Metal Stud Wall Systems — Thermal Disaster, or Modern Wall Systems With Highly Efficient Thermal Insulation?

Abstract

Metal stud wall systems for residential building are gaining in popularity. Thanks to their low cost, construction simplicity, and similarity to the existing wood frame technology, metal stud wall systems can share a considerable part of the residential and commercial markets, very soon. The prognosis of American Iron and Steel Institute predicts that in 1997 about 25% of the new residential buildings will be assembled with the use of metal stud's technologies in the U.S.A. The application of the light gage metal technologies in building has either economical or environmental aspects, because the replacement of the construction lumber by metal wall and roof components can reduce construction costs but also save a forest. In addition, metal studs are 100% recyclable material. The authors believe that tremendous markets are available around the world for the deployment of the metal stud wall technologies. A deployment of the metal stud wall technologies can create a great chance for modern, low-cost and energy efficient buildings in many world regions. This system has been already successfully introduced in Europe, Central and South America, Australia and New Zealand. However, these technologies require serious redesign to improve their thermal performances. Commonly, commercially available metal stud wall systems are initially designed by simple replacement of wood studs, joists, headers, etc., by structurally equivalent metal components. Metal substitutes of the wood structure are very often being installed without consideration of the difference in thermal conductivity between wood and metal. Strong thermal bridges caused by highly conductive metal components worsen thermal performance of these walls. In metal stud walls, the reduction of the in-cavity R-value can reach 50%. Because steel has higher thermal conductivity than wood and intense heat transfer occurs through the metal wall components, thermal performances of a metal stud wall are significantly lower than for similar wood stud walls. A reduction of the in-cavity R-value caused by the wood studs is about 10% in wood stud walls. That is why metal stud walls are believed to be considerably less thermally effective than similar made of wood. However, properly designed metal stud walls can be as thermally effective as wood stud walls. Relatively high R-values may be achieved by installing insulating sheathing, which is widely used as a remedy for a weak thermal performance of metal stud walls. A series of the promising metal stud wall configurations is analyzed using results of finite difference computer modeling and guarded hotbox tests. Some of these walls were designed and tested in the ORNL Building Technology Center, some were tested in other laboratories, and some walls were developed and forgotten long time ago. Also, a novel concept of combined foam -metal studs is considered. The main aim of the present paper is to proof that it is possible to build metal stud walls performing as well as wood stud walls. The key lies in designing; metal stud wall systems have to be treated in special way with particular consideration to the high thermal conduction of metal components. In the discussed collection of the efficient metal stud wall configurations, reductions of the in-cavity R-value caused by metal studs are between 10 and 20%.