New Pergola roof - Concept and drawings
The pergola canopy was a great success and, but as described previously, we needed to think about it's replacement.
The flexible canopy was a test piece and it worked well for shading, but because of the edge seam, rainwater ponded near the lower edge. This would be a problem with another flexible sheet. A rigid sheet was the answer, but we didn't like the polycarbonate sheeting that most lean-tos were made of. And they wouldn't give us the shading we required.
The existing sheet also stopped short of the pond, which had enabled us to grow a Wisteria along the front. Instead of a new sheet discharging into the pond, we now wanted to keep the Wisteria. How could we resolve the issues?
In June 2006, the redesign process came to a head when the South-East suffered the latest in a series of 'highest temperatures on record'. We had the usual hose pipe ban, but this time a drought order imposed. We needed to collect more rainwater and the canopy was larger than the garage, which we already diverted to a water tank.
The answer (like most good ones) came in a flash .... TWO roofs. An upper rigid roof to collect the rain efficiently and a lower, shading sheet for shade and to create the plaster ceiling effect at night.
The upper roof would require a new frame which would be thick enough to allow a gutter, behind the Wisteria, to collect the rain. The new frame would be fixed at the ends only, allowing a shading sheet to be slotted underneath. And even removed in the winter to let more light in. A real Eureka moment!
The existing structure
The proposed 'Extension' frame
New and old together. The gap between the two is where the shading sheet goes
The plan, showing the 3m long roof sheets set out spanning between the main rafters and the gutter position. The purlins were required for roof sheet fixings, but because of the long spans of the new rafters, they have become more useful as frame spacers / stiffeners.
What the plan doesn't show is that the roof isn't square. This wasn't a surprise, as a 100mm (4") difference in the patio was found when the pergola was built. Basically, the patio is 100mm bigger (house to pond) on the left, so the pond is not parallel to the house.