North Eave

A problem with our house design is the lack of any roof overhang on the north side. There is instead a timber pergola. The idea was to grow deciduous vines on it for summer shade. And we did grow a grapevine, but it was chewed into irrelevance by the local possums. (We tried many things to stop them.) Another option was to put up shadecloth in the summer seasons. I did that for a few years but it was quite troublesome. The rolls of shadecloth were very long and it’s all awkwardly high.

Having no eave meant that:

• summer sun penetrated directly into the house. Every square metre of direct sun on windows is like a bar radiator. So shading should be the first priority for managing overheating.

• windows had to be closed in rain because rain could come straight in to our casement windows. On summer nights that meant closing off cooling cross-ventilation.

• window frames bore the full brunt of weathering: rain and summer sun. Several of our window frames have already cracked and rotted significantly (despite regular repainting).

• we didn’t have a covered entry (at least on that side), which is not very welcoming when it rains.

One should consider whether a structure can withstand the wind load from roof sheets. Our house is well protected from wind: it is low-set, in a topographic depression, surrounded by trees and other buildings. The pergola beams are strong (120mm) and well secured.

Practically speaking it could hardly be easier. Just lay some metal roofing sheets on the pergola beams and screw them in. The only question is how deep the eave should be.

• in midsummer the sun is directly overhead so even a small eave will stop direct sun.

• in winter the sun is at a low angle and an eave will not block much sun (being well above the window head).

• shoulder seasons are the times when a compromise must be made. For example, Autumn:

Average temperatures in April are 7º night – 20º day; this is around the time of year when direct sun starts to be desirable. The shadow diagrams above show that a 1500mm eave is not blocking too much. So 1500mm (2 roof sheets wide) it is.

First of all I treated the tops of the pergola beams with a bitumen waterproofer. This is to prevent cracking and water intrusion. I should have done this years ago.

The pergola structure already has a 6º slope which is good for drainage. At one end I put up a standard gutter.

The other side of the roof drains to a valley. I had a small box gutter made up to fit there.

Finally, here is the effect in summer, before and after.

No more direct sun. It’s good not to have to close the curtains during the day.

The roofing sheets cost $620 (total length 30m), the gutter $60, and the box gutter $50.