How to Remove Water from a Flat Roof Building

When we recently had an additional air conditioning unit installed in our commercial building, we noticed quite a bit of standing water on the roof. The water was caused by a leaking swamp cooler which was an easy fix. What was a little tougher was determining a way to change the slope of the roof so that water drained away instead of pooling.

Before the roof could be repaired, the water had to be removed. Sweeping it off the roof wasn’t an option since the water and sludge would rain down on the pedestrians below. Pushing it over to the rain gutters also wouldn’t work since the sludge and algae would clog the gutters and down spots. The only other option to to vacuum up the water using our commercial size Wet Dry Shop Vac. Here’s how it was done.

Gathered supplies. In addition to the Shop Vac, we gathered up 5 gallon buckets (to hold the waste water), cheesecloth (for straining the sludge), a small bucket for bailing, 100 ft extension cord, and a rope. Protective goggles were also worn since the water had a tendency to slop around during the straining.

Assembled the Shop Vac. Preparing the Shop Vac for suctioning up the roof water meant removing the filter and emptying the collection tank so that we wouldn’t be adding water to old debris. For tools, we used the wand and crevice tool. Since our Shop Vac doesn’t have a drain plug which could be attached to a garden hose for easy draining, our plan was to dump the collection tank into the buckets which were then hoisted downstairs.

Collecting the sludge. Vacuuming up water is not much different then vacuuming the carpet in your home. We would vacuum water for a few minutes and then stop when there was 3-4 gallons of water in the collection tank. Any more than that, the tank would be too heavy to pick up and dump into the buckets. The filled buckets were then lowered to the street level using the rope.

Strained the sludge. Before pouring water down the drain, we filtered it through several layers of cheesecloth to trap algae, debris, and roof sand. The clear water was then flushed away while the solids were tied up in a plastic trash bag and placed in the dumpster.

From start to finish, it took us less than an hour to remove the standing water from the roof of our commercial building. With sunshine in the forecast for the next 7 days, the roofing material will be thoroughly dried by the time our contractors will be ready to repair the sag.

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