Plan a new waterproofing surface over a metal roof that is suitable to remain in place. DERFLEX supplies TPO membrane rolls for contractors, project buyers and roofing-material distributors sourcing a retrofit membrane specification.
Installing TPO over metal roof panels requires a coordinated assembly: a roof survey, profile-matched flute fill, a supported overlay, designed attachment and welded details. Discuss membrane thickness, reinforcement, backing, roll format and required documents with DERFLEX before ordering; the project team confirms the roof-system design.
Reinforced / backed optionsHot-air welded seamsProject & OEM roll supply
A new roof surface. A considered build-up.Metal-to-membrane application reference. Existing roof condition, drainage and attachment determine the retrofit design.
The short answer
Can TPO be installed over a metal roof?
Yes, when the existing roof and structure are suitable for a designed recover system. A typical build-up fills the spaces between metal ribs, adds insulation or a cover board to support the new surface, and secures a heat-welded TPO membrane. Covering rust damage, wet insulation or weak attachment does not correct those defects.
01 / Start with the existing roof
A recover candidate or a replacement project?
An occasional leak is a symptom, not a complete condition assessment. Use the survey findings to decide what can stay and what needs repair, replacement or further investigation.
Pre-purchase decision matrix for the project designer and roofing contractor
Survey finding
Decision direction
Evidence to obtain
Sound panels and structure; localized leaks
Evaluate recoverInvestigate leak paths and repair local defects before overlay.
Roof survey, panel condition and the proposed recover specification.
Wet or damaged insulation
Resolve firstIdentify the extent; remove and replace detrimental wet components.
Moisture assessment and an agreed replacement scope.
Corroded panels, loose supports or uncertain strength
Structural reviewDetermine repairs or replacement before relying on the old roof.
Condition report and designer acceptance of the supporting structure.
Unknown purlins or weak fastener holding
Attachment reviewVerify the proposed anchorage rather than using a generic screw pattern.
Purlin layout, substrate information and project-required pullout tests.
High internal humidity or condensation
Moisture designEvaluate air leakage, insulation and vapor control as one assembly.
Building use, indoor conditions and a climate-specific design.
Restricted drainage or low curb heights
Detail redesignAccount for the added roof thickness before setting membrane quantities.
Roof sections, outlet locations and revised flashing details.
Recover suitability also depends on local project rules, permitted roof layers and added loading. Have the project team confirm these before purchase.
02 / Build the supporting surface
What goes between the metal panels and TPO?
Flute fill supports the overlay between ribs. The layer above it creates the surface required by the selected membrane and attachment system.
1TPO field membrane Weldable weathering sheet; specify construction and thickness.
2Insulation / cover-board overlay Continuous support matched to the approved assembly.
3Profile-matched flute fill Fill geometry follows the actual metal rib profile.
4Retained metal roof and supports Condition and structural suitability must be established.
Concept only, not an installation drawing. Attachment, vapor-control layers and exact layer thicknesses depend on the project.
Measure the profile
Record rib spacing, height and shape. A generic filler width can leave unsupported areas; confirm the fitted profile before ordering.
Select fill and overlay together
Polyiso and EPS are used in different published assemblies. They are not automatic substitutes: support, spanning ability, fire performance and system compatibility matter.
Resolve moisture within the assembly
A new waterproofing surface does not by itself stop condensation beneath it. The designer determines whether and where air or vapor control is needed.
Compare attachment concepts before selecting rolls
The complete load path matters. Membrane attachment, insulation attachment and retained-roof attachment are related decisions, but they are not the same fastening task.
Design concepts; exact components and layouts require project approval
Concept
How it works
What changes the purchase order
Mechanically attached
Designed fasteners, plates or attachment strips secure the sheet. Many metal retrofit systems anchor membrane loads into structural purlins.
Purlin locations, pullout capacity, attachment-zone design, roll layout and compatible reinforced membrane.
Fully adhered
The membrane bonds to a compatible continuous overlay. The overlay and layers below still need a designed attachment method.
Adhesive and substrate compatibility, backing, surface preparation and application conditions.
Induction / plate bonded
A compatible membrane bonds to purpose-designed coated plates anchored through the assembly.
