When creating the openings for your doors and windows you need to create a beam above the opening. There are several ways of achieving this in garden room design. Although, we don’t suggest you replicated some professional garden room designers choice of using the door and window frames themselves as a support.
A double timber lintel is one option you could consider. You can take this a stage further and strengthen the lintel with a steel plate. This combination is known as a Flitch beam.
The Flitch beam is a sandwich of timber with the steel plate bolted in-between. These plates are relatively inexpensive, a 2.4m x 100mm x 10mm plate, for instance, costs £25 plus VAT & delivery.
The plates come in different thicknesses, depths and lengths and are pre-drilled for the bolts. All you have to do is drill your timbers and assemble the sandwich.