Timber vs Steel Framing
In the debate on steel vs timber frames, there are many misconceptions and myths that can confuse those who wish to build a home. When deciding whether to build your home with timber or steel frames it is important to understand the options available and the implications that your choice can have on future costs and circumstances for your home.
When steel framed houses are mentioned people often think of a heavy structural steel structure commonly used in commercial construction. The steel products used in residential construction are the opposite. The steel used is a light weight cold formed steel. The strength and ductility of structural cold-formed steel (CFS) framing, along with the holding power of CFS connections make the frames very strong.
With timber framing, innovation has seen the emergence of products manufactured with laminated veneer lumber (LVL).
J Frame® is one such product which has revolutionised timber framing systems with engineered timbers that are stable, extremely strong and durable. J Frame is made from plantation pine timbers with less than 1% wastage. The interlocking solid timber system by Fraemoh Homes although not technically a framing system is another good example of LVL.
Timber can be prone to twisting and warping but this mainly due to incorrect seasoning, storage and handling. Moisture, which can lead to mold growth and rot in timber can be eradicated through quality control and organic preservative treatments which now replace the once toxic treatments. Insect damage from critters such as termites and borer beetle is also controlled with the relevant timber treatments.
Steel is very stable but not immune to moisture and can rust therefore vapour barriers between external claddings or dampcourse membranes between concrete floors is important. Vapour barriers are extremely important with building within sea spray zones. A common misconception is that steel frames will protect your home from termites. While termites cannot eat the steel frame a typical steel frame home will still contain a high percentage of timber products.
Speed of Construction
Steel framing is lighter and takes up half the space of timber because of its hollowed shape. This makes for easier transporting and storage. Steel framing is easier to handle because the studs weigh a third less than timber and connections are made simple with screws using an impact driver. On the other hand, kiln dry timber framing is also much lighter and is easy to handle. Nail guns and plate connectors make timber connections quicker and simple. The one thing that most construction professionals agree on is that if a prefabricated frame, be it timber or steel, is used the time that it takes to construct a house on site is reduced. This is because the frame is usually erected in a matter of days rather than weeks as in the case of blockwork.
Quite obviously timber can burn, whilst some of the alternative materials such as steel and masonry do not, although they will eventually crumble and disintegrate if subjected to sustained high temperatures. This may lead to the hasty conclusion that timber buildings are not as safe in the event of a fire, but the real picture is not so simple. The progress and level of destruction of most house fires and the likelihood of death or injury are determined by many factors.
If asked whether a steel beam or a timber beam is most vulnerable when exposed to flames most people will say timber. This is a natural response, because steel doesn’t burn. In fact the answer is when steel reaches a critical temperature it will fail, suddenly and catastrophically, because in great heat it softens and eventually melts.
When a timber beam is place in a fire, the outside starts to burn immediately, as you would expect. But after the outer parts of the beam have been burnt, they turn into charcoal, which does not burn and actually insulates against heat. Because of this charring effect, the centre of the beam is protected from damage for a long time before the beam actually fails and collapses.
The studs that make up the structural walls in a typical timber frame are not oversized in this way, due to cost and practicality. However the frame is clad in material that resists heat and flames, usually plasterboard or sheets of similar material and also there are barriers built into cavities in the building to block flames from spreading.
Provided that a home has been designed and built by people who understand the technology, the risks from fire in a typical timber frame home is no different from those that are faced by the occupants of steel or block equivalent.
In Fiji there is a disturbing trend to clad timber framed house interiors with plywood sheets, these sheets do not offer any heat or flame resistance. All prefabricated homes that PPS offer both timber and steel frame are designed to the New Zealand Building Code fire safety standards.
Timber has many environmental benefits not found in other building materials. The level of carbon dioxide (CO2) in the air is increasing significantly. Trees lock away carbon dioxide (CO2) in their wood, which is retained throughout the existence of the timber. The use of timber as a building material encourages the growth and expansion of the forests that provide the supply, which absorb CO2 and therefore help to reduce the level of global warming.
Timber is said to be ‘renewable’ because, in order to replace it, another tree is planted. Provided that a similar tree is planted for every one that is felled, the supply is infinite. This is in stark contrast to steel, blocks and concrete, all of which rely on the extraction of raw materials from the earth, which ultimately will run out. Apart from the ability of trees to absorb and store CO2 itself, the production processes of timber products need less CO2 producing activities. To make steel for example, raw materials have to be mined, transported and then combined together in steel mills which consumes a massive amount of energy while producing waste. By contrast, timber production waste is kept to a minimum – even sawdust is used for chipboard or paper production. Timber is also a natural insulator which allows your home to have greater energy efficiency. This can also reduce your energy bills.
Direct cost comparisons are difficult to make between timber and steel frame as there are many variables between the systems. The price difference can be relatively minor with smaller homes. As already mentioned, the labour cost element can be higher with steel framing as many contractors in Fiji are not familiar with steel framing techniques
At PPS we have found there’s no definitive answer to which is better; timber or steel frame? Each system has its Pros and Cons and one is not inherently better than the other. Which system will depend upon many factors including requirements of the project, the preferences of the client, the location and constraints of the site.
No matter which material is ultimately chosen a building's frame is its backbone so it's essential that it is designed and constructed properly and that’s why PPS offers a full range of homes available in both steel and timber framing with our two experienced and respected kit homes companies in New Zealand, Fraemohs and Trenz Homes.
This post was written by Gareth Williams. Gareth is a Director of Pacific Property Solutions Pte Ltd and is also a Professional Quantity Surveyor and Member of the New Zealand Institute of Quantity Surveyors