The modern, usual method of constructing a house roof is to use factory assembled roof trusses that have been designed using a computer aided design (CAD) modelling tool. This is generally quite economical for simple roofs since the trusses can be fabricated from lightweight lengths of timber of small cross-section. Economy is achieved through minimising the amount of material and by achieving a commonality of truss so that the roof is implemented using a repeated number of the same truss design. This repetition in the manufacture of trusses is ideally suited to low cost factory production techniques. The disadvantage of this method of construction is that generally a large number of cross braces are required in the truss design to achieve the required strength from the lightweight timber sections. This coupled with the frequency with which the trusses must be placed renders the enclosed roof volume fairly unusable because of the intervening trusses and their cross braces. To my mind a roof of this sort of construction resembles “knitting in match-wood”; cheap construction but the roof void becomes unusable for anything substantial.
In the case of the Ridge End roof, examination of the plans, elevation and sectional drawings in the “Architectural Style and Floor Plans” page of the blog shows that the roof is a complex structure. Firstly it comprises four main intersecting ridges that run with the perimeter of the building with a flat roof area in the centre of the building over the central staircase. Additionally there are two octagonal bay sections to the front of the house along with an intersecting triangular gable over the central part of the front, necessitating yet another intersecting ridge. To complicate things further, closer examination reveals that the roof ridges to the front and rear of the building are slightly lower than the ridges over its two side wings. This degree of complexity means that a large number of different truss deigns would be required and that there would consequently be few repeated trusses. If such a construction method had been adopted it would have still required skilled carpenters to assemble the roof and construct in-situ the parts of the roof not amenable to factory production. The resulting increased design cost and scope for cock-up seemed to outweigh the advantages of a factory produced truss design approach. We therefore decided to fabricate the entire roof as a “cut in -situ” traditional structure with ridge beams and rafters fashioned as necessary by skilled carpenters/joiners. The side advantage of this method of construction is that it produces a roof void space that is wide open. This openness makes the useable for installing the various mechanical and electrical items that will be the subjects of future bulletins, whilst allowing easy access for future maintenance and repair. Moreover the open roof space provides an attic space that allows a huge amount of storage should it be necessary in future.
We would have preferred to have had a slightly higher roof pitch. Unfortunately our planning permission restricted the overall height of the building to be no more than 1metre higher than the current house. With a ground floor ceiling height of 3.1metres and bedroom ceiling heights of 2.7metres this restricted the roof pitch to 28 degrees. This angle added to the complexity of the build since a lot of trigonometric calculation was required to determine the various rafter forms. Thank goodness for CAD tools! An unfortunate consequence of the 28 degree roof pitch is that the internal height of the roof space is quite low meaning that movement through the roof void will be at a “stooping walk”. Nevertheless a large useful space has been achieved.
I believe that it is remarkable that just about the whole of this complex structure was accomplished by just two men; Niall, a highly skilled craftsman, aided by his apprentice, Lee. The really remarkable aspect is that Niall is just 24 years old and owing to his all-round capability has become the principal overall craftsman/carpenter on the project.