Options for your method of construction
As a self-builder you have a choice of four principle methods of building. These are modern masonry construction (brick and block), a steel framed structure, conventional timber frame and SIPS (structurally insulated panel system). We consider only the first and last of these as viable options.

A steel frame would be prohibitively expensive and would only be considered if you have vast open areas within a building e.g. sports halls and community centres. So this form of construction is currently really only suitable for public buildings. Conventional timber frame in our honest opinion has no real merit for those building their own home. It offers no cost saving on masonry build; it is not quicker in real terms, is less energy efficient, has inferior sound insulation and provides a much lower thermal mass. It is a method of construction more suited to volume house building where standard house types are repeated on a large estate.

So our considered view is your real options are modern masonry construction and SIPS. The most popular of these amongst self-builders (and the building industry in general) is masonry build and by some distance. However SIPS is growing in popularity especially as conventional timber frame struggles to cope with the demands of the Code for Sustainable Housing (see 'ECO Design' on the main menu).

Our Company Architect gives his in-depth view of modern masonry construction in his article Build in Silence (click here for link). So lets look at SIPS in more detail.

SIPS
This is a form of timber frame but differs from the conventional 'open frame' systems in a number of areas. The panels have a skin of plywood on both sides, the insulation is factory bonded and generally of a higher standard, they are inherently stronger, they provide a more airtight structure and the system can also be used for roofs as well as external walls. It is however a significantly more expensive option.

Wall Panels
Panels are available in a range of thickness from 119mm to 190mm with 119mm or142mm wide being the most common. In conjunction with a cavity and brick outer skin 119mm panels provide a 'U' value of 0.210W/m²/°C. This compares quite well with brick and block which provides a 'U' value of 0.250 W/m²/°C, however it is worth noting that brick & block can be improved to match the thermal performance of SIPS for a lot less money.

In the past conventional timber frame has been let down by poor on-site installation of the insulation. SIPS has no such problems as the insulation is factory fitted by pumping expanding foam into the air space between the outer skins of plywood.

Roof Panels
These are used to create rooms in the roof and provide a completely open space. 'Attic' trusses and traditional 'cut and pitched' roofs require sidewalls usually at a height of around 1.2m. So with SIPS you have the feeling of more space however it has to borne in mind that below 1.2m the additional area created in the eaves has little or no practical use. Also with this system the designer has to give careful thought to where the services run.

Cost
Compared to brick and block and conventional timber frame, 119mm SIPS wall panels add around 6% to your build costs (c7% for 142mm panels) and roof panels add another 3% to 7% depending on the configuration of the roof. So for a conventional house with a build cost of £200,000 opting for SIPS external walls and roof will typically add around £20,000.

Conclusion
In our opinion SIPS is an excellent system and certainly worth consideration but it is quite expensive. You need to carefully weigh up the advantages against the additional cost before making your final choice. So when do we think SIPS would be the right choice for you?

We believe the cost premium for SIPS may be worth paying for two main reasons. Firstly to achieve a very low 'U' value for the external walls. In which case you should be looking at the 190mm wide system, which gives an unrivalled figure of 0.165 W/m²/°C. This will translate into the minimum of energy/fuel being required to heat your living space. The payback time may well take some years (just how long is difficult to calculate in the current volatile energy market) but to the energy conscious self-builder there are other considerations such as the impact on the environment and what if energy is rationed?

The second reason is speed of erection. Unlike conventional timber frame SIPS is genuinely quicker. Because of the modular nature of the panels you don't have the same long lead in times as timber frame and an overall building programme of 6 months or less is a realistic objective.

One other advantage of SIPS is that although it is not as flexible as brick & block construction it does offer more leeway for the designer than timber frame, essentially because the panels are stronger.

If the SIPS system interests you we can provide cost comparisons and an impartial overview for your design.