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ICF Construction

Building with Polybloks

ICF Construction is increasingly popular amongst house builders because it is an easy to use, very fast method of construction.

Polysteel concrete forms are manufactured in the UK and uniquely use steel ties to create a rigid structure.

ICF Blocks

What is ICF Construction?

Insulated Concrete Forms are made with two sheets of EPS (expanded polystyene) that are held together by ties (or webs).

ICF blocks are made by heating and expanding tiny beads of polystyrene with steam inside a mould. This mould also holds the ties (steel or plastic) in position whilst the EPS is formed around them.

ICF walls are built by laying one course of foam blocks at a time – starting from the corners and making sure that each course is straight and level. The next course follows with the vertical joints off-set like brickwork bonding. The internal void is then filled with concrete to form a composite concrete / EPS insulated concrete wall that is much stronger than brickwork and completely fireproof.

Styrofoam or Polystyrene

Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam, or XPS. Also referred to as “Blue Board”. It is used for building insulation, thermal insulation and water barriers.

Styrofoam is owned and manufactured by The Dow Chemical Company and is a different material from the EPS used in ICF block construction.

Historically, EPS has been confused with Styrofoam. In fact, the previously popular disposable coffee cups known as Styrofoam cups were actually made of EPS.

Advantages of ICF Houses

large custom house built with insulated concrete formwork

People are initially attracted to installing ICF block walls thanks to its reputation for providing high levels of insulation. It certainly does provide an economic way of meeting insulation standards required by the UK Building Regulations.

What is the main benefit of ICF?

ICF construction is an easy to use, very fast, building method that is not weather sensitive and does not rely on the availability of brick layers.

Invented as Simple, Easy & Quick Use

Origins of ICF

Durisol was founded in 1938 near Zurich in Switzerland. The forms were made from a mixture of treated wood fibers and Portland cement. The company grew rapidly after WW2 in the Netherlands, France, and Belgium when there was a massive requirement for a quick, cost effective and solid construction method using largely unskilled labor.

Conservation of Energy was the last thing that countries worried about after WW2 – everyone needed buildings that were quick and easy to build.

Making ICF with EPS

Werner Gregori, a German born naturalized Canadian building contractor patented a concrete form system in 1966 to cut construction costs, increase build speed and promote the use of unskilled labor.

His block, “FrothForm,” measuring 16″ high x 48″ long with a tongue-and-groove interlock, metal ties, and a waffle-grid core is very similar to the forms made today by Polysteel.

Fast Construction Method

ICF speeds up house building

By using ICF to build a house, the walls can be brought up to eaves level and ready for the installation of the roof trusses within 3 weeks of ordering the blocks.

The roof trusses and tiling can then be installed so that the internal finishing works can progress at the same time as the outer brick skin is laid.

Services are also easily installed by cutting slots in the EPS for pipework and cabling. Holes though the concrete core for service entries can be provided using cast in PVC pipes as ducts. If they are forgotten it is easy to core drill though an unreinforced wall.

large custom insulated foam house built with icf

1. Ordering Materials

We can provide Polybloks for insulated concrete block homes to any site in the UK within a few days of the order being placed.

2. Foundations / Footings

The structural rigidity of ICF allows the use of trench footings for most ground conditions that occur in the UK.
If the trenches are 1m deep with 400mm of concrete at the bottom, the primary walls of the building can be brought up to the underside of the ground floor level using a single course of 600mm high ICF blocks.

The beam and block ground floor can then be installed.

3. Walls Up To Eaves

The ICF walls can then be extended up to eaves level with two concrete pours into the formwork that would require only two visits by the concrete pump. The primary structure of an insulated concrete home can be established in about 3 weeks – at most.

The inserts for the construction of the timber first floor are built into the concrete core and the trusses are bolted down onto it.

4. Reinforcement

Very few residential buildings require ICF to be reinforced, apart from a few bars that are needed over wall openings – steel fixers are therefore not required.

ICF apartment buildings and most custom ICF homes do not require the walls to be reinforced if the floors are used as structural diaphragms.

