From the Archives

Please note: this article is no longer being maintained by LABC Warranty. It may therefore contain information that is out of date. For up-to-date technical guidance, please visit our Resource Hub or refer to the latest edition of the LABC Warranty technical manual.

Tech Update: Timber Strength, Storage and Grading

Timber is a key component in a broad range of builds as it’s sustainable, lightweight, durable if properly treated and available in abundance. However timber requires extra care to be taken in its storage and preparation. If that care is not taken from the beginning of the build the timber will degrade quickly, require replacing or potentially cause structural issues.


Timber should always be stored in the proper way to ensure it does not deteriorate. This involves keeping it dry and covered in colder conditions so as to prevent surface freezing and keeping it off the ground and spaced to allow air to move around the timber freely. You should always keep timber stored flat so as to prevent it from warping or twisting over time. 

The diagram above shows the ideal way to store timber on site.

Durability and Grading of Timber

You should make sure that any timber used in your build is treated so it is able to resist insect attacks. Some species of timber have a natural ability to resist attack. Timber should be the appropriate strength to meet its design intention. For timber that’s intended to be used for structural purposes (e.g. floor joists, rafters etc.) the strength classification should be C16 unless appropriately stamped with it specific strength classification.


Timber treatment

Timber should ideally be preserved in a factory environment and should be approved according to the relevant Code of Practice or British Standard, or have third-party accreditation.


Pre-treated timber exposing untreated end grain

It is important that any pre-treated timber; which is then cut, exposing untreated end grain; must be re-treated before works continue any further.  Ideally, you should use a coloured preservative so it can be seen at a later date that the end grain has been treated.

Metal fixings

Metal components should be galvanised where they are to be fixed or used adjacent to treated timber.

Green and air dried/ seasoned Oak

Please note: For LABC Warranty purposes, Green oak, air dried/seasoned oak is not acceptable for external wall construction, frame, window/ door construction or internal wall or roof constructions, regardless of whether it forms part of the water proof envelope or not.


For further information on using timber you can download Chapter 2 of our Technical Manual:
The information used in this article is taken from Version 8 of the LABC Warranty technical Manual and is provided as guidance in meeting our technical standards. If working on an LABC Warranty site please check which standards apply.

Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.


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