Architectural Technologist – Two different roof types in one roof

September 9, 2009 in CAD, Vectorworks

: Image by Scays via Flickr

Its always the same, a simple survey and you get this, two different roof types in one roof, OK so I admit, its an old barn about C 1750, and its already been hacked about in the past, but I saw it and though, just how interesting it is. First there are two slightly different roof constructions, and second see how the purlin span has been reduced but the use of splayed braces, a trick you often see on older roofs. Look carefully at the timber capping to the top of the wall, the photo just about shows the added shoe detail, that’s been rounded and shaped, a nice feature. So why are there two different roof types, well the answer is simple, no builders yard in those days, the carpenter took what he needed from the local forest, and made it fit, so no two roofs were ever the same. Or he simply made good use of an existing timber truss he had from another roof, no waste here. Oh and all dry fitted with pegs and solid mortise and Tenon joints.

The CPD here is simple, research roof types and learning about mortise and tenon timber joints, and peg joints, not what you might expect, offset holes in the tenon, to the mortice, strong pegs to pull the joint together. Load spread within a roof truss is another area, purlin spans from trada, and can we still use the extra brace to reduce the spans.