Structural Options for your Self-Build Project

Choosing a building system for your new home is a big decision. Find out the pros and cons of the main options
by Build It
26th November 2012

The method you choose to build your dream home will have implications on practically every level of your project – costs, build speeds, internal layout and energy efficiency are just some of the areas that could be affected.

From the hands-on familiarity of brick-and-block to the ultra-fast build speeds and super-airtightness of structural insulated panels, there’s something to savour in every system.

Local authorities are usually more concerned with the external look of your home rather than the build system at its heart. That’s because, at the end of the day, every new home has to meet Building Regulations – and every system is capable of doing so.

Naturally, if you’re building in an area filled with timber-frame houses, planners and neighbours are more likely to be amenable to a similar build. But unless you opt for a really unusual route (such as an earthship) or your plot lies in a protected area, it’s rare to encounter any problems at planning level with this fundamental decision.

To help make things easier, we’ve put together a guide to each of the major build systems’ pros and cons – and highlighted a few of our favourite alternative routes to boot:

Brick and block

This is still the most popular build route in the UK, accounting for around 70 per cent of all new homes. Brick and block consists of an outer brick skin and an inner block skin. The two leaves are held together with wall ties. Internal load-bearing walls are also made of blocks, while timber studwork is used for non-load bearing walls.

In the past, cavities were restricted to around 100mm – more than enough to satisfy Building Regulations, but nevertheless a limiting factor on insulation levels. Recent innovations in wall tie manufacture, however, have led to dramatic improvements. “We regularly deal with brick-and-block constructions involving cavities up to 300mm in width,” says Jamie Hayes, technical officer for insulation manufacturer Celotex.

Houses are built entirely on site, beginning with concrete foundations. Work progresses to first-floor level, at which point internal load-bearing walls are constructed and timber floor joists or a pre-cast concrete floor added, before continuing up to the roof.

Build speed: Around 20 weeks for a three-bedroom home (180m2). Site work progresses slower than alternatives such as a timber frame, but lead times for materials are drastically reduced.

Cost: Around £80-100 per m2 for the blockwork, cavity insulation, brick outer wall, lintels, wall ties and cavity closers.

Brick and Block Pros

  • Local tradesmen readily available
  • Hands-on self-builders can do own bricklaying or assist builder
  • Discrepancies in foundations and levels easily rectified on site
  • Excellent thermal mass helps even out internal temperatures

Brick and Block Cons

  • Wet system requires time to dry out, slowing construction
  • Building work cannot proceed in heavy rain or freezing conditions
  • Need for internal load-bearing walls makes open plans difficult to achieve

Timber frame

Almost 22 per cent of all new homes are built using this method, many of them by eco-conscious self-builders. In this system, the frame acts as a superstructure, supporting the entire building so there’s no requirement for internal load-bearing walls.

There are several different construction methods to choose from, including post-and-beam, green oak and conventional timber frame. In each case, the frame is prefabricated off site. Timber framing is a specialist skill, so don’t expect to get too hands-on with this part of the build. Most manufacturers require you to commission them to both fabricate and erect the frame, taking it at least to watertight stage – and some even provide a full turnkey service. Alternatively, the company may have a list of recommended contractors in your area.

Often, you can either choose from a range of standard designs, which can be tweaked, or ask your timber-frame supplier to work to bespoke plans drawn up by an architect. Design options range from ultra-modern homes clad in swathes of glass to traditional beamed properties.

Build speed: A timber frame home can be erected and made watertight in as little as five days.

Cost: Around £90-120 per m2 for the structural frame.

Timber Frame Pros

  • Speedy on-site construction – standard houses can be complete in 8-12 weeks
  • Ideal for creating open plans
  • Characterful beamwork can be left exposed
  • Excellent insulation levels with thinner walls than masonry

Timber Frame Cons

  • Frame fabricated off-site, with lead times of 4-8 weeks
  • Foundations must be perfectly level within small tolerances
  • Little room for modification of frame after fabrication

Insulating Concrete Formwork

If you enjoyed playing with building blocks as a child, then insulated concrete formwork (ICF) could be for you. Basically, it involves stacking a series of hollow blocks (options include expanded polystyrene and bonded wood fibre, while panelled versions are also available), which interlock to create a mould that can then be pumped full of ready-mixed concrete for an ultra fast build.

