Lightweight steel-framed thermal bridges mitigation strategies: A parametric study

Abstract

In building applications (e.g. industrial, offices and residential), the use of lightweight steel-framed structural elements is increasing given its advantages, such as exceptional strength-to-weight relation, great potential for recycling and reuse, humidity shape stability, easy prefabrication and rapid on-site erection. However, the high thermal conductivity of steel presents a drawback, which may lead to thermal bridges if not well designed and executed. Furthermore, given the high number of steel profiles and its reduced thickness, it is not an easy task to accurately predict its thermal performance in laboratory and even less in situ. In a previous article, the authors studied the importance of flaking heat loss in lightweight steel-framed walls. This article discusses several thermal bridges mitigation strategies to improve a lightweight steel-framed wall model, which increase its thermal performance and reduce the energy consumption. The implementation of those mitigation strategies leads to a reduction of 8.3% in the U-value, comparatively to the reference case. An optimization of the wall module insulation layers is also performed (e.g. making use of new insulation materials: aerogel and vacuum insulation panels), which combined with the mitigation approaches allows a decrease of 68% in the U-value, also relatively to the reference case. Some design rules for lightweight steel-framed elements are also presented.

Energy efficiency and thermal performance of lightweight steel-framed (LSF) construction: A review

“…[5] along with an extensive review of the main advantages of this type of construction. As suggested by several authors [3,[6][7][8], LSF construction presents certain advantages over heavyweight construction, such as: small weight with high mechanical strength; reduced disruption onsite and speed of construction; great potential for recycling and reuse; high architectural flexibility for retrofitting purposes; easy prefabrication allowing modular construction, suited to the economy of mass production; economy in transportation and handling; superior quality, precise tolerances and high standards achieved by off-site manufacture control; excellent stability of shape in case of humidity; and resistance to insect damage. However, the high thermal conductivity of steel elements may lead to significant thermal bridges.…”

“…As suggested by Martins et al [7], the use of new and more efficient insulation materials may also allow a great thermal performance of walls, dealing with lower thicknesses of the insulation layers. Aerogel blankets may be seen as one of the most promising thermal insulation materials as they have a thermal conductivity 2-2.5 times lower than that of conventional MW [60].…”

“…Finally, in the latter strategy, an insulation strap is attached along the steel framing using button head screws or adhesives. Martins et al [7] added that fixing bolts can be used instead of horizontal steel plate connections to reduce thermal bridges.…”

“…The authors pointed out that the heat flow through a steel profile decreases as the number of narrow slots increases, and they concluded that the thickness of a standard steel profile has to be decreased by a factor of six to achieve the equivalent thermal properties of a slotted steel profile. Martins et al [7] carried out an extensive study to evaluate the impact of single and combined thermal bridges mitigation strategies on the thermal performance of a reference LSF wall. The analysis was performed using a 3D finite element method (FEM) derived from a previously validated 3D FEM reference model proposed by Santos et al [40].…”

“…4b. The ETICS is very suitable to minimize steel stud thermal bridges as the exterior thermal insulation layer may be continuous [7]. The requirements for EPS thermal insulation products for buildings are specified in EN 13163:2012+A1 [28].…”