What is ICF Construction?

Insulated Concrete Formwork (ICF) is a modern construction system that uses hollow, lightweight blocks made from Expanded Polystyrene Foam (EPS). Once assembled into a wall, concrete is poured into the void between the forms. This creates an incredibly strong, insulated, and fireproof wall for any building project. ICF construction combines the benefits of excellent insulation, structural integrity, and ease of use into one efficient system.

Why should you consider ICF construction?

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Quick To Build

ICF systems are quick to install and don’t require rare and expensive joiners and bricklayers. This reduces labour costs and eliminates delays.

Indestructible

ICF structures are virtually indestructible, resistant to moisture, pests, fire and flooding.

Built To Last

The core marerials in an ICF form – concrete and the Neopor insulation do not deteriorate at all if protected from the environmnent by the wall finishes and so an ICF home could last forever!

Comfortable

ICF construction provides superior energy efficiency and eliminates draughts to provide an incomparably comfortable living environment.

Insulated Concrete Formwork

What is ICF?

Insulated Concrete Formwork is an in-situ Modern Method of Construction. It combines Neopor (A highly specialised type of expanded polystyrene) blocks with concrete to deliver superior levels of performance over alternative construction techniques like timber frame or cavity wall construction.

Neopor is a rigid, closed cell, thermoplastic foam material produced from solid beads of polystyrene that includes a polymeric flame retardant (PolymerFR), and graphite. . After processing, it becomes a very lightweight, rigid, moisture proof material that has very high insulation qualities. The manufacturing process involved is complex but this wonderful material is absolutely ideal for the walls of very high quality disaster resistant domestic homes.

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Building ICF Homes

ICF In The UK

Block Systems

All ICF Construction systems available in the UK from members of the Insulated Concrete Formwork Association are known as block systems; although in the early stages of UK development the large area forms from Nudura and Polysteel would be have been referred to as panel forms.

Configuration

The basic module of a block system consists of parallel sheets of EPS, joined by polypropylene or steel wire cavity bridges acting as ties (Commonly known as webs), forming a hollow block, which is ﬁlled with concrete.

The blocks typically ﬁt together by castellation or tongue and groove joints on the mating surfaces. Vertical joints are staggered as they are typically in blockwork.

Shape

In a typical range of block components with differing insulation wall thicknesses, the blocks range between 500–2500mm long and 250–600mm high.

In general, the larger the form the better because they are quicker to install and have less joints.

Joints

The type of joint is very important as they stop the concrete from leaking out!

Most of the forms have castellated joints restricted to the horizontal surfaces.

Polysteel has tongue and groove joints on both horizontal and vertical surfaces.

Benefits of ICF Construction

Comfort

Thermal mass is provided by building materials that have high density and conductivity and the most effective economic material is high strength concrete.

The materials inside a home’s insulation envelope act like a temperature battery. They absorb heat from the sun, keeping the house cool, and then slowly release warmth after the heating system turns off, maintaining a comfortable temperature. Because of this, thermal mass works really well with heating systems that deliver warmth gradually, like underfloor heating paired with a heat pump.

ICF construction offers exceptional thermal mass within its concrete core. This “sandwich” design is incredibly effective, creating a stable indoor environment by protecting against overheating in the summer and rapid cooling in the winter. This makes ICF homes perfectly suited for efficient heating by electric heat pumps.

In comparison, cavity wall construction does not include any high thermal mass materials. This is because most of the insulation is provided by the inner wall which is made of lightweight blocks. However, the outer layer of bricks does help to slow down how quickly the temperature rises when exposed to sunlight. Timber frame homes, on the other hand, have essentially no thermal mass. This can lead to them becoming uncomfortably hot in the summer months. Click here to learn more about why this makes consistent heating year-round a challenge for new homes.

Insulated Concrete Formwork provides extraordinary sound insulation and sound proofing at no extra cost, creating a quieter and more comfortable indoor environment. There are plenty of ICF examples where noise resistant homes have been provided by the use of ICF in a very noisy external environment.

