When a Recover is Practical (and When it Isn’t)
When a commercial roof reaches the end of its service life, a full tear-off and replacement isn’t always the only option. In some cases, a roof recover can provide a more economical, efficient way to extend the life of the building’s roofing system.
A recover involves installing a new roof system over an existing one rather than removing everything down to the deck. This can reduce demolition, landfill costs and installation time while allowing the existing insulation to remain in place. It can also provide better protection for the building interior during construction and reduce disruptions to ongoing operations.
However, not every roof is a candidate for a recover. The condition of the existing roof, applicable building codes and the structural capacity of the building’s roof deck all need to be evaluated before work begins.
Can My Commercial Roof Be Recovered?
The first consideration is the condition of the existing roof system. A recover generally isn’t appropriate if the existing assembly has widespread moisture, a history of significant leaks, deteriorated insulation or a compromised roof deck.
Contractors may use visual inspections, core samples, and infrared thermography to identify moisture and evaluate the condition of the existing assembly. The condition of the deck is especially important. A corroded steel deck or deteriorated wood deck may require repair or replacement before a new roofing system can be installed.
Building codes are another important consideration. Codes limit the number of roof assemblies that can be installed over an existing system, particularly when insulation is involved. The proposed recover must also meet requirements for fire resistance and wind uplift.
Finally, the building must be able to support the additional weight of the new roof system. A licensed structural engineer evaluates the structural load capacity of the commercial building’s roof deck to determine whether it can safely support the existing roof assembly plus the proposed recover system. This evaluation is an important step before proceeding with the project.
If these requirements are satisfied, two common recover options are single-ply membrane over metal and single-ply membrane over an existing single-ply roof.
Single-Ply Membrane Over Metal
One of the primary challenges of installing membrane over an existing metal roof is the uneven surface created by the ribs or standing seams. Flute fill insulation is typically installed between the ribs to create a more uniform surface. Polyisocyanurate and expanded polystyrene are common choices, with factors such as R-value, cost, and fire requirements influencing the selection.
A layer of rigid insulation or a coverboard can then be installed over the flute fill to create a suitable substrate for the new membrane. The insulation is typically mechanically fastened through the flute fill and into the metal panels, while the single-ply membrane is attached according to the requirements of the roofing system and manufacturer.
Attachment is particularly important on metal recover projects. Fasteners that penetrate only light-gauge metal panels may not provide adequate wind uplift resistance. In many systems, attachment into the structural purlins beneath the metal panels provides the necessary pull-out strength.
Before proceeding, the roof’s structural capacity, manufacturer requirements, and insurance requirements should all be considered.
Single-Ply Membrane Over Single-Ply
Installing a new single-ply membrane over an existing single-ply roof can make sense when the existing membrane and underlying assembly are still in sufficiently good condition to serve as a substrate. Leaving the existing roof in place can minimize demolition and preserve usable insulation while reducing the amount of material sent to a landfill.
However, the existing membrane should not simply be covered without an evaluation. Areas with trapped moisture, damaged insulation, significant deterioration or other problems may need to be repaired or removed first. The new system also needs a suitable substrate and attachment method that meet the membrane manufacturer’s requirements.
Know Before You Recover
A roof recover can offer meaningful advantages, but it isn’t practical for every situation. The existing assembly must be evaluated carefully to determine whether it can support a new system and continue performing beneath it.
The best first step is a thorough roof assessment by an experienced commercial roofing contractor. The assessment should address the existing roof’s condition and applicable building-code requirements, while a licensed structural engineer evaluates the roof deck’s structural load capacity. Together, these evaluations can determine whether a recover is appropriate.
When the conditions are right, recovering can extend the useful life of a commercial roof while reducing disruption, waste, and the cost associated with a complete tear-off.
Wondering if a recover is right for your roof? Contact D. C. Taylor Co. at 319.731.4118 or [email protected] today.
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