This report will look at the increasing popularity surrounding timber frame construction in the construction industry. It will look at why this trend is continuing across the UK and how this form of construction can be applied to various building types. Timber frame construction is most notably used in parts of the world such as USA, Canada and Australia but it is being used more frequently throughout the UK in more recent times as well. Year on year the market share for timber frame construction has increased. Scotland is leading the way in this field by using timber frame construction much more than their neighbours.
The timber sourced for this type of construction can readily be found in Scotland and this may go some way to explaining why it is indeed so popular in Scotland.
1.1 FACTS AND FIGURES
For the tenth consecutive year; the market share for timber frame construction has increased. 25% of all new houses in the UK are timber frame.
As previously stated, Scotland is the most popular country for timber frame construction in the UK but even considering this; 75% of all new houses in Scotland are timber frame and that percentage continues to rise.
Also, even during a recession when the construction industry has possibly been hit as hard as any other industry; timber frame construction only dropped by 26% while other construction methods dropped almost 38% in 2008. UK timber frame association preview 2010 page 5 (www.timber-frame.org)
The trend is also growing outside of the UK, in Ireland for example. This is endorsed by the following quote. "Timber frame homes currently account for 25% of new build homes in Ireland" (www.ramstowndevelopments.com)
2.0 METHOD OF CONSTRUCTION
Timber frame construction means that the weight-bearing walls are indeed timber panels. In other buildings this could be steel or blocks for example. These timber panels are made off site to an exact size and when they are required, they are simply transported by truck from the factory to the site. They can then be installed by men using pulleys and ropes or if the panels are too large and heavy- a small crane can be used to carry out this task.
The panel itself is usually made up of solid timber- to take the load of the structure and this is sheathed usually by plywood or OSB- Oriented Strand Board, which is usually sourced from Scotland. These members ensure that the panel has suitable strength and is also rigid. Once the timber frame installation is complete, the external leaf of the building can then be installed. This can be brickwork or any form of cladding or a rendered finish.
There are in fact two types of panels available- namely the Open Panel meaning the panel will be dry-lined after the insulation, vapour layer and services have been installed on site. The other panel is the Closed Panel and is this case this is all done in the factory. UK timber frame association preview 2010 page 11 (www.timber-frame.org)
There have also been advances in the design of I-Joists in timber frame systems. There are now lighter I-Joists available but they have the greater strength and durability because the flanges are wider and the joist itself is not solid wood as has been the case in previous years- it can simply be plywood or OSB.
2.1 BALLOON FRAME
There are actually two forms of timber frame construction. These are called Balloon Frame and Platform Frame. Balloon Frame has been superseded nowadays by Platform Frame but a brief outline is explained on both.
The Balloon Frame form of construction simply means that the studs that make up the exterior wall are one long section which spans from the ground to the ceiling height of the top floor. â€œA balloon frame consists of two-storey height panels with an intermediate floor suspended from the formwork.â€? Chudley and Greeno (2008, p.386)
Problems are obvious with this form of construction;
- Fire can spread easier because of the large panels
- Large panels may be more difficult to find
- Large panels will also be more difficult to handle
- Heating bills could be higher because there is no insulation between a room and the exterior walls
Drawbacks such as these mean that the Platform Frame is more popular and is used today in preference to the Balloon Frame.
2.2 PLATFORM FRAME
As previously mentioned, this is the form of timber frame construction favoured today in the UK. It differs from the Balloon Frame, as the structure is built up floor by floor.
Basic sequence of events would include;
- Engineer calculates out sizes required by looking at the client's drawings
- Materials ordered and prefabricated in factory
- Materials arrive on site- only as required
- Base of the structure is marked out
- Timber floor joists are lifted into place using a small crane
- Walls are erected and positioned on top of floor joists- again using a small crane
- Prefabricated roof is also positioned in by a crane on top of the wall panels
- Cavity barriers/fire stops are installed
- Felt and battens are applied to roof- structure is now watertight
- External layer can now be can applied as well as tiles or slates on the roof
- Internal services can now be installed
3.0 ADVANTAGES OF TIMBER FRAME
Timber frame construction holds quite a few advantages over brick and block or steel frame construction;
Quick to erect - can be completed faster than using brick and blocks as there is no need to wait for mortar to dry. Also, timber can still be installed in the rain; when brick or blocks cannot and is also not affected by the frost like mortar is.
Easy to transport- panels, trussed roofs, timber floors etc… are easily loaded on to a lorry and delivered on site as needed also ensuring the site isn't cluttered up with materials that are not yet needed.
