If you’ve been looking for a new build material recently, you may have come across Insulated Concrete Formwork. Commonly referred to as ICF, this Modern Method of Construction has grown in popularity for many reasons. As an insulated solid wall construction method it can quickly construct properties that deliver a high build quality and superior levels of energy efficiency. But what is ICF construction and how can it solve issues commonly found on a building site?
Our step-by-step guide covers each key stage in the construction of an ICF building.
Step 1: ICF blocks
Not all ICF systems are the same and can vary in size and type of blocks, insulation levels and material. What connects all ICF systems is the principle of using two facing layers of insulating material to form the block. Each block has a hollow which is then filled with concrete to create the solid wall of the building.
Within the UK the most commonly available systems are made from either expanded polystyrene (EPS) or woodcrete.
EPS
EPS systems are available in two formats – panel or moulded. Panel systems are available as two EPS sheets which connect using metal or plastic ties to form the block. EPS panels are available in varying formats and may be delivered to the site either pre-formed or assembled before construction. Moulded EPS systems are manufactured and delivered to the site as pre-formed blocks.
Woodcrete
Woodcrete forms use natural material wood mixed with cement and water to create a solid block. The units are available pre-insulated or without insulation.
Step 2: ICF Training
Regardless of which system you choose, the main principles of constructing with ICF are the same. However, each system does have its idiosyncrasies which a contractor must be aware of before starting on site. It is for this reason, and to ensure a high-quality build, that we expect all ICFA members to provide training on their system before supplying the products.
As a simplistic system, training is easy. It is possible to reach a competent standard on ICF much quicker when compared to other construction methods. Without the need for mortar to fix the blocks in place, it also provides the perfect training ground for apprentices new to construction while also minimising the expensive cost of a skilled bricklayer.
Step 3: ICF delivery
Material lead times are typically short for ICF blocks making it possible to get the build started on site within a short planning window.
To get started on the build you usually need only two simple materials, the blocks and steel rebar. Due to their lightweight and stackable nature, the ICF blocks are incredibly easy to transport with fewer deliveries and a reduced requirement for lorries to get them on site. In fact, for locations with limited accessibility, it is possible to deliver the materials on the back of a truck. An ideal option if access is only via a small country lane.
Once on site, you can move the blocks around by hand, reducing the need for heavy plant and equipment.
Step 4: Preparing the site
When preparing the groundwork, considerations for the foundations are generally the same with ICF as with standard build methods. Both slab and step foundations are easily accommodated. When laying the foundations, you may need to insert rebar tails to tie the walls to the base.
Another key benefit of ICF is the ability to use the same system for almost every part of the build. The combined strength of the concrete core and rebar allows you to use ICF for retaining, above and below-grade walls. It is also one of the approved walling systems for domestic basements recommended by The Basement Information Centre.
As with any structure below ground level, and to conform to basement waterproofing regulations, it is critical contractors ensure the joints are protected and use the correct concrete specification. Your ICFA supplier will have who the technical knowledge to advise on the process.
Step 5: ICF Construction – building the wall
On the surface, the ICF system has a lot of similarities to traditional build methods. It consists of large building blocks which stack, like brick or blockwork, to create the wall of your building.
The simplicity of ICF is delivered through a raised profile along the block edge which enables them to slot into place. This simple feature significantly speeds up the build process enabling the blocks to fix securely. This removes the need to apply mortar. The construction process is so quick it is possible to build the ground floor wall of a simple structure in as little as three days.
With most ICF builds you will construct the walls in stages. This is typically to first-floor height during the first phase although you will need to check with your ICF supplier because every system and project has slightly different requirements.
Getting the first course correct is essential for the rest to the build and your installer should ensure the ICF wall is set out plumb and level across all planes.
Step 6: Constructing unusual shapes
The large size of the ICF blocks makes them ideal for quickly covering an entire wall of a building but what happens when you need to create such as corner or curved walls? ICFA manufacturers and suppliers have a wide variety of standard forms which can include straight, T-wall, 90-degree, 45-degree and even curved blocks. If needed, you can standard construction tools to cut the forms to suit the design.
You should always speak to your ICFA supplier to understand what blocks they have available. They can also advise on how to get the most efficient method of building your design with their system.
Step 7: ICF and detailing
One common question that often arises around ICF systems, is whether they can interface with other common construction materials and products.
ICF blocks offer enhanced adaptability throughout the build process which enables them to work with most commonly encountered systems. Details such as windows, doors, floor joists and service pipes typically cut into the blocks as you build the wall. The flexible nature of ICF means that some detailing such as whether to recess doors and windows and to what extent are much easier to achieve when compared to standard detailing practices.
As with any stage of constructing an ICF property, we always advise pre-planning of detail elements to ensure it minimises labour resources throughout the process. Each ICF system is slightly different, and some may require cutting out while constructing the wall or post-concrete pour. We advise speaking to your supplier to find out what your system requires.
