Sunday, January 19, 2014

Modern Methods of Construction - Insulated Concrete Formwork (ICF)

The benefits of using MMC’s are well documented and include improved quality, speed of delivery, less waste, reduced risk to health & Safety, minimises disruption etc.  These will vary depending on the method used in addition to the size and nature of the project. Just like using traditional methods of construction the benefits of MMC will only be realised if the project is planned and implemented (and managed) efficiently. 

The term Modern Methods of Construction (MMC) has been used for many years now, to describe alternative methods of construction and processes that move away from the traditional methods of masonry construction that we have used historically for many hundreds of years.  There are a number of commonly used and now commonly understood forms of MMC and these include the likes of off-site fabricated components such as Pre-Cast Concrete, Panellised Components such as Structurally Insulated Panels (SIPS), Timber Frame, Volumetric (often referred to as pod construction).  There are also a number of MMC’s that are site based and categorised as non-offsite manufacture methods and these include the likes of Tunnel Form, Thin Joint and Insulated Concrete Formwork (ICF).  There are also hybrid and sub-assemblies and components that provide additional MMC options, demonstrating that there is a range of different possibilities offered compared to traditional construction methods.

Of course we could have the debate about when a particular modern method of construction stops being modern.  For example pre-cast concrete has been used extensively in the UK for the best part of 35 years so is this really that modern anymore?  For simplicity however we seem to be happy to generalise modern methods of construction as alternatives to traditional construction methods for which pre-cast concrete still fits this definition.  The benefits of using MMC’s are well documented and include improved quality, speed of delivery, less waste, reduced risk to health & Safety, minimises disruption etc.  These will vary depending on the method used in addition to the size and nature of the project. Just like using traditional methods of construction the benefits of MMC will only be realised if the project is planned and implemented (and managed) efficiently.  MMC also has the potential for cost increases, relies on very tight delivery dates and can be affected by manufacturers capacity if off site methods are being used.  It is clear therefore that careful consideration needs to be given in order to decide if modern methods of construction are appropriate and if so which is the most appropriate to use, which will vary on a project by project basis.

I will consider a number of MMC’s in future articles however for this particular article I will focus on Insulated Concrete Formwork (ICF). This form of construction uses polystyrene blocks which act as permanent shuttering and are filled with in-situ concrete. provide a good description of ICF:  ‘ICF is an insulated in-situ concrete system  comprising hollow blocks or panels, usually made of polystyrene, and ready-mix concrete. The blocks are stacked and fastened together with metal or plastic connectors to create the walls of a building and are pumped full of concrete to form the structure. The polystyrene is used as a permanent part of the structure’

ICF offers a number of advantages compared to traditional construction methods, however the ease and speed of construction are arguably the biggest advantages.  Firstly, the polystyrene blocks, which are connected with metal or plastic connectors, use semi-skilled labour for installation.  There is no bonding material such as mortar so the polystyrene formwork can be connected and installed in a very short period of time, saving money on time and labour.  Take a look at the video below to see how ICF is installed.

The polystyrene formwork is usually constructed to first floor level before it is filled with concrete.  Once the concrete has cured, floors (often pre-cast concrete) can be added followed by further polystyrene formwork and eventually a roof, depending upon the height of the construction.  The formwork provides excellent thermal efficiency, achieving U values of between 0.30 and 0.11 W/m2K, which are capable of not only achieving, but exceeding current UK Building Regulations requirements. The process of constructing a traditional cavity wall requires external masonry, a cavity with insulation and internal masonry (usually blockwork).  This is labour intensive and often time consuming to complete, something that is not such an issue with ICF.  Whereas traditional construction may be vulnerable to disruption due to the weather this is also less of an issue with ICF due to the reduced time needed during construction. Once the ICF system has been installed the external walls can then be clad in a variety of different materials.  Renders, timber cladding or brick slips are examples of materials that could be used which give the building a modern or traditional appearance from the outside.  

How then does ICF compare to traditional construction from a cost point of view? identify that although initial costs may seem high compared to traditional construction methods, costs savings will be made due to reduced site installation time and the use of semi-skilled labour:

‘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. 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’

It is clear that ICF offers a good alternative to traditional construction methods with many benefits. Perhaps this method of construction will become more commonplace in the future, particularly as we explore alternatives to traditional construction.  With ever changing Building Regulations powering a drive for higher thermal efficiency in buildings and more efficient ways of creating, using and conserving energy, maybe ICF is a step in the right direction?

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  1. In addition, consider the quality of the completed product.
    I have see many masonry block walls cracked from settlement or earth heaving, leaving the owners with an unsightly wall subject to weather, vermin and even vegetation penetration.
    To the contrary, an ICF wall is a monolithic, reinforced concrete mass, tied together completely around all corners and openings as well as bonded to the footers, acting as a full height grade beam. It's resistance to settlement or heaving is far superior to block or wood frame,
    A further benefit of the double insulated ICF concrete mass wall is its resistance to sound penetration. The interior is left exceptionally quiet, free from intrusion of traffic or other external noise.

  2. Great article as always!
    How does such construction fare in the mortgage industry - are banks and building societies willing to accept these non-traditional building methods?

  3. Does anyone know if this construction method is suitable for mid-rise and high-rise buildings? How many stories can be constructed using ICF system? Is there any multi-storey example?