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All too frequently customers are told by timber framing companies that you can’t glaze directly onto green timber frames but must have the glazing in its own joinery frame and set into the structure. This just isn’t the case and they’re often relieved to see the system we use. Indeed we would strongly recommend against setting the glazing into the green frame because as the timber dries and settles over time the movement in the timber can crush or twist the glass to destruction.
We use a double seal, pressure equalised system similar to that used on multi storey office blocks. In simple terms the ‘double seal’ means that water is allowed to penetrate the first seal and then drain away through a series of channels. ‘Pressure equalised’ means that as water is allowed to escape from the channels air is allowed in which prevents the build up of water in the channel through surface tension. If this isn’t allowed to happen buffeting of the glass by the wind can set up a pumping action and water in the channel will be forced past the second seal.
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Arched braced trusses are probably one of the most majestic forms of truss and we get asked to incorporate them into timber frames on a fairly regular basis. Interestingly this presents frame design and timber engineering challenges that aren’t well understood by many people. The arched brace truss was traditionally designed to be buttressed on each side either by timber aisles or by very thick masonry walls, which in turn were often buttressed. Why? Well, from an engineering perspective the bracing is tucked right into the intersections of the posts and principle rafters and provides very poor triangulation for the forces in the frame. This makes them prone to spreading and in some period buildings there are signs that they have failed to some degree.
Having said this I wouldn’t want to put anyone off them as a style of frame. Obviously if the building is wide enough then aisles can be incorporated down either side and properly engineered these are likely to provide sufficient buttressing in their own right. In addition it’s possible to incorporate some hidden stainless steel reinforcement to ensure the frame doesn’t spread in the next few hundred years!
More blogs by Andy Parker
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