Recover System Options and When Each Applies
TPO recover over existing membrane: The most common recover configuration in the St Louis market for commercial low-slope roofs. New polyiso cover board over the existing membrane (adds insulation value, creates a smooth substrate for the new TPO), mechanically attached or fully adhered TPO over the cover board. Manufacturer 20-year NDL warranty available on qualifying substrates from most major TPO manufacturers. Appropriate for EPDM, BUR, and modified bitumen substrates where the core assessment shows dry insulation.
EPDM recover: Mechanically attached or fully adhered EPDM over existing membrane with polyiso cover board. Often specified for industrial buildings, distribution centers, manufacturing facilities in Earth City, Hazelwood, and Berkeley, where the 60-mil EPDM's resistance to mechanical traffic is a priority and the building's thermal environment favors EPDM over TPO.
Modified bitumen recover: SBS or APP modified bitumen cap sheet over existing BUR or existing modified bitumen. The recover system that makes the most sense on older BUR-substrate buildings in the South City industrial corridor and on institutional buildings in the CWE that have concrete decks. Modified bitumen recover can be torch-applied, cold-applied, or self-adhering depending on the substrate and project conditions. Torch application is not appropriate on substrates with combustible components, we specify cold-applied or self-adhering systems in those situations.
Moisture Core Protocol, The Recover Decision Gate
Every recover assessment pulls cores. Not probes, not infrared alone, physical cores that cross-section the membrane and insulation stack and give us direct visual and tactile evidence of moisture condition. Infrared scanning is a useful screening tool on large roofs to prioritize core locations, but it reads temperature differential, not moisture content, and can miss wet insulation in overcast conditions or during periods without adequate temperature cycling. We use infrared when it adds value, and we follow up every suspect infrared zone with a physical core.
Our core locations are determined by roof zone, we pull at the interior field of each distinct drainage area, at each interior drain, at parapets (the most common moisture entry points on St Louis commercial roofs), and at any location showing visible surface distress. Core results are documented by location, photographed, and mapped to a roof zone diagram. The core report is the basis for the recover-versus-replace recommendation, the owner sees the data, not just the conclusion.
The 25-percent wet-insulation threshold is the standard recover-qualification criterion across major TPO and EPDM manufacturers. At or below that threshold, targeted tear-off of wet zones with new insulation installation and cover board over the dry field is the recover path. Above it, we recommend full replacement, not because we prefer the larger scope, but because recovering a system with widespread wet insulation produces a warranted roof that will fail again on the same timeline as the existing one, for the same reasons.
Recover vs. Replace, The Capital Decision
Recover is the right scope when the substrate qualifies. Replacement is the right scope when it does not. The capital difference matters: a 50,000 sq ft flat roof in St Louis is a $200,000 to $300,000 replacement scope and a $120,000 to $175,000 recover scope if the substrate qualifies. That difference is meaningful for a property manager running a capital budget that has to cover multiple buildings.
The cases where owners push for a recover on a substrate that does not qualify are the cases that produce early warranty claims and contractor disputes. We document the qualification decision in writing, the core results, the wet-area percentage, the deck condition observations, so the owner has the information they need to make the capital decision, not just our recommendation. If the owner decides to recover a marginally qualifying substrate, we document that decision and the associated warranty limitations clearly in the project scope.
Missouri Code and St. Louis Recover Eligibility
Missouri's adoption of the IBC limits commercial buildings to two total roofing membranes before tear-off is required. The City of St. Louis, St. Louis County, and the major municipalities in the metro all enforce this limitation through the building permit process. We document the existing assembly ply count through core sampling before recommending any recover scope, and we advise when the code limit has been reached.
Missouri's energy code also requires that recover membranes meet the minimum cool-roof reflectance standard for Climate Zone 4A. A recover specification that installs a dark or non-compliant membrane over the existing system is not a code-compliant installation in the St. Louis metro, and it will not pass the building permit inspection required for permitted recover work.
Recover System Selection for St. Louis's Freeze-Thaw Climate
Mechanically attached TPO recover over existing single-ply or modified bitumen is the most common recover scope on St. Louis commercial buildings with dry insulation. The specification needs to account for Missouri's wind uplift exposure and ensure the fastener pattern meets the design criteria for the building's specific exposure classification. Cover board installation between the existing membrane and the new TPO is standard in our St. Louis recover scopes.
EPDM recover over modified bitumen or BUR is sometimes specified on St. Louis buildings where chemical resistance or cold-process installation is preferred. The adhesive and seam tape application temperature requirements for EPDM recover impose the same shoulder season scheduling constraints as new EPDM installation. We factor these constraints into the project schedule for St. Louis EPDM recover projects.
