FREQUENTLY ASKED QUESTIONS
We get asked all kinds of questions at The Silver Frames Company about our custom steel framed buildings, and we love telling people how great steel is compared to timber framing... and although we encourage everyone to ask questions, we have compiled a short (yes short) list of the most commonly asked questions we answer - in case ya don't feel like contacting us right now.
A colleague builder friend has just erected a steel framed house and said the weight of a steel frame is only one third that of timber. Is this true?
What is the difference in cost between timber and steel framing?
How is it that we have built timber houses with timber weatherboards in New Zealand for a hundred years and now you are saying steel is better.
The timber houses of the past were built with heart timber, either native or pine, clad in building paper and with wall and roof cavities that could “breathe” and were relatively lightly insulated. This protected the timber from condensation and hence ensured its durability. Modern houses have claddings and building wraps that don’t protect from condensation to the same extent, the walls are highly insulated which restricts air flow and the timbers are “young crop” Pinus Radiata which is much less durable, sometime with surface only treatment against rot and borer.
Steel is an inorganic man- made engineered product which is much better suited to retaining durability in modern house construction and has a proven track record of this over 60 years in NZ. Furthermore it does not absorb water and change dimensionally meaning no cracking of gypsum board linings. Its rate of expansion with temperature is also comparable with that of typical cladding and lining materials. (See also the question below on thermal breaks).
Steel needs a thermal break to meet modern insulation requirements while timber does not. Why is that and does it mean timber is better?
The reason steel needs a thermal break is because of its high heat conductivity relative to timber. Without the thermal break it means that when the inside of an external wall is warm compared with the outside, sufficient heat will flow through the steel stud to cool the inside surface of the wall and cause condensation as well as compromising the wall’s insulation rating.
This high thermal conductivity is often portrayed as being a weakness with steel but is in fact one of its greatest strengths. It means that when the thermal break is in place, all the steelwork on the inside of the thermal break remains above the temperature at which condensation from moisture in the wall cavity will occur. This ensures long term durability of the stud. In contrast with timber studs, the outside of the stud will attract condensation during winter, with resulting increase in moisture content, movement that damages linings and long term durability problems. This will occur irrespective of the weather tightness of the external cladding.
What type of barrier should be used in between the steel frame and treated timber?
For H1 treated timber normal building paper will act as a separator and will suffice if the area is closed.
If however the situation is sheltered or exposed and H3 timber is used then a more substantial separator should be used such as window tape. This separation is more important if the site is severe or very severe marine and if the frame is not clad then an additional paint coat is necessary. NASH provides guidance on barriers to use in all applications of steel framing and there is a good New Zealand standard on which this information is based.
Does LSF conduct sound through inter-tenancy walls?
Sound vibrations are conducted through any wall with solid material. LSF is very slightly better at acoustic insulation than timber framing, due to the flange flexibility, but the differences are only 1 or 2 dB and not usually noticeable. It means that a different design of wall is used between apartments or flats. This can be one wall with several layers of gypsum linings plus sound insulating fiberglass or consist of two separate walls each insulated and disconnected from one another. Care must be taken when cutting penetrations into in the inter-tenancy walls for power or TV outlets or air-conditioning units as these will provide a sound path. Good details are available from a number of sources including NASH and some linings suppliers.
Has LSF got a fire rating? What happens in a fire?
Neither light steel framed construction nor light timber framed construction have a fire rating in themselves. Both require the application of fire resistant linings and when these are applied, both can deliver whatever magnitude of fire resistance is required.
With regard to performance of houses in fire, LSF has two very significant advantages over light timber framed construction. The first is that, being non combustible, when fire burns through the linings it will not spread within the framing cavity in steel framing, whereas this is a major cause of hidden fire spread in timber framing. The second big advantage is that it does not increase the fire load. Timber is combustible and there is at least 20 kg of timber per square metre of floor area in a timber framed house. This is 75% of the design fire load of a house contents, which means that a timber framed house is carrying at least 1.75 times the fire load of a steel framed house. The higher the fire load, the more severe the fire.
