Technical
Structural floorboards for timber joists and their weather resistance
Interior view of a residential building under construction with exposed wooden framing, OSB subfloor, and large windows letting in natural light.

Introduction

This technical document provides additional guidance relating to how the functional requirements in the Technical Manual may be satisfied in relation to appropriate protection when structural floorboards for timber joists are exposed to the effects of weather on site.

What are structural floorboards?

Structural floorboards by type and thickness are defined within the Technical Manual as follows:
Joist centres
Board Type 400mm 450mm 600mm
Softwood 16mm 16mm 19mm
Particle board (chipboard) 18mm 18mm 22mm
Oriented strand board (OSB) 15mm 15mm 18mm/19mm
Plywood 15mm 15mm 18mm/19mm
Please note: This table applies to normal domestic loads (imposed loads of 1.5 kN/m2).

What are the warranty provider's concerns?

Where structural floor boards are built in as the work proceeds they are often exposed to the effects of weather. This leads to concerns around how the long term durability, performance and service life of the boards is being affected.

Warranty stance

Failure to provide appropriate protection to structural floor boards or using materials that have tested weather resistance capabilities but without protection is considered to compromise the ability of the floor construction and associated materials in meeting with the functional requirements and performance standards stipulated by the Technical Manual, notably those relating to durability and expected service life.

What developers should action after reading this article

Developers should ensure that all materials, products and building systems are appropriately tested and approved for their intended purpose.

As part of any guidance issued for their materials, manufacturers will state how their structural floor boards should be stored, installed and protected correctly in a manner that will not cause damage or deterioration of the product.

Where the developer has determined that the structural floor boards do not require protection during the build process, the warranty surveyor may require evidence of a third party product approval certificate from a UKAS accredited organisation which confirms the weather resistance performance and the period of time the boards are to be left exposed on site.

Any boards that are left exposed, either without protection or beyond the period stated in the third party product approval certificate for boards that do not require protection, will need to be replaced. 

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Disclaimer

This technical document has been prepared by Premier Guarantee exclusively for the benefit of our registered customers. Its sole purpose is to provide guidance on the utilisation and interpretation of technical requirements pertinent to the warranty cover offered by Premier Guarantee.

Please note that this document is not intended for circulation or use beyond the aforementioned purpose. The information presented herein is for general guidance only and does not constitute professional advice. Registered customers and any other party accessing this document are advised not to rely solely on the information contained within.

Nothing in this document is intended to establish, nor should it be construed as creating, any contractual or legal obligations. In the event that any third party chooses to rely on the information provided, they do so entirely at their own risk. Premier Guarantee explicitly disclaims any duty of care or liability that may arise from the use of or reliance on this document by any third party, howsoever arising.

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