The existing flat roof is leaking in a couple of spots but the deck underneath still feels solid. I'm trying to weigh up a liquid overlay against a full tear-off and new build-up, partly on cost but also because the client cares about the carbon side.
If the deck is genuinely sound, overlaying is usually the lower-carbon choice by a clear margin, because a liquid-applied system bonds over the existing surface and avoids both the embodied carbon of a whole new build-up and the waste and transport of tearing off the old one. The key word is sound, so the deck and existing membrane need to be dry, well-fixed and free of trapped moisture, since overlaying a wet or failing substrate just buries a problem you will pay for later. Where isolated damp or delamination is present, targeted repair before overlay can still keep you out of a full strip-out. The note on flat roof overlays as a sustainable solution walks through when overlay stacks up and when it does not. Get a proper moisture check done first, and if you want a second opinion on the survey findings, get in touch and we will talk it through.
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