Given these two advantages, it is not surprising that fire case histories show steel houses perform very well in house fires, with little or no damage to the framing structure. Furthermore if steel framed members are not visibly distorted they can be left in place, cleaned and if necessary recoated. If they are distorted then they need to be replaced.
Electrical faults are the most common causes of fires in wall cavities but cannot ignite a steel frame.
Can a steel frame house still be energy efficient?
How can architraves and skirtings be fixed to steel frames?
The use of light gauge metal in steel frames allows the use of needle point self-drilling screws which unlike nails will never spring out. A combination of screws and adhesive can be used for timber while plastic skirtings can be secret fixed with clips.
Are more trade skills required to work with steel framing?
No. Building and finishing with steel frames and most trade skills are the same as they are with timber. Some trades may require specific information which is provided by NASH or the steel frame manufacturers. Builders that have worked with timber all their lives and changed to steel framing have been surprised how easy it is to work with steel. Furthermore steel framing is now an integral part of apprentice carpenter training so the next generation of carpenters will be trained from the start of their careers in both materials.
How does steel framing perform as a support for wall lining materials and plaster cornices?
Because steel screws and adhesives are used to fix linings and also because there is no frame shrinkage to cause cracking and nail popping, steel framing is the preferred option. Lining materials in steel framed houses can be expected to perform better and look better than in houses built from timber.
Can I alter a steel-framed home at a later date?
Yes. Additions are made in the same way as any other building system but the original steel structure will be straight and true regardless of its age, making the job of matching up the addition much easier.
Do copper pipes and lead flashings have to be isolated from the steel frame?
Yes. These metals must be isolated because in the presence of moisture they will develop bi-metallic corrosion that could damage the protective zinc coating of the steel frames. The recommended method is isolation by underlay or plastic membrane or the use of grommets or clips.
Are the frames protected against rust at cut edges and drill holes?
Yes. Steel frames are zinc coated or galvanised which protects steel from cut-edge corrosion by cathodic or galvanic action. Where the underlying steel base becomes exposed at cut edges holes or mechanically damaged areas, the zinc coating will corrode in preference to the steel. The ability of a hot-dipped zinc coating on steel to protect it against corrosion is known as sacrificial, or cathodic protection because the cathode metal, which is the cathode, is the one protected. In this way the zinc coating adjacent to the edge or hole protects the cut area. Furthermore because corrosion is a surface phenomenon the cut surface protects the steel inside from corrosion. Rust cannot spread through steel from a point on the surface or cut edge, unlike rot in surface treated timber in which all cut ends need application of a rot preventing chemical to preserve the durability of the stud.
What about the environmental impact of steel framing construction?
The overall recycling rate of the steel industry is 66%, the highest in the country, offering an environmentally sound home framing alternative. Steel is 100% recyclable and can be used time again and again without losing its properties. Because it weighs less transport costs are lower and it doesn't end up as waste. So its environmental credentials are as good as timber framing
What about mold?
Mold requires an organic nutrient source and moisture to grow. Kiln dried Pinus timber has between 10-18% residual water content and without chemical treatment it will rot and promote mold.
Steel cannot promote the growth of mold because it is not absorbent. Mold will grow on paper backed lining where there is inadequate ventilation and it is kept moist by wet timber framing.
How well does steel framing stand up to earthquakes or hurricanes?
LSF can be engineered to meet the highest seismic and wind loads prescribed by the NZ Building Code. Steel has the highest strength to weight ratio of any framing materials and a lighter structure with stronger connections results in lower damage from earthquakes. Steel framed houses in Christchurch suffered only superficial but no structural damage. Stronger connections (screws vs. nails) can withstand greater winds including cyclones
Are there any environmental benefits when using steel framing?
Yes. Steel offers owners and builders an environmentally friendly alternative to timber. There is little waste when using steel framing materials because all metal is engineered and cut to length in the factory.
Any small amount of steel scrap has value and can be recycled. If for any reason your steel framed house has to be demolished then it can be reused, relocated or recycled. Even steel framing scrap is a valuable commodity so it will not end up as landfill.
Will a steel frame rust?
No, not in normal use. Steel frames used in New Zealand are all galvanised and as framing is used in what is termed a closed environment it is not normally subject to severe corrosion from marine salts or industrial pollution.
If steel framing is to be used outside and unclad then it should be protected by painting which will need to be maintained.
This is not necessary if it is completely enclosed and protected from the weather except in some very severe marine environments. Details are given in the durability statements from New Zealand Steel that support the AXXIS framing
Aren’t steel frames noisier than timber?
No. Steel homes are quiet inside. The exterior walls and ceiling are filled with thick insulation, restricting outside noise. Wood contracts as it dries and at ambient temperatures it expands whereas a steel framed home doesn't creak at all due to humidity variations and temperature changes have less effect.
A steel frame is mechanically jointed and in a well constructed and insulated home thermally induced movement is not an issue. Steel framing expands and contracts at rates very similar to the other materials used in building, which means it is unlikely that there will be noise or cornice cracking problems. If a dark colour profiled metal roof cladding is chosen, it is good practice to use an insulating separator between the metal cladding and the purlin and to tell the roofer to use oversized holes.
Is a steel frame safe when exposed to a live electric wire?
Steel frames are safe because they are earthed and it is a requirement that all new housing be fitted with one or more RCD (Residual Current Device) circuit breaking safety devices. If the frame is exposed to a live-wire the earthing creates a short and trips the residual current safety switch and prevents the chance of electrocution so there is little chance of you touching anything live. A broken or pierced wire in a conventional building can remain live and leaking current can cause troublesome faults and create a fire risk.
How are different external claddings fixed?
This depends on the cladding as there are many different types of screws that are suitable for all claddings. Brick and stone veneers are very popular and use standard brick ties screwed to the metal framing, and E I FS plaster systems can also be used as well as weatherboard and fibre cement. . Thermal breaks are fixed to the exterior face of all steel frames before the building underlay or wrap is applied and the cladding fixed.
My architect has designed our new home in timber. Can I convert my plan from wood to steel?
Yes. Most steel frames are made to the same dimensions as standard timber dimensions and therefore there is no problem in converting your plans to steel. Sometimes the biggest problem is the architect who has perhaps never worked with steel. BUT once converted they usually become a fan.
Can I use brick veneer with steel framing?
Yes. Most steel framing in New Zealand uses brick veneer as a cladding because like the steel frame behind it will last a very long time. New Zealand LSF has been seismically tested at Swinburne University in Melbourne to many more times the seismic forces than we ever have had in New Zealand. There was no damage to the structural frames and only minor dislodgement of bricks. This was due to the great flexibility and strength of LSF. These tests were witnessed by experts in their field as well as BRANZ.
What about steel floors in a two-storey building
- Because there are no issues with moisture, a steel joist floor system avoids, swelling or shrinking problems associated with timber framing and floors, A viable alternative is to use a metal deck concrete floor in conjunction with steel joists. The strength and dimensional stability of steel framing lends itself to suspended concrete floors typically cast onto profiled steel decking. These floors offer thermal mass, good airborne sound insulation and better impact sound insulation than most processed timber product floors.
Will my home get a warranty?
Yes, because most manufacturers belong to NASH, the National Association of Steel Housing and use AXXIS® steel for framing which is produced by New Zealand Steel. New Zealand Steel provides a 50 year durability statement to meet the requirements of the NZ BC B2 Durability. The components are precision manufactured using computer-aided design and computer-controlled roll formers and assembled to very tight tolerances.
Because of the high thermal conductivity of steel and the thermal breaks it stays dry under all but exceptional weather circumstances and if water gets into the wall cavity it is not absorbed by the framing and so can readily evaporate.
Does the steel frame interfere with radio, mobile phone or TV signals?
No. Electro magnetic waves pass through the spaces between studs which allow the use of radios, phones, and television sets in a steel frame home without interference. The steel framing will provide marginally better protection from outside electromagnetic fields if you happen to live under
a high voltage overheard power line.