Solid walls are making a comeback - Insulated Concrete Formwork
Cement in various forms has been used since the ancient Egyptians and naturally occurring for the last 12 million years. In recent history, this supported the boom for low cost, fast build housing post-World War II but by the 1980’s we had fallen out of love with the grey, concrete jungles which had emerged.
However, solid wall construction is making a comeback…
Insulated Concrete Formwork (ICF) is, as the name suggests, solid concrete with insulation either side. The Polystyrene used as a mould for the concrete then becomes the insulation. Pump grade concrete can provide up to 4N crushing strength.
Concrete has a reputation for not being green due to the energy required to produce it. However, these methods have developed over time. Concrete can be recycled and up to 70% can be replaced with scrap materials as none of this is evident in the final finish. Bar reinforcement can also be used from scrap metals and expanded polyurethane is the easiest and a better environmental option for the insulation.
What are the Benefits of ICF?
- Design: Build to any shape or style. Gables up to 47 degrees are achievable with this method. Render will bond directly to the insulation so thin or thick coat can be used. This must have 3rd party accreditation to be applied directly to ICF.
- Structural strength: Provides a minimum of 35 newton strength and can be reinforced if required. There is no thermal movement due to the insulation and no movement joints are required. Concrete is stronger and more stable so there is less risk of settlement damage.
- Durability: Becomes a stable system and not subject to rot or corrosion once cladding has been added as the structure is protected from the elements. The system is simple to repair or alter. The DPC is included in the concrete core.
- Air quality: No condensation on the walls provides a better environment for the building occupant.
- Resources: ICF developments can be built with minimum resources and an ideal solution for remote sites. ICF systems must be installed by trained personnel.
- Speed of build: Up to 3 metres in storey height can be poured in layers per day. There are reduced disruptions due to bad weather (except in freezing conditions) and waterproof concrete gives continuity of build.
- Energy efficiency: ICF will achieve minimum Building Regulation requirements but thicker insulation will upgrade the U Value. There is an increased thermal mass and it offers better acoustic insulation and air tightness properties. There is less thermal bridging due to it being a complete insulation system.
- Affordable: Can be a more economic solution for affordable housing and its energy efficiently means reduced energy bills.
- Fire resistance: Is flammable but will self-extinguish away from a flame. It gives off less heat then timber and less likely to lead to building collapse.
- Flood resistance: Water resistant and when water recedes will dry quicker than other construction materials.
What can go wrong?
Along with any pros come the cons and working with concrete is no different. The main issues can be messy blow outs down to inexperience of working with these materials and honeycombing. Blocks must be located properly, closures added where required, adequate propping and the correct grade of concrete should be used.
Things to consider when working with ICF:
- Accuracy of insulation alignment and installation.
- Chose a material provider who can provide system training.
- Is the concrete mix too wet or dry?
- Check the grade of concrete required. This can lead to concrete voids. These are most likely at the top of opening reveals.
- Pumping too quickly can lead to increased pressure and blow outs.
The Insulated Concrete Formwork Association (ICFA) requires any members to have 3rd party accreditation and provide a full training programme or competent person’s scheme.
The Valuation Panel of the Council of Mortgage Lenders confirmed that ICF (Insulating Concrete Formwork) construction is acceptable for mortgage purposes as a standard form of construction, subject to provision of valid product certification and monitoring of ICF System providers by the ICFA (Insulating Concrete Formwork Association) of the UK.