Insulated Concrete Formwork (ICF)

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1 Insulated Concrete Formwork (ICF) If you have ever been to a Homebuilding & Renovating Show, you cannot have failed to notice various stands full of polystyrene building blocks. Maybe you have stopped for a chat and picked up a leaflet, or maybe you ve simply hurried on by, but, to date, not that many of you have been brave enough to actually build your houses using them.

2 However, during the past couple of years, there seems to have been a sea change taking place and the suppliers all report sharply increased sales. Not just to self-builders, but to hard-nosed developers as well. An appearance on Grand Designs, albeit not without its problems, has further projected the whole concept into the limelight. So what are these polystyrene houses all about? Is it now time to seriously consider using them as an alternative to the mainstream choices of blockwork and timber frame? Insulating Concrete Forms Of course, these are not really polystyrene houses at all. The polystyrene is used as a mould or form into which you pour ready-mixed concrete and it is this concrete that forms the structure of the house. The idea seems to have originated in Germany after the war when they were looking for new methods to reconstruct the bombed-out housing stock. Concrete walls are traditionally constructed using timber formwork, which is taken down after the concrete has set. Timber formwork is fiddly to make and a lot of it cannot be reused. Using polystyrene in place of timber effectively kills two birds with one stone: it acts as formwork to mould the concrete and is then left in place to provide insulation for the walls. Hence this building system is known generically as Insulated Concrete Formwork, or ICF. Whilst ICF is a European innovation, its uptake has been most dramatic in North America. Unlike Europe, North America does not have a tradition of masonry work and if you want a heavyweight structure the options are limited. ICF has thus proved popular for basements and in hurricane areas such as Florida. During the past 20 years, ICF manufacturers and builders have sprung up across the USA and Canada, and most of the systems now available in the UK and Ireland hail from across the Atlantic, often set up here under licence. In Britain, the first ICF houses were built in the 1970s but they have remained something of a curiosity until recently. What seems to have triggered the recent surge in interest in ICF is the demand for ever-greater levels of wall insulation, which is finally causing builders to question the sense in continuing with cavity wall blockwork. The latest changes to the energy-efficiency regulations, which came into effect in early 2006, seem to have accelerated this process further still.

3 Advantages over brick and block In common with most of the new build systems, ICF is fast to build and requires less in the way of traditional building skills. The formwork goes up with remarkable speed and there are far fewer elements than you get with cavity wall work: no lintels; few, if any, wall ties or cavity trays. Fitting doors and windows is at least as straightforward as it is with masonry work and finishing inside and out is essentially the same. In return you get fantastic insulation levels built in: most ICF systems give a wall U-value of around 0.2, well inside the level demanded by Building Regulations. And ICF systems are flexible enough to allow you to build in any style, to virtually any dimension. Advantages over timber frame Timber frame in the UK is primarily built in factories. This is both a strength and a weakness. It is a strength because any structure built under factory conditions tends to be accurate and well made, and on-site assembly is very quick; it is a weakness because in ordering a timber frame you are at the mercy of a factory s production schedule and it may take weeks or even months for the frame to arrive on site. ICF requires two basic components: the polystyrene forms that should be available on most jobs within days, and ready-mix concrete, which is available at a few hours notice right across the country. Some ICF systems require special fixtures and fittings and on occasion jobs get held up because of unavailability, but in principle ICF is not only fast to build but also does not involve long lead-in times. Costings Perhaps the main factor that turns many potential ICF builders away from the whole idea is their headline cost. They appear to be very expensive when compared with blockwork wall costs. Most ICF systems on sale in the UK cost between 25 and 35/m²; add ready-mix concrete at 10/m² plus a few extras and you have a wall cost of well over 40/m² before you have even taken labour into account. In contrast, blockwork can be built for around 20/m² including labour. But, as so often happens when you come to cost out elements of building work, a more thorough comparison shows the ICF cost model in a very different light. A blockwork wall on its own is only a small part of the overall wall assembly: it needs an insulated cavity and a waterproof outer skin, usually built from bricks, stone or a rendered second skin of blockwork. Also, the joinery openings require steel lintels over them and there is additional work required with wall ties and cavity closers. A truer figure for the cost of a brick and block wall is between 70 and 100/m². In contrast, the labour costs on ICF are very low: an experienced ICF crew is capable of laying 5m² of wall per hour. Combine this with an external render coat, costing around 25 or 30/m², and you end up with a wall cost of between 80 and 90/m², slap bang in the middle of the cost range for masonry and timber frame walling.