Because the walls of an ICF home consist of a solid core of concrete the only place where draughts can occur is around the door and window openings. Hence if these are installed correctly ICF homes are draught free.

Quality

The durability and resistance of ICF construction to various weather conditions, including extreme temperatures, hurricanes, and earthquakes has been proven over and over again. Have you seen those pictures of devastated areas in the US after hurricanes, floods, earthquakes or fires and the only buildings left standing have been built in ICF. See here for more information on how ICF construction is becoming a vital choice for protecting livelihoods

It’s generally overlooked that ICF construction is a highly sustainable house design. Not only do ICF systems incorporate recycled materials in their EPS foam elements and ties, but they also deliver a massive reduction in energy consumption over a building’s lifespan. This is thanks to the incredible thermal mass of the concrete core, which makes ICF homes far more energy-efficient in the UK than traditional timber frame builds. See here for more information on the sustainability of ICF Construction.

ICF construction is incredibly versatile, accommodating a wide range of architectural styles. It even allows for flexible designs, including curved walls and other unique features. All of this is achieved while delivering the outstanding energy efficiency that’s crucial for modern sustainable homes. See here for more information on how to design ICF homes.

Wood in the form of furniture is the largest source of fuel in domestic fires and has x10 more calorific value than EPS. The EPS used in Insulated Concrete Formwork is treated with a small quantity of flame retardant. As a result, when EPS is exposed to an open flame the foam will quickly draw in, thus pulling away from the source of heat and reducing the probability of igniting. Furthermore, the Polymeric Flames Retardent Additive’s decomposition products extinguish the flame so that when the ignition source is eliminated, EPS does not continue to burn.

Value

ICF construction is often faster than traditional methods, as the interlocking forms are relatively easy to set up, and the concrete can be poured quickly. This leads to cost savings in terms of labor and construction time that has been proven time and time again in ICF projects.

ICF Construction systems are designed to be user-friendly and do not require highly specialised skills. This can reduce labour costs and make it more accessible for a broader range of construction professionals. See here for more information on construction details to build ICF homes.

ICF homes often have a higher resale value due to their energy efficiency, durability, and other benefits, making them an attractive option for homeowners. See here for more information on the different project types that can be built with Insulated Concrete Formwork.

The concrete and foam materials used in ICF building construction are non-toxic and do not emit harmful gases, contributing to a healthier and safer indoor environment.

How Does ICF Compare?

ICF compared to Timber Frame or Cavity Wall Construction

Characteristics	ICF	Timber Frame	Cavity Wall	Notes
Sound Proofing	Excellent	Poor	Average	The dense concrete and EPS layers provided by ICF is one of the most efficient methods of sound-proofing.
Long Term Maintenance	None	Unknown	Unknown	The life of timber frame and wide cavity wall construction has yet to be proven.
Service Installation	Ducts must be cast in walls	Needs Planning	Easy to Install	Slots can easily be cut into the EPS to accommodate cables and pipework.
Exterior Wall Finishes	Timber, Brick, Brick Slips or Render	Timber or Brick Skin	Brick Skin	ICF is very flexible as any type of wall finish can be accommodated.

Characteristic	ICF	Timber Frame	Cavity Wall	Notes
Anticipated Building Life	100+ years	30-60 years	60+ years	Softwood timber will rot in the presence of moisture irrespective of any pressure treatment.
Thermal Mass	Very High	Very Low	Medium	SAP Calculations never accurately reflect the additional comfort & the reduced running costs of residential units with a very high thermal mass.
Resilience to Fire & Flood	High	Very Poor	Poor	It is impossible to ensure that structural timbers are properly dried out after a flood & cavity batts can take a significant time to fry out.
Thermal Bridging	Good	Poor	Poor	The continuity of the EPS panels reduces thermal bridging to a minimum.
Air-tightness (Draught-proofing)	Excellent	Poor	Poor	The June 2022 Building Regulation revisions require every new dwelling to be pressure tested before approval can be granted.
Carbon Footprint	Low	High	High	Heating & Cooling account for 90% of a building’s environmental impact. The airtightness and thermal efficiency of ICF results in low carbon impact.

