Flat roof collects pool of water when it rains

You cannot stop it pooling unless you rest everything under the boards, so in reality a new roof with the correct fall in place before reboardling & recovering.

Re fall roof and new roof will sort the job out

If water is regularly sitting on the roof and you’re now seeing staining inside, it usually means the roof covering has started to fail somewhere, even if the leak isn’t directly above the stain. At around 10 years old, the roof may still be repairable if the issue is isolated, but if there’s widespread ponding or the roof has sagged, it’s often better to replace it properly and build in the correct fall so water can drain away. A roofer should check the condition of the covering, the joints, the drainage outlets, and whether the roof structure has dipped over time. Ignoring standing water normally leads to more leaks and eventually rotten roof boards underneath.

Pooling water is usually a sign that the roof doesn’t have enough fall, and once you’ve started getting internal staining it suggests water has found a way through the waterproofing. At 10 years old it’s definitely worth having it inspected properly rather than just patching the symptoms. If the deck is still structurally sound and a moisture test comes back within acceptable limits, a high-quality GRP overlay system such as the Restec Flexitec system can often provide a long-lasting solution. I’m a Restec approved installer, and when the substrate is suitable it avoids a full strip while giving you a seamless, durable waterproof finish. If the deck has deteriorated or the falls are incorrect, the best long-term repair is to strip the roof, install firring strips to create the correct drainage falls, replace any damaged decking, and fit a new warm roof system. That eliminates the cause of the ponding rather than just treating the symptoms. A site inspection and moisture test would determine which option is the most cost-effective.