Thursday, October 25, 2007

Wall plates installed

On Tuesday of this week the builders spent the morning fitting the wall plates (also called 'sole plates'). In timber frame construction these set out the plan of the ground floor layout and form the interface between the walls (both external and internal) and the ground floor slab/foundations.

The wall plates comprise timber of the same width dimension of the wall panels they support (ie. 140mm and 89mm), and are simply cut to length and laid on a bed of mortar (and damp proof course at the outside walls).

Whilst an apparently straightforward process, locating the wall plates in the correct positions is critical to the ultimate accuracy of the frame installation.

As an aside, this process also introduced a simple but effective airtightness detail to the building, in that the overhanging damp proof membrane (from under the slab) is folded back over the slab at the edges for later trimming and connection to the vapour membrane to be installed on the inside of the wall panels. Whilst not an essential detail (and usually omitted), this ensures an airtight and flexible linear floor/wall joint that should last through the first few years of the building 'settling' and drying out, a process often responsible for significant degradation of airtighness as cracks open between differing materials (eg wood/mortar) and thus worsening energy efficiency. Polythene membrane, being a flexible material, withstands this movement.

As an aside, airtightness is a key component to low energy building design alongside insulation, the minimisation of thermal bridges, orientation and glazing. Coupled with this it is essential to have an effective ventilation system to ensure good air quality inside - more on this and other airtighness details as the house takes shape.

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