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The Metal Home

A Canadian Engineer’s Experience

by
Wilfred Siu, Ph.D., P. Eng.
Merwin Engineering Ltd.
Edmonton, AB, Canada

Introduction

In the premiere issue of the Metal Home Digest, many excellent articles have zeroed in on the reasons for the emergence of steel as a construction material in the residential sector. These reasons can be summarized as:

1. Strength and ductility of steel
2. Uniformity of production quality
3. Inorganic composition and resistance to termite and other pests
4. Non-aging and maintenance-free performance
5. Non-combustibility
6. Environmental friendliness (recyclability)
7. Price and supply stability

Some of these factors (1, 2, 4, and 5) have long been responsible for the wide use of steel as a superior construction material of choice in commercial, institutional and industrial projects. Other factors will gain recognition in time. The recent fires in Malibu, CA, and Oakland have brought home the benefits of non-combustible construction in residential neighborhoods and, hopefully, will lead to more sensible control of neighborhood development beyond that of mere aesthetics.
Growing environmental awareness will slowly but surely tip the scale of balance to the use of steel and other environmentally friendly products in construction. The Greater Toronto Home Builders’ Association and Ortech International, with support from the government of Ontario, have recently started a Build Green program in the province of Ontario, Canada, to encourage environmentally friendly products in construction.

Canadian Residential Construction

It is encouraging to see the metal home industry taking hold in the United States, with projected market penetration of 25% of all new home construction by 1998. In Contrast, Canada lags behind. At the time of this writing, Western Canada has seen only a handful of metal homes and there has not been an anrticle published in any Canadian engineering or trade journals on the metal home industry.
This lag in the development of the metal home industry in Canada cannot be explained by the relative size of the Canadian economy alone. At a recent home show in Edmonton, where this writer displayed the first complete metal home in Canada, the typical responses, aside from relative costs, were:

Would it expand and/or contract?
How about cold bridging?
Would it be noisy?
Would it rust?

These concerns are deeply rooted in the Canadian experience with harsh climate. It is not unusual for Canadian designers to deal with design temperature range from +104 deg F to -40 deg F (+40 deg. C to - 40 deg. C) in urban areas, and the design temperatures down to -85 deg F (-65 deg C) have to be accounted for in designs for the far north. These temperature extremes and the long Canadian winters have significant impact on the choice of construction materials and systems.

Building envelopes are as important as framing systems. As foundations have to be below frost lines, basements are a natural consequence, heightening concerns for inter-floor sound transmission even for bungalow type residences. With condensation problems still plaguing some of our early attempts in air- tight super-energy-efficient homes, the public is justified in being concerned about rusting (as a result of condensation). These concerns explain the slow acceptance of new construction materials and/or systems in Canada. To develop the metal home market in Canada requires an integrated approach to residential construction.

An Integrated Approach to Metal Homes

This writer had the chance to develop the first complete metal home in Canada. The instruction from the client was simple. We were given floor plans that suited the client’s space requirements, featuring a 2,600 sq. ft. (242 sq. m.) one-and-a-half story home with a large solarium off the master bedroom. The mission was “to push steel residential construction to the limit” (and damn the cost). Given such a carte blanche, we decided to look at metal home construction from scratch.

The concerns raised at the home show were not unexpected and the reasons for steel construction were well known. Earlier attempts at metal home construction were studied. All have chosen the safe route of stud-for-stud and joist-for-joist substitution method of construction. The inherent strength of steel and the large body of knowledge in steel (and composite) construction in non-residential sectors have been greatly under-utilized. From very early on, a decision was made to seek a drastically different approach to highlight the advantage of steel construction and allay the concerns arising from the harsh Canadian climate.

To dramatize the strength and performance of steel construction, a composite floor system was selected, giving a 30’ (9.15m) clear span with only a 15" (380 mm) deep floor assembly, comprised of 3” (75 mm) concrete on sheet metal decking on 12" (300 mm) C-joists. The mass of the composite floor also provides the rigidity and sound insulation not afforded by the conventional wood floor. To capture public imagination (and get around the potential problems of winter concreting), a metal stud basement wall system was designed, and is believed to be the first of its kind. As expected, the column-free basement with its clear span and living space under the garage attracted a lot of attention from the start. Since then, the home has received considerable local media coverage.

To bring home the point of non-combustibility, no wood sheathing was used in the project. Sheet metal was used as the exterior sheathing both for the basement and the superstructure. Non-combustibility was carried right through to its logical conclusion in the metal tile roof system. Fire-proofing was carried one step further through the use of our patent-pending Jay-Jay drywall blocking system, which reinforce the paper-taped joints between drywall panels. The drywall blocking system provides a fire/smoke stop, and prevents ceiling collapses resulting from water-soaked insulation in fire fighting.

Building science studies played as important a role as the structural selection in this integrated approach.

Taking advantage of the composite floor system, a multi-zoned in-floor hot water heating system was incorporated in all floors, inlcuding the basement. While this heating system can be incorporated in other types of construction, its inclusion in a composite floor system is a natural, and its use in a non-allergenic framing system makes a might first step in the design of non-allergenic construction.

At the heart of the mechanical system is a single boiler, which provides for all the heating (in-floor hot water heating and domestic hot water) and ventilation requirements. Air is discharged at window locations and at the top of the olarium to keep air circulation over the glass surfaces to minimize condensation at cold temperatures. A zone for heating and ventilation is dedicated to the solarium because of the large glass area, causing a high heat loss and heat gain situation.

For the building envelope, two layers of 1.5" (38 mm) Perma-Therma (a new phenolic insulation by FibreGlass Canada), with joints staggered to eliminate cold bridging at insulation joints, were used on the outside of the exterior walls both above and below grade level. A torch-applied bituminus waterproofing membrane (by Suprema) was applied below grade, with details specially worked out for the metal basement. Triple glazing low-E windows complete the super-energy-efficient building envelope.

The wrap-around exterior insulation achieves several objectives.

By keeping all the structural components on the warm side, it eliminates thermal bridging and thermal movement of the structrual system. Thermal performance of the building envelope is further enhanced by the fact the entire cavity of the exterior wall is available for mechanical and electrical services, without squeezing the insulation as would be the case for traditional between-stud insulation (batt or foam).

Having the air/vapor retarder on the exterior of the structural components eliminates all possibility of condensation and condensation-related damages to the structural system. It also eliminates penetration of the air/vapor retarder by mechanical and electrical services, as is often the case in traditional construction.

The First Complete Metal Home

The result of this integrated approach to design if the first “complete” metal home in Canada.

The 2,600 sq. ft. (242 sq. m.), one-and-a-half residence starts with a metal basement wall system, with an insulation rating of R-21 (RSI 3.7) on the exterior. It boasts of a 30’ (9.15 m) clear span structure with only a 15" (380 mm) deep floor assembly, complete with built-in multi-zoned hot water radiant heating system. The composite floor system provides a rigidity and sound retardance not available in any conventional residential floor construction known to this writer. A single boiler provides all the heating and air circulation. The exterior wrap-around insulation provides a uniform insulation rating of R-21 (RSI 3.7) with no cold bridging at stud and corners, and eliminates all possibility of condensation damages and thermal movement.

At the time of this writing, the first complete metal home is almost ready for occupancy. Started out on a push-to-the-limit-and-damn-the-cost approach to design, it is especially gratifying to learn that the final cost of the house came in about $95 (Canadian) per sq. ft. (C$1022 / sq. m.). While cost comparisons among custom designed homes are often misleading, it appears that this is in line with conventional timber-framed custom-designed homes in Edmonton, Alberta. It once again reaffirms our belief that good design does not have to cost more.

Conclusion

Several lessons can be gleaned from our experience with metal home construction in Canada.

1. The harsh Canadian climate poses specific challenges to the design of metal homes. However, when properly dealt with, these challenges can be turned into opportunities. The wrap-around exterior insulation system and the ready incorporation of multi-zoned in-floor hot water radiant heating in na composite floor construction are all results of meeting the challenges head-on. Similarly, the metal basement concept is our attempt to get around the usual problems with cold weather concreting. With pre-fabricated panels for the basement and superstructural walls envisioned for future projects, it is realistically estimated that construction time can be cut considerably.

2. Too much time and emphasis have been spent on decrying the increase in lumber prices and decrease in lumber quality. Granted that these are all true, structural cost should be cost in its proper perspective. Experience in custom designed homes in the Edmonton area has shown that the structural cost is only about 15% of the overal costs. This percentage will decrease even further with more upscale homes. In other words, concern for the “structural” cost has been overstated. Cost comparison with lumber depends on lumber price on the particular day of making the comparison, though the overall trend of lumber prices is upwards. Accepting that steel framing and timber framing are cost equivalent within a narrow range, quality and environmental responsibility are what we should be concerned about.
We firmly believe that steel can stand on its own as a construction material in the residential sector. A change in attitute is recommended. Instead of decrying the deficiencies in lumber, while at the same time imitating the lumber construction through stud-by-stud and joist-by-joist substitution, the design professionals should look at the new material on its own merits and look for ways to exploit its full potential.

3. As with an “new” material, a total, integrated approach to the problem on hand is required. Lumber construction has been around for hundreds of years, with the accessory systems being developed over the same length of time. Nothing short of a concerted effort to tackle residential construction in its entirety can establish metal homes as a truly viable alternative. To start a new trend in residential construction is obviously too daunting a task for any one firm or even any one discipline alone. A multi-discipline task force, to be modeled on the AISI Steel in Residential Construction Advisory Group in the United States, is highly recommended for Canada. Instead iof competing with is U.S. counterpart, such a task force in Canada can concentrate on the potential problems arising from steel residential construction unique to Canada due to its harsh climate. In cooperation with like-minded organizations such as the Build Green program in Ontario, it should also take on the task of raising the public awarenesss (and that of building officials and professionals) of the environmental imperative of alternative construction materials and techniques. After all, it does take 41 trees (but only 6 junk cars) to frame an average North American single-family home.

* Paper published in Metal Home Digest, Winter/94 issue.