Moisture is one of the most dangerous risks in roof refurbishment because it is not always visible from the surface.
A roof may look suitable for repair or overlay.
The membrane may appear stable.
The surface may look dry.
The defects may seem localised.
But the real problem can be hidden inside the roof build-up.
Moisture can be trapped within
- insulation
- old waterproofing layers
- vapour control layers
- timber or structural decks
- previous patch repairs
- poorly detailed junctions
- areas affected by long-term water ingress
If this moisture is not identified before refurbishment, the new waterproofing system may only cover the problem rather than solve it.
Trapped moisture can lead to
- saturated insulation
- reduced thermal performance
- blistering or debonding
- decay of timber decks
- corrosion of metal decks
- mould and internal damage
- repeated leaks
- premature system failure
This is why a roof assessment should never rely only on surface appearance.
Before approving an overlay or refurbishment, it is important to ask
- Is the insulation dry?
- Has moisture testing been carried out?
- Are previous leaks still active?
- Is the substrate sound?
- Is the existing build-up suitable to remain in place?
- Could trapped moisture affect the new system?
- Is replacement required in affected areas?
Moisture hidden inside the roof build-up can turn a simple refurbishment into a long-term problem.
A new waterproofing layer may stop water from coming in from above.
But it will not remove moisture already trapped inside the roof.
If moisture is not assessed, the specification is incomplete.
Inspect → Assess → Specify → Perform
A new membrane does not remove moisture already trapped inside the roof.