Leaking walkout deck – Part I

This  week, today and also this coming Friday, we will look at a roofing issue in a two-part series.  This is a case study of an upper level balcony on a residential building where the balcony has an outdoor space and a roof below. . In this case the balcony / flat roof is leaking in several areas. And although the area below is exterior, not interior, we still treat it as something that should be protected because there is a water sensitive wood beadboard ceiling below which will be damaged by the water leaking through the balcony.

This type of installation just does not work, plain and simple, with their several reasons and several points of failures.  We’re going to show several of those areas of failure and leakage up close.

An abbreviated list of some of those points of failure follows below.  Today, we will look at items 1-4.  Then this coming Friday, we will look at items 5-9.

  1. Inappropriate membrane
  2. Guardrails posts through membrane
  3. Escutcheons not strong enough to withstand foot traffic
  4. Exposed fastener heads in membrane in horizontal plane
  5. Oxidized ferrous metal resulting in decoupling
  6. Delaminated seams / fishmouthing
  7. Improper counterflashing
  8. Counterflashing separation at masonry regret
  9. Exposed fastener heads in horizontal plane of counterflashing

Inappropriate membrane

The material used as the roof membrane looks very similar to torchdown modified bitumen roofing material. However, in reality, this is a cheap alternative material, often used on sheds or buildings that are not actually over interior spaces. This material is a very cheap alternative to professional materials, and should only really be installed on roofs that have above a 2.5 to 12 pitch ratio.

inappropriate membrane

Guardrails posts through membrane

Since this is a balcony, with 3 open sides, they have installed guardrail post through the roof membrane at all locations of mounting. There are alternative methods of mounting the guard rail post, for example, it could have been installed mounted to the edge of the roof deck, but In this case, they took a big shortcut and installed the post right down through the roof membrane. That in itself isn’t against the building code or isn’t an area that is guaranteed to leak at all types of installation, with here they didn’t seal any of the post penetrations properly.

guardrail posts through membrane

Escutcheons not strong enough to withstand foot traffic

Just as wrong as the post installation is by itself, here they used a metal cover to cover the exposed fasteners in the post plate, but the lightweight aluminum coil stock metal that they used is in the area of foot traffic, or where people will walk on the deck and it is not strong enough to resist the weight of someone’s foot or a person standing on top of the metal.  At all locations throughout the deck the metal is bent and damaged and therein has debilitated or damaged the area of seams which were intended to keep water out of the area of the fasteners below.  We want to be clear and explain, even if this had not been damaged, water still could get underneath of the escutcheon cover because that as well is not properly sealed, but here there are now multiple areas that are open in allowing water to enter.


In the next picture below you can see a different plate from a different angle.  The plate has been created by bending a flat piece of coil stock aluminum into a small square shape box with a seam to join the two coupled pieces together on each side of the post base. Originally, they used a gun applied sealant to seal that seam but the sealant has been damaged by exposure to ultraviolet rays and has not had proper maintenance upkeep applied to reapply the sealant.

cover plate sealant

When you look closely at most of the cover plate inside corners, the thin aluminum is bent and has caused a fishmouth type shape which will allow water to enter under the plate.

damaged cover plate

Exposed fastener heads in membrane in horizontal plane

It should be a simple rule that no faster heads should be exposed in a horizontal installation of a low-slope or flat roof membrane. Those faster heads should always be overlaid with a portion of roof membrane or appropriate type of cover. Here though in this case the installer hasn’t even bothered to apply gun sealant such as elastomeric or even asphaltic caulking.   Water can leak down through small places, especially when a roof membrane is either applied in a low-slope or near flat type of orientation.  Here, leakage is almost guaranteed to happen at every one of these fastener heads.

nailheads fully exposed

A closer view of this problem follows below. You can see that not only are the nailheads fully exposed, they are both even set flat and where overdriven they have caused the unsecured membrane to lift away from the substrate.

closer view of nailheads

In the last photo below, you can see how prolific this problem is because the installer took a big shortcut and used small pieces of membrane to overlay areas where there were joints around the post penetration.

small pieces of membrane

Upkeep, Care and Maintenance of Washington DC Historic Roofs

This case study is a perfect example of why a professional roofer should be used for all types of roof installation, even things that seem as simple as a balcony.  Consulting with a roofing professional, like Dupont Roofing, familiar with the specific climate conditions and the building science of roofing in Washington DC is advisable to ensure the roof assembly is appropriately designed and constructed to manage the flow of water, ice damming, capillary action and condensation effectively.

The upkeep, maintenance, and general care of flat and mansard roof systems should be driven by an understanding and passion for historical methodologies, waterproofing principles, engineering and building science. Washington DC, a city built with both vintage charm and contemporary modernities, residential and commercial buildings of substantial value. 

The roofs of these buildings are their defensive shield from the harsh elements of nature. To our clients, as well as all readers of this article and our blog, we emphasize the importance of quality construction and active building maintenance.  Our website includes informative resources you can use to understand and learn about best practices on preservation of your building.  If you are in need of further guidance on the roof and its associated systems for your Washington DC property, we are here to assist, where we can. Simply contact us or complete the webform below and drop us a line and we’ll respond if we can help.

On Key

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