A recover, or overlay, installs a new roof over the existing one. A replacement tears the old roof off to the deck first. A recover can save a large share of the cost, but only when the existing roof qualifies. Here is how that is decided.
What the code allows
Building codes based on the International Building Code, which Wisconsin's commercial building code adopts, generally don't allow a recover when:
- The existing roof or its insulation is water-soaked or has deteriorated to the point it can't serve as a base.
- The existing roof covering is slate, clay or cement tile, or other materials the code lists.
- The building already has two or more roof layers.
The deck also has to carry the added weight, and the new roof's flashings and edges have to be done properly, not stacked on top of the old ones.
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Why core cuts decide it
You can't tell from the surface how many layers are on a roof or whether the insulation under it is wet. A few small core cuts, patched the same day, show every layer down to the deck. A moisture survey shows how much of the roof is wet. Together they answer the question in an afternoon. See leak detection and moisture surveys.
Recover vs. replacement at a glance
| Recover | Full replacement | |
|---|---|---|
| Typical cost | $4 – $8 / sq ft | $6 – $13 / sq ft |
| Allowed when | One dry, sound existing layer | Always |
| Deck inspected | Only at core cuts | Entire deck exposed |
| Fixes ponding | Yes, with tapered insulation | Yes, with tapered insulation |
| Next re-roof | Requires tear-off of both layers | Could be recovered once |
Hidden costs on both sides
A recover still needs wet areas cut out and replaced, gravel removed from built-up roofs, edges and copings raised, and drains extended. A tear-off can uncover rusted or rotted deck that has to be replaced. Good bids put unit prices on both, so surprises are priced before the work starts. See roof recover and overlay and replacement and installation.