How do I fill a dip in a commercial roof?

Answered by Jeffrey ~ January 28, 2011 ~ Comments

We have a flat rubber roof on a small commercial building. Near the bottom there is a dip or belly that holds standing water and is now leaking and damaging the ceiling inside. Is there a product that can be poured to fill this void and make the area flat? We plan on going over the old rubber with a new rubber roof or a roll roofing but are not sure how to fill the void.

Mark S. ~ Bloomington, Illinois

Jeffrey Anderson

Hi Mark, I'm not aware of any product that you could use to fill the void and I don't think that's what you should do even if there were any. Flat roofs are prone to leaks anyway so I suggest finding out what is causing the dip prior to going to the expense of installing new roofing material and finding out you have a leaky roof again in a few months.

Most flat roofs have metal or wood decking installed under the roofing material and that decking is supported by metal or wood roof trusses. If you have a dip, I would think that some decking has failed between the trusses for some reason. Hopefully one of the trusses hasn't failed.

You mentioned that there's a ceiling under the leaky roof that has been water damaged and that's going to need to be removed. Most commercial buildings have dropped ceilings so it might just be a matter of popping a few ceiling tiles out and if you take care not to damage the track, your ceiling repair might be just a matter of sticking in a few new tiles. If the ceiling is drywall, then you are going to have to tear out the water damaged drywall and replace it with new. In either case once the ceiling is out you should be able to see the underside of the roof to determine what is causing your dip. You may have to remove some wet insulation, but most commercial buildings use roll or batt insulation, so that shouldn't be a big job.

If you see a place where the decking has failed and the decking is wood, you may be able to do the repair yourself, but if the decking is metal, you're going to have to find a metal building contractor around Bloomington to do the repair. Either way the repair will need to be done from the top so you definitely want to hold off on getting your new rubber roofing installed until the repair has been done.

An area as large as Bloomington, Illinois might have a commercial roofing contractor who is capable of fixing the leaks and then applying the new rubber roofing without getting a second contractor involved. If you are able to find someone like that, it might save you a little money.

If the decking is metal, you might have the contractor look at the bottom of the roof from inside the building. There is a slight possibility that something heavy landed on the roof to cause the dip and the decking might be popped or braced back into place without having to replace any. A dip can cause water to gather and if it sits somewhere long enough, it can eventually find its way inside. If the decking can be pushed up to eliminate the dip and you don't need any new decking installed, that could save you quite a bit.

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