Construction Choices

What type of house will you build? Or to put it another way, which construction method will you use? This can affect the cost, performance and feel of your new home.

A generation ago, brick and block was pretty much the only option. Today, there are many other choices including timber frame, structural insulated panels (SIPs), insulated concrete formwork (ICF), cross-laminated timber (CLT) light gauge steel frame (LGS) and even straw bale and cob.

Modern methods of construction such as U-build, based on Ikea-like assembly (u-build.org) and modular volumetric systems, are also emerging.

Each system has its pros and cons, and each will influence your approach to your build — whether it’s a turn-key or a DIY project.

Timber frame

Timber frame has long been popular in Scandinavia and Scotland because the quick erection time makes it ideal for short summers.

Modern frames are prefabricated to a high specification in a factory. Section panels, which can make up an entire wall, are then transported to site on lorries and craned into position by a specialist erection team. A water-tight shell can be achieved in a matter of weeks or even less.

The highly insulated, airtight structure lends itself to achieving the Passivhaus standard, the German benchmark for energy-efficient buildings, though the building team will need to be familiar with the exacting standards of achieving an airtight membrane.

Manufacturers offer different packages in terms of the frame specification, fixtures and fittings such as doors and windows, and frame erection on site, so it is essential to check what’s included when comparing quotes.

Oak frame is a more traditional form of timber construction with many fine examples dating back centuries still in evidence today. Specialist knowledge is required with the design, manufacture and erection of oak frames, which can look spectacular when exposed internally. Heavy lifting equipment will be required to crane the large beams into place. A combination of softwood and SIPs can be used with an oak frame to improve energy performance and reduce costs.

The main drawbacks with any timber frame is that there is little room for flexibility once the frame has been made, and you will need to pay for it up front, which will affect your cashflow. Delivery time can be around 12 weeks.

For more detail see our Next Steps Guides – Timber Frame; Oak Frames and What is Passivhaus?

 

Structural insulated panels (SIPs) and cross-laminated timber

As mentioned above, SIPs are often used in conjunction with a timber frame to achieve highly energy efficient homes. Consisting of thick slabs of solid insulation sandwiched between sheets of OSB, the structural panels can be used to form walls and roofs. The latter is a popular option as it can do away with the requirement for trusses and makes vaulted ceilings possible. Cross-laminated timber comprises plywood sheets glued together to form solid wood up to 300mm thick. Wall, floor and roof panels can be manufactured to slot together on site. Interiors can be left unfinished, while the exterior is insulated and clad in a suitable protective shell.

For more see our Next Step Guide Structural Insulated Panels

Brick and block

Unlike timber frame, brick and block lends itself to pay-as-you-go, with pre-agreed payments made as work progresses. General builders will be familiar with this tried-and-tested form of construction, and it won’t cause any problems securing a mortgage.

The weather can have a huge bearing on progress.

Mortar won’t go off in wet or cold conditions, and you will need to wait till the load-bearing walls are erected and the roof is on before other trades can start on the interior. Good brickies are also increasingly difficult to find, and the situation could get worse after Brexit. Innovations such as light, thin-joint blocks, which make for quicker erection, have been introduced to help address the problem. Both cost- and time-wise brick and block is similar to timber-frame construction (taking into account the delivery time), if the weather is kind. A summer build is recommended.

Insulated concrete formwork

ICF come in several forms. Popular systems comprise an insulated formwork made from polystyrene blocks or similar, which lock into place Lego-style to form inner and outer walls. This cavity is then filled with concrete to form solid walls with the polystyrene left in situ as insulation. Cladding, such as render, can then be applied externally, while the internal walls are dry-lined with plasterboard. ICF is more expensive than other forms of construction, though it does lend itself to DIY, and most manufacturers offer guidance to clients.

For more see Next Steps Guide Insulated Concrete Formwork

Light gauge steel frame

Light gauge steel (LGS) has been used all over the world as a framing system for many years and is now rapidly becoming a popular option for mainstream house builders here in the UK due to its strength, weight, and speed of erection advantages over more traditional materials such as masonry and timber. 

Like timber, LGS frames are manufactured in a factory. Made from galvanised steel plate just 1mm to 3mm thick, this non-combustible material can be used for all parts of the building – structural and non-structural elements, internal and external walls, floors, and roof.

For more detail see our Next Steps Guides Light Gauge Steel Frame

Straw bale and cob

Straw bale and cob are other forms of construction with a strong DIY ethos, though these tend to be limited to committed enthusiasts rather than mainstream selfbuilders. The Centre for Alternative Technology in Wales is one of several venues which host weekend courses. Straw bales can be used within structural timber framing, acting as very thick insulation, or structurally, like giant building blocks. Lime render is usually applied to the internal and external walls. Cob, a traditional building material popular in the West Country, is made from clay and straw, and is usually roofed with thatch. Though these methods have a long history (straw bale was originally used in Nebraska more than 100 years ago) don’t be surprised to encounter a few raised eyebrows from mortgage lenders and Building Control.

For more detail Next Steps Guide Natural Building Materials