It was Emperor Marcus Aurelius Antoninus who said we should never be satisfied with superficial knowledge. Absolutely. So without wasting time, let us ride the wave of this counsel before it break on the heads of those who have chosen to ignore it. Roofing is much like a building foundation- it is both relatively expensive and easy to make costly mistakes. What you want to avoid is a leaking roof or one that threaten to be blown away whenever the there is strong wind. Which is why you should never save money by hiring second rate or unqualified roofers.
Erecting a gable roof should follow on the heels of a building walls completion. This sequence in important because while the load-bearing walls shoulder the weight of the roof, the roof on the other hand provide stability to the wall. In the absence a roof the top courses of wall will be weaker and may even pose a risk of collapse.
The process tees off by the Mason fixing the wall plates on the wall. Then the roofers takes the lead role by first measuring the position of the wall plates and transferring them to the rafters. The rafters are the main load-bearing timber beams in a roof which are cut to fit the ridge and over the wall plates.
Second, the ceiling joist are craned in place and nailed on the wall plate. Joists are horizontal beams that run t across from one wall to the other, on which both the ceiling board and a pair of rafters are fixed.
Then two A frames are prepared, with space for ridge board and brace nailed to them to make it easy to handle them. The A frames are craned into a vertical position at either end of the roof and nailed for good , into the wall plate and ceiling joist. To hold the A-frames upright , makeshift braces are used.
Fourth insert the ridge board on the pair of A frames and nail it in again for good. Once the structure is stabilized with temporary braces, install a series of a pair of common rafters by fixing them with nails on wall plate and the ridge board, along the length of wall. Fix the purlins-which are timber beams that run across and provide support to the rafters in their mid sections. For an overhanging verge, a gable ladder must be installed on the last common rafters.
Fifth , apply the cover which may be clay tiles or corrugated iron sheets. For iron sheet covers, the roofer must see to it that all overlaps and the exposed roofing nails are not sources of rainwater leaks. Once the cover is properly installed the masons is called in again to finish gable end walls.
Finally a skilled carpenter is called in to finish the roof at the verge and eaves with fascia board and soffit.
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Sources: Carpentry &Joinery by Peter Brett.