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Internal walls for new or existing buildings – Timber frame

Since July 2003 it has been a requirement, under Part E of The Building Regulations 2000, that houses, flats, and rooms for residential purposes are designed and constructed to provide reasonable resistance to sound from other parts of the same building and from adjoining buildings.

This application note gives examples of an internal wall construction which, when built correctly, will achieve the performance standards set out in Approved Document E, ‘Resistance to the passage of sound’. For other construction elements please refer to Thermafleece application notes for separating walls, separating floors, and internal floors.

Performance

The minimum value for airborne sound insulation of an internal wall (i.e. a wall between two rooms within the same dwelling) is Rw = 40dB.

Rw is a laboratory rating for sound reduction and field testing of internal walls and internal floors is not normally carried out. However a building inspector, or acoustic specialist carrying out pre-completion testing on other elements of the construction, will check that the design specification for internal walls and floors is based on construction methods that should achieve Rw = 40dB.

Building a separating wall with a timber frame
Approved Document E gives construction guidance on “Internal wall type B: Timber or metal frame”. For further information please refer directly to Approved Document E - Resistance to the passage of sound.

The resistance to airborne sound in this construction depends on the mass per unit area of the leaves, the cavity width, frame material and the Thermafleece in the cavity between the leaves.

Construction guidance

The construction consists of a timber frame, with plasterboard linings on each side of the frame and with Thermafleece in the void.
• The minimum distance between inside lining faces should be no less than 75mm
• Each lining should be one layer of plasterboard of minimum mass per unit area 10 kg/m2 such as 12.5mm British Gypsum Wallboard TEN or 15mm British Gypsum Wallboard. Standard 12.5mm (half inch) wallboard is not suitable for this construction.
• 50mm Thermafleece can be friction fit between timbers. Staples may be used to ensure Thermafleece is secured in place and will not fall to the bottom of the cavity
• All joints should be well sealed

Good design and construction are essential

Using a good design and applying the correct construction techniques are essential in achieving a high level of sound insulation.

How does Thermafleece improve sound insulation?

When you fit Thermafleece in a internal wall it improves sound insulation in three ways:
1. It lowers the resonant frequency of the wall by altering the characteristics of the air-gap in the cavity.
2. It dampens sound waves as they are transmitted through the wall.
3. It dampens sound waves that are contained in the void of the wall.
The addition of Thermafleece in a wall can typically result in a 6-12dB improvement to the sound. insulation.