Construction Methods – What is ICF?
At Jearchitecture we have been using this construction method in numerous new builds in North County Dublin in recent years. We believe in a projects timeline it offers many positives over traditional construction methods which make it a viable option with todays increasing building and energy standards in the housing sector.
Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. ICF construction has become commonplace for both low rise commercial and high performance residential construction as more stringent energy efficiency and natural disaster resistant building codes are adopted.
The basic principle, though, is very simple – even elegant. Large, hollow, lightweight polystyrene blocks (a bit like Lego bricks), lock together to create instant formwork, that is then filled with concrete to make structural walls.
Advantages of ICF
- Quick. The blocks fit snugly together vertically and horizontally and the two leaves are kept in position by various patented metal, plastic or polystyrene spacers. Blocks can be cut on site with a hot wire or a hand saw and specialised components (such as lintels) can be ordered with the package. Many companies have flooring systems that allow you to cast both walls and middle floors at the same time. Manufacturers claim that self-builders can save up to three months on their build using this method.
- Cost-effective. Although it’s about 5 per cent more costly than standard domestic construction methods, the speed of construction usually more than offset this initial extra outlay.
- Immune to bad weather. Because the system is so robust and quick, it’s very good for situations where the weather could be against you. As soon as it’s complete, it’s watertight. Once roofed, follow-on trades can get cracking much earlier than with other building systems. This can be a real time and money saver.
- Strong. Almost every ICF system uses reinforcing steels within the walls and floors. You’ll be guided by the manufacturer as to what’s needed for your unique situation. Some companies supply all the steel reinforcement cut to size ready for installation.
- Good thermal performance. U-values can be as good as 0.11W/sqmK. The very nature of the system also means it is easy to make airtight.
- Improved acoustics. The polystyrene formwork is intrinsically good at absorbing sound, and mass concrete reduces airborne noise transmission. People who live in ICF homes (especially those who have used it for middle floors), say how exceptionally quiet it is.
- Fire-retardant. Although the polystyrene inner lining could, theoretically, eventually catch fire, even though it is treated with a fire retardant, normal plasterboard used in the normal way provides an excellent inhibitor in the first place. After that, the concrete walls cannot, of course, burn. Intermediate timber floors are still vulnerable.
- Heat storage. If you use ICF for your internal walls you’ll find that they’ll act as thermal stores, giving off heat long after your central heating has turned off.
- Flexible design. One of the best things about ICF is that it can very easily cope with curves, arches and all manner of odd shapes, provided they are planned for right from the start.
- Chasing for services. The inner polystyrene leaf can easily be chased for electrical and other services. It’s wise not to chase the structural concrete element. Some companies offer different thicknesses of insulation that make this chasing very easy and practical. With careful preparation it’s possible to pre-plan and create service voids within the concrete walls for say, rainwater pipes.
- Can be clad externally with any material. This means that whatever external appearance you want, the underlying ICF can cope with it. You could, at this stage, add even more insulation, depending on the U-values you’re aiming to achieve, before your final cladding. The outer skin of the polystyrene blocks has to be clad (using built-in fixings or wall ties) with something – it can’t be left open to the elements. This outer skin can, though, be easily chased to make room for rainwater downpipes and even other utilities.
- Very little waste. Because you order only the exact number of polystyrene units (and their accompanying accessories) you need, and the blocks are easily cut on site, there’s very little wastage. Concrete can then be ordered in exact amounts per pour, a real plus if you have no room to store aggregates, sand and cement.
Disadvantages of ICF
- Poor image. To some extent in Ireland there’s still some resistance to new construction methods. Many small builders especially seem reluctant to try new things. Because ICF can be done by anyone with a high level of DIY competence this also deters professional builders who pride themselves on their skilled, professional tradesmen.
- Confusing choice. Because there is no agreed ‘best method’ in this market, the different types of products make it all seem more complicated than it is. Needless to say, every company boasts its superiority in one way or another and, in a world where there are very few ICF ‘experts’ it can be hard to know which way to turn. It’s probably best to discuss all this with your designer, then to talk with a proposed supplier to see if what they have to offer makes sense to all the parties involved. Different designs and technical specifications call for different methods. You may need to do your homework on several systems before deciding.
- Hard to make later alterations. When building with this method it’s vital get your design right the first time. This means telling your designer you’re intending to use ICF, then having him or her design the house around the unit sizes and the methods used by the company you intend to use. This can usually be easily achieved but has to be taken into account from the start. There are several different ICF systems, some of which can cope very well with concrete middle floors, internal walls and all kinds of design requirements. But because what you’ll be building is essentially a concrete-walled house, making changes later (for example adding or moving doors, windows or services) can be difficult and expensive. You’ll find yourself having to rely on ICF experts with specialist cutting tools and they don’t do this work cheaply.
- Concrete pour not as simple as it seems. Without a doubt, the most skilful part of ICF is the pour. Most companies will advise you on this well before you start your project and at your training days you’ll learn how to support the walls so they don’t sag or, even worse, burst as you load them with tonnes of wet concrete. You’ll be told how high you can build any given wall before it needs filling. Different companies have their own recommendations on this. You’ll need access for a concrete pump. The concrete itself also has to be at exactly the right consistency (wetness) or it won’t flow into all the cavities of the formwork. Some companies insist that you use a particular grade of concrete (aggregate size). Finally, if you are going multi-storey bear in mind that multiple visits of the delivery trucks will cost a lot.
- ‘Green’? Because the wastage is small and you can use thermally-efficient concrete (aerated) or lower-embodiedenergy concrete (GGBS), this system can be ‘greener’ than some other similar methods. Where it isn’t ‘green’ is at its life’s end. It is still concrete, steel and polystyrene, none of which are intrinsically sustainable. But this said, concrete buildings have an extremely long life.
- Must consider a mechanised ventilation system. Because these homes are so airtight you’ll have to manage ventilation really well.
At Jearchitecture we have built up a good base of knowledge in relation to this construction method having completed numerous projects in North County Dublin using ICF. The architect is always the best person to seek advise from when determining construction methods during the design process. If your considering a new build or an extension feel free to get in contact with us and we would be more than happy to help with this and advise where we can to help.