We carried out extensive testing during the development of our product to ensure that there is no reduction in flow rate so that the gutter still complies with its British Standard approval.

The testing that we carried out confirms that the Gutter Clear product creates no restriction in the flow rate.
All gutters are manufactured with a British Standards approval for flow rate.
If a gutter filter product is placed into the gutter it will reduce the flow rate and therefore not comply with its British standard approval and a new installation will be outside of building regulations
GutterClear tested many products on a test rig at leading UK gutter Manufacturer. The test rig used measures the flow rate of the water through a gutter by a metered flow of water over a specified area of roof section of the test rig.(see clip)
The result of the testing was that any obstruction within the gutter causes a significant reduction in flow rate which meant that the gutter no longer conformed to its British Standard Approval for flow rate.
Products tested included a Gutter Foam strip which led to a 30% reduction in flow rate and a Gutter Tube (which was a plastic mesh tube that fitted into the gutter) which resulted in a 15% reduction in flow rate.
A Gutter Brush type product would fall somewhere between these 2 and I estimate it would cause a reduction in flow rate of between 20-25%.

It has also been reported that the Gutter Brush type of solution can block with leaves over a relatively short period of time , which will reduce the flow rate even further.

The reason that people are installing Gutter protection is to stop the gutters blocking with leaves and reducing the flow rate. If the flow rate is reduced then a gutter can overflow and cause serious building damage. If the Gutter Brush product has caused a reduction in flow rate which has resulted in building damage then surely this is no different to the reduction in flow rate caused by a blockage of leaves and there could be liability issues?

Another product which is widely distributed is a flat rigid plastic mesh product is that sits below the top edge of the gutter and the material is quite thick. . I would estimate that this product would create a reduction in flow rate of between 10-20% if it were tested. If there were high rainfall conditions and the gutter overflows and causes building damage because of the reduction in flow caused by the gutter mesh, then there could again be serious liability issues

The GutterClear product fits above the gutter and therefore will not reduce the flow rate of the gutter at all and the gutter should still comply with its British Standard approval

In some cases the mesh may curve into the gutter slightly which may cause very minimal reduction if flow rate (but not enough to impact approval flow rates)