The Pros and Cons of Exterior Gutters
March 6, 2019
Never having been a fan of exterior gutters for roof drainage/water diversion, we typically advise our manufacturing, education, healthcare and other commercial building customers to avoid the use of gutters if at all possible. The main reasons for such recommendations include:
- Gutters and downspouts require periodic cleaning. Clearing debris that collects on roof surfaces and makes its way into gutters over time is an ongoing maintenance and safety issue. Whether it’s leaves or other items that can clog gutters and downspouts, this issue leads to water backing up, overflowing the gutter and frequently running back into the building’s interior. Cleaning exterior gutters is also a safety issue as it typically exposes workers to fall hazards as they are working (often precariously) from ladders or near the roof’s edge to clear debris.
- Gutters must be sized properly to handle the large volume of water that can collect on commercial buildings with large roof surfaces. Over our many years of providing roof maintenance and repair for commercial roof applications, we frequently find that perimeter water leaks are a result of gutters being too small to handle the volume of water that can be produced by heavy rain in a short period. Gutters that are too small often cause water to back up and run into the building. Making matters worse, problems related to gutters being undersized are often hard to recreate for evaluation purposes as it is nearly impossible in many roof/gutter applications to recreate the volume of water that can inundate a roof in a downpour.
- Gutters must be installed with a slope to drain at least 1/16” per foot. This requirement obviously carries a very narrow margin for error so, if the installing technician fails to honor this long-held measure, the gutters will hold water and not function properly. This frequently leads to water finding its way through the building envelope and into the building’s interior.
Challenge: One such case we discovered was on a large hospital in Florida. The gutters were much too small and, in heavy Florida downpours, filled-up and allowed water into the building’s interior along a ninety-foot section of the building’s edge. Over time, mold and mildew developed in seven patient rooms and the resulting damage was so severe the rooms had to be taken out of service and sealed off.
Solution: Since we regularly perform building envelope maintenance, repair and re-roofing projects for this facility, we were called in to help assess the situation. We quickly determined that the gutters were too small for the amount of rainwater that was being collected by the portion of the roof where this span of gutter was installed. While we are not proponents of the use of gutters in commercial building applications, the best solution for this case required the replacement of the existing gutter with properly-sized, larger gutters. Another part of the solution was replacing the downspouts (that were also much too small) with much larger downspouts in a greater quantity/frequency than the existing gutter system provided.
Result: After completing the work, the moisture infiltration problem was eliminated, the mold was abated, and the rooms were renovated and placed back in service.
Takeaway: In this client’s case, the problem was caused by a previous contractor being unfamiliar with the requirement of properly-sized gutters and downspouts, along with the proper frequency of downspouts. Typically, downspouts are placed at forty feet on center; however, certain conditions may require greater frequency of downspouts. In many cases, the existing condition of in-place gutters may require that new gutters be installed as the only means of roof drainage due to the original design/construction of a building. If this is the case, a good rule of thumb is that it’s always better for gutters and downspouts to be too large/oversized rather than too small.
If your commercial building does require gutters, they should be inspected at least twice a year, if not quarterly. Two common yet difficult issues to look for when performing exterior gutter maintenance include:
- Sagging gutters due to fasteners becoming loose over time, thereby losing the 1/16” per foot slope to drain. The maintenance solution for such cases is to tighten all of the fasteners, ensure the that fasteners are secured into an adequate substrate so that they will remain tight and use a laser level to ensure the gutters have the proper amount of slope to drain.
- Leaking gutter joints. Aluminum and steel gutters have joints secured with rivets after which caulking/sealant is applied inside the leading edge of the overlapping gutter section. Over time, rivets become loose and caulking deteriorates leading to joint leaks. The maintenance solution for such cases is to thoroughly clean the gutter joints using Simple Green or a similar solution and ensure the gutters are dry prior to repair. Then install new rivets, apply a flashing grade elastomeric coating and embed a polyester fabric into the coating before the coating sets. The coating and fabric application is typically four inches wide and centered over the joint.
Of course, some existing design and in-place construction dictates that the only viable drainage choice is gutters and downspouts. In this case, the proper sizing of these drainage components is vital. Experienced technicians should be employed during original installation, as well as during periodic maintenance of gutters and downspouts.
If you are designing a new building, every effort should be made to avoid the use of gutters and downspouts as a means for rooftop drainage. If you have leaks entering the building at roof edges, have an experienced technician inspect the gutters.