4 But in return, you get very high energy-efficiency levels built in at no extra cost, good soundproofing, excellent airtightness and less room for poor detailing, as often happens with masonry cavity wall work. Another plus factor for ICF costing stems from the speed of build, which reduces the preliminary costs of building, the money spent on fencing, plant and scaffolding. Several of the systems offer the possibility of building the walls up entirely from the inside, thus further reducing the need for external scaffolding until much later in the job. ICF no longer looks expensive and as if to emphasise that point, it is now being taken up by commercial developers as well as self-builders. Differences Although ICF tends to be lumped together as if it were one homogeneous product, the reality is that the various systems are very different from one another. They all use polystyrene and they all use concrete but just how they go together varies a lot. Many are based on a moulded block format, such as Beco, Styrobuild and Logix. Others are based around large flat panels that you have to tie together on site: this is how Polarwall, Quadlock and Eurozone work. Others, like Polysteel, use a hybrid system. By and large, the panel systems are cheaper to purchase but require a little more work on site. The variations reflect the piecemeal way ICF has developed, with lots of relatively small producers working through prototypes to develop their ideal format. You d be right to infer from this that some systems are more suitable for DIY construction than others and as a rule it is the small-format moulded block systems that the inexperienced find easiest.

5 Follow-on trades You can clad ICF externally with any material. However, it is true that through-coloured flexible renders tend to work best, as you can apply these directly onto the polystyrene. If you want a brick or stone façade, you have to tie into the structural shell. How you do this varies from system to system: with some there are fixings built in, with others you have to set wall ties through the polystyrene before the pour. Internally, the walls are routinely finished with plasterboard, stuck on to the polystyrene with sticky dabs. This is very similar to how blockwork homes are finished. Electric cable and pipework can be run within the polystyrene in channels cut with a hot wire cutter. Internal walls Internal walls are one area where ICF walls are much more expensive than the industry standard solutions, timber or steel studwork. However, they also produce fantastic acoustic insulation without the need for any additional work. And any ICF wall is also a structural wall, capable of taking the load for precast masonry floors. For these reasons, many self-builders specify ICF walls for at least their downstairs room-dividing walls, as well as their external walling. 3 reasons to use formwork It is quick: As you might expect with a construction system so brilliant in its simplicity, the structure of houses built using ICF goes up incredibly quickly. There are also far fewer elements than you might get with cavity wall work no lintels, few (if any) wall ties, and no cavity trays. Taking into account the fact that the structural element of a home s construction accounts for around 30%?of the total, self-builders using ICF can expect to save 1-3 months on their project time. It is inherently warm: ICF houses come with fantastic insulation levels built in most systems give a wall U- value of around 0.2, which is well inside the levels demanded by the Building Regulations. It is flexible: While it could be argued that some homes wear their construction method on their sleeve, it is impossible to tell an ICF?home from a house built using masonry or timber frame. ICF?homes can be contemporary, traditional; curved or straight.

6 ICF vs SIPS Many self-builders weigh up ICF against Structural Insulated Panels, a new construction form rapidly gaining popularity in the UK. There are some similarities and some differences. Similarities Both systems use insulation structurally, rather than adding it later to the structure. Both systems could be categorised as being fast, when compared to their mainstream alternatives, and both demand much less in the way of traditional building skills, like masonry work and carpentry. The presence of one experienced supervisor on site is probably all that is required. Differences ICF is wet: the concrete has to be added on site. SIPs are a completely dry method. ICF is built up on site from pre-formed modular units. In contrast, SIPs tend to be made to order in a factory, just like timber frame. ICF depends on the concrete for its strength: SIPs are inherently strong without the addition of anything on site. SIPs, therefore, give you a narrower wall profile. Whilst both can be used for walls, SIPs can t be used for basements whilst ICF can t be used for roofs. Several homes have now been built using both ICF and SIPs.

7 Commercial builds.

8 Residential Bob Turner