Choosing a build system
No construction method scores a perfect 10 on all fronts, but for every scheme there’s an optimum way to build, depending on your priorities. Emily Brooks takes a look at how the decision gets made in the real world
With a wide array of structural methods on the market, here’s our guide to finding the right option for your project
Abroad range of factors goes into working out the best structural system for your project. The balance could be tipped by a combination of considerations, or it might be a single influence that tilts the scales in favour of a particular technique.
Professional project manager Charlie Laing’s last few builds for clients offer an excellent insight into the thinking that goes into choosing a construction system. For a house in Croydon, the owners went for timber frame that offered them the right combination in terms of budget, aesthetics and performance (better than Building Regs standards).
A scheme in Buckinghamshire was constructed with insulating concrete formwork (ICF) to help achieve some demanding airtightness targets; whereas the architects for an Oxfordshire house specified steel frame to ensure the highly detailed bespoke design would be fully realised.
For another self-build in London, meanwhile, masonry proved to be the best fit: “The house may get rented out at some point, and the clients have a perception that brick and block will be a robust solution for this purpose,” says Charlie, who is operations director at CLPM.
So, what do you need to know when deciding which system will best suit your goals for a new home? And how can you come to the right conclusion?
The main systems
Before we get into the nuts and bolts, it’s worth a quick run through of the key options. Building in conventional masonry (brick and block) is still the standard choice for many new homes. With this familiar route, cavity walls are constructed by hand and filled with insulation on site.
Next up is timber frame; popular across the UK, but especially prevalent in Scotland, it comes in a few guises. With stick builds, the frame is all assembled on site, but this is an approach that’s becoming less commonplace as premanufactured methods take precedence. You can go for open-panel systems, which see a factory-made frame delivered to site with the inner studwork left open (so the insulation, plumbing, electrics etc are installed in situ). Or opt for closed-panel, where even more of the work is done off-site, with insulation pre-fitted and openings for fenestration already cut. In some cases, windows, doors and external cladding may even be in place.
Structural insulated panels (SIPS) are another factorymade system. These wall and roof elements consist of a layer of insulation sandwiched between two sheets of timber. If you prefer a more solid feel, insulating concrete formwork (ICF) is made from hollow blocks of polystyrene, reinforced with steel rebar and pumped full of concrete.
Sometimes more than one system is used. For example, ICF might be specified for a basement, with another
technique from the ground up. Meanwhile, oak frame homes – which are popular for their innate character – are typically wrapped in SIPS or similar insulating panels in order to achieve the desired energy performance and airtightness. And most masonry and timber builds will include some steelwork to support dramatic design features such as wide spans of glazed doors.
The tipping points
With the exception of green oak frame, a house’s final appearance has little to do with the underlying structure. Timber panels can be clad in brick slips, for instance, while blockwork walls can be hung with timber cladding. Selfbuilders therefore tend to be guided by three big factors: cost; how long the project will take; and energy efficiency.
“You could build any design you can think of with any form of construction. What people want is for it to be costeffective,” says architectural technician Granville Falshaw of Falshaw Homes. That idea is backed up by the Build It Estimating Service guide on page 83, which shows that walling systems for masonry and timber frame come in at very similar price points. Using SIPS or ICF will add to your construction costs, but these systems can offer benefits in other areas. Green oak is often at the top-end in terms of upfront prices, but the premium you pay will usually be reflected in the end value of the house.
Charlie Laing points out that it’s tough for novice selfbuilders to get to grips with assessing the cost of different systems. “It’s possible to go shopping for timber frames – which is something you’ll struggle to do with masonry – but you do need to be clear about who’s in charge of the design and who’s invoicing for which elements. You don’t
want to end up paying for the same thing twice,” he says. “Frame prices can also be difficult to compare: do all the quotes allow for the same things?”
As for getting quick build times, it’s not all about what happens once the materials are delivered. “Timber frame, SIPS and ICF are championed for their speed. If by this they mean speed on site, then that’s true,” says Charlie. “But if you include time spent on the design, then things start to even out.” If you’re using a prefab system, once the plans have been agreed, you’ll also need to factor in a lead time for production, which typically takes anywhere from 8-12 weeks for systems such as timber frame and SIPS.
When it comes to energy efficiency, it’s possible to achieve high standards with any system. As a rule, however, the more off-site fabrication there is, the more straightforward it will be to achieve the build quality and performance you wanted. This extra degree of certainty is, for many, a deciding factor. “Time in the factory is much more efficient as you don’t have to contend with the weather, or constraints with the site or equipment,” Jonathan Tipper from Gregory Phillips Architects says of using SIPS construction: “Imagine building a window on site rather than in a factory – there’s no comparison. The latter route allows a greater degree of quality control.”