Characteristics	ICF	Timber Frame	Cavity Wall	Notes
Speed of Construction up to wall plate	1 Month Not weather dependent	3-4 month order time + 4 weeks on site	3-4 months & highly weather dependent	Once a builder has our drawings, they can start construction & weather-proof buildings in a few weeks and will not have to wait for bricklayers or kits from timber frame suppliers.
Required Scaffolding Period	1 month	1 month	4 months	Required for the construction of the exterior walls, roof, gutters and down-pipes and windows.
Labour required	Experienced site workers	Joiners	Bricklayers	With some basic training, multi-house developments built in ICF can be completed in a few months.
Foundations	Strip footings or slab	Strip footings or slab	Strip footings or slab	Walls of a rigid rectangular box of ICF in residential units virtually never crack due to foundation movement.
Timber floor installation	Yes	Yes	Yes	Fixings are easily provided by casting screwed rods & plates into the concrete core of ICF walls to provide very secure, high strength fixings.
Beam & Block floors	Yes	No	Yes	Beams can be cast into the ICF walls.

Characteristics	ICF	Timber Frame	Cavity Wall	Notes
Materials	£100	£100	£120	ICF forms £60, concrete £20 and concrete pump £20 Facing bricks £75, Cavity insulation £25 and Lightweight block inner skin £20
Site Labour	£50	£65	£100	Assumes machine made bricks
Brick Skin	£100	£100	inc
Scaffolding	£15	£10	£25	12 weeks+ for cavity walls and 3 weeks for ICF and timber frame
Total (£/m2)	£265	£275	£245	*If render is used as the finish ICF is the cheapest form of Construction*

ICF Construction History

Quick & Cost Effective Construction

Durisol was founded in 1938 near Zurich in Switzerland. The forms were made from a mixture of treated wood fibers and Portland cement. They are completely different from modern ICF forms using EPS but were the first type of ICF to be used in volume. The company grew rapidly after WW2 in the Netherlands, France, and Belgium. There was a massive requirement for a quick, cost effective and solid construction method using largely unskilled labour.

Not Limited To Skilled Labour

Conservation of energy was the last concern for countries after WW2. Everyone needed buildings that were quick and easy to build and in post-war Europe. Durisol ICF quickly caught on as a quick, cost-effective and solid construction method that didn’t require highly skilled labour. By 1959 Durisol was promoted as cutting traditional construction costs by 20-30% and was being produced in 13 countries. Modern Insulated Concrete Formwork using EPS can be made very quickly in a large press whereas Durisol blocks used slow setting cement to bond the wood fibers together.

Polystyrene ICF

Polystyrene ICF didn’t appear until the late 1960s. The first person accredited with introducing a polystyrene ICF was contractor Werner Gregori. In 1966, he filed the first North American patent for a foam concrete form or “modern plastic” ICF. This was granted in the US and Canada in 1968 to cut construction costs, increase build speed, promote the use of unskilled labor. and at the same time provide energy efficient home design.

American Polysteel

ICF forms were the start of what has become a mainstream sustainable house building system in the US and Canada. American PolySteel was founded in 1978 as Foam Form and was the first North American manufacturer. It procured the manufacturing rights from Werner Gregori, the Canadian who was issued the first patent for insulating concrete forms. American Polysteel sold the UK rights to Polysteel (UK) Ltd in 2008. The current Polysteel products, which include unique tongue and groove perimeter joints, are very similar to the original design by Werner Gregori.

It is just a matter of time before this sustainable house building system becomes more mainstream in the UK.

ICF: Building Better to Live Better

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