Understanding Timber Grades: What Does It Mean for Your Project?

At UK Timber, one of the most popular questions we hear is: "I am looking for some timber for my project; but what is the difference between the various different grades?"

This question is quite understandable. While browsing for structural oak beams, Douglas fir for constructions and other species of timber, you will frequently see mentions of such grades as C16, C24, TH1, TH2 and other letter-numeral combinations which are likely to cause confusion.

However, in our experience in dealing with different kinds of timber and the various grades, we have learned one thing: knowledge of grades matters. Without it, you could end up with a timber which is too strong or, conversely, insufficiently strong to suit your needs.

So stick with us as we give explanations as to what timber grades are and what they are needed for.

What Exactly Is Timber Grading?

Grading is a quality control procedure which also implies classification of timber according to the strength parameters. During grading, the characteristics of timber are estimated; namely the number of knots, grain angle and direction, growth rate, the presence of splits, the amount of wane (bark edge) and some other characteristics.

Thus, the grade of a certain timber piece will indicate its capabilities. Contrary to the opinion of many people, a lower-grade timber can look beautiful while a higher-grade timber can have knots and other visible defects; however, the latter will possess higher strength and stiffness.

Why Do Grading Matters? This is important since according to regulations and specifications by engineers or architects, certain grades should be used in constructions. Choosing the wrong grade will imply breaking of those rules or overspending.

The Two Common Grading Types Used in the UK

When working in the UK, you will usually encounter two types of timber grades:

Softwood Grades (C-grades): This type of grading implies carcassing and structural frames. The following grades are widely used here:

• C16 – general structural grade

• C24 – higher structural grade

C16 is commonly used in domestic construction works while C24 is approximately 50% stronger than C16 and thus should be chosen where load-bearing is crucial.

Hardwood Grades (TH/D-grades): This type of grading implies oak and other species of hardwood. You will see the following grades:

• TH1 / D40 – highest structural grade for hardwood

• TH2 / D30 – good structural grade for most purposes

• THA/THB – appearance grades (THA has the highest rating in terms of appearance)

While "TH" denotes temperate hardwood, "D" refers to density-related strength classes.

What Makes the Same Tree Produce Different Grades

You will be surprised, but the timber from one tree (even one log) can receive different grades depending on the position within the tree.

For instance, if you cut an oak beam near the centre of a mature oak tree with narrow growth rings and few knots, the timber will be graded as TH1; however, in case you cut the beam near the branches where there were more knots and irregularity of the grain, the result will be different, i.e. TH2 or worse. However, both pieces are made of the same wood.

That is why, in order to supply you with, for example, 20 oak beams, all of which should be graded TH1, we will need to choose from a wider range of sawn timber pieces.

The Cases Where Grade Matters (And Where It Doesn't)

Grade is important in the following cases:

• In all structural applications (roof beams, floor joists, load-bearing posts);

• In case your project requires approval by Building Control;

• According to the specification of an engineer/architect;

• If you need to replace structural timber beams of period buildings.

In these situations, certified grade-stamped timber will be necessary; otherwise, you cannot succeed in completing your project successfully. However, there are also cases where grading does not matter:

• Oak beams used only for decoration (railway sleepers in landscaping, e.g.);

• High-quality cladding;

• Decorative timbers;

• Garden structures (where appearance prevails over certified strength of timber).

For these purposes, you will require timber which fits well aesthetically while the question of grading is secondary.

Cost Considerations

Obviously, higher grades cost more. In order to provide you with timber graded TH1, we have to:

• Choose the appropriate timber from a log;

• Let a TRADA-qualified grader evaluate your timber;

• Maybe even reject some pieces of timber which fail to meet the criteria;

• Make sure of certification and provide you with grade marks.

As you see, these actions take time and effort. Consequently, for instance, an oak TH1 beam will cost you 30-40% more than a similar-size TH2 beam. In case you need structural timber with a specific grade, we can hardly reduce its price; however, if you purchase graded timber for decorative purposes, you are wasting money unnecessarily.

We have faced a situation where our client insisted on TH1 graded oak for landscaping purposes; however, this was unnecessary in the given case.

The Most Frequent Myths about Timber Grading

"Higher grade = better appearance" – Not necessarily. Grade is the indicator of structural capability of timber rather than an appearance. You will be surprised to know that sometimes TH2 oak can look more attractive than TH1; it will have more character knots and finer grain.

"Specialist suppliers sell only graded timber" – Not necessarily. In many cases, timber is not graded while being perfectly suitable for use. Landscaping timber, planks for planters and boards for decorative purposes rarely require grading.

"You can easily determine the grade by observing the timber" – This is impossible. There are several characteristic features graders take into account and not all of them are visible; for instance, a knot location relative to edges and other things influence grading. Two identical pieces of timber may be evaluated differently.

"C24 is double better than C16" – The numbers denote the strength class of timber, and it does not mean that C24 is twice better than C16. In many cases, C16 is perfectly adequate while C24 is unnecessarily strong and expensive.

Choosing Grade Depending on Application

For new builds with the structural timber we normally advise:

• to use the specified grade (normally C24 for critical applications, C16 for framing);

• not to try to substitute or "upgrade".

When replacing the timber of period constructions, try to match or beat the existing grade of the timber. In case you have any doubts, consult a conservation officer. Normally, TH2 will be appropriate.

In the garden structures which do not require building control, grading of timber is not necessary. Focus on timber quality and treatment.

When using timber as an interior decorative element, the grade becomes irrelevant. Here the choice depends solely on what you want.

The Role of TRADA Certification

Our company uses TRADA-certified graders. This is essential in the process of grading. In order to be considered certified, one should have completed a rigorous examination process and obtain the certificate of qualification which has to be renewed periodically.

That is why TRADA-grade timber has legal status and allows you to satisfy the requirements of Building Control service. Not all timber sellers employ TRADA-graduates, and thus the question becomes vital in the situation requiring such graders.

Being able to grade our own timber in the sawmill, we can offer it to you at a better price since it is not necessary to transport it somewhere else for grading.

When Should You Consult Us?

If you are unsure about which grade is appropriate for your project, ask us before placing an order. We prefer spending a couple of minutes explaining the grade characteristics rather than seeing you purchasing the wrong timber.

Your architect or engineer can specify the required grades in the plans. However, in case you are working without professional specification while having to deal with timber constructions, we can strongly recommend consulting an expert. The reason behind timber grading lies in safety and functionality of timber in particular projects.

We can assist you in choosing the right type of timber depending on your project, loads which the structure will have to bear and environment. Some cases require ungraded timber while others necessitate a specific timber grade.

Planning a Project Involving Timber? Talk to Us!

In case you plan to complete a project which requires structural timber, we are glad to offer our services. We have TRADA-certified employees who can help you select an appropriate grade. Contact us at 01536 267107 to learn more.