Flanking Transmission in Framed Buildings - Phase III

Transmission Via Structural Connections at the Wall/Floor Junction

Objectives

For the multi-family construction where the joists are perpendicular to the partition wall and discontinuous, develop a series of construction details that provide adequate sound insulation without compromising the fire resistance and structural integrity, as required by the building codes. Using the results of this project and previous NRC-IRC flanking projects, develop a practical design and retrofit guide suitable for architects, engineers, and builders.

Background

Flanking Phase II used two reference floor/ceiling assemblies with a continuous subfloor to assess the effect of different wall type, blocking details, joist type, and the effectiveness of various floor toppings to control horizontal and vertical flanking. The first reference assembly had only the subfloor continuous because the joists were parallel to the partition wall. The other assembly had the joists continuous under the partition wall in addition to the subfloor.

For these assemblies there was a significant difference in the sound insulation for rooms separated by the partition wall indicating the severity of horizontal flanking (between rooms sharing a continuous floor element) was largely determined by the degree of structural coupling at the wall/floor junction. In both cases, the sound insulation was limited by flanking paths that did not involve the partition wall (nominally separating element). An apparent STC 38 was measured when the joists and subfloor were continuous, despite the STC 53 wall. The project clearly established the need for a systems approach when designing for sound insulation.

The systematic study showed flanking introduced by continuous floor elements can be controlled using a topping applied to the subfloor. The topping should be chosen to reflect the degree of structural coupling at the wall/floor junction as well as the sound insulation of the partition wall. Floor toppings also have the added benefit of increasing the sound insulation between rooms separated by the floor/ceiling assembly since they attenuate the direct path as well as the dominant vertical flanking path (from the subfloor to the lower wall).

The project answered many questions about the effect of continuous elements at the wall/floor junction, which are quite common in large structures such as two and three-storey wood framed hotels and residential homes. However, time and budget constraints prevented examination of an important case where the joists were perpendicular but not continuous under the partition wall. Scope

The work of Phase III: Transmission Via Structural Connections will address the important case where the joists are perpendicular to the wall/floor junction but are not continuous - a potentially common joint detail for wood framed hotels, residential homes, row housing, and apartments. The discussion sketch below shows how this might be accomplished using joist hangers on a load-bearing single stud wall. (Note: The actual assemblies and their details will be determined by the Steering Committee, once priorities have been established in the first meeting.)

Vertical section through the wall/floor junction showing the discontinuous wood-I joists supported by hangers. Plan section through the wall/floor junction showing the discontinuous wood-I joists supported by hangers

It is anticipated that the sound insulation between rooms separated by the partition wall will be limited by flanking paths involving the floor and that a floor topping will be required to achieve adequate sound insulation. The project will have two components. The first is a measurement component and technical evaluation of an intermediate case of flanking. This is required before the result of the previous study can be generalized and widespread technology transfer begins. The second is a technology transfer component. Technical results from this project, and previous NRC-IRC flanking projects, will be summarised in the form of a best practice guide.

Technical Reports and Information

Flanking Transmission at the Wall/Floor Junction in Multifamily Dwellings - Quantification and Methods of Suppression
Nightingale, T.R.T. Halliwell, R.E. Quirt, J.D. King, F.
Research Report, NRC Institute for Research in Construction, 168
pp. 401. 2005-03-01
[Full citation / Référence complète]

Guide for Sound Insulation in Wood Frame Construction: Part 1 - Controlling Flanking at the Wall-Floor Junction
Quirt, J.D. Nightingale, T.R.T. Halliwell, R.E.
Research Report, NRC Institute for Research in Construction, 193
pp. 85. 2005-03-01
[Full citation / Référence complète]

Related Projects

• Phase I: Fire Stops
• Phase II - Effect of continuous elements at the wall/floor junction

Related Information

Institutes:

• NRC Institute for Research in Construction