TPO Roof Replacement vs TPO Recover: How to Decide

A TPO recover is the right call when the existing flat roof is dry, the deck is sound, only one roof covering is in place and the drains, edges and curbs have room for the extra height. If one of those fails and cannot be corrected, tear-off and replacement usually pays off better. A moisture survey and a close look at the deck settle most of the question before anyone should price either option.

What recover and replacement actually mean

A recover leaves the existing roof in place and installs a new TPO system over it, normally with a recover board between the old surface and the new membrane. A replacement strips everything down to the deck, repairs the deck where needed and builds a new roof from the insulation up. Both finish with a new heat-welded TPO membrane on top. The difference is what stays hidden underneath it.

Recover is attractive because it avoids tear-off, keeps the building protected throughout the work and sends far less material to the landfill. Those advantages hold only when what stays underneath is fit to stay.

Start with a moisture survey

Wet insulation ruins more recovers than anything else. Water sealed under a new membrane has nowhere to go. It ruins the thermal value of the insulation, corrodes fasteners and steel deck, and can surface later as blisters, soft areas or leaks with no obvious source. Three common methods find it, and each has its place.

• Infrared scan. After a sunny day, wet insulation holds heat longer than dry insulation. An infrared camera on the roof after sunset shows those areas as warmer patches. It covers a large roof quickly.
• Nuclear moisture meter. A gauge set down on a grid across the roof counts hydrogen in the layers below, and most of that hydrogen is water. It reads through surfaces where infrared struggles, such as heavy gravel.
• Core cuts. Small samples cut down to the deck confirm what the scans suggest, show how many layers are there and what they are made of, and expose the deck for inspection. Each cut is patched right away.

The survey produces a map. Wet areas come out and are replaced with new insulation whichever option you choose. When the wet areas are widespread, the economics usually swing toward full replacement.

Deck condition and what is already up there

Core cuts and a look from the underside tell you about the deck. Steel deck with light surface rust is common and usually acceptable. Steel deck with rust-through, broken welds or sag between joists is not something to bury under another roof. Wood, concrete and older cementitious decks each raise their own questions, mostly about whether fasteners will hold.

Then count the layers. The building code does not allow a recover where the roof already carries two or more roof coverings, and it does not allow one over a roof that is water-soaked or too deteriorated to serve as a base. A building that was recovered once before, perhaps with single-ply over an old built-up roof, has already used its recover. Older built-up roofs and their mastics can also contain asbestos, so testing before any tear-off belongs in the plan.

Recover board, attachment and wind uplift

A recover board gives the new membrane a flat, stable base and separates it from the old surface. High-density polyiso, gypsum-based boards and other cover boards are used, chosen to suit the existing roof, the attachment method and the impact resistance you want. Over a gravel-surfaced built-up roof, the loose gravel is removed first and the surface leveled so the board lies flat.

The attachment pattern is designed for the uplift the building will see, which depends on its height, exposure and roof zones, with heavier fastening at corners and perimeters where uplift is greatest. In a mechanically attached recover, fasteners pass through the new board and the old roof into the deck, so pull-out tests on the deck confirm the fastener type and spacing. Where the deck holds fasteners poorly, the boards and membrane can be adhered instead, once bond tests show the existing surface will hold them. Induction-welded systems cut the fastener count, because the same plates hold down the board and bond the membrane. The new attachment also has to hold the old roof down, because a recover cannot rely on old insulation that has already come loose.

Drains, edges and rooftop units

Every recover raises the roof surface, and that change has to work at every edge and opening.

• Drains need retrofit inserts or resetting so water still reaches them at the new level, without a dam of board around the bowl.
• Roof edges need added wood blocking and new edge metal or gutters to match the new height.
• Curbs and walls need enough height left for the membrane flashing to turn up to the manufacturer’s minimum above the new surface.
• Doors and scuppers that open onto the roof need checking, because a threshold that ends up level with the roof surface lets water in during the next downpour.

Rooftop units often decide the question on retail and office buildings. If the HVAC curbs are too short for the new roof, they have to be raised, which means the mechanical contractor disconnects and resets the units. That cost belongs in the comparison from the start, not as a surprise halfway through the job.

Insulation, taper and the energy code

A tear-off is the one time the insulation lies fully exposed, and the energy code adopted by your city may expect it to meet current levels when the roof above the deck is replaced. Ask that question at the start, because added insulation thickness drives everything at the perimeter: edge height, curb height, drain sumps and door thresholds. A recover can add insulation too, beneath the recover board, but every inch of it has to fit under the same flashings and above the same drains.

Tapered insulation follows the same logic. Where water ponds on a dead-flat roof, tapered boards and crickets steer it toward the drains. On a replacement, the taper starts at the deck. On a recover, it sits on top of the old roof and adds to the height problem at the edges.

When replacement wins

Choose full replacement when the survey finds wet insulation across a large share of the roof, when the deck needs more than spot repair, when two roof coverings are already in place, or when edges, curbs and thresholds have no room for added height. Replacement is also the cleaner route when ponding has to be cured with tapered insulation and the perimeter cannot take that extra build-up on top of the existing roof, or when the insulation upgrade you want only fits once the old layers are gone.

Recover wins when the roof is mostly dry, the deck is sound, one covering is in place and the perimeter and units can accept the height. On an occupied warehouse or retail building, that combination means less disruption, no open roof and a shorter schedule.

Planning either option around an occupied building

Tear-off exposes the deck, so every section opened in the morning is dried in before the crew leaves, and the sequence follows the forecast closely, because Central Texas storms can build in a single afternoon. A recover keeps the old roof in place as protection the whole time. Both need agreed crane positions, material staging and protection for loading docks and entrances, which we agree with the facility manager ahead of mobilization. After 20+ years in commercial roofing, we would rather spend an extra day on the survey than leave a wet roof sealed under a new one.

For buildings around San Antonio, from retail centers inside Loop 410 to industrial space along Loop 1604 and out toward Seguin, see our page on TPO roofing in San Antonio. Buildings in the Austin area, including Georgetown, Kyle and San Marcos, are covered on our page about TPO roofing in Austin. Our commercial TPO roofing service explains how we build new, replacement and recover systems, and the Technical Library holds data sheets for GAF EverGuard and Elevate UltraPly TPO membranes.

To compare recover and replacement on your roof, get in touch with the building address, past roof reports or drawings if you have them, and photos of the drains and roof edges, or call (210) 775-0995. Our answer will rest on what the survey finds, not on which job is bigger.