Happy reading.
Original Article by Tony Lowland
Timothy Lea and Griffiths
