The Recover Over Wet Insulation
A 12,000-square-foot single-story warehouse near Joliet has a 1970s four-ply asphalt built-up roof with gravel surfacing over 2-inch fiberglass insulation on a 22-gauge steel deck. The owner wants the cheapest code-compliant solution: 60-mil mechanically attached TPO installed directly over the existing roof, no tear-off. Interior staining appears each February above the northeast corner, where the roof ponds up to 1-1/2 inches after heavy rain. Two of the four roof drains sit at that low corner and one is clogged. The owner says the building will be sold within three years and asks you to 'just cover it.'
1. What must you determine before you will sign a recover proposal, and how do you determine it?
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A recover is only defensible over a dry, sound substrate, and right now you have evidence it is not.
- Moisture survey: infrared scan at dusk plus several core cuts - one at the February stain, one in the ponding area, one in a known-dry control area. Measure the insulation; wet fiberglass loses most of its compressive strength, so membrane fasteners will not develop pull-out and the membrane will blister and billow.
- Deck condition: corroded deck flutes under the wet zone, and whether the existing membrane is well adhered enough to receive fasteners.
- Code and manufacturer: the locally adopted code's reroofing provisions and the TPO manufacturer's written recover requirements (substrate, fastener density, number of existing layers, and whether wet insulation must be removed).
If the cores show wet insulation, the honest recommendation is a tear-off of the wet field with a recover over the dry remainder - priced as an alternate, not hidden in a lump sum.
2. What does the ponding and drainage situation require before any membrane is installed?
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Ponding is a structural and code issue, not a cosmetic one.
- Positive drainage: the adopted building code requires roofs to drain, and the plumbing code requires secondary (overflow) drainage in addition to the primary drains. Two working drains at the low corner with one clogged, plus 1-1/2 inches of standing water, is a design deficiency you cannot membrane over.
- Fix the drainage first: clear and repair the clogged drain, verify strainers, and add secondary scuppers or overflow drains at the low point. Consider saddling or tapered insulation to eliminate the pond.
- Check the structure: repeated ponding plus a new membrane assembly adds dead load; if the deck shows deflection, refer it for structural review before you bid.
The new membrane's weight and the fastening pattern make ponding worse, not better. Any warranty you sign will be measured against water sitting on it.
3. The owner refuses the tear-off and wants your standard warranty. Draft your position.
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Put it in writing and hold the line:
- Written inspection findings (cores, photos, moisture readings) delivered to the owner before contract - this is what protects you when the ceiling stains again in year two.
- Proposal with alternates: base bid = recover over verified-dry areas only; alternate = removal and replacement of wet insulation and deck remediation at a stated unit price per square. Do not bundle the unknown into the base scope.
- Exclusions: no warranty for blisters, ridging, ponding-related deflection, or membrane failure over substrate you identified as wet; a clearly stated substrate disclaimer tied to the inspection report.
- No 'sale in three years' discount. Your liability runs with the roof, not with the owner's ownership period, and an assignable manufacturer warranty is exactly what the buyer's inspector will test.
If the owner still insists on covering wet insulation, decline the work. A three-year exit for the owner is a ten-year defect list for you.