mmc techniques

7/21/2019 MMC Techniques

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Combining traditional with innovative

It is important to establish right from the start that, where MMC is used, the final product may

still be a mix of traditional and innovative technologies. A number of house builders, forexample, continue to build houses in a traditional manner, but use sub-assembly technologiesas well. Preplumbed and fully fitted-out en-suite wc and shower room pods complete withplastic tiles and grout are now available and can be incorporated into traditional masonryconstruction. Even some of the panel systems which are delivered to site complete with afacade of brick slips are likely to require the skills of a bricklayer to join the panels up at thecorners. There are so many ways to build, and so many variations on a theme, it is best not tohave too many preconceived ideas about the building you may be about to survey, until you'vefinished your inspection. Cost is still a driving force in the contruction industry. At present, theprospect of losing our manufacturing base to our overseas competitors seems unlikely, giventhe potentially huge transportation costs.

Construction techniques fall into the following broad categories:

- panel systems;- volumetric systems;- sub-assemblies and components; and- on-site technologies.

In some forms of construction a mixture of technologies is employed, such as bringing togethervolumetric and panelised systems. These are categorised as hybrid systems.

Panel systems

As the name implies, where these systems are used, the manufacturer produces a largefactory-made panel from either wood or metal. The panel is then either delivered as it is, orenhanced depending on the client's wishes. Enhancement could be adding insulation,services, internal or external facings, windows and doors, or all of these. Completed panelsare then delivered to site and fitted together. The way in which the DPC works, or theinteraction between internal walls and the roof may differ from project to project. Often thecontractor or developer will be choosing the materials and forms of construction for other partsof the building. By using highly energy efficient foam insulants, the thickness of timber can bereduced as low as 89mm.

Galvanised light steel C-section metal can also be used for metal-framed buildings. Theinsulation is added to the outer side to prevent cold bridging. The frames are used for thewalls, floors and roof trusses and are used in combination with a wide variety of otherproducts, including traditional brick outer skins, cladding, insulated render and screed floors.There are also mobile rigs that allow the frame to be made on site.

Concrete panels have been around for many years (in high-rise blocks of flats for example)and concrete panels with brick slip facings are also being manufactured. Another variation is'structurally insulated panels' or SIPs. The panels consist of an outer facing of timber-basedboards bonded to rigid insulation. They fit together with male/female joints and are clampedtogether on site. They are very strong and can be used in roof and wall construction.

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Figure 1: Hospital extension with self-supporting Metek structure walls and flooring

This photograph is reproduced with permission from Metek Building Systems - part of theMMP Group

Volumetric systems

Unlike panel systems, volumetric systems consist of a room or whole floors being factory

made, and craned into position on site - often with one unit sitting on top of another. The use ofmaterials can be similar to some forms of panel construction, in that the carcass is often madefrom lightweight steel, which is fitted together and then insulated and lined internally. Theservices are prefitted, and connected on site to risers or other service provisions.

Volumetric forms have been popular in student accommodation projects, hotels and some fastfood outlets. Sometimes referred to as pods, they can be integrated into traditional forms ofconstruction. The external facade can also be constructed on site to suit planning conditions.Some manufacturers even fit out the internal space, complete with carpet, wall coverings andfixed beds and desks.

One feature of volumetric systems is the thickness of floors and walls. Each unit has its own,so consequently the floor depth and wall thickness are likely to be greater than those intraditional construction. The walls are also likely to be load bearing.

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Figure 1: Module with brickslip for Innovation Park at BRE

This photograph is reproduced with permission from Metek Building Systems - part of theMMP Group

Sub-assemblies and components

Some contractors use a mixture of technologies. Preplumbed hot water systems have beenavailable for some time, as have electrical looms and associated services.

Floor and roof construction has also progressed. Prefabricated floor beams emerged a fewyears ago - they give longer spans, are less prone to squeak and come complete withknockouts for services. Whole floor and roof assemblies are now available. The floor is madeto fit in the factory, from traditional flooring-grade chipboard, supported by a lattice of steelwebs, large enough to receive waste pipes or light steel beams. Craned into position, theyoffer enormous savings on time and offer the benefit of being able to pass services through.Plasterboard ceilings however, are still site-fixed. The same principle applies to roofconstruction, where the contractor can order prefabricated roof assemblies which are rigid and

insulated, to be installed, for example, in cross wall construction or from eaves to ridge.

BubbleDeck

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BubbleDeck is a form of construction, which as the name implies, incorporates bubbles intothe construction in order to reduce the dead weight. The concept has been popular inDenmark and Holland for over 10 years. The bubbles are created from incorporating recycledhollow plastic balls in between the steel reinforcement, before the concrete is poured.

Under manufactured conditions, the plastic bubbles are trapped between the top and bottom

reinforcement, and cast into a concrete biscuit to create a semi-precast unit. The unit is thencraned into position and concrete is poured on top, the lower section acting as permanentformwork.

The site concrete is poured on top to form a structural topping. The load transfers in twodirections back to the columns or load bearing walls. The use of a splice rebar joint stitches thepanels together to enable spans over 21 metres to be designed. In a more traditional form ofprecast concrete flooring, the floor 'planks' span from beam to beam in one direction, which inturn dictates the length of the span. These beams of steel or concrete can be seen to theunderside of the floor and are known as 'downstand' beams. Bubble Deck constructioneliminates the need for downstand beams.

How can you spot them? You can't, so look through the health and safety file and look for theabsence of downstand beams.

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Figures 1-2: BubbleDeck

Figures 1-2 are reproduced with permission from BubbleDeck. For more information go toBubbleDeck

Flooring

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http://www.bubbledeck-uk.com/http://www.bubbledeck-uk.com/


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Figure 3: Timber PosiJoist floor cassette under construction off site

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Figure 4: Finished PosiJoist floor cassette ready for shipment

Figure 5: PosiJoist floor cassette being lowered into position - note the deep servicevoid beneath the floor finish

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Figure 6: Floor construction nearing completion

Figures 3-6 are reproduced with permission from AC Roof Trusses Ltd

Bathroom options

Figure 7: Accessible WC

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Figure 8: Rear view of preplumbed services

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Figure 9: Section of completed product

Figures 7-9 are reproduced with permission from Concargo Composites

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On-site technologies

The application of thin bed mortar techniques is still very popular, albeit the skills required to

apply the mortar are different from traditional brick laying skills. Another form of construction isinsulated concrete formwork. There are many manufacturers but the principle remains thesame. Hollow polystyrene blocks are fitted together with male/female connectors, and built upin stages before reinforcement is added and concrete pumped and tamped into the void. Thereare no lintels over openings, and the insulation remains in place to dry line or to renderexternally. It is quick, lightweight and simple to use.

Figure 1: Insulation and brick tie system

Figure 1 is reproduced with permission from Metek Building Systems - part of the MMPGroup.

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Figure 2: External walls being assembled

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Figure 3: External walls - note internal spacer bars and position of reinforcement

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Figure 4: The concrete is levelled off in a traditional manner

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Figure 5: Door opening former in position

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Figure 6: Note how the insulating block is easily positioned over the opening

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Figure 7: Traditional timber joists form floors

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Figures 10-11 are reproduced with permission from Hanson Building Products

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