[Greenbuilding] Green roof drainage question

Sat Jul 23 12:29:15 CDT 2011

Hi Marilyn

Funny to talking about snow in the middle of you heat wave.

Sounds like the issue is not just the weather (or weather maintenance i.e.
snowshoveling) but some failure around the door and roof membrane.

The code allows for a 2" separation between a deck and a door which is
pretty minimal. (a deck is classed as a roof in this case). I've had to try
and reduce that distance further for accessibility issues but if not it is
nice to increase it.

For it to have a hope in hell of working there needs to be a good membrane
connection of the roof up and over over the plate under the door sill and
the plate itself needs to have a slope (I usually specify plastic lumber
sill with the top planed to a bevel). The membrane over the sill also needs
to extend up the door jamb forming a continuous waterproof seal. The roof
membrane also needs to extend up the wall and connect to the seal around the
door jamb and sill.  Also the door needs to open out so that the
weatherstripping and doors seals can drain to the exterior.  The door frame
(sill and sides) also has to have a good connection to the membrane (usually
a foam backer rod of the right diameter sealed in with a good quality
polyurethane caulking - with good expansion and contraction). That is a lot
of connections and they have be layered and adhered properly to allow for
movement.

If all those connections are done properly and the snow is cleared from
against the wall and door it will work - if one of the seams separates and
water gets in and freezes opening up a seam further - it all goes to hell.

It is nice to have the seams at the building wall edge open for inspection
and maintenance.  A u channel plastic gutter works well and can drain into
the drain layer below the soil (are we talking 3-4" extensive type soil?).  

In terms of fixing the problem I think you need to pull back the
soil/drainage layer from the wall about a foot or so. You have to pull the
door out and remove the siding to expose the weather barrier and roof
membrane flashing. You probably have some damaged sill under and around the
door area as well as sheathing and that would need to be replaced. I would
recommend a plastic lumber sill under the door (less expansion and
contraction and forms a better seal to the membrane). I would have an
experienced roofer run a new membrane flashing over the existing roof
membrane and up the wall and over the door sill (and warranty the work).  I
would recommend increasing the height from deck to door to about 6-8"  (if
stepping up and over is not a problem) and having a short door put in
(outswing).

I would lay in some kind of gutter channel with cover (plastic u-drains for
driveways work well) against the building and under the door - you may have
to have holes drilled in it so it drains to the drain layer.  I would
recommend putting a heating cable in the gutter channel (can be a plug in
type if you have an exterior outlet).  Typically at the roof wall junction
there is less insulation and more building heat loss that would keep the
drain from freezing but you never know.

Do NOT put a drain through the membrane in front of the door - your plumbing
system drain is probably not designed for the extra flow and it is just
another hole in the boat.

Best

John

JOHN SALMEN ENVIRONMENTAL DESIGN

station design & millwork

4465 UPHILL RD DUNCAN BC V9L6M7 250-748-7672 C 250-246-8541 F 250-748-7612

From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Marilyn
Sent: July-23-11 8:59 AM
To: greenbuilding at lists.bioenergylists.org
Subject: [Greenbuilding] Green roof drainage question

Hi List: 

Here's the problem, best as I can state it. 

When I had my green roof put on the addition to my home, the roof came
higher than the place it would have been without due to necessary
engineering, so the 'ground level' is only about 2 inches below the door
sill where I go out there. 

For a couple of years in a row now we have had much snow and a giant fast
thaw in February. 

What seems to be happening, best as I can figure out, is that the sun has
sort of 'glazed' the surface of the ground due to the sun and cold so when
the rapid thaw hits, the water cannot get to the normal drainage channels,
and because the glazing has evened out the roof surface and counteracted the
roof drainage slope, the water backs up through my door and causes mucho
damage. 

I've been trying to figure out what to do for a couple years now, talking to
contractors, none of whom seem to be familiar with green roofs or have run
into any similar problems, so they're winging it with the  ideas. 

One idea was to put a drain right in front of the door that would tie into
my washing machine drainage below - would mean keeping the drain clear all
winter, but that can be done unless we get enough snow that I can't open the
door to the roof, which has happened.  The biggie with this one was that the
contractor couldn't figure out how and where the drain needed to be sealed
with all the layers (torch-down, root barrier, drainage layer etc) of stuff
he was unfamilair with.  He consulted a roof and a plumber, but no joy. 

The other idea was just to keep dumping lots of de-icer in front of the door
so that the water had a place to get down to the drainage layer, but my
hesitation with this is that with only 6 inches of light-weight soil mix,
wouldn't the drainage channels in the mat likely be frozen?  Could this
actually work? 

Sorry this is lengthy, but I'm trying to explain something I don't really
have the language for, nor likely a full understanding of the situation.
This is the worst part of 'going green' is that there's no help from
contractors when things go wrong since most of them haven't a clue and won't
even (and don't want to) think about it or learn. 

I hope some of the group here has some ideas or can evaluate the ideas above
- or anything.  I'd be most grateful for any inspiration or guidance. 

TIA, 

~marilyn 

Cybercrone 

http://www.eol.ca/~cybercrone 

Hm-m-m-m . . . 

In arithmetic as in politics, the importance of one 

is determined by the number of zeros behind him. - Unknown 

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