Leaking walkout deck – Part II

 In our last article, we took a look at a balcony with a roof membrane as the walking surface.   Water sensitive wood framing and wood ceiling materials were used below the balcony so It is important that the upper side of the balcony does not leak yet the installation was so poorly done that leaks were coming through at a multitude of locations.

An abbreviated list of some of those points of failure follows below.  Today, we will look at items 5-9.  In the last article, we looked at items 1-4

  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

Oxidized ferrous metal resulting in decoupling

We recently looked at the issue of ferrous metal embeds and penetrations through low-slope or flat roofs and why those areas were critical to prevent leakage and why ferrous metal has the tendency to decouple or delaminate from attached materials when it oxidizes.

A picture of a rusting guard rail plate at the base of the post follows. 

rusting guard rail plate

Delaminated seams / fishmouthing

The last article we talked about the fact that the material used here is not actually torch-down modified bitumen and the type of material used is a cheap makeshift type alternative material which should have not been used at this type of installation.  Saving money by using this type of material is a bad idea!

delaminated seams

Throughout the installation, at the lap joints, the material is delaminated at the seams. This is particularly problematic because this is a very low-slope installation. Even low-slope or so-called “flat roofs” should have a grade of at least 1/4 of an inch per linear foot in the direction of the drain.   Here, in this case, the grade is barely sufficient, and since it is such a low low-slope roof, when you have delamination at seams like this, water will enter back upwards through the seams when there is prolonged periods of rain, very heavy rain, and particularly when there are freeze-thaw conditions with precipitation at temperatures hovering around 32°F.

seam space

Here, in the picture below you can see I slid my finger right up under the seam without even applying any pressure.

seam joint delaminated

Improper counterflashing

There are several different approved methods for installation of counter flashing and termination bars at low slope of flat roofs. Here though, they used an assembly of aluminum coil stock metal to cover over top of the low slope membrane, but they did not run the low slope membrane up as base flashing on the bottom of the vertical surface of the wall. This is incorrect and will not work because as water goes under the flat portion of the metal it will reach the edge of the flat roof membrane and then go inside of the roof framing.

improper counterflashing

Counterflashing separation at masonry reglet

Without destructive investigation, we’re not certain that they did not install the aluminum counter flashing into a recess in the mortar of the brick, referred to as a raggle or reglet, but considering all of the shortcuts, defects and problems in their installation, here we also assume that the top of the counterflashing has probably been set into the masonry. Nonetheless, it’s important from an upkeep and maintenance perspective that the top of the counterflashing is recessed and sealed with a flexible sealant and in this case the seal has become defective and damage by prolonged exposure to ultraviolet rays.

damaged seal

Exposed fastener heads in horizontal plane of counterflashing

In addition to the exposed faster heads in the horizontal plane of the roof membrane, as described in the previous article, there are also several fasteners that have been installed in the horizontal plane of the counterflashing. This is also equally as problematic and will lead to leakage in the exact same way.

For context, a picture of the underside of the roof follows below. Not only has the framing been damaged, but the beadboard ceiling has also been damaged from exposure to water leaking in from the upper side of the roof above.

exposed fastner heads leakage

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.

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