Leaks

Sherene from Florida asks: I have a concrete parapet and wall in a South American climate with seasons of rain then hi heat that has some leaks and no flashing. Roofing contractor will remove & replace crumbling uneven concrete and will use Tremco Vulkem 801 & Akkro-7T & liquid silicone and that flashing is old -school. Everywhere here in FL I see flashing. I don't want to revisit & have to redo anything. Also complicating is that a 500 gal water tank used as a gravity feed system will be placed on the roof. Roofer said he will use something to distribute the load (2 tons). I am unsure how that will work and if I need a system that uses the supports on the perimeter of the parapet. 2nd, the parapet leaks through to the outside wall so proper cleaning first and sealing that crack makes me think I need a flashing system.

Below is what our roofing expert John Kenney from Cotney Consulting had to say in response to your question:

Sherene, after reviewing the photo and video, I would not treat this as simply a matter of filling cracks and applying another coating. You have several conditions that need to be addressed as part of a complete waterproofing and structural solution.

The parapet and wall show cracking, deteriorated material, previous repairs and visible evidence of water movement. The first step is removing all loose and unsound material, properly preparing the substrate and determining where the water is entering. Cracks, penetrations and the roof-to-wall transition need to be repaired before the final waterproofing system is installed.

I would also clarify the statement that flashing is “old-school.” Proper flashing is still fundamental to waterproofing. What has changed is that flashing does not always have to mean traditional sheet metal. A properly designed reinforced liquid-applied flashing system can perform that function at parapets, penetrations and roof-to-wall transitions. The important part is creating a continuous waterproofing transition from the horizontal roof surface onto the vertical wall or parapet rather than relying primarily on caulk or surface coatings.

The products you mentioned may be appropriate components of a restoration system, but compatibility, substrate preparation, reinforcement and application sequence all matter. I would want the roofing contractor to provide the complete proposed system and have Tremco’s technical department confirm that the products and details are compatible and appropriate for this application and climate before proceeding.

The 500-gallon water tank is a separate and potentially more serious issue, especially since it is already sitting on the existing roof deck. Five hundred gallons of water weighs approximately 4,170 pounds before adding the weight of the tank itself and any supporting framework. That is a substantial concentrated load.

Even if the tank has been there without an obvious problem, I would not assume the deck and framing were designed to support that load. A structural engineer should evaluate how the weight is being transferred through the roof assembly and determine whether additional support is required. Simply adding a pad, plate or other material beneath the tank may spread the load over a larger area, but it does not necessarily solve the underlying structural issue.

The waterproofing beneath and around the tank also needs to be considered carefully. A large tank sitting directly on the roof can make inspection and maintenance difficult, trap moisture and place concentrated stress on the waterproofing system. Any repair or restoration work should account for the tank location, drainage, protection of the roof surface and future access.

My recommendation is to treat this as two coordinated issues. First, have the roof and parapet waterproofing developed as one continuous system, including the cracks, penetrations and roof-to-wall transition. Second, have the existing tank support reviewed by a structural engineer so you know whether the current deck and framing are adequate before additional work is completed.

Taking the time to address both issues correctly now is far better than relying on coatings and load-distribution pads and having to revisit the roof or structure later.