Designing and Constructing with ICF – Part 2

Aug 6, 2019

In the second part of this feature, Insulating Concrete Formwork Association (ICFA) outlines best practice for architects looking to detail and construct buildings using insulating concrete formwork.

One of the advantages of insulating concrete formwork construction is that it is comparatively simple to design and install. As with any building system it is important that architects are familiar with and knowledgeable about how the system is designed, constructed and monitored on site. It is also useful to know what manufacturer resources are available, as this can make the design process easier and faster.

Building from the ground up

Work on site begins by casting the foundations of any type. Both slab and step foundations are easily accommodated using ICF. In terms of footing size, specifiers should remember that ‘edge projection distance’ is the distance from the concrete wall surface inside the form to the footing edge – not the exterior wall surface of the formwork to the footing edge. Vertical reinforcement dowels placed in the footing or slab edge provide lateral support at the base of the wall.

Wall assembly

The form units are stack bonded on site with horizontal steel reinforcement inserted at each course, or as specified by the engineer. Standard forms are cut to suit the wall length and butted to preformed corner or T-form units. A proprietary alignment system is erected to facilitate safe access and alignment of the form assembly during concrete pouring. The structure typically remains in place until lateral connections to the wall are made.

Stack heights with ICF construction can be particularly important when considering aspects such as footing elevations to grade, brick finishes relative to grade levels, and floor bearing heights relative to finished grade and each other. Higher walls are possible by adding multiples of the form height (457mm) to the 11-metre wall. By nature of the material, it can be easily cut to accommodate any desirable height.
ICF is one of just four approved walling systems for domestic basements (see www.basements.org.uk).

Wall openings and concrete placement

Window and door openings are placed in the wall using formwork that is able to support the concrete during placement. Upon reaching the desired height, vertical steel reinforcement is inserted into the wall cavity. Concrete pouring is recommended using a boom pump and internal vibration to ensure even placement and consolidation. The concrete can be poured in any weather due to the insulating properties of the formwork.

Floor and roof connections

Once the concrete has cured, wall-to-floor and roof connections can be made. Floor types typically used in conjunction with ICF walls are in-situ concrete, hollowcore planks, timber, and block and beam. Roofs tend to be timber or light-gauge steel. Concrete roofs are easily achievable.

Services installations and finishes

The formwork walls are chased to receive electrical wiring and pipework (up to 50mm in diameter). One of the key constructional advantages of ICF is that it takes external cladding off the critical path. Windows and doors can be installed as soon as the concrete is cured, ensuring a weathertight envelope.

A wide range of external facing materials can be applied to ICF structures, including brick, stone, render and timber, as well as steel, aluminium and cement cladding panels. Specifiers should note that screws must be used in place of nails when it comes to installing external facings. Plasterboard is the most common internal finish and can be installed directly onto the walls using 42mm plasterboard screws. Acrylic/silicone render can be used in flood-prone areas.

All ICFA members offer training courses and won’t supply their products to site unless the contractor has attended their course, providing peace of mind to specifiers and clients.

Reproduced by kind permission of NUDURA and Architecture Today

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