Cross Laminated Timber Construction. Traditional methods of construction bring with them huge challenges in terms of loss of efficiency through the construction process. This is particularly exacerbated now with loss of skilled labour in the marketplace and fluctuations in prices.
Taking the example of the construction of a traditional two storey detached masonry with standard cavity walls and traditional trench foundations house, CLT can offer huge economies in time, efficiency, cost, and reduction in waste
Groundworks and Sub-structure
In building the example house, groundworks are the first stage with excavations and foundations relating directly to the imposed loads from the structure. Masonry is a heavy superstructure. The load is spread across the structure, trenches must be deep and mass filled with concrete. Concrete whilst having a high carbon footprint (estimated at up to 8% of global CO2 emissions) is effective in providing support to superstructures and so as far as possible this should be reduced to lessen the impact.
Any reduction in excavation will save time and money, lorry movements, industrial processes and fewer loads going to landfill, all of which has a benefit to the environment. CLT is lighter as a superstructure than masonry and so will require shallower foundations and as a result will reduce the impacts referred to above.
Cross Laminated Timber Construction Superstructure
We have assumed that the house will have a lightweight block inner skin and external skin of brickwork. For rendered systems which are blockwork throughout and or have steel frames or heavy concrete blocks within them the impact will be more detrimental.
Bricks and blocks are heavy, difficult to move and store and are prone to weather as regards when and how they are laid. Skilled bricklayers are expensive and work in teams, and in short supply.
Securing price stable costs and programming can be challenging. This is simple not the case with Cross Laminated Timber Construction.
With the same house in CLT the whole of the superstructure is supplied in two or three deliveries and with the correct lifting equipment being in place would result in a complete CLT superstructure within one week. There are of course inherent transportation considerations with CLT as it is heavy and being panelised requires larger lorries generally, however as these all happen in short time frames the consequences of those lorry movements in terms of road closures and effect on neighbours will be significantly reduced.
CLT will have external finishes, which could include brickwork, in which case some of the same challenges apply. However because the superstructure is built at an earlier stage, this can follow at a time which is suited to the site, rather than having to follow through the cavity wall construction.
Floors
Ground floors and intermediate floors would generally be suspended timber in most houses.
Ground floors can be concrete block and beam or cast concrete. Generally CLT would have a timber floor as the ground floor which it is built from.
Constructing intermediate floors in a traditional way involves other trades who have to be scheduled in line with the tradesmen constructing the superstructures. This brings with it challenges in procurement, pricing, programming, quality control and collaborative working. If upper timber are being constructed then these involve carpenters installing joist hangers and then laying the timber floor joists as the building is being constructed. The same challenges apply as above however additional measures for working at height, health and safety and fall arrest apply. This all takes time to put in place, and relies upon the basis of the contractors working professionally and in line with each other
With CLT all upper floors are supplied and installed within the superstructure erection.
Internal walls
Traditionally these would be loadbearing masonry or timber studwork. In both cases these are separate from the superstructure so the same trades have to return to construct these walls. This must be scheduled in line with the floors and external walls. Quality control can be problematic at this phase due to the numerous different works being undertaken simultaneously by several different trades.
With CLT all internal walls are supplied and installed within the superstructure erection.
Roofs
Traditional cut and pitched roofs require a large supply of timber which can be difficult to store, secure and maintain. Flat roofs likewise require the use of large amounts of timber.
With CLT all flat roofs can be supplied and installed within the superstructure erection. Pitched roofs would generally be via prefabricated trusses
Other Considerations
Cross Laminated Timber Construction. Windows and door openings are Pre Cut.
No need to check built opening sizes.
0rder windows from drawings and have them supplied and ready for installation at the required time.
Quality control is simpler as the erectors of the CLT are specialists, and work with the precision CLT requires. All panels are cut on Computer Numerical Control (CNC) machines which ensure millimetre perfect panels. All engineering is completed before the panels are cut and supplied.
Fixings, lifting and safety measures are known prior to anything arriving on site.
There are huge benefits in terms of the minimal waste which arises from CLT structures. Minimal waste means minimal skips, traffic movements, debris to landfill and pollution.
The build process is shortened and quieter than traditional construction. This benefits neighbours and the local environment.
Huge Environmental Benefit
Finally, there is huge environmental benefit. The CLT panels are sourced from sustainable forests and are cut when they have maximised their carbon sequestration. New trees are planted in their place of the trees removed.
The regrowth of this timber for a standard house, due to the number of trees within our supplier’s forests, is a matter of minutes.
We have concentrated here on a simple single domestic house to demonstrate the advantages of CLT.
The benefits against other types of construction such as steel frame, concrete frame and traditional timber frame are all also relevant.
In-Fact, larger projects are exponentially more profitable. The benefits of CLT become more evident, as highlighted in our Benefits of CLT section.
Robert Bowden BSc (Hons) MRICS – Bowden Property Consulting Ltd Lamella MMC Director