A catalog of non-toxic building systems.
Saturday, June 11, 2005Light Steel Framing - Cold-Rolled Shelter
Originally used chiefly for the non-load-bearing portions of commercial construction, light gauge steel framing has become increasingly popular in conventional housing in the past two decades and, since such homes are often indistinguishable from wood frame homes due to the structure being hidden under sheet-rock paneling, many home owners are completely unaware that there is actually steel behind their walls rather than wood. At one time much more expensive than lumber framing, rising lumber costs have made steel cost-competitive. Rapidly fluctuating steel prices in recent years, however, have forced manufacturers to provide pricing on an almost daily basis rather than use standardized pricing.
Typical commercial steel construction is charactized by the use of heavy steel beams -the so-called 'red iron' steel framing named for the once typically reddish colored primer coatings sprayed on it. Light gauge steel framing is based on the use of thin galvanized steel sheet formed in a stamping and cold-rolling process into roughly 'C' chaped channels which, like the pressed steel bodies of automobiles, rely on their corrugations and folded shape for rigidity and compression strength. Used very similarly in terms of construction method to stick-built wood framing, light steel framing is assembled using self-embedding screws rather than nails, the flexibility of the metal allowing the steel channels to nest against each other or to be easily cut and folded to form attachment flanges allowing the screws to the driven through the layered sheet metal for attachment. A crimping tool is also used to attach framing members rather than screws where framing is not load-bearing so as to create a flatter surface for attaching wall board. Though dimensions are similar to lumber, light steel framing is offered in a variety of gauge thicknesses so as to allow building engineers to employ the least amount of metal for necessary strength. The contractor or designer for a steel frame home must thus be a little more careful in the calculation of loads in order to prevent unecessary costs. There are also a number of specialty channels offered which simplify the attachment of finishing products and infrastructure components to the framing.
A number of successful non-toxic homes have been built using light steel framing, exploiting the inherently non-toxic composition of the material and combining it with the less toxic alternative finishing materials. But there is an important caveat to consider when using this for such housing. The steel channels sometimes come from the manufacturer with a machine oil coating still on them. This is sometimes a residue of manufacture and other times is actually added by manufacturers as bonus corrosion prevention -though it's rather redundant for galvanized steel if it is of nominal quality to begin with. This oil is toxic, odorous, and can seep into sheet rock paneling and should be washed off, ideally using a non-toxic non-residue detergent like trisodium phosphate (TSP) This washing can add significant labor overhead to the cost of a home -especially if the need for it is unexpected. In some cases costs of homes have been doubled by this. But there are also low-toxic home designers who claim that this oil is very quickly evaporated and poses a minimal problem. For the average home this may be true. For those already with environmental illness and very sensitive, the washing is probably necessary. Thus the cost of this type of framing can become very expensive even if the material cost is the same as lumber.
Light steel framing is also often offered in packages which can greatly reduce their cost. But since these homes are in no way designed to be non-toxic, it would take experienced builders or non-toxic housing contractors to make sure they can be effectively adapted to this purpose.
Note that there is an extruded aluminum alternative to light steel framing alled Aluma-Strut which is offered by a Texas based firm of the same name. Aluminum has some potential advantages over galvanized steel in that it is non-magnetic and so may be more suitable for individuals with EMF sensitivities, never has an oil coating which might need to be removed, and is recyclable with much less energy than steel making it slightly more environmentally friendly. This particular aluminum framing is used in a similar manner to light gauge steel but relies on bolt-together assembly using specialized connectors which also offers the bonus advantage of potential demountability.
Unfortunately, the Aluma-Strut product is based on a proprietary profile and connector design with this one company the only source for it in the world. The company does not sell components by themselves, only housing packages which they will custom engineer to order for any architect's design submitted. This seems to be an astounding business blunder since the need for repair and expansion is common for all housing and this firm seems to have no plan for addressing that. Any contractor asked to work on a home made with this will do is scratch his head in bewilderment. The company web site also seems to be having some difficulty of late and may automatically send users to a dead page. Not sure what this implies for the health of the company, though they have definitely built structures in the past so it is a proven product, to some degree.
A similar custom aluminum profile based product is the Modular Housing System of US Systems. MHS is a very sophisticated building system that originated in a product designed for store display and kiosk construction and has many similarities to the later discussed T-slot framing technology. Again, used similarly to light gauge steel in framing design, it uses a proprietary connector system with a key-bolt lock mechanism that makes for very rapid assembly and uses modular panels which integrate in-line with the grooved shapes of the frame profiles. This allows for simpler frame systems as the panels share in the structural strength, though even without them the system is much more rigid than light steel framing and can work in post & beam designs. Panel materials are made of conventional SIP materials but the company had great interest in the potential of the non-toxic housing market and the system is able to accommodate alternative materials. This system was extensively researched and strongly considered for this author's own non-toxic housing needs.
US Systems is a bit wiser in that it has offered its building components separately from the housing packages it also offers and is willing to perform package engineering to order. Unfortunately, the company has yet to actually ship product. They have encountered much difficulty in finding American aluminum extrusion companies sophisticated enough to fabricate profiles of such large size and complexity. It's yet another one of the many industrial areas this country has ceded superiority to the rest of the globe. So it remains unclear when this potentially powerful building product will actually become available.
