27/08/2026
- Trapped moisture
If the existing roof is damp, rotten, or leaking, boarding over it traps the problem.
- Hidden rotten decking/joists
You cannot properly inspect or repair the structure underneath.
- Fixing issues
New boards need secure fixings into sound substrate/joists. Simply screwing through soft or failed existing boards can be inadequate.
- Poor falls remain
Overboarding often just follows the existing roof, so ponding and incorrect drainage are not solved unless falls are designed into the new build-up
- Condensation risk
Adding layers without considering the complete warm-roof/cold-roof design can create interstitial condensation.
- Existing layers can become unstable
Failed felt, bubbling membranes or loose layers can move beneath the new deck.
- Hidden defects remain undisclosed
Potentially a problem for guarantees, future repairs and proving the condition of the roof
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