Hardwood timber: what is it and why choose it for your next project?

Glulam is made from a variety of timbers, both softwood and hardwood. The choice of timber is influenced by factors such as cost, design, suitability, and simply personal preference.  

Here we look at some of the differences between hardwoods and softwoods and share some recent hardwood glulam examples. 

How does hardwood differ from softwood? 

Hardwoods are wood from broad-leaved trees, the most common European ones being Oak, Maple, Walnut, Cherry, Beech and Ash, (although in our experience we haven’t been asked for maple or cherry yet). Softwoods on the other hand come from trees which usually have needles and cones. 

The structure of hardwoods is more complex than softwoods, visible pores are used for transporting water and nutrients, whereas softwoods move water around the tree using cells medullary rays, which do not have visible pores, and produce sap. 

Most hardwoods have a deeper or richer colour than softwoods, which tends to make them a popular choice for furniture and flooring rather than larger projects such as a glulam portal frame, but it does not mean it is not a great choice for some projects. 

Are hardwoods more durable? 

It varies – oak is very durable for example, but beech is not at all durable for outdoor use. We also must bear in mind that in the production of glulam a durable glue bond can be more difficult to achieve with hardwoods than softwoods. 

Hardwoods are denser than softwoods – because they grow more slowly, they have a greater density which helps with the increased durability. This also means they are heavier than softwoods (an advantage or disadvantage depending on your project). 

Is hardwood suitable for larger frames? 

When a tree is harvested it will contain a lot of water. The volume of water in a piece of timber can be measured and is referred to as moisture content. The moisture content of timber is expressed as a percentage of its weight when dry.   

Oak that has recently been cut (referred to as green Oak) typically has a moisture content of 60-80%. This timber is easy to cut and work with as it is soft and flexible – traditional timber frame manufacturers like using green oak for this very reason.  

However, it is very common to get a lot of splits and cracking in these Oak frames as they continue to dry out. These cracks are usually nothing to worry about structurally as the beams have usually been oversized to allow for this, but they can spoil the aesthetics and become a home for dust and insects.  

Does this mean I shouldn’t use hardwood for glulam? 

Not at all. If you have your heart set on a hardwood, we can reduce the amount of cracking and splitting by drying it out – hardwood is generally left outside under cover for 1-2 years to season naturally, and the larger the section of timber the more time it will take to season.  

Seasoned hardwood still has a moisture content of around 20-30% which is still too wet to produce glulam (glulam manufacture needs the moisture content to be below 15%) so the next step is kiln drying the timber – a special process that is done with care and control. 

It is very difficult to dry a big solid section of sawn hardwood down to a very low moisture content, however when we make glulam, we use smaller planks to make big sections. In the case of hardwoods, this allows us to dry the oak or hardwood down to very low moisture content and then bond together sections, which means we can make hardwood glulam beams for much larger structural sections. 

This the main benefit of using glulam if you want to use hardwood, as opposed to solid hardwoods for building frames. You get a much more stable frame, and if you do get cracks in the glulam beams, they’ll be much smaller than the cracks you can get in solid hardwood beams and less likely to spoil the visual aesthetic. 

 Some curved Oak glulam beams in production ready to go to a project in Hertfordshire 

Why is hardwood more expensive? 

The rate of growth for a hardwood is much slower than a softwood. It takes more time, space, and resources for a hardwood tree to reach its full felling potential compared to a softwood.  

Hardwood is slower to grow, and as mentioned above it takes more time and resources to dry to a low moisture content. Softwoods however are easier and quicker to grow, easier and quicker to dry to a lower moisture content, which makes them more affordable all round. It is the additional time which makes hardwoods more costly to work with. 

Hardwood glulam examples:

1. Equipoise House

Featuring a Sweet Chestnut lattice roof structure. This is a CGI image of a proposed project in design.

Images shared with permission from Hyde + Hyde Architects: https://www.hydearchitects.com/equipoise-house

2. Great Sidelings

A residential project using Larch externally and UK grown Beech on the inside. 

3.Private residential project

A residential extension featuring Ash roof beams.

You can find more examples over on our project page. If you have a hardwood project in mind and would like to talk it through do get in touch, and we’ll be happy to help.