Specific sheet/plate compatibility, equipment, fastening layout and an approved system. Confirm availability separately.
Do not copy another roof’s fastener spacing. The roof’s height, wind exposure, geometry, perimeter zones and verified substrate capacity affect attachment. A wider roll is only useful when it fits the approved layout and the crew’s handling plan.
For an adhered option, compare fleece-backed TPO for recover applications; confirm the exact backing and adhesive combination rather than assuming fleece makes any substrate acceptable.
04 / Define the membrane order
Metal roof retrofit TPO specifications
Use DERFLEX’s published membrane directions as a starting point. Specify the exact grade and documents needed for your roof; published options do not establish a project’s system approval.
Membrane RFQ framework — final production specification to be confirmed
Item
Published sourcing direction
Define in the RFQ
Construction
TPO sheet; reinforced and fleece-backed directions are available for discussion.
Roof-field grade, reinforcement, backing and attachment concept.
Nominal thickness
1.2, 1.5, 1.8 and 2.0 mm directions.
Exact contract thickness, tolerance and any thickness-over-scrim requirement.
Roll dimensions
Common width directions: 2, 3 and 4 m; length and custom format to be confirmed.
Seam layout, lifting limits, roll mass and scheduled quantities.
Color / exposed surface
White, gray and tan directions; custom color subject to discussion.
Color reference and product-specific reflectance documents if required.
Field seams
Hot-air weldable TPO.
Compatible flashing materials, trial-weld procedure and field inspection.
Performance documents
Confirm available reports for the offered grade.
Required material standard, edition, test fields and acceptance criteria.
Packing / OEM
Roll labeling, private-label and export packing can be discussed.
Batch identification, handling protection, pallet plan and destination.
Is 60 mil enough?
60 mil is a common market reference, not a universal retrofit recommendation. Select sheet thickness with the assembly, service traffic, detailing and contract requirements. Extra thickness does not compensate for unsupported ribs or poor attachment.
Keep metric and mil values precise
60 mil = 1.524 mm; 80 mil = 2.032 mm. A 1.5 mm sheet is approximately 59.1 mil; a 2.0 mm sheet is approximately 78.7 mil. Agree the nominal requirement instead of substituting a rounded trade name.
Use the TPO technical specification guide to prepare the material submission. Material test data and installed roof-system fire or wind performance require separate verification.
Details that change the retrofit scope
Budget for transitions, not just the roof field
01 / RIDGE & MOVEMENT
Preserve the movement strategy
Metal panels and building joints move. Establish ridge, expansion-joint and tie-in details before covering existing features.
02 / EAVES & DRAINAGE
Allow for the raised surface
Overlay thickness changes edge and outlet relationships. Check gutter interfaces, overflow paths and water flow at transitions.
03 / CURBS & PENETRATIONS
Check flashing clearances
Account for the new build-up around curbs, pipes and skylights. Existing flashing heights may need changes.
04 / SERVICE ROUTES
Plan maintenance access
Locate walkways and equipment service points in the takeoff. Identify hot exhaust or chemical exposure for compatibility review.
Ridge and penetration planningApplication reference from the DERFLEX website. Final details must follow the selected system and roof geometry.Roll format affects installation logisticsCoordinate roll dimensions, lifting, staging and seam layout before confirming the material order.
Two approval gates
Approve the membrane and the roof system separately
A sheet-level test report answers a different question from a roof-system submission. Keep both document sets aligned with the actual materials and retained roof.
Gate 1 / Material release
Agreed construction, thickness and dimensions.
Product-specific required test reports.
Approved sample, surface and color reference.
Batch labels, quantities and protective packing.
Define the inspection scope using DERFLEX’s quality-control process; confirm the TPO-specific records required for your order.
Gate 2 / Project acceptance
Survey acceptance and agreed repairs.
Compatible layers and designed attachment.
Project-required fire, wind and code documentation.
Trial welds, cooled seam checks and completed detail inspection.
The project designer, contractor and applicable system provider confirm this gate. Another manufacturer’s approval does not transfer to a substituted membrane.
