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June 20, 2014

Re-roofing Over Built-up with a PVC Membrane? Be Aware…!

If you are considering re-roofing your commercial building, it’s important to keep in mind that not all “new” roofing materials are compatible with “old” materials. Case in point: PVC roofing membrane is not compatible with asphalt-based built-up roof products and can be damaged if the two come in contact. Building owners as well as commercial roofing contractors should be aware of potential issues that could arise with a new PVC-over-asphalt roofing installation.

  • Tear-offs of asphalt roofs often create dust that can contaminate new membrane. To avoid this, steps should be taken to ensure that dust blows away from PVC materials. A tarp can be placed on PVC materials that are near the tear-off so that asphalt dust does not get on the new membrane. Asphalt-contaminated work shoes or boots should not get on the membrane. And the entire asphalt tear-off should be completed before the PVC installation begins.
  • Proper, compatible sealants must be used on the new membrane installation. Many caulks, sealants, and pitch pocket fillers contain asphalt, and should never be used on PVC.
  • If your project involves re-covering the old built-up roof rather than tearing it off, a suitable separator sheet (typically made from polyethylene) can be installed between the old asphalt and new PVC roofing system. Insulation materials such as EPS or EXPS rigid foam (as long as it has an approved facer) and polyiso foam board work well.
  • If asphalt does come into contact with the new PVC membrane, it should be cleaned immediately, because it will “bleed” into the membrane and become impossible to remove. A solvent should never be used to clean asphalt off the membrane. Solvents melt the asphalt and soften the membrane, making the problem worse. DeWitt’s Remove-It Citrus Spray Cleaner, Simple Green®, or a non-solvent based whitewall tire cleaner are compatible and effective.

Royalty Roofing is an Elite Contractor for Duro-Last®, manufacture of the leading PVC roofing system on the market. We’ve installed Duro-Last systems on all types of facilities, including those with old asphalt, built-up roofs. If your old roof needs replacing, give us a call.


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