The “before and after” photographs (below) of this fully adhered single ply roof installation solved problems with the original built up hot asphalt roof installed in 1989 at this retail commercial property.
This particular center had very good positive slope engineered into the original deck design which undoubtedly contributed to the extended life of the original roof. Some of the parapet walls are angled directly into the sun, so it was important to select a material with strong resistance to ultraviolet degradation.
Local Building Department Architectural Design Considerations
The original parapet walls were covered with standard asphalt shingles. This may have been an appearance enhancement for the original design, but by submitting photographs to the local building department, we were able to show while this could have been a factor during the initial construction, mature landscaping now shielded surrounding homes from a direct view of the roof areas. Once approved, we removed all the existing wall coverings to improve adhesion and facilitate full, secure bonding to the substrate.
Minimizing Wind Uplift Potential
To mitigate wind uplift potential, in addition to fully adhering the new membrane, we also mechanically fastened the perimeter of the field sheets using termination bar beneath the overlap of the wall coverings at the base of the walls.
Sealing Rooftop HVAC Ductwork
Exterior ductwork delivers air directly into the building with the result that leaks in the ductwork create misnamed “roof” leaks, where even the slightest deficiency in the air plenums, such as a missing sheet metal screw, can generate interior leak complaints. As a result, where old ductwork is present, we require that it be sealed as part of the roofing project.
Sheet metal moves with temperature change. Combined with high heat, this causes standard asphalt roofer’s mastic to dry, crack and split open. We had the Contractor remove all loose or deteriorated sealant and seal all ductwork seams using a three course method with polyester reinforcement encapsulated within layers of premium elastomeric sealant and also replace any loose or missing fasteners. By then coating the ductwork with elastomeric reflective coating designed to seal galvanized steel, thermal movement is reduced, extending the life of the repairs.
Plasticizer Selection – High Molecular Weight Equals Longevity in Weathering
In a retail commercial environment, it is useful to have a membrane that can be repaired throughout its life because new tenants can require different improvements which may require roof penetrations to be sealed. The membrane we selected has the highest concentration of DuPont’s KEE resin which serves as a high molecular weight plasticizer to impart permanent flexibility to PVC which is brittle in its unmodified state. Other lower molecular weight plasticizers “migrate” out of the membrane over time resulting in chalking and loss of mil thickness.
The alternate to PVC is TPO which avoids plasticizer use altogether, however it it neither flame resistant nor UV resistant without the addition of chemical modifiers. The fundamental formulations have been “improved” four times in the last ten years.
Single Ply Membrane Puncture Resistance
Another concern in a retail commercial environment is puncture resistance of the membrane. Mechanics servicing air handling units and other roof top workers can leave behind debris which punctures single ply membranes. The tiniest pinhole can allow water to penetrate, however this particular material has the highest puncture resistance of any single ply membrane because the proprietary design of the polyester reinforcement is knitted in their own factory by a company with a sixty year history of designing rugged fabrics for water bladders, waste containment, truck tarps, and tension structures.
Most single ply membranes are manufactured by extruding the coating through the polyester core so that it oozes through both sides. With a very dense fabric, this is not possible, so the coatings are fused with heat bonding and adhesive then quality control checked in the lab with a sample from the end of each roll manufactured.
Ponding At The Base Of The Wall
The original roof design incorporated “crickets” at small outcroppings along the tall parapet walls to help direct water to the sump drains, but they fell far short allowing significant accumulation of ponding water.
We had the roofing Contractor add much larger crickets, extending them to the drains to eliminate the ponding water condition. Because there was such good positive slope in the main area of the roof, raising and extending the crickets allowed us to direct the water efficiently, rather than have it create new ponds at the base of the revised crickets.
Cool Roof Rating Council
Being a Southern California air conditioned structure, code provisions of Title 24 “cool roof” requirements applied to the design planning, and the specified membrane meets the heat island reduction prescription in reflection and emittance.
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