What is a Sole Plate?

Sole plates are a critical component of timber frame construction. They provide the interface between a substructure and the timber frame superstructure.

Sole plates are usually the first timber components to be installed in a timber frame construction. They provide the basis from which the rest of the superstructure is erected, ensuring the superstructure is level and positioned correctly. Sole plates also assist in transferring loads to the foundations.

A crucial interface between foundation and frame

Omitting the sole plate from a timber frame design is not recommended as this makes it more difficult to accurately locate, level and fix the wall panels or floor joists.

Setting out and installing the sole plate is the first – and one of the most critical – stages in the erection of a timber frame. If a sole plate is correctly installed, the installation of all the subsequent elements should be fast and accurate. As such it is vitally important to ensure that sole plates are installed accurately and in the correct manner.

It is vital that the foundation is correctly laid to provide an accurate and level datum for the sole plate. If the foundation is not sufficiently level, then the sole plate must compensate for any inaccuracy to meet the necessary tolerances required to install the timber frame correctly.

Sole plate size and design

Diagram showing a sole plate and how it relates to other elements.

A single timber sole plate with a depth of 38mm is most often used for timber frame construction, though other sole plate thicknesses and configurations may be used – including double members fixed on top of one another.

The purpose of the sole plate – and the potential impact different configurations might have elsewhere – must be understood to design the sole plate specification accordingly.

Getting the alignment right

The correct alignment and packing of sole plates will:

  • Assist the effective transfer of horizontal and vertical loads to the foundations
  • Ensure the building is in line, level, square and plumb in accordance with agreed tolerances
  • Avoid compromising the building’s thermal performance

Whose responsibility is it?

The main contractor and timber frame erector must understand and agree their responsibilities for the installation of sole plates.

Only when the sole plate is installed in compliance with the agreed tolerances, or when a structural engineer gives additional instruction, should construction proceed beyond the sole plate.

Diagram showing bedding of a sole plate.

Durability and preservative treatments

The sole plate is the first timber member installed above the damp proof course. The need for preservative treatment depends upon the durability of the timber and risk of decay and insect attack.

Given their location, likelihood of exposure to moisture, and the difficulty of gaining access to the sole plate for inspection and remedial works, sole plates are recommended to have an approved preservative treatment, e.g., copper-organic types, in accordance with BS 8417 Preservation of wood– Code of practice.

In BS 8417, sole plates (above the damp proof course) are given as one of the examples of service situations for Use Class 2 (interior or covered but where wetting can occur).

The Use Class definitions are given in detail in BS EN 335:2013 Durability of Wood and wood-based products – Use Classes.

To read more about sole plates, see the timber knowledge sheet Sole Plates, exclusive to TDUK members.

This provides further practical information such as:

  • Recommended tolerances for sole plates
  • Relationship to the damp-proof course
  • Installation of a single sole plate
  • Installation of a double or twin sole plate
  • Gas membranes
  • Fixings for sole plates

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