Mounting rail, spruce, dry, 30x45x3000/6000mm - manufacturer's price

The frame rail is the foundation of everything. Everything rests on it, and if it's so-so, the entire structure will be... not quite right, to put it mildly. A quality rail is a direct investment in the peace and stability of the future structure. After all, who wants everything to warp or fall apart in a year or two?

What does a frame rail do? Well, firstly, without it, there won't be a level surface, meaning the finishing materials won't lay crookedly. Secondly, it provides the correct gaps so everything can breathe and prevent cracking from temperature changes. It also distributes the load evenly, meaning there won't be any point pressure or risk of sagging. And, of course, there are no voids for utilities—where would we be these days?

What makes a good rail? Kiln-dried—because when it's raw, it "flexes" and everything moves. Geometry is important—so you don't have to fiddle with the installation; just a quick fix. Big knots? No need, thank you. They only weaken and can stick out sideways. The surface should be smooth, without any major defects—that's a must-have.

In short, if you make the frame from a proper rail and assemble it properly, you can forget about repairs for ten years or even longer. It'll save your nerves, and it'll look great.