Smartflo gutter , in common with all enclosed gutters, has only a limited ability to handle the concentrated flow from conventional spreaders, which typically take the water from a large upper roof and distribute it through 4 or 5 50mm holes cut into a 500mm length of downpipe mounted horizontally.
While this arrangement is satisfactory for an open gutter, the entry points for Smartflo gutters are spaced at 500mm (to restrict the inflow of airborne dirt), and consequently the whole of the concentrated flow is focussed on only one or two entry points leading to localised overflow.
The ideal solution, from the point of view of drainage and water collection, is to contain the concentrated flow in a downpipe running laterally down the lower roof, and cut into the top of the lower gutter.
This means the filter holes for the lower gutter only have to cope with the water from the lower roof, and the water from the upper roof is directed into the lower gutter through a new, larger aperture.
A less effective alternative is to cut additional filter holes into the top of the lower gutter, immediately below the spreader, to locally increase the draining capacity of the top of lower gutter.
Each 500mm spreader should be draining into at least five filter holes. While this solution is less visible, it is also less effective in heavy storms.
In the residence shown above, the high roof (approx 70m² on each of four sides) is drained by two 100x50mm downpipes running laterally over the lower roof and cut into the lower gutter.
The filters on the lower roof need only drain about 38m² per side, and then two 100x75mm downpipes on each side take all the water from both the high roof and the low roof to tanks at the rear of the house.