Green Roofs - Living Architecture Monitor - Spring 2020 - 16

The original vegetation was a mix of seeding 85 per cent and planting 15 per cent. A mix of perennials and grasses were sowed, and
sedum, chives as well as iris were planted sparsely over the whole
surface. An irrigation system was installed several years after the
green roof was completed. There was maintenance done in the
first few years, but the roof has been left unattended for many years
now, with little to no maintenance on the plants. This has resulted
in a wild, outgrown prairie, composed of beautiful flowering perennials and wild grasses. A partial survey of plants conducted in 2019
revealed the following species, listed in the table below.

SPRING PLANTS AT THE MEC
GREEN ROOF DURING ITS FIRST
YEARS IN 1999

Photo courtesy S. Peck

PLANT EVOLUTION

LATIN NAME

COMMON NAME

ECHINACE PARADOXA

YELLOW CONEFLOWER

PRUNUS VIRGINIANA

CHOKECHERRY

FRAGARIA X ANANASSA

STRAWBERRY

PHEDYMUS

SEDUM SP

PHLOX SUBULATE

MOSS PHLOX

ALLIUM SCHOENOPRASUM

CHIVES

GEUM TRIFLORUM

THREE FLOWERING AVENS

FESTUCA OVINA

SHEEP FESCUE

MONARDA FISTULOSA

BERGAMOT

SOLIDAGO CANADENSIS

GOLDEN ROD

THE WATERPROOFING TEST AND RESULTS

After the MEC building was sold to developers in 2018, GRHC
received approval to go up on the roof and perform cut test on
both the exposed surface and the green roof covered portion of the
Soprema build up waterproofing. The testing of the samples was
then done to assess how the bitumen and different components of
the waterproofing have evolved and degraded over time.
In order to take the samples, we had to peel back the green
roof and expose the underlaying waterproofing. A section of 12" x
12" was cut from the two sections, packed and sent to our testing
facilities in Drummondville. Once the sample reached the lab, the
bitumen was scraped off, diluted in a solvent and passed through a
GPC (Gel Permeation Chromatography) testing machine. In the
GPC, the smaller molecules are slowed down by the microporous
material packed inside the column. A series of detectors allow to
accurately determine the weight of the SBS elastomeric polymer.
This evaluation allows us to measure the break down of molecular
chains, in other words, how the SBS characteristics have degraded
LIVING ARCHITECTURE MONITOR / SPRING 2020 / 16

SPRING PLANTS AT
THE MEC GREEN ROOF
IN 2019

Photo courtesy S. Peck

SELECTED PLANT SPECIES IDENTIFIED
ON 22 YEAR OLD EXTENSIVE GREEN ROOF

over time from long molecular chains to very small chains.
The 2 ply SBS membranes are composed of bitumen,
elastomeric SBS polymers and a support reinforcement that can
be composed of polyester or fiber glass. The bitumen gives the
membrane it's waterproof capacity. The elastomeric polymers
(SBS) will give the product its elasticity and capacity to hold a
specific shape, or go back to it, like an elastic would. As for the
reinforcement layer, it gives the waterproofing membrane its
rigidity and resistance to puncture.
The GPC testing method is specific to SBS and bitumen. It
measures the length of the polymeric chains of molecules. When
exposed to aggressive environments, SBS polymeric chains are
broken down, resulting in a possible loss of elasticity. The testing
was done on a new SBS membrane as well as the two samples,
taken from the MEC green roof (See graph). The results were then
compared to a brand new SBS modified bitumen to evaluate the
degradation of the SBS molecule. It is important to understand that
these tests allow us to compare the degradation of the elastomeric
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Green Roofs - Living Architecture Monitor - Spring 2020

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