Easy for the Contractor to forecast the completion date of the project - the job will run on time easier and will not be delayed due to weather as wintry conditions can delay progress on site.
Cleaner site - as everything is measured to specification; there will be very little material waste on site meaning more profits, less money spent on dumping waste in landfills and less chance of an injury also.
Smooth and dry - the surface is easy to decorate and also easy to render.
Better quality - as the frame is fabricated off site to meet Building Regulations; there is less chance of human error.
Can be installed by small crane to meet a tight deadline or by workmen as a cheaper option.
Extensions can easily be incorporated, as timber and plasterboard are easier to remove than blocks.
Also easier to design a building to suit the client's exact taste and possibly make a building unique form others. (www.trada.co.uk)
Once the shell of the building is complete - this means it is watertight and the internal works can begin. It only takes around 5 days to achieve a watertight house.
3.1 THERMAL PERFORMANCE
Timber is an excellent insulator and this in turn means that timber framed buildings store heat very well. This therefore leads heating bills being reduced, which in turn also means less fossil fuels are being used- be it oil for central heating or coal for a fire. How much money can be saved on heating bills varies and bold claims are made about this. It is hard to calculate because other factors need to be considered such as the specification of the building, the occupants of that building and so on. One timber frame company called Ramstown Developments claim that â€œTimber framing is an energy saving system that cuts an average of 33% off the annual cost of heating your home.â€? (www.ramstowndevelopments.com/)
How accurate these figures are will be open to debate but there is little doubt that timber frame construction does have an advantage when it comes down to thermal performance. Many different timber frame companies exist and because of this they will specify the materials and construction and installation of the components slightly differently, thus giving slightly different results. However, the UK Timber Fame Association, who represents over 85% of UK timber frame manufacture states that â€œUsing a standard timber frame system achieves U-values between 0.30 and 0.27 using readily available and standard insulation- and using higher performance insulation and insulating breather membranes can boost these figures even more.â€?(www.timber-frame.org)
The keyword in the aforementioned statement is standard- meaning this is the minimum level of thermal performance that can be expected, so obviously this can be improved upon by having a higher specification. One such company is "Scotframe" who have designed a timber frame system which has a U-value of 0.11 which is very impressive when the U-value limit for walls in 1965 was actually 1.7.
The system is a closed timber-framed panel, usually includes140mm studs sheathed both sides with Oriented Strand Board (OSB) and factory filled with Polyurethane foam insulation.
The internal side of the panel has a vapour control heat reflective membrane and an air gap is created between this and the internal wall cladding to make a service zone.Â The exterior side has a breathable waterproof membrane and 50mm of polyurethane foam cavity insulation.
To prove that these panels are indeed extremely thermally efficient- they have been tested by the National Physical Laboratory who confirmed a U-value of 0.11 W/m2K; when the external cladding is taken into account. This system can be installed without the cavity insulation- but as can be expected, the U-value results will not be as good. This system from Scotframe actually meets the meets the C02 targets which have been set at intervals of 2010, 2013 and 2016- at this stage. (www.scotframetimberengineering.co.uk/)
3.2 ACOUSTIC PERFORMANCE
Since timber frame performs so well in thermal performance, it isn't very surprising to gather that it also performs well in the acoustic aspect also. This could be largely down to the fact that so many layers can absorb sound just like curtains and carpet absorbs sound better than an empty room with hard surfaces. In fact BRE’s “Case study TF2000” found that even a multi-storey project would out perform building regulations for acoustic insulation. (www.framewiseltd.co.uk)
This statement therefore echoes these thoughts and actually emphasises that it more than satisfies Building Regulations. What is even more interesting is that this is not for a small cosy dwelling - it is actually in terms of a multi-storey structure.
3.3 FIRE PERFORMANCE
Timber is more susceptible to fire than materials such as concrete, bricks, blocks or steel. This however, does not mean that timber frame structures are more of a fire hazard. Timber frame structures are more likely to be burnt down during the actually construction phase, when the installation is not complete. This could be due to an accidental fire starting on site or probably the more likely case of vandalism. The HSE's figures of 11 fires each day in the construction industry advocates this theory. Fire Safety on Timber Frame Construction Sites, page 5 highlights this, Government's annual UK fire statistics show that two thirds of fires in construction industry premises are started deliberately.â€? (www.timber-frame.org/)
Fires that do start accidentally will not spread as easily once the installation has been complete, because the fire resistant plasterboard will see to this and also the external cladding will prove a difficult surface for the fire to engulf.
There are of course ways in which the threat of fire can be minimised;
Design out the need for hot-works, i.e. working with a blowtorch.
If hot-works are required then that area should be monitored for 1 hour and again 2 ours later as a precaution.
Keep the site tidy with no timber shavings or pieces of paper lying around, as these could start a fire easily (this of course would be good practice on any construction site)
Ensure good site security to keep potential thieves and vandals at bay- again just like on any construction site. Fire Safety On Timber Frame Construction Sites page 10 (www.timber-frame.org)
At this stage it should be stressed that timber frame construction is quick to install and because of this it is easy to reach a point when fire resistant materials are in place and the risk of fire is therefore greatly reduced. Also, cavity fire barriers will reduce the spread of fire. They are placed at openings in external walls, at corners, at each floor level, at eaves level, around pipes, cables etc.
It is also worthy to mention that timber frame buildings do of course have to pass the relevant Building Regulations; as fire is a very serious matter. So if they satisfy these needs; they are as safe as any other form of construction in that aspect.
Terms such as C02 emissions, global warming, carbon footprint and greenhouse gases are often the topic of conversation in today's world. Everyone is being urged to think about the environment and the construction industry is probably under the microscope as much as any other sector.
As mentioned previously one of the advantages of timber frame construction is that it reduces the effects of burning fossil fuels- such as oil or coal. This therefore means it also minimises the greenhouse effect as well.
Unlike steel or concrete- there is no need for any manufacturing, refining or extracting as timber is natural.
Strength for strength, concrete uses 5 times (and steel uses 6 times) more energy to produce than timber (www.timber-frame.org)
Overall C02 emissions for timber construction (the em-bodied carbon are up to six times lower than the emissions associated with masonry construction materialsâ€? UK timber frame association preview 2010 page 19 (www.timber-frame.org)
That statement may not hold much relevance until the Government's stance on this subject is made clear - Come October 2010, the Government will slash the level of permissible CO2 emissions generated by new builds by 30%. There is a further reduction of 30% planned for 2013 and yet another of the same amount due to come in to force in 2016 (www.scotframetimberengineering.co.uk/)
This further proves just how big of a concern this matter is and that the Government are acting quickly and have very clear targets in mind for the future.
Some timber frame companies are also trying to convey this message to the public, as advocated by Deeside timber frame - Raise awareness of environmental issues with our customers, suppliers and staff is listed as one of their objectives regarding environmental matters. (www.deesidetimberframe.co.uk)
Also, since timber is being sourced locally; in Europe and frequently in Scotland- it means there is no long journeys to transport the material overseas as can often be the case with steel when it is in short supply.
Timber is a very sustainable material. This is simply due to the fact that the timber comes from managed forests and for every tree that is cut down - two are planted to replace it. As well as this; the Government also introduced a scheme titled the Code for Sustainable Homes in 2006. UK timber frame association preview 2010 page 7 (www.timber-frame.org)
To summarise, this basically states that the Government wants homes to be more energy efficient and that Level 3 is the basic standard expected in the average housing scheme, with this rising to a Level 6 for all new homes by 2016.
Issues which affect what level the structure will be credited with depend on two things- how energy efficient the buildings fabric is and also how the material itself was sourced. Timber can achieve a good rating on both fronts because as previously mentioned; it is easy to source and doesn't have to be transported long distances and also timber frame buildings have a very good thermal performance and can reduce heating bills.
5.0 NON-DOMESTIC BUILDINGS AND OTHER PROJECTS
It would be fair to say that when most people think of timber frame construction, they think of low rise buildings like domestic dwellings. However, timber frame buildings are not just bungalows and two storey houses. Timber frame buildings include hotels, student accommodation and such like. With Building Regulations always being updated and changed; Timber frame can currently go up to 18 metres within the current regulations. This has already allowed the construction of a 7 storey building in Bedminster in Bristol…. (www.timber-frame.org)
Further examples of surprising projects include a primary school which has over 400 children in attendance. St Luke's Primary School in the Wolverhampton area was actually completed in 16 weeks- which was 2 weeks ahead of schedule! It cost £5.9m to construct and was given a rating of Excellent by BREEAM. This rating was of such a high standard that it is actually the first time it has been awarded to a building in Britain. (BREEAM is the BRE Environmental Assessment Method.)
