Want to make sure your home extension is built as quickly as possible?  We look at some structural systems that offer super-speedy builds on site.

When planning a building project, one of the biggest decisions is your choice of structural system. Traditional bricks and mortar are still the most common construction method in the UK. But masonry isn’t the only option. Alternative materials and techniques can reduce build time while increasing your home’s energy efficiency.

Insulated Concrete Form (ICF)

Insulated concrete form (ICF) is one of the leading players, offering ultra-fast build and airtightness. ICF systems vary greatly, including type of material, size of blocks and insulation levels. But the basic principle is the same - stacking lightweight, hollow blocks usually made from expanded polystyrene (EPS) which are infilled with concrete.

As the pre-cut blocks or forms are interlocking, no mortar joints are required to connect them as in a masonry wall - enabling speedy construction regardless of weather. The foam panel framework is reinforced with steel bars to lock them into place. Concrete is then pumped into the cavities. The result is a strong and well-insulated structure ready to be finished inside and out.

Each lightweight block can provide up to 1.1m2 of wall area and is easy to cut with a saw, so building with them is faster than with bricks. Plus, there is no need to add insulation at a later stage, as in a conventional build. The framework and pour for a single-storey extension can be done in three to four days.

Alternative systems use blocks made from specially graded recycled waste wood chipped into wood fibre and then bonded with cement. The resulting cement-bonded wood fibre mix, known as woodcrete, is then moulded and stamped out to form the ICF units.

In addition to speed, the principal benefit of ICF is energy efficiency. Dense concrete is the structural core with layers of insulation ensuring the building is warm inside when its cold outside and vice versa in summer. ICF also offers better soundproofing than other quick-to-build systems such as timber frame.

SIPs (structurally insulated panels)

This superstructure consists of a rigid EPS insulation core sandwiched between two sheets of wood, usually oriented strand board (OSB).  The panels are then assembled on site. SIPs can be used as a standalone structural method or to wrap around a timber frame skeleton to add insulation.

The structural components are factory-made to specific requirements based on your architect’s design. This means all openings, for example windows and door frames, are pre-cut, so only minimal tweaks are required on site, reducing build times.  Like ICF, work on a SIPs site can continue whatever the weather, so there is less delay.

A typical two-storey 200m2 SIPs house, for example, will take two to three days to fabricate in a factory and around 10 days to erect the house shell and make it watertight, according to Ian Clay, partner SIPs@Clays. Depending on the design, the build could be even quicker.

While the construction times are super-fast and predictable, you will need to factor in lead times. It may take weeks or even months from placement of order to delivery on site.  While there will be lower on-site labour costs and no bad weather disruption, precision-engineered SIPs panels can be expensive, so you will need to do your sums.

Thin joint blockwork

Modern masonry construction typically consists of an inner layer of blocks and an outer lay of bricks with a gap in the middle for insulation. Conventional blockwork uses a cement mortar at standard 7mm-10mm depths. This can take 24 hours to dry which limits the number of courses that can be built in one day to around six about half a wall. The mortar will still contain a lot of moisture and won’t reach full strength for days or even weeks.

Thin joint blockwork, on the other hand, uses a special quick-set adhesive that’s just 2mm-3mm thick. The slender mortar joint reaches close to full bonding strength in just 15-20 minutes. This allows your builder to continue the block layer up to the full wall height in a single day, ensuring a speedier build.

Another claimed advantage of thin joint masonry is its green credentials with less air leakage through joins and better thermal performance. The thin joint system can be used for solid, cavity and party walls as well as internal partitions.  

Timber frame

Timber frames are pre-cut in factories and delivered to site ready to be assembled. A wall that might take two to three days to construct in blockwork can be built in half a day using conventional timber framing techniques. Opting for a panellised system, such as SIPs, further increases the time savings – the walls and roof structure of the timber houses can be erected on site in just days. Of course, the external walls of the house will still need to be constructed on site with brickwork, for example.

One of the advantages of timber frame is that the first fix – including putting plaster on the internal walls and inserting cables for electrical supply and pipes for water - can progress at the same time as enveloping the structure in brickwork. It’s this overlap that saves a lot of time compared to a masonry build and the fact that wet trades are adversely affected by bad weather.

Modular builds

Specialist companies now offer modular timber frame systems delivered to site not just with the walls and roof panels pre-insulated but with the windows fitted, plumbing and electrics pre-installed and internal walls drylined. Benefits of factory-made kit homes includes saving money on skilled labour and a uniform quality of construction as well as less time on site.

It means there will be fewer labour-sourcing issues and less coordination of trades to worry about, such as carpenters, brickies and plasterers turning up on site to complete their jobs. This can significantly cut build times. In some cases, these modular kits can be completed in less than a month depending on the size and complexity of the design.  

Facit Homes, for example, uses digital technology to develop 3D models of new homes that shows every detail, even where electricity switches will be placed. The software generates all the information from material quantities and prices to the size of each window. Computer-controlled machines then cut sheets of engineered plywood into 3D components that are numbered, stacked and sent to site to be assembled. A 200m2 home will take about two months to make weatherproof once the groundworks are completed, says the company.

This type of structural system will, however, take a significant amount of planning. It’s essential to carefully consider every element of the design as it’s harder to make changes on site than in a conventional build. On the downside of modular homes is more limited choice of overall design and internal fit out.

So, how important is speed?

Clearly there are some structural systems that score high when it comes to speed.  That said, building a home extension is not something that should be rushed. More important is making sure it’s well designed and constructed and meets your requirements. Shaving a few months off the construction time may be tempting but once inside your new living space how long it took to build will soon be forgotten.