05 / Turn the survey into a quote
Compare quotations with the same scope
Membrane price per square metre and installed retrofit cost are different figures. Ask each supplier or contractor to identify exactly what its quotation includes.
Cost and quantity fields to reconcile before awarding an order
Scope
Main variables
Avoid this comparison error
DERFLEX membrane roll order
Construction, thickness, color, dimensions, quantity, documents and packing.
Comparing sheet prices with different thicknesses or backing.
Local retrofit components
Profiled fill, overlay, attachment hardware, adhesives, flashing and edge materials.
Treating the membrane price as the whole material package.
Preparation and installation
Survey, repairs, wet-component replacement, access, lifting and detail work.
Leaving necessary repairs outside the quoted scope.
Delivery and acceptance
Destination, freight terms, inspection, required submissions and agreed warranty scope.
Comparing different delivery terms or assuming a system warranty is included.
Quantity rule: separate measured roof-field area from order quantity. Add project-approved laps, detail material and layout waste; use actual sloped dimensions rather than relying only on the building’s plan area. Coordinate these allowances with the roll-size and handling guide.
A defined factory order
Discuss the offered membrane grade, thickness, roll format, sample and document package before comparing bulk prices.
Distributor consistency
Align private labels, batch references and packing instructions with the approved specification for repeat orders.
Export coordination
State destination, shipment terms and delivery window. MOQ, sample availability and lead time are confirmed for the order.
Send a roof brief with your RFQ
A useful enquiry describes both the existing roof and the membrane being purchased.
Existing roof information
Location, building use, area and slope.
Panel profile, rib dimensions and purlin layout.
Survey findings, insulation condition and roof photos.
Drainage, curbs, penetrations and proposed attachment.
Membrane and commercial information
Construction, thickness, color and roll dimensions.
Required test documents and project approval route.
Quantity, labels, packing, destination and delivery window.
DERFLEX quotes the agreed material supply scope. Confirm local design, installation and roof-system warranty responsibilities with the project team.
Can TPO go over a metal roof without removing the panels?
Yes, if the roof survey and project design confirm that the panels, structure and existing components are suitable to remain. Necessary repairs and removal of detrimental wet or damaged components come before the recover system. Local recover rules also apply.
Does a metal roof retrofit need flute fill?
Published ribbed and standing-seam retrofit systems typically use fitted insulation between ribs to support the layers above. Confirm the profile, filler material and overlay with the selected assembly; do not expect the membrane to bridge unsupported metal ribs.
Can TPO be glued directly to corrugated metal?
Do not assume a direct bond to bare corrugated panels is acceptable. An adhered retrofit normally needs an approved supported substrate and compatible adhesive. A fleece backing does not remove the need to confirm support, preparation and system compatibility.
Should I choose 60 mil or 80 mil TPO for a metal roof?
Use the specified assembly and service conditions to choose, including traffic, detailing and contract requirements. 60 mil equals 1.524 mm and 80 mil equals 2.032 mm. Confirm the exact offered thickness; neither class corrects deficient support or anchorage.
Will TPO stop condensation inside a metal building?
Not by itself. The outer membrane addresses roof waterproofing; condensation also depends on indoor humidity, air leakage, climate and insulation. The project designer should assess air and vapor control and address moisture already in the assembly.
How much does a TPO metal roof retrofit cost?
It depends on condition, repairs, fill profile, insulation, attachment, membrane, details, access and local labor. Request separate membrane-supply and installed-system quotations with matching scopes. A reliable project price needs the roof survey and takeoff.
Can DERFLEX provide samples, custom rolls or OEM packing?
Discuss the offered grade, roll format, labels, packing and sample requirement with DERFLEX. Confirm MOQ, sample availability, custom-production conditions and lead time for the exact specification, quantity and delivery destination.
Does buying the membrane include a complete roof-system warranty?
Do not assume it does. Confirm material warranty terms separately from system and workmanship coverage. Complete roof coverage depends on the system provider, approved components, installation and inspection requirements, and agreed responsibilities.
Bring the roof details. Get a clearer membrane quote.
Send the profile, area, attachment concept, exact thickness, order quantity and destination. Add roof photos and required documents so DERFLEX can review the material specification.