Although it’s common for houses to be designed without the architect knowing how they’ll be built, some features might suggest the use of one system over another. SIPS can bridge further than timber frame, for example, but dramatically large spans can only be achieved with steel. If you want some curves, masonry is ideal and ICF can cope with a few, but factory-produced systems may not suit.
Another consideration is that designers experienced in using particular systems may be better placed to get the best results for your project in terms of buildability and affordability. Oak frame is a case in point, as it’s important to plan the living spaces to suit the span capabilities of the structural posts and beams. Similarly, with prefab methods, if you can work to standard sizes as much as possible, you’re more likely to keep costs down.
In terms of flexibility of internal layouts, building with masonry means you can hang pretty much anything off the walls and, should you wish, specify beam and block floors (see page 111 for the benefits of this flooring system). Meanwhile, most timber frame methods allow you to easily choose between open plans and partitioned interiors – but the walls aren’t as solid for fixing. Try upgrading to linings you can screw directly into, such as Fermacell or British Gypsum’s Gyproc Habito plasterboard.
If you want flexibility about how the design plays out on site, prefabricated systems may not be for you. “You don’t want to be cutting into structural panels, as even small holes will impact on thermal performance,” says Charlie. On the other hand, masonry structures are pretty adaptable. “You can bash holes in them without too much concern,” he says.
The potential for future changes may also be a factor for you. Generally, timber systems and ICF are harder to alter than brick and block builds (and in all cases you’ll need to seek advice from a structural engineer). You can, however, look to insert lintels and even capped-off services at points where you might want to extend further down the line. It will cost a little more now, but provide greater flexibility for you and any future owners.
Who makes the decision?
Ultimately, the joy of self-building is that you get to choose everything that goes into your new home – but many people are happy to be guided by their designer. Jonathan
says it’s quite rare for clients to have already made up their minds; although sometimes they come with the looser idea that they want their project to be eco-friendly, which may nudge the architect in a particular direction. “We generally take the lead on construction method and advise on the most practical option depending on the site, the size of the house and the longevity required,” he says.
With all of the recent projects CLPM has worked on, either the self-builder or their architect already had their structural choices in mind. “They were looking for us to double-check their logic and the deals they’d struck with their suppliers,” says Charlie.
If you’re taking on the role of project manager yourself, this may sway you towards one build system or another. The more prefabricated the method, the less on site labour and materials there are to manage, which can make things simpler. But you may feel more comfortable with the slowand-steady pace of masonry, and how the various trades’ works are staggered. And if there’s more to do on site, there are more opportunities to pitch in and learn practical skills, which is a big draw if you want to be hands-on.
Finance & warranties
If you need a mortgage for your self-build, the lender will usually require you to secure a 10-year structural warranty. You’ll need to ensure your warranty provider has approved the products and systems you intend to use (most have a list online that you can search through or download).
With specialist self-build mortgages, the money is released in stages – exactly how this is done will shape your cash flow profile, which may suit different structural systems over others. Arrears products release funds after the project has reached a certain stage (foundations, wall plate, etc). This may not be ideal if you’re working with timber frame (unless you have a healthy cash reserve), as with this method a large percentage of the budget gets paid out up front for the bespoke house shell. An advance stage payment mortgage, where the funds are released prior to each phase of work commencing, may be a better solution for you – but it will narrow your choice of lenders.
Specialist self-build lending has come on greatly in terms of the availability of finance for a breadth of different structural systems. Things can be a little different in the broader mortgage market, however. The conservative financial industry tends to consider anything outside of conventional masonry walls with a slate/tile roof to be ‘non-standard construction’. This means, if you decide to sell, prospective buyers may have to search harder for a mortgage. This is where that 10-year warranty you arranged comes into play: with this in place, things will be much easier for any future purchaser. If you’re building with a view to selling up and making a profit, check out Tim Doherty’s guide to what you need to consider on page 94.
Independent research commissioned by the Modern Masonry Alliance shows that 76% of homeowners never asked what the building was made from when buying their home. This suggests the pros and cons of different structural systems aren’t on most people’s radar; but for self-builders looking to create something tailored to their needs, the choice can be crucial to a successful project.
SIPS panels on the move in the factory of Scottish design and build company Makar. The more off-site construction goes into your project, the more straightforward it will be to get the airtightness and thermal efficiency you set out to achieve
A brick-and-block house by Falshaw Homes. Masonry systems are still considered the norm and most properties are built this way in the UK
Left: The highly bespoke nature of this Hampshire project by AR Design Studio required the use of a steel frame build system
Weberhaus uses a breathable closed-panel timber frame system to create healthy, efficient homes – including this stunning contemporary design
Insulated concrete formwork (ICF) consists of locked-together polystyrene blocks, which are reinforced with steel rebar and then filled with concrete; this is a Nudura system, shown mid-pour. The technique can deliver strong airtightness and insulation, and is quicker and more weather-resistant than blockwork construction