Wood is a living thing that continues to respond to external elements. This same quality that gives its natural beauty also causes some disadvantages during and after it has been processed. Structural timber must go into controlled drying before it can be used. Even after the drying process, once the timber is used to make a final product it will need to adjust to its surroundings. If the environmental conditions continue to change such as being in the outdoors, the wood will keep on changing: It will shrink in summer, expand in damp seasons and in the midst of that change it will twist and bend and crack. Therefore the product made out of such wood will not be reliable.
Glulam is a type of structurally engineered wood product where a number of layers of certain sizes of timber are bonded together using a moisture-resistant bonding agent. The fact that the layers comprising the Glulam are from different sections of a tree means that the imperfection of one layer is compensated by the other layer and each layer would effectively lessen the movement of one another. And since they are unlikely to all move in the same direction, the end product would not lose its shape, get twisted etc. Glulam is therefore is known to be more reliable than a single solid sawn beam of the same size.
Glulam also creates endless possibilities aesthetically as the texture of different layers result in different looks. Its use architecturally has increased rapidly as it is stiff and sturdy and can be bent and shaped. It is able to make longer arches than traditional heavy timber and not require a supporting beam or post.
Ecologically, it is also reported to be more sustainable. It allows younger trees from plantations to be used effectively therefore is decreasing the cutting down of ancient forests.