Over the past few months the timber frame industry, along with other construction sectors, has been busy with the issues surrounding Part E.
Historically, mass has been seen as the answer to sound insulation but that has negative implications for both cost and for the depth of walls and floors. It is now increasingly recognised that decoupling or isolation of sound-bearing components can be very effective. The combination of both mass and decoupling, such as occurs in timber frame, is even better and is certainly the most cost-effective.
Accordingly the UK Timber Frame Association has been a prime mover in the effort to provide suitable Robust Standard Details (RSDs) which comply with Part E and avoid onerous pre-completion testing (PCT). Currently four RSDs in respect of timber frame construction are with the Building Regulations Advisory Committee (BRAC) for consideration. The RSD acoustic targets are even more onerous than those in approved Document E.
But what happens in the meantime? Building continues apace and designers, engineers and contractors need solutions they can be confident will meet Part E. The UKTFA is therefore compiling a Guidance Document on Part E which is scheduled for release in August. Of course, until BRAC reports on the submitted RSDs, all solutions contained in the Guidance will still be subject to PCT. Even when accepted, only the actual RSD solutions with the higher performance levels will not require PCT.
Range of solutions
UKTFA’s approach is to provide the construction industry with a range of solutions allowing designers and specifiers flexibility in selecting the method which best suits their circumstances – and still meets Part E. This has been spoken of in-house as a ‘pick and mix’ approach – a description lacking gravitas perhaps, but not too far off the mark!
UKTFA’s approach has nonetheless been comprehensive and the Guidance includes solutions using a wide variety of timber products.
Key areas of the document are highlighted below.
Experience of many years of on-site acoustic testing of timber frame buildings to meet Scottish requirements has highlighted the importance of workmanship issues. No matter how good the design, good workmanship will result in the best acoustic performance. Key workmanship advice to assist with successful performance forms a major component in the Guidance – reflecting the UKTFA’s wider commitment to quality construction through quality workmanship. In the case of party walls, workmanship advice is given in 10 specific bullet points. Key workmanship advice on timber party floors is also given prominence, again in 10 bullet points.
Services installation is covered fully for both party walls and floors and detailed, worked examples of a complying timber frame party wall and a complying timber party floor are included.
Party wall solutions
Current timber frame separating walls do not need to change much to meet new Part E. Indeed using existing separating wall technology, except for some extra low cost insulation in the wall, RSDs for timber frame have achieved excellent results with up to 54dB sound reduction, against a target of 50dB (45dB for approved Document E). Because sound is measured on a logarithmic scale this improvement is much more significant than the numeric difference would suggest.
A typical timber frame party wall comprises three discrete layers – the timber frame layer; the absorbent layers and the lining layers. There is a set of performance requirements and one or more specification options for each of these layers. Options from any one of the discrete wall layers can be combined with any option from any other layer to give an overall wall solution which should meet the sound insulation performance requirements of Approved Document E (2003 edition).
In the UKTFA’s Guidance, two timber frame layer options will be described, one for load-bearing and one for non load-bearing walls; two options will be described for the absorbent layer, which must be fitted to the timber frame leaf to absorb part of the sound energy transmitted; and two options will be described for the wall lining layers, which must provide the appropriate surface mass of at least 20kg/m2 for sound insulation.
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“UKTFA’s approach is to provide the construction industry with a range of solutions allowing designers and specifiers flexibility in selecting the method which best suits their circumstances – and still meets Part E” |
Crucially, the Guidance will also cover junction details with:
Party floor solutions
A typical timber frame party floor comprises eight discrete layers: floating layers; resilient layers; perimeter layers; structural deck layer; structural joist layer; absorbent layer; ceiling isolation layer and ceiling lining layers. There is a set of performance requirements for each layer and the Guidance gives various specification options. Options from each of the discrete floor layers can be combined with any option from another layer to give an overall floor solution which should meet the sound insulation performance requirements of Approved Document E (2003 edition).
Floating layers must be isolated from the timber frame structure which provides a walking surface and mass. Further layers must isolate the floating layers from the structural floor. These layers must be resilient but must provide support to ensure the floating layers do not have excessive bounce. Perimeter layers ensure that the floating layers are isolated from all timber framed internal, party and external wall upstands and the skirting board on any wall or upstand.
There must be a structural deck on top of the structural joist layer which is part of the building wind bracing as a diaphragm and which forms a working platform for site operatives. For joist spacings up to 600mm centres options include four types of structural board.
There must be a structural joist layer to support the structural deck layer and to transfer the dead and imposed loads safely to the load-bearing walls below. Options given are solid timber joists; engineered I-joists; and timber flanged metal web composite joists.
There must be an absorbent layer fitted between the structural joists which can absorb part of the sound energy transmitted. The ceiling layers must be isolated from the structural floor layer and the load-bearing walls. Options for ceiling isolation layers are described, involving metal resilient bars and solid timber ceiling joists.
The Guidance on party floors also covers junctions between timber party floors and external, internal and party timber frame walls.