Spaces for the windows and doorways are cut out of the block as the wall is constructed. Be aware that these areas may need framing with timber prior to pouring the concrete and then either removed or left in place on which to fix the frames. ICF blocks can work with most commonly encountered floor and roof types including wooden joists, concrete beams and block concrete hollow core plank or corrugated sheet steel. Walls connectors, anchor bolts or cutting in of the block may be required to accommodate the system.
Take your time to research advanced or expensive heating systems of devices such as underfloor heating, heat pumps, wind generators etc. In some cases, it may be necessary to lay the appropriate pipework or ducting in preparation for the additional systems at the carcass stage.
Step 8: ICF wall bracing and rebar
Depending on the ICF system you choose and the design of your project, you may require rebar adding to the blocks. You will more commonly see this on flat packed EPS forms with the steel rebar placed either vertically or horizontally into the block although this may not be required with pre-made blocks. The amount you need is project specific.
Using ICF systems to construct larger openings such as bifold doors, retaining walls, basements or cantilever structures typically requires reinforcement steel inserted inside the block. The simplicity of the method to create strength without complicated structural solutions usually makes these features much easier to design with ICF over traditional forms of construction. Your ICF supplier and a structural engineer can advise on what reinforcement your project requires.
Your chosen ICF system may require a proprietary support system prior to the concrete pour to provide additional stability. These are removed once the concrete has set.
Areas that may require support are:
- Timber frames to window and door openings.
- Proprietary support structures for some EPS forms will ensure alignment of the system while the concrete is poured.
- Additional bracing may be required to support corners, cut units, ends of walls etc.
Step 9: Concrete pour
You complete each stage of your ICF structure by pouring concrete into a central cavity in the block. A benefit of building with ICF is the ability it provides to make last-minute adjustments or alternations to your build. You can make these right up to the point of the concrete pour with very little expense. Due to the insulating properties of the formwork, concrete can be poured in most conditions and inclement weather won’t slow the build process down.
The concrete pour is often seen as the most difficult stage with an ICF build. However, take the correct steps and it shouldn’t cause any problems.
- ICF blocks – before commencing with the concrete pour ensure the walls are straight and the blocks aren’t damaged. If there are problems, now is the time to make any last-minute improvements as necessary.
- Bracing – make sure there is adequate and suitable bracing is in place to keep the walls straight during the pour.
- Concrete – getting the consistency of the concrete is important. Too dry and the concrete won’t flow evenly throughout the formwork. However, if the concrete is too wet it will place additional pressure on the wall potentially resulting in ‘blow-outs’. Concrete mix designs may vary for different applications, and you should check first with your supplier.
There are many different methods of concrete placement including concrete pumps, crane and bucket, by hand or directly from a truck chute. The concrete pump is typically the method of choice. Once poured, the concrete is vibrated to expel air and increase concrete density and avoid honeycombing within the core. Your installer should get a copy of the concrete delivery batch ticket as part of the sign-off to mitigate any future problems if there is an issue with the build.
Step 10: Finishing the build
Once the concrete has set, the ICF blocks stay in place which provides two benefits for the build. Without needing to spend time removing the shuttering this speeds up the process and enables the contractors to achieve a watertight envelope incredibly quickly. The make up of the ICF block has an additional benefit to the property. The insulating material enables the concrete to dry quickly but cure very slowly. This process allows the concrete to gain additional structural strength with minimal cracking.
Floor and roof options are usually installed post-concrete pour. ICF systems can easily connect with a wide range of standard options including hollow core planks, OWSJ composite decks, block and beam, proprietary steel joists and traditional timber joists and trusses. You can install any style of window or door, and these are held in place with frame anchors as they would be in a conventional build. A bead of high-quality silicone sealant is applied to seal around the edges. When finishing the build, particular attention should also be made towards correctly sealing penetrations using a fit-for-purpose sealing system.
Internally, forms are chased out to accommodate electrical wiring and pipework. Plasterboard is the most common internal finish and can be installed directly onto the walls. The external walls of an ICF building will need protection to provide weather resistance. The system is compatible with a range of facing materials including render, regular brick skin, timber cladding and stone or rainscreen cladding. The chosen facing material will determine how quickly the build is completed and should have relevant third-party accreditation.
Interested in building with ICF?
As with all construction planning and preparation are essential for the build process. ICF systems have their logic and methodology. Involving your supplier early in the design stage will enable them to flag up areas that may require special consideration.
To meet the necessary mortgage and insurance requirements your chosen system should have third-party accreditation acceptable to your provider. The structural design of an ICF structure should be conducted by a suitably qualified structural engineer or engineering consultancy who has experience in the use of ICF. Some mortgage and insurance brokers may also require a system supplied by an ICFA member.
If you would like any more information on building with ICF contact us here. Alternatively visit our ICFA members page to contact an ICF supplier directly.