Mike Silvers, CPRC, Owner of Silvers Systems Inc. and FRSA Technical Director
2020 Florida Building Code, Existing
Building, 7th Edition
REROOFING. The process of recovering or replacing
an existing roof covering. See “Roof recover” and
“Roof replacement.”
ROOF RECOVER. The process of installing an additional
roof covering over a prepared existing roof covering
without removing the existing roof covering.
ROOF REPLACEMENT. The process of removing the
existing roof covering, repairing any damaged substrate
and installing a new roof covering.
Recovering has its advantages and is particularly appealing in Florida where, during the summer, the chance of rain is probable almost every day. Protecting the building from water intrusion during roof removal can be challenging. Recovering reduces labor cost and allows the contractor to complete more work each day. It also eliminates the need to immediately handle debris and to pay for its disposal. The previous statement said “immediately” for a reason. Eventually these costs will be incurred by the building owner, either when roof replacement has to occur (more on this later) or rarely when the building is demolished and the debris is disposed of. Recovering doesn’t eliminate the use of landfills or reduce the volume of debris disposed of; it just postpones it. A section of the existing building subcode shown below addresses recovering versus replacement. Some portions are in bold and underlined for emphasis.
706.3 Recovering versus replacement.
New roof coverings shall not be installed without
first removing all existing layers of roof coverings
down to the roof deck where any of the following
conditions occur:
1. Where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.
2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile.
3. Where the existing roof has two or more applications of any type of roof covering.
4. When blisters exist in any roofing, unless blisters are cut or scraped open and remaining materials secured down before applying additional roofing.
5. Where the existing roof is to be used for attachment for a new roof system and compliance with the securement provisions of Section 1504.1 of the Florida Building Code, Building cannot be met.
Exceptions:
1. Building and structures located within the High-Velocity Hurricane Zone shall comply with the provisions of Sections 1512 through 1525 of the Florida Building Code, Building.
2. Complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to transmit the roof loads directly to the building’s structural system and that do not rely on existing roofs and roof coverings for support, shall not require the removal of existing roof coverings.
3. Reserved.
4. The application of a new protective coating over an existing spray polyurethane foam roofing system shall be permitted without tear-off of existing roof coverings.
5. Roof Coating. Application of elastomeric and or maintenance coating systems over existing asphalt shingles shall be in accordance with the shingle manufacturer’s approved installation instructions.
Let’s address several areas in this section. The first sentence tells you that you cannot install new roof coverings without removing all layers down to the roof deck where 1 through 5 occur.
Number 1 states that if the roof is “water soaked” or the existing is “not adequate as a base for additional roof covering.” Possible issues could involve fastener corrosion or deck or insulation deterioration. Such conditions can also interfere with proper bonding
when using adhesives. Presence of liquid water turning to vapor can impact the long-term viability of the new roof covering. Granted, this language is subjective but when taken as a whole, the intention seems fairly clear. If there is moisture present that could affect the performance of the recover, then the roof should be replaced.
Number 2 simply says that you can’t recover over certain steep slope roof coverings that will not provide an appropriate substrate for a roof recover.
Number 3 makes it clear that if there are two or more roof coverings present, then all existing layers of roof coverings must be removed down to the deck. This requirement has the potential to have major consequences when a recover has been done over an
existing high R-value roof system and the building now needs to be reroofed again. The opportunity to install a new roof covering and cover board over the existing high R-value insulation may be lost. Because two or more roof coverings exist, you would need to remove all layers “down to the deck.” This requirement does not allow for more than two roof coverings and requires that all the material will eventually be removed and end up as debris. It may actually increase the amount of waste that is generated by forcing unnecessary insulation replacement.
Number 4 addresses the presence of blisters in the existing roof covering and how they should be addressed. This condition is being encountered less often than when bitumen (asphalt and coal tar) based systems were the predominate existing roof systems.
Number 5 is very important because it pertains to the ability to meet the uplift requirements of the code. All new roof coverings must meet the wind uplift resistance requirements called for in the code, currently ASCE 7-16. If the new system is being mechanically attached (screwed or nailed) to the deck, the manufacturer’s installation instructions or product approval will provide the proper fastening patterns for a recovery. However, if you plan to adhere your new roof system to the existing roof covering, the existing roof covering attachment method must be considered. The uplift resistance requirements of the code have steadily
increased over the last several decades. A mechanically attached roof system or an adhered roof systems that uses spaced ribbons
of adhesive installed under the previous editions of the code, most likely wouldn’t comply with the current code. Using that existing roof covering as part of the load path for the new roof covering by adhering to them would, in most instances, not meet current requirements. I said likely wouldn’t comply in most instances because there is a small chance that the existing roof applicator added additional fasteners or adhesive. But we know that isn’t very likely. So, it is best to accept that it most likely will not comply and plan accordingly. You may be able to add additional mechanical attachments before adhering to the roof covering. However, unless the manufacturer’s product approval or recommendations describe how to accomplish this, you would need site-specific engineering. Keep in mind that if the roof system was set in continuous adhesive (e.g., mopped to a concrete deck), the uplift resistance may be high enough to act as part of the load path. Verifying the quantity and quality of the existing adhesive
may prove difficult. This section applies to all roof coverings that use the existing roof system as part of the load path. Yes, even
to sprayed polyurethane foam and liquid applied roof systems. A maintenance coating does not constitute a roof covering.
The advent of new or improved cover boards, adhesives and fasteners have greatly increased the options available for both new construction and reroofing. When “reroofing” – both replacement and recovering of existing roof systems – these code requirements should always be taken into account.
Mike Silvers, CPRC is owner of Silvers Systems Inc. and is consulting with FRSA as Director of Technical Services. Mike is an FRSA Past President, Life Member and Campanella Award recipient and brings over 45 years of industry knowledge and experience to FRSA’s team.
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