" Ch Ch Ch Changes"....Don't Always Improve IT (Your Roof, Your House) .
The Roof View
Here's a view of a 'flat' roof that has been shown on some of my other blogs.
Flat roofs are not actually flat. They either slope to a central drain or drain to one edge.
This angle is gradual so the drop from the high part of the roof to the drain is not much. Here it is about 6".
Thats fine when it's just raining and there is no blockage of the drain(s).
Blockage from debris is only a concern if you have large trees nearby and even when you don't, you equip it with a wire bulb strainer and check it several times a year.
Parapet Wall Detail
This is not a typical roof vent . It is small and built into the parapet wall and the opening is close to the roof surface.
This is not a concern in light rains, but when there is a real downpour any debris blockage at the drain will cause water to pond and back up on the roof surface.
In winter with snow and ice built up on the roof any drain freezing or blockage will result in back ups that will be up to those vent openings in no time.
Typical Gooseneck Roof 
This is a typical gooseneck roof vent. It is shaped that way to shed rain but allow air to move in and out of the roof space. This is actually 3 times higher in space above the roof surface than the vent shown in the parapet of the photo above.
So What is the significant change here?
For that look at the first photo. We see a chimney that has been abandoned and capped with that big mounded piece of concrete. That's fine but what it tells us is the the heating system of the building has been changed and the chimney is no longer needed.
That part is ok, but what does that change mean to the roof. Well it means there is no longer an almost constantly warmed masonry mass in the centre of this roof keeping the components from freezing, most significantly the drainage piping of the roof drain.
Now that drain is liable to freezing and blockage for much of the winter season. Just a result of the heating system change and the chimney being capped.
Now what happens when the drain is blocked? The water stays on the roof and freezes into thicker and thicker lenses of ice plus snow as the winter drags on (Winter always drags on doesn't it?).
But when we start to warm up towards spring, the drain remains frozen under ice, while snow melt water and rain accumulate on the roof. On big roofs that can cause structural damage.
But here our concern is the water that gets backed up and drips into those low parapet wall vents. That water soaks into the brick wall layer and does the damage we saw on a previous blog.
Also with about the same amount of flooding the water is bypassing the edge of the membrane at the front wall (where there is no parapet wall). The water runs through the soffit overhang and into the front wall of this building. We saw this shown here with theses two clues.
When the chimney was operating it and the area around it was constantly warmed and kept the nearby drain open and functioning to clear the roof of any water accumulation, therefor there was less ice. Water getting up to the vent edges or the front limit of the roof membrane would have been a rare occurrence. That was part of this buildings systems.
Every time you make changes the other components and systems are affected.
So changes may make sense but there can be aspects that are not considered, and those can cause damage as we see here.
If you are in the Montreal area and want a professional consult before making changes to your property please contact me for a quotation. I can also direct you to associates in other areas as well.
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