Other ICF Construction Advantages

Weather Sensitivity

Building with ICF can continue in freezing conditions if the concrete is delivered by truck mixer and won’t need to stop when it rains. In cavity wall construction, brick and block laying is on the critical path of any builder’s schedule because it’s easily influenced by the weather.

With ICF, the weather influence is removed because even if a full brick skin is being installed on the outside of the ICF walls, the roof can be installed and any internal finishing work can proceed.

Foundation Settlement

Cracks caused by foundation settlement in homes built with insulated concrete forms are virtually unknown. This is because the dwelling walls form a rigid box that is much more rigid and stiff than the foundations that support the house. Costly raft foundations can therefore be avoided.

Bricklayer Availability

There are reportedly about 70,000 bricklayers in the UK, of which 7-8% retire every year. Productive bricklayers who produce the most high quality work can earn around £125,000pa. On this basis, a group of two brickies and one hod carrier will cost about £300,000pa and if they lay 250,000 bricks a year each brick will cost about £1.40 to lay.

An average detached house will cost over £30,000 in bricklayers wages without the cost of the scaffolding that will be needed for at least 3 months for cavity wall construction.

ICF Construction Considerations

The major risk in ICF construction is that there is no visual method of making sure the poured concrete wall forms are filled with good quality concrete. The only way to eliminate this risk is to:

1. Make sure the concrete supplier knows the concrete is being pumped so that the correct mix is provided with the additives required.

2. Slump test every delivery of concrete.

3. Vibrate the concrete with a small diameter poker.

4. Provide slots in the timber infills at the bottom of window openings to allow concrete to be placed there (gaps in the concrete core could result in structural and long-term weatherproofing issues).

Every course of ICF should be installed with a stringline and spirit level to ensure the top of each course is level and straight before the next course is added. Walls that are not vertical or flat can cause numerous problems with wall finishes.

Insulated concrete forms should be installed on a flat level footing and glued together with the foam adhesive provided. Many installers do not take sufficient care with the initial alignment and use adjustable jacks to move the top of the wall into the correct alignment after 3 or 4 courses have been installed. This can shear the adhesive bond at the joints and create more movement at one particular joint – promoting concrete leakage at that point.

If failure does occur, concreting should stop and plywood straps provided across the failed joint using screws to fix the plywood to the ferrule strips in the ICF.

Openings for windows and doors are easy to provide. The best approach is to adjust window and door positions so that the vertical edges occur midway between the ferrule strips in the Polybloks – and if possible locate them at the end of a form to reduce cutting. It is also easier if the cills and heads of windows are aligned with the horizontal course joints in the ICF (this is particularly appropriate if the windows are bespoke). The voids around the opening need to be filled with 50mm thick pressure treated softwood that is held in place with screws through the EPS with PVC fixing discs. The timber then needs to be braced with vertical and horizontal bracing to resist the pressure of the concrete. The Polysteel installation manual provides full details of this.

The flashing to windows and doors needs to be made on a bespoke basis or installed in accordance with the details in the Polysteel manual.

Polysteel provides detailed instructions on how to use scaffolding to ensure that the ICF forms do not move during concreting. The scaffolding must be designed to be independent of the building and capable of resisting windloading.

The scaffolding will need to be in place slightly earlier than normal but it will still cost less overall as it will only be in place for roughly half the time required for cavity wall construction using bricklayers.


Particularly Suitable For Large Houses

Using ICF for large new houses

Many new houses are built to very modern designs with large open areas and cantilevers. ICF construction can be very useful in these circumstances because when it is reinforced the amount of structural steelwork required can be substantially reduced – especially if the Structural Engineer is experienced in the design of ICF.

It is also easier to provide complex roof shapes because the steelwork can be fixed to the top of the ICF walls at random locations.

large custom icf built house

Using ICF in new housing developments

The use of ICF can speed construction enormously, especially in the winter months when the building shell can be waterproofed in a month or so.

The ICF industry has struggled to keep up with the volume of material required but Polysteel has a manufacturing base in South Wales and can meet most orders from stock and large orders with a few weeks notice.

Polysteel is one of the original manufacturers of ICF blocks and is considered by many experienced ICF house builders to be the best ICF building system available.

ICF Construction

If you are looking to use ICF on your next project but need more detailed information before you start, give us a call.