Insulating concrete formwork (ICF) otherwise known as permanently insulated formwork (PIF) is an insulated in-situ concrete system of building that is quick to construct and offers levels of performance significantly better than that available from slower, more traditional approaches to building.
Popular in Germany where it was born in the early 50's, it is grown rapidly in North America starting as a basement construction and now has approximately 8% share of the low rise housing market in Canada and the USA. It has been growing in the UK self-build sector for some years with a performance far in excess of the Building Regulations but with the recent increases in performance demanded by Building Regulations, Eco-homes and now the Code for Sustainable Homes it is broadening into mainstream and is currently on trial with a number of UK housing associations and regional house builders. It is recognised as an MMC system (Modern Method of Construction) by the BRE (Building Research Establishment).
ICF is based on hollow lightweight block components that lock together without intermediate bedding materials, such as mortar, to provide a formwork system into which concrete is poured. The block is formed of sheets of insulation materials normally expanded polystyrene tied together with plastic or steel ties or an integral web of the same insulation.
The later is manufactured as a complete block whereas the forms with ties are formed from sheet material. Some systems are delivered complete and some with ties which are clipped together on site to make the 'forms'. These latter have the panels delivered flat packed. Some of the systems which are complete with hinged ties are also delivered flat packed. Fresh concrete is poured into the forms built up to 3 metre high as a complete wall. This is normally dome by pump.
Once the green concrete wall is set, it becomes a high strength concrete frame structure with the formwork remains in place as thermal insulation, providing u-values ranging from the standard 0.30 w/m²k as required by the current Building Regulations down to 0.11 w/m²k - ideal for zero energy buildings Star Level 6 in the Code for Sustainable Homes. The building process is quick, tidy and precise, with lower equipment requirements than alternative methods and only semi-skilled labour.
Creative design (without compromising performance) is encouraged by the availability of a comprehensive range of components, further enhanced by the option to incorporate reinforcement for basements or multi-storey projects. The highly insulated structure may be clad internally and externally with a wide range of finishes, including plaster, masonry, curtain walling and renders. Most of the systems are marked on the outer faces of the forms to indicate where positive screw fixing can be made with self tapping screws into plastic or metallic webs. There are several different designs of ICFs world-wide.
ICFs are made of insulating foam, such as EPS (expanded polystyrene), and are manufactured either separate panels that are connected with plastic connectors or ties or preformed inter-locking forms or galvanised steel ties in preformed inter-locking forms. The differing insulating concrete formwork systems cause variations in the shape of the concrete within the wall: "Flat" systems (3rd generation) form even thickness concrete throughout the wall area similar to a conventional in-situ concrete wall.
In areas where there are high seismic or severe weather conditions, flat wall systems predominate as the system of choice. "Waffle Grid" systems (2nd generation) form create a waffle pattern were the concrete is thicker at some points than others. "Post & Beam" or "screen grid" systems (1st generation) form discrete horizontal and vertical columns of concrete. The areas within the grid are solid insulation, increasing the overall U-value but offering reduced fire resistance.
The concept of assessing the value of something is as much an art as it is a science. This observation is particularly true of decisions related to a new home purchase. One person may determine “best” value by lowest cost or highest quality while another makes a decision purely on intangibles (i.e., comfort, aesthetics, “peace of mind”). Regardless of the method to determine value, a homebuyer, builder, or designer should make informed decisions about house construction options.
Several benefits of Insulated Concrete Formwork construction are as follows:
Reduced energy bills
Homes built in ICF block construction require considerably less energy - in heating and cooling. The savings in bills costs have been registered as high as 70% when compared to a wood-frame house.
Comfort and reduced noise
Though somewhat intangible, comfort deals with important issues such as even distribution of air temperature in the home and the quietness or acoustical properties of the home. ICF construction provides considerable improved reductions of "outdoor" noise relative to standard home construction practices. The houses built with Insulated Concrete walls have the air temperatures more even and there is no draft. The barrier formed through the insulation and concrete sandwich design reduces the air infiltrations sometimes as much as 75% than a comparable wood frame house. With the concrete high thermal mass that buffers the home's interior from extreme outdoor temperatures and the continuous insulation layer that minimizes the fluctuations of the temperature inside the house the cold spots issue, that can be found in a timber frame wall along the studs or at gaps in the insulation, is being eliminated.
The concrete and the insulation concrete forms are not a desirable environment for rodents, woodworm and insects that often reside in wood framed walls.
Healthier indoor environment
As there is no organic composite within the ICF walls the growth of mould, algae and any other hazardous microorganisms is unlikely. The polystyrene insulation is non-toxic and free from asbestos, fibreglass and methanol. The tests carried out to the indoor air quality in ICF homes environments did not find any harmful emissions.
The ability of ICF construction to resist damage and protect occupants from wind and earthquakes are considerably better than most of the traditional building systems. In general, Insulated Concrete Formwork wall construction provides 5 to 10 times the racking resistance of conventional wood-frame walls. The racking strength of these walls prevents the building from collapsing or being pushed over by wind or earthquake forces. The concrete is able to maintain its structural capabilities over a long period of time and extend the life-expectancy of buildings. Life-expectancy and maintenance of a home is a concern of homebuyers and designers with a long-term perspective.
Reduced maintenance costs
As the ICF walls are made of non-biodegradable materials, they are not vulnerable to rot or deterioration. Also being a reinforced concrete structure there are no settlement cracks that often appear in the render or plaster long after new buildings are finished.
Fire resistance is important to the protection of occupants from fire and to allow sufficient time for warning and evacuation. Concrete walls have superior fire resistance in comparison to most other building materials. Solid concrete ICF walls can generally sustain as much as four hours of extreme fire exposure.