Book Description

This Information Paper describes research carried out on visual methods to assess the strength of Douglas fir. Current standards for visual grading use the growth rate (ie width of growth rings) to draw conclusions for wood density, but testing the wood density of samples grown in various parts of the UK found that these standards underestimate the mean density. This often results in capable structural timber being downgraded and used for lower value applications. Using the ratio of earlywood to latewood in the growth rings can be used successfully to assess the wood density, and this alternative method would lead to less wastage of serviceable structural timber. The use of Douglas fir in structural applications is also briefly considered. This Information Paper is aimed at timber processors and users of timber products, as well as designers and architects considering using UK-grown Douglas fir for their projects. After reading this they should be inspired to use a material that supports part of the UK’s sustainable rural economy and have the confidence to specify Douglas fir in structural applications.

Contents:
IntroductionResearch findings
-Density distribution based on the growth rate meeting the criteria in BS 4978:2007
-Determining the ratio of latewood to earlywood that would meet the density requirements for the C24 strength class
-Results for a ratio of 20% latewood:earlywood ratio
-Results for a ratio of 30% latewood:earlywood ratio
-Results for a ratio of 40% latewood:earlywood ratio
Grown in Britain: the home-grown timber supply chain
-Carrochan: The Loch Lomond and Trossachs National Park HQ-Mildenhall Warren Lodge, Suffolk
-Elleray Preparatory School, Windermere-Southern Timber Offices, Newton Abbot
-Contemporary farmhouse, East Anglia
Conclusions and recommendations
References 

A4, 8pp, 6 drawings, 10 photos