A simple test of your roofers knowledge! August 1st, 2017. Welcome to ORCN, find local pre-screened roofing contractors here or with our free app "Oregon Contractors".One way you can test your roofers knowledge of his job: Ask them if they are cutting the tabs in the valley. If they say sure with a question on there face ask them why the tab needs to be cut. Answer: If the tab is not cut, the rain water can be caught on the tab as it goes down the valley, once this happens the water will follow along the top of the shingle (under the top layer of roofing) tell it finds away down hill (gravity). This will cause A LEAK.The tab on the top of this shingle has been cut. This will stop the rain water from catching the top of the shingle. notice the shingle does not come to a point at the top.Many roofing manufactures now put these instructions on each bundle of roofing because it is such a problem.Once the valley is installed you will not see the cut tabs. But very important to do.