Question mark over steel frame Code Compliance

Authoreste 13 September 2010 Comments

Steel-framed homes built in some parts of New Zealand may not meet the Building Code requirements for thermal performance, according to new research.

Conducted by Green Being Ltd, independent Consulting Engineers, the research concludes that to achieve code compliance in the South Island using steel frame construction, a house would need to have additional insulation than that required for timber framed construction.

According to Green Being director Paula Hugens, most builders and specifiers are aware of “thermal bridging” problems that occur with steel framing and the need to use thermal breaks.

Thermal breaks are typically polystyrene strips or sheeting, approximately 12mm thick, additional to the steel framing and fitted between the framing and the external lining.

“However, even with these thermal breaks, steel frame homes will only meet the minimum building code requirements in the North Island, while in the South Island, they often don’t meet the standard at all unless additional measures are undertaken”, says Ms Hugens.

Because steel transfers heat and cold much more readily than wood (400 times more readily), steel studs create thermal bridges to the outside of the home, which can significantly compromise thermal performance.

“I think what the industry in general doesn’t realise is that creating thermal breaks is only one part of the solution”, says Ms Hugens.

“To achieve the same level of performance as a timber framed home, you have to up-spec the insulation when using steel framing.”

Ghost marks

Ms Hugens says particular care should be taken when installing thermal breaks with steel framing.
“If they are not correctly installed, condensation and mould can form on internal and external linings. In some cases, this leads to the appearance of “ghost marks” (shadow-like outlines of the framing) on the interior walls.

While “ghost marks” are unsightly, condensation and mould can have more serious consequences and may adversely effect the environment of the home and the health of its occupants.

Heat loss through ceilings?

Ms Hugens points out that while the National Association of Steel Framed Housing (NASH) recommends a thermal break for walls constructed with steel framing, there is no recommendation for a thermal break in ceilings where steel framing is used.

“Given that the greatest heat loss in homes is through the ceiling, it is likely that a steel framed ceiling and roof space will also require a thermal break to achieve code compliance. Even a continuous blanket of insulation will still have thermal bridges at truss verticals and diagonals”

Ms Hugens advises anyone considering building with steel framing to thoroughly investigate what extra measures will need to be put in place to ensure the home is insulated to a performance level equal to a home constructed with timber framing.

Higher standards to come

Ms Hugens believes that although people building new homes start out with high expectations for warmth, comfort and energy efficiency they are sometimes disappointed with the end result.

“The fact is that the insulation values given in New Zealand’s standards for insulation are very low compared to many other countries with similar climatic conditions. For example, in San Francisco, the minimum insulation value for Package C is R4.4 whereas in the South Island of New Zealand, it’s R2.0.

“I think that in New Zealand we will ultimately review and upgrade our insulation standards in keeping with overseas trends because of the positive gains that can be made in terms of health and energy savings.”

Source: http://www.greenbeing.co.nz/news/11/

Tags: construction, industry

19 Comments

This report obviously forms the basis for Carter Holt Harvey's www.framingfacts.co.nz website.

Unfortunately, the report is full of flaws from the steel framing specs to the required thermal break specs and more. For those interested in steel framing, I suggest checking out "NASH N-10 Thermal Break & Cavity Construction" and "NASH N-11 House Insulation Guide" at http://www.nashnz.org.nz/publications/nash_publications.html

Also note, the 3rd edition of the BRANZ House Insulation Guide referred to in the report has been superseded by the 4th edition which includes lots of useful information for steel framing.

As a parting thought I was amused at the headline "New Zealand's most trusted building material" on www.framingfacts.co.nz given some of the recent media attention which the timber sector has brought on itself. Read these stories to see what I mean ...

http://www.comcom.govt.nz/carter-holt-harvey-timber-claims/

http://www.comcom.govt.nz/media-releases/detail/2006/koppersarchtopayarecord36millionin/

http://www.comcom.govt.nz/media-releases/detail/2010/company-executive-fined-for-fair-trading-act-breach/

As someone who is planning to build a new home in the coming year and looking minimise our carbon footprint, this article is of particular interest. Given that wood beats steal hands down when it comes to energy efficiency and environmental sustainability, I don’t understand why anyone concerned with the environment and global warming would choose anything but wood to build a home.

Paula Hugen could have saved herself and her sponsor (Carter Holt Harvey)a lot of time & money by simply buying a copy of the recently published 4th Edition of BRANZ Home Insulation Guide and choosing appropriate thermal breaks and insulation from the well presented tables. Prospective purchasers of steel framed houses can be assured that there is no "question mark over steel frame Code Compliance" (other than in Paula's mind) and the steel framing industry and the regulatory authorities have the research, knowledge and experience to ensure warm, comfortable and energy efficient steel framed homes that more than meet the Building Code requirements for all parts of NZ.

Interesting comments regarding mould from Ms Hugens.

Timber will act as a food source for toxic mould such as Stachybotrys.

