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Timber frame construction is the developed world’s most widely used residential building method.

 

Overview

Tried and tested, timber framed construction fulfils a 21st century agenda, offering a method of construction which is engineered, energy efficient, sustainable and quality assured. With a huge supply of plantation timber readily available in the UK and Ireland this form of construction is environmentally friendly.

“Timber framed construction is contributing to the drive to provide people with good, modern homes of proven sustainability and efficient construction. It also serves my Government’s aims of reducing C0₂ emissions” - Rt, Hon Nick Raynsford MP, Minister with responsibility for Building Regulations 2002

Advantages

• Construction is faster, with a home often weather proof in 4 to 6 weeks after work begins.
• A wide range of U-Values can be achieved depending on Building Regulations and the required level of thermal performance.
• Excellent thermal efficiency (potentially better than masonry construction)
• Potential for easy future renovation
• Pre-fabrication enhances quality control due to off site manufacture, thereby reducing the risk of on-site workmanship problems.
• Relatively lightweight requiring reduced footings and foundations compared to masonry construction.

Knauf Insulation Products

• Crown FrameTherm: a lightweight unfaced glass mineral wool available in both slab and roll form in a number of thermal conductivities.
• Crown DriTherm Cavity Slab: a lightweight semi-rigid slab of noncombustible glass mineral wool having a water repellent additive.
• Knauf Breatheline: a breathable membrane with a polypropylene non- woven coating on both sides.
• Polyfoam Linerboard is a laminate of Polyfoam high performance 100% ozone friendly extruded polystyrene, rigid board insulation and 9.5mm plasterboard.

Summary

 

Typical U-value requirements for external walls in new build dwellings :

	U-value (W/m2K)
England, Wales & NI	0.27
Scotland	0.25
Ireland	0.27

The importance of condensation control

A vapour control layer is essential on the ‘warm’ side of the insulation to reduce the risk of condensation forming. The vapour control layer may be incorporated within the plasterboard or installed separately. Joints should be as few as possible and sealed, with special care taken around penetrations for services.

A breather membrane on the outside of the sheathing is also necessary to protect against water penetration whilst allowing water vapour to escape. As a rule of thumb, the vapour resistance of the materials on the ‘warm’ side of the insulation should have at least five times the vapour resistance of the materials on the ‘cold’ side of the insulation. Or, calculations should be carried out to assess the risk of interstitial condensation by referring to BS 5250: 2002.

 

In some timber framed systems, such as the Twin Insulated Crown FrameTherm and Crown DriTherm Cavity Slab systems, the insulation in the cavity maintains the timber frame above the dewpoint temperature thus reducing the condensation risk even further. If in doubt call the Knauf Insulation Technical Advisory Centre for a free condensation risk calculation.

A half hour fire resistance in domestic external walls is required by the Building Regulations. Timber frame walls with mineral wool insulation are ideal for meeting this requirement. In most timber frame construction the cavity must be divided with cavity barriers in order to reduce the risk of fire spread.

 

In the Crown FrameTherm and Crown DriTherm Cavity Slab full fill system, cavity barriers are not necessary because the cavity is completely filled with non-combustible mineral wool insulation (this has been tested and assessed by TRADA Technology Ltd (report RD92061) – available on request from Knauf Insulation).

Building in timber frame provides the designer and homeowner the scope for easy future refurbishment and or extension.

1) Single layer – Crown FrameTherm between the studs

External wall panels to be insulated between studs using Crown FrameTherm 40/38/35* ......mm thick (*delete as necessary). Insulation to be cut as necessary and friction fitted between studs.

The breather membrane stapled*/ nailed* to the sheathing and extended below the lowest timber member. (*delete as necessary)

Cavity barriers and fire stops should be installed as required to meet the Building Regulations.

Alternatively, refer to NBS clause: P10/210

2) Double layer – Crown FrameTherm between studs and Polyfoam Linerboard

External wall panels to be insulated between studs using Crown FrameTherm 40/38/35* ......mm thick (*delete as necessary). Insulation to be cut as necessary and friction fitted between studs.

The wall panels to be lined internally with Polyfoam Linerboard, ......mm thick within integral 9.5mm vapour check plasterboard, nailed/screwed* to the timber studs at maximum 150mm centres. (*delete as necessary)

The breather membrane stapled*/ nailed* to the sheathing and extended below the lowest timber member. (*delete as necessary)

Cavity barriers and fire stops should be installed as required to meet the Building Regulations.

Alternatively, refer to NBS clause: P10/210, K10/205

3) Double layer – Crown FrameTherm between studs and Crown DriTherm Cavity Slab in the cavity

a)Twin insulation full fill system:

External wall panels to be insulated between studs using Crown FrameTherm 40/38/35* ......mm thick (*delete as necessary). Insulation to be cut as necessary and friction fitted between studs. The breather membrane stapled*/ nailed* to the sheathing and extended below the lowest timber member. (*delete as necessary)

Cavity formed between internal and external leafs to be fully filled with Crown DriTherm Cavity Slab ......mm thick. The lowest run of wall ties to be located at 600mm centres horizontally (at a level to be decided by the specifier). Ties thereafter to be at 450mm centres vertically and at 600mm centres horizontally. All work to be in accordance with manufacturer’s instructions.

Alternatively, refer to NBS clause: P10/210, F30/150

b)Twin insulated part fill system:

External wall panels to be insulated between studs using Crown FrameTherm 40/38/35* ......mm thick (*delete as necessary). Insulation to be cut as necessary and friction fitted between studs.

The breather membrane stapled*/ nailed* to the sheathing and to extended below the lowest timber member. (*delete as necessary)

Crown DriTherm Cavity Slab ......mm thick to be fitted against the breather membrane on the face of the sheathing and held back using insulation retaining clips fixed to the wall ties.

The lowest run of wall ties to be located at 600mm centres horizontally (at a level to be decided by the specifier). Ties thereafter to be at 450mm centres vertically and at 600mm centres horizontally. All work to be in accordance with manufacturer’s instructions.

Cavity barriers and fire stops should be installed as required to meet the Building Regulations.

Alternatively, refer to NBS clause: P10/210, F30/151

 

 

Residential Timber Frame External Wall Solutions
Timber Framed Wall - Insulation Between Studs | Double Layer Timber Framed Wall | Twin Insulated Timber Framed Wall