Box Gutters Can be Bad

Our house requires a box gutter, as we have kept the roof line low with two ridges instead of one. Box gutters are called box gutters, as they are often folded with right-angles at the bottom (so the cross-section is rectangular) and are often seen where the roof meets a parapet wall. In our case the folds at the bottom are a much bigger angle than 90 degrees, but its still called a box gutter.

I designed the gutter, by referring to the Australian Building Code. It provides tables giving 100-year rainfall intensities for various parts of Australia. However, it usually happens that the 100-year-rainfall-event ocurrs the week after you move into the house! So to err on the safe side, our box-gutter has 5-times the capacity of the 100-year rainfall event. I hope it never overflows, as it would make a mess inside.

The gutter sits on timber-flooring (left over from the platform flooring) fitted into the top-chords of the roof trusses. This means you can walk along the gutter without damaging it -- that's very useful for maintanence. Personnally, it looks wide enough to have a tea-party up there....

All the water from the box-gutter flows onto a short section of slate-shingled roof, so we are going to put flashing over the top of the shingles, as it is too much water for shingles to take.