Steel is considered to be inert and won't act as a food source. I guess that's why AXXIS Steel has been recognised as a 'Sensitive Choice' by the Asthma Foundation.

Steel is also 100% recyclable again and again without losing its properties.

Firstly, I work in the steel industry. This article should start: Conducted by Green Being Ltd, independent Consulting Engineers, with funding by Carter Holt Harvey. Really. There have been hundreds of steel framed houses constructed in the south island over the past four years, I challenge you to provide evidence of ghosting, factual rather than theoretical. Further investigation outside of the confines of your office would show that the industry is meeting the code in the South Island, but I guess Carter Holt Harvey funding does not stretch to a full and propper investigation. Patrick Dodd, do you work in advertising and marketing industry and provide services to the timber industry?

We are considering building using the Zog steel framing system in a Golden Home. Having researched the green considerations in depth I am convinced that a timber home requires more energy and leaves a deeper footprint on the environment. Even down to the simplest points such as steel being railed once to fabricators and not trucked from forest to mill, then to the yard, then again on onto the building site. The entire houselot of Zog framing arrives on a toyota landcruiser and a trailer. For my money, and I'm not a raving greeny but understand the green consideration well enough, I will be building a Golden Home with Zog steel framing. Straighter, stronger, safer.

Interesting read and a great photo of a commercial project, no thermal break required there! If energy efficiency is the issue maybe BRANZ and their corporate partners should look at alternative sources of insulation rather the holding us to ransom while stuffing their pockets from over priced products like like glass wool. Which by the way is banned in other counties that care more about their citizens than profit for a few. If carbon footprint is the issue we should be focusing on emission controls and not burning coal as an energy source. I would compromise carbon footprint rather than breath timber treatments any day. Any way you slice it, steel is what holds timber structures together and makes them appear ok to the eye i.e. steel ceiling battens, gang nails, brackets, wire dogs, hot rolled sections and the list goes on and on.I challenge anyone to build a chem free pinus radiata structure that will stand on its own. Like it or not, light weight steel construction is proven and will continue to grow in it's use.

"I challenge you to provide evidence of ghosting, factual rather than theoretical." - Craig Exactly the problem with a wide variety of legislated restrictions on our lives. Good practice is 99% common sense, not a volume of prescriptive rules. E.g. take a look at how much better durability would be achieved if insulation didn't get in the way of construction methods. Our buildings are woefully temporary in concept and unsustainable in the sense of needing constant attention to keep them operating well into the future, or early replacement (less than 250 years durability is temporary). No guessing why we have so few real heritage buildings! Better to use copious amounts of cheap renewable energy (e.g. biomass) for heating a relatively thermally inefficient building with good durability characteristics than the current brood of soft offerings....

Comparing timber used for house frames over the last 150 years is like comparing chalk and cheese. Over this time different timber species (with varying levels of natural durability)have been used and with varying levels of quality for any given species. From a performance perspective (eg stability, strength) I'd rate today's radiata pine - not so good, radiata pine 10+ years ago - good, Douglas Fir - better and steel - best. Today's radiata pine is faster grown and milled younger than in the past leading to problems with stability. Ask any roofer about compression timber in roof framing and how it can cause steel roofs and ridge flashings to buckle and you'll get the picture. CHH also needs to get real and stop being so purist; without steel you don't have a timber frame system. As Jake says you still need nails, nail plates, steel strapping, joist hangers etc to put a timber house frame together and in terms of the wider LCA you need a lot of steel plant and equipment to cut and mill trees (eg chainsaws, saw blades, trucks, steel cables and the list goes on). In terms of carbon let's also create a bit of balance/perspective; fortunately, the ETS has started to encourage reforestation but between 2003 and 2008 NZ saw around 35,500 hectares of deforestation which was the biggest period of deforestation since WW2. At 800 tonnes CO2/ha this equates to a massive 28,400,000 tonnes CO2 sequestration foregone. Food for thought.

Once again the timber industry has let itself down. Sure the report is based on some steelframe construction and is probably correct for the construction as shown. Unfortunately the authors failed to find out how steelframes are constructed and thermal breaks applied in New Zealand. This report is not relevant. Check out www.nashnz.org.nz or www.rboard.co.nz for the facts.

Whoa! Reading through these comments, this is turning into a marketing disaster for CHH. Just shows you need to do your homework and have your facts straight before trying to knock your competition.

I’m the Marketing Manager for Woodproducts NZ and have found the response to the Green Being research by Paula Hugens very interesting. Her independent research has shown that there are issues with the thermal performance of steel and I would encourage anyone who is thinking of designing and building in steel to ensure they have the full facts before making their final building decision. I also note that many of the current responses to this article are from people who are active in the steel industry – it would be helpful to the debate if you would declare your position so that information can be assessed constructively by readers.