Other such projects include a NHS Adolescent Unit in Wales, where in this instance timber frame was ideal due to the fact that it was manufactured offsite and this meant less time onsite, making noise and disrupting the patients. A further example includes the theatre that was built on the Isle of Mull. Since this structure would be subject to winds and rain- it would be anticipated that steel or concrete would be the material of choice. However, cost of transporting these materials proved to be a huge factor, coupled with the fact that once again timber frame could be installed much quicker.
As well as these structures, timber frame prototypes have also been erected to improve our knowledge and findings on the performance of timber frame. One such prototype is the Kingspan Lighthouse which was designed and built to show how well timber frame would or would not perform when the structure was going to be an unorthodox shape. As with all buildings, small faults were found and good feedback was received on how improvements could be made. However, a Level 6 rating under the Code of Sustainable Homes was reached- even though this target doesn't need to be achieved until 2016.
6.0 MOISTURE CONTENT
All timber that is to be used for construction purposes will have a certain moisture content. Different timbers will have different moisture content depending on their use. For example, timber that is going to be used at junctions in the building where dampness could form will need to have a low moisture content. Kilns are used to dry timber out to a certain specification. Moisture content can be calculated by completing the following calculation;
Moisture Content %= (wet weight)-(dry weight)/ dry weight x 100% Chudley and Greeno (2007, p.175)
6.1 THREAT OF ROT
Rot spreading throughout a building is the nightmare of every client and builder, as it can cause unlimited damage and mean that in the extreme cases the building cannot be repaired. However, Dry timber, which is a timber with a moisture content of under 20%, is not at risk of decay. Lyons (2007, p.105) noted that the reduction in water content to below 20% will arrest any incipient fungal decay, which can only commence above this critical level.
This should dispel any doubts that timber is very exposed to rot. Furthermore, the timber is also sprayed with necessary preservatives before installation to satisfy Building Regulation requirements.
This report has briefly looked at how timber frame structures perform in numerous fields. It has also outlined how timber frame can be used in a variety of different structures- some of which many people would not associate timber frame construction with. It is therefore clear to see that this market will continue to grow, with the market possibly accelerating more so in Ireland in the near future. This is because Ireland is possibly the country which has the most room for growth in this sector, coupled with the fact that Scotland is nearby and would prove to be a very good source for timber.
This report has also addressed concerns relating to timber and the perception many people still have about using timber in construction- such as fire hazards, risk of rot, unable to be used in multi-storey buildings; to name just a few. Once people are better educated and made more aware about using timber as the structure for buildings - then these myths will soon be dispersed. After all, as mentioned in the introduction; this form of construction is used in countries such as USA, Canada and Australia. It is of course the most popular form of construction used in the developed world- meaning it can handle the hot summers in Australia and also the windy wets nights and wintry conditions in Scotland. It has taken Britain and Ireland many years to adopt this practice and some will no doubt wish to never embrace timber frame construction.
However, the old adage the times are changing, certainly springs to mind at this point. With the Government endorsing the use of timber frame and with environmental and sustainability concerns the topic of conversation on a regular basis- this definitely seems like the route to take. Timber Frame is probably the biggest single advance in building methods in recent years (www.walkertimbergroup.com)
The above quote certainly is a bold one but with the facts in figures produced in this report; it is hard to argue against such a statement.
Source- UK timber frame association preview 2010 (pdf file) (www.timber-frame.org) [accessed 4th February]
Source-Fire Safety on Timber Frame Construction Sites (pdf file) (www.timber-frame.org)
http://www.ramstowndevelopments.com/index.php?id=47 [accessed 4th February]
http://www.framewiseltd.co.uk/Systems/i-joists-the-simple-framing-system.html [accessed 4th February]
http://www.trada.co.uk/techinfo/library/view/6BA4B8A2-79A8-451B-AB6F-474D37137B4F/Timber+frame+construction+-+an+outline/ar01s02.html [accessed 5th February]
http://www.timber-frame.org/html/Building_And_Construction/Benefits_of_Timber_Frame/ [accessed 5th February]
http://www.scotframetimberengineering.co.uk/ [accessed 5th February]
http://www.deesidetimberframe.co.uk/environmental.htm [accessed 5th February]
http://www.walkertimbergroup.com/walkertimber/products/products/timberframe1 [accessed 5th February]
Chudley, R., & Greeno, R. (2008) Building Construction Handbook. 7th ed. Oxford: Elsevier Ltd
Chudley, R., & Greeno, R. (2007) Construction Technology. 4th ed. Essex: Pearson Education Limited
Lyons, A., (2007) Materials for Architects &Builders. 3rd ed. Oxford: Elsevier Ltd.
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