With a little training, which is often offered by ICF suppliers, self-builders can get very hands-on with building work. The trick to proper construction is getting the first course absolutely plumb, level and square. It’s well worth getting professional assistance at this stage to set the pattern for the rest of the work, as any misalignments tend to get amplified as building progresses.

ICF is a quick build system, so even if you employ skilled workers for the duration of the project you should still save on labour costs in comparison to brick-and-block. Once the concrete is set, the structure can then be finished in your choice of cladding

Build speed: Basic structure can be up in a matter of days.

Cost: Around 5% higher than for a typical brick and block build.

ICF Pros

  • Excellent insulation levels ‘built in’ to structure
  • Minimal need for skilled labour
  • Very little construction wastage
  • Envelope is watertight before cladding, so other trades can start early
  • Insulated blocks mean work can continue in freezing conditions

ICF Cons

  • Errors in foundations/early courses costly to remedy
  • Adaptation difficult and expensive, requiring specialist tools and professional advice

Structural Insulated Panels

Structural insulated panels (SIPs) are made up of two layers of oriented strandboard (OSB) bonded around an inner core of insulating material. These precision-engineered panels are prefabricated in a factory, which makes for time and labour cost savings on site. When used for load-bearing purposes, they’re suitable for building walls, ceilings and floors. In fact, they’re so sturdy that they can be used to create truss-less roofs for liveable loftspace that make best use of available height – we’ve heard of many self-builders who’ve combined other build methods with a SIPs roof for this reason.

SIPs is also growing in popularity as a wrap-around for structural timber frames, combining this system’s airtightness with the charm of internal exposed beamwork. Whether you choose a full SIPs build or a wrap-around, a successful project will result in an exceptionally airtight building envelope.

As the panels are lightweight, pile and pad foundations are appropriate, and will save you time at the construction stage. Experienced teams can erect the structure of a SIPs house in as little as three days (or seven to 10 days for a timber frame with SIPs wraparound). Other timesaving bonuses include pre-cut (or even pre-fitted) door or window openings.

Build speed: Up to 60% faster than conventional timber frame on site, but prefabrication of panels takes around 10 to 12 weeks.

Cost: Can be around 15 per cent more than a standard timber frame up front, but you’ll save on labour costs and heating bills.

SIPs Pros

  • Labour costs reduced due to quick build times
  • Excellent levels of air tightness
  • High levels of insulation built in to the structure
  • Features such as open plan layouts and habitable lofts easy to achieve

SIPs Cons

  • Extremely precise measurements are required
  • Any alignment issues, especially in foundations, will lead to severe delays on site
  • Experienced labour is a must, and harder to find than with conventional timber frame

Thin joint blockwork

This is a variation on conventional brick-and-block. For self-builders, the immediate appeal is that construction speeds rival those of prefabrication systems such as SIPs, assuming you use a contractor experienced with the method.

That’s thanks to the use of quick-drying 3mm mortar lines as opposed to 10mm for traditional masonry (hence the name ‘thin-joint’), and the optional use of oversized aircrete blocks. Aerated for lightness and to improve their insulating qualities, these blocks are surprisingly strong, and can even be used for foundations.

This system shares many of the advantages of brick-and-block. For example, it’s relatively easy to adapt or extend a thin-joint home and labourers should be fairly easy to come by, as brickies only need a little retraining to acquaint themselves with the technique. In fact, most trades should find working on a thin-joint home to be a familiar experience.

The use of thin mortar beds allows for greater build accuracy, which means time-saving thin-coat spray plasters or renders can be applied to finish the walls inside and out.

Build speed: Watertight in around five days, total construction time 10 to 12 weeks.

Cost: Comparable to brick-and-block, with the best labour savings to be had on large projects.

Thin Joint Pros

  • Excellent acoustic and thermal insulation
  • Reduced wastage of building materials
  • Contractors will find the system familiar to work with

Thin Joint Cons

  • Deviations in level or plum cannot be made up in the mortar bed – your contractor may build in conventional masonry up to the damp proof course to even out discrepancies
  • Conventional scaffolding may not be suitable – ‘quick staging’ versions offer more flexibility

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