What does MMC mean?

Simon Jones, business development director, at Boise EWP explores the meaning of MMC.

Sometimes it seems as if the quest to build enough homes for our growing population is a race against time.

We need more homes now and we're going to need a lot more over the next decade.

Last autumn, housing minister Yvette Cooper confirmed the government's target to see 240,000 new homes per year being built by 2016, up from 167,000 in 2006.

The challenge, therefore, is to build better homes, more quickly.

For many years now, the Government has championed the adoption of Modern Methods of Construction (MMC) on the basis that they accelerate the building process, deliver better quality, improve safety by reducing site operations and deliver better value for money.

MMCs come in a variety of different forms, from light-gauge steel frames to lightweight 'thin-joint' concrete block designs, via several variations on the theme of timber frame.

The latter is without doubt the most promising of these MMCs.

Timber's environmental credentials are strong (and hence widely touted) and its inherent thermal characteristics allow very warm buildings to be designed; ones that require very little energy to heat.

Use of the term 'MMC' inevitably suggests something quite separate from more familiar 'traditional' construction methods.

But although some MMCs do incorporate elements which are seldom (if ever) found in more conventional structures, most are, in reality, a refinement, or combination, of existing technologies.

Engineered timber - Boise's own area of specialisation - is a case in point.

This phrase describes any product in which timber's natural qualities are enhanced through a simple manufacturing process - plywood being the most familiar example.

The emergence of engineered timber I Joists, in more recent years, extends this concept by producing a structural building product that is superior in every way to the raw timber from which it is made.

This ability to transform raw timber into an engineered building product is what makes timber frame systems the most successful of all MMCs.

A number of leading timber frame manufacturers choose Boise BCI-Joists (I-joists comprising Oriented Strand Board webs with Laminated Veneer Lumber flanges) because they fit seamlessly into the factory-based production process.

One of the main advantages of MMCs is that much of the construction process is taken off-site and carried out under controlled factory conditions.

The manufactured components which then emerge from the factory are delivered to site 'just in time' where, thanks to the quality control achievable in the factory, they are fitted together quickly and easily.

Boise's engineered I Joists are also factory-made and delivered to the customer ready for use.

However, it is not only the MMC manufacturers - or, indeed, even timber frame - which benefit.

It is estimated that roughly 75% of the top 25 housebuilders in the UK now use I-joists in preference to traditional sawn softwood joists.

Sawn softwood timbers are natural products which have naturally-occurring characteristics, not all of which are desirable.

They include knots, 'shakes' or cracks, they tend to warp and bow and their density is, within certain limits, variable.

Sawn timber from builders' merchants must conform to certain minimum criteria relating to bending stress and straightness.

Yet the tolerances imposed mean that there will still be a degree of variation in any batch of timbers.

Engineered wood overcomes this problem because natural imperfections are designed and manufactured out of the finished product.

Hence, every I Joists will be as straight and as rigid as the next.

Similarly, while the length of natural sawn timbers is limited by the length of the log, manufactured I Joists can be made in lengths of up to 20m (in the UK, the longest is just over 14.5m due to transport restrictions).

In masonry construction, the use of timber I Joists can speed up construction considerably.

I Joists can be cut to length in the factory according to the builder's design and all service penetrations cut into the web before delivery to the site.

Each joist is labelled and so it is simply a matter of putting the right joist in the right place.

Speed and efficiency is the key to profitable construction, and using engineered wood products can help enormously.

Typically, solid wood joists are installed at 400mm centres, but engineered I Joists are generally installed at 600mm centres so fewer are required for any given floor.

As they are delivered to site fully finished, there is no wastage from having to saw them to length during installation.

The dynamics of the I Joist provides for performance equal to, or better than, a similar overall section size of solid wood, whilst containing only half of the timber fibre.

This high-strength-to-weight ratio not only saves on raw materials yet produces a much lighter joist that is easy to handle on site.

Whilst eyes are bound to be drawn to the latest MMC to hit the market, it's worth remembering that innovative and modern products can equally be applied to traditional designs.

Engineered timber I Joists are just as effective, and deliver as much value to the traditional masonry house-building sector as they do to the latest cutting-edge off-site methods.

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