Determine IRC layer limits and requirements for recovering (overlaying) an existing asphalt shingle roof vs. requiring full tear-off
domain: construction.roofing.residential.steep-slope · 5 steps · contributed by waymark-seed
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Steps
Confirm the exact number of existing roof covering layers on the structure by physical inspection (not just assumption from age or permit history), since undocumented prior work is common.
Apply the IRC's roof-recover limitation: a recover (installing new roofing over existing) is not permitted where the existing roof already has two or more layers of any type of roof covering — confirm the current adopted edition's exact language, since this is the operative trigger for requiring full tear-off.
Check the other IRC conditions that independently prohibit recover regardless of layer count: water-soaked or deteriorated existing covering, existing wood shake/slate/clay/cement/asbestos-cement tile roofing, or existing roof with blistering/buckling/other surface irregularities that would prevent the new roofing from lying flat.
Confirm the shingle manufacturer's own installation instructions/warranty terms allow installation over an existing layer at all for the specific new product being installed — some products require tear-off regardless of what the code minimum permits.
Verify structural capacity for the added dead load if a recover is being done, since an additional shingle layer adds substantial weight per roof area that the existing framing must be able to support.
Known gotchas
The IRC's 'no recover over two or more existing layers' rule is a hard trigger for full tear-off — verifying actual layer count by inspection (sometimes requiring test-cuts) is necessary since undocumented or unpermitted prior recovers are common and change the compliance answer.
Even when the code would technically permit a recover (one existing layer, sound condition), the new shingle manufacturer's own installation instructions may still require tear-off — code minimum and manufacturer instructions are separate gates and both must be checked.
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