In response to Bill, I am the Marketing Manager for New Zealand Steel, manufacturers of AXXIS Steel for Framing. The fact is the Green Being report by Paula Hugens is flawed. What is more, I have personally handed copies of "NASH N-10 Thermal Break & Cavity Construction" and "NASH N-11 House Insulation Guide" to your plywood Product Manager who requested information from me to help him point your clients in the right direction when they ask how to fix Shadowclad plywood cladding to steel framing. Fact is you had the correct information but ignored it and to my knowledge Paula Hugens did not contact a steel framing sector representative (eg NASH) to verify the steel framing and thermal break specifications on which she based her report were correct. End of story.

I was interested to see CHH state on their website that “it is likely that the impact of a small fire in a steel framed house will be potentially more damaging and costly to repair than if the house was built with timber framing”. It would be useful if CHH could address the recent international concerns regarding the performance of timber-framed buildings in fire. According to the annual Fire Statistics Monitor, published by the Communities and Local Government department in the UK, if there is a fire in a dwelling under construction, then 28% of timber-frame buildings will suffer more than 200m2 of damage, compared with only 4% of non-timber frame structures (see http://www.building.co.uk/news/insurers-call-for-urgent-probe-into-timber-frame-fire-risk/5004700.article). It is also interesting to note that, on 18 September 2010, the Chief Fire Officers Association (CFOA) in the UK called for an urgent review of the regulations governing the construction of timber-framed buildings (http://www.bbc.co.uk/news/uk-11354755)

Thanks Chris, for the copies of the two NASH documents - but far from being ignored, they in fact prompted our company to act on specific recommendations included in your ‘Conclusions Section’ of the NASH document - ‘Thermal break and cavity Construction’ (P15). I quote:

‘Further research is recommended into the following areas:

- Thermal performance of typical roof truss and ceiling framing assemblies [my comment -important as 35% of a homes’ heat escapes through the ceiling!]

- Thermal imaging of walls constructed using the recommended assemblies would provided [sic] more detailed information on the conditions required for condensation and ghosting [my comment - this alerted us to the need for further investigation into steel framed wall insulation practice]’

The facts are that NASH has accepted that further research into the thermal performance of steel framing is required and we commissioned further research by a reputable, independent consultancy (Green Being Ltd) which clearly questions the thermal performance of steel framed homes.

Great debate. As a person on 2 to 3 different sites a day including numerous leaky buildings. Both products timber vs steel has its benifits. To me steel is a product that is an unkown to many therefore seen as a threat instead of being utilised, who would dream that rondo battens or similar products would be accepted ? To add to the debate of intrest designers and installers out there should do there home work before specifying metal jamb liners where wall board butts into and timber flooring into metal joinery, both with no thermal bridging-end result mould at point of contact (double glazing makes no difference) Thermal bridging required in joinery. Hope you designers know the products are fit for purpose.

Bill, "we commissioned further research by a reputable, independent consultancy" Commisioned and independent can't really be used in the same sentence, further more, unbias research would require input from both sides of the debate, have not seen any evidence of this. On the Nash document suggesting further research into thermal breaks, I would think any industry should continue to develop their products. As CHH does with the continued changing of treatments to their timber to combat rotting. Geoff, Aluminium jamb liners as supplied by Bradnams do have a thermal break in the joinery and jamb component. Roger, Yes, "small fire" The difference between steel and timber is the fact that steel doesn't burn therefore not supplying fuel for the fire enabling the fire to remain small, extinguishable and not a danger to life. There is a tangable benefit to being alive to assess the damage to your property. Some see the timber industry attack on it's competitors as a threat. I see it as fantastic for the steel industry as it creates great debate and interest in alternative methods of construction so I thank CHH for the free advertising.

CORRECTION to comment #9.

The deforestation figures quoted in comment 9 are overstated and should read "fortunately, the ETS has started to encourage reforestation but between 2005 and 2008 NZ saw around 30,500 hectares of deforestation which was the biggest period of deforestation since WW2. At 800 tonnes CO2/ha this equates to a massive 24,400,000 tonnes CO2 sequestration potentially foregone. Food for thought". Sources: Deforestation figures available from Ministry of Agriculture & Forestry. 800 tonnes of CO2/hectare figure is taken from a statement from Minister for Climate Change Issues, Hon Dr Nick Smith dated 25 March 2010 available at www.beehive.govt.nz.

The steel framing industry actively welcomes any questions. It is right you should ask them. I encourage you to directly contact gm@nashnz.org.nz or info@nzsteel.co.nz for further discussion. Steel framing offers a number of compelling benefits and provides NZers with another option to traditional framing - an option with a long history of use in NZ and overseas.

Very interesting comments on this article. The Carter Holt thing aside, there are still question marks over the 'thermal bridging' of steel frame houses. Timber frame houses have similar issues in the soffit area as well. This particular area is not addressed well when it comes to 'thermal breaks'. The soffit is essential in New Zealand houses(should be mandatory) but lacks any real guidance as to how best to insulate from the exterior. The use of cement board products here is not ideal either. As far as steel framed houses go in accordance with the insulation requirements for the South Island, they fall short of the mark. It would be a better solution if the Steel frame house designers were to step up their own values, beyond the 'minimum', something the concrete house industry has done already.

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