Making Steel Framing as Thermally Efficient as Wood

Abstract

In many world regions like North America and Scandinavia wood framing is dominant technology for residential buildings. During last two decades several companies around the world started to promote a low-gage steel framing for residential and commercial buildings. Steel framing has many advantages over wood framing; strength, low weight, dimensional stability, resistance to termite damage, almost 100% recycleability, etc .. However because of several reasons an application of steel as a framing material in US residential building market is relatively low. Steel industry has noticed much more success on commercial building market which is not as rigorous regarding thermal efficiency and energy conservation. Steel framing has one significant disadvantage over wood; Steel members conduct heat extremely well. This effect is known as thermal bridging, and it can sharply reduce a wall's effective Rvalue. The simplest and most common way to overcome this problem is to block the path of heat flow with rigid foam insulation. Adding rigid foam insulation not only increases the whole wall's R-value, but it also reduces the temperature difference between the center of the cavity and the stud area, which cuts down on the possibility of black stains forming from dirt getting asymmetrically attracted to cold spots on a wall's surface. However, rigid foam insulation is an expensive solution. Several material configurations were developed in the past to increase thermal effectiveness of steel-framed structures. This paper is focused on most common options of thermal improvements of steels framed walls. They were as follow: 1) diminishing the contact area between the studs and exterior sheathing materials, 2) reducing the steel stud web area, 3) replacing the steel web with a less conductive material, and 4) placing foam insulation in locations where the thermal shorts are most critical. Researchers at Oak Ridge National Laboratory (ORNL) have utilized both hot box testing and computer simulations in aim to optimize thermal design of steel stud walls.. While examining several material options, ORNL's BTC was also striving to develop energy-efficient steel stud wall technologies that would enable steel-stud walls to beat the performance of traditional 2 x 6 wood stud walls. Several, most current, ORNL developments in steel framing are presented below.