| For those of you
who read my column, you know that my opinion of the “green”
movement is that it has its good aspects and not-so-good aspects.
When an idea comes out of the green movement, it needs to be
scrutinized to see if it is really a worthy idea. Such is the
case of “green roofing”.
Green roofing is done by installing soil on
top of a roof in order to growing vegetation. It has been done
for many years in countries like Germany, where in its cities
high density development leaves little room for vegetation.
It has been estimated that about ten percent of Germany’s roofs
are now green, and that almost 350 million square feet of green
roofs were installed between 1989 and 1999. The city of Tokyo
now requires all new construction to include green roofing.
The reasons that the environmental movement
gives for green roofing are numerous, and most of them have
merit.
If done well, it can be very aesthetically pleasing
to see a roof covered with vegetation instead of an ugly roof
covering. This is especially true for those who live or work
in high rises and look down out of their windows at the roofs
below.
Vegetation will reduce the heat island effect
that occurs when roofing absorbs heat from sunlight. The combination
of paving and roofing can significantly raise the ambient air
temperature around buildings, creating a greater heat load for
air conditioning systems to overcome. The heat island effect
creates the need for larger systems and causes the systems to
work harder, thereby using more energy. Vegetation will not
absorb the amount of energy that a roof will, so it reduces
these loads.
The soil on a green roof is a good insulator,
so it reduces the heating and air conditioning needs of the
building. Because of its mass, temperatures of the soil remain
more stable, and this reduces the temperature swings in the
building.
More vegetation reduces the amount of carbon
dioxide and increases the amount of oxygen.
The soil will remove nitrogen from rainwater
when the vegetation absorbs nitrogen from the soil, effectively
filtering the nitrogen out before the water drains away.
Environmentalists claim that the soil has the
ability to neutralize acid rain as it filters through the soil.
Vegetation has the ability to absorb noise,
which will reduce the amount of noise that traffic produces.
It will also reduce the amount of stormwater
runoff by absorbing the rainwater. If you have done any construction
here in Tulsa, you know that stormwater management is a big
deal, as it is in many other parts of the country. Impervious
surfaces like roofing will cause a great deal more rainwater
to be diverted into our drainage systems.
Finally, the vegetation creates a habitat for
birds.
All of this sounds great, and it is all pretty
much true. But you should look at the practical aspects of this
system before ever considering it. Here are some things you
should.
Soil is heavy, especially when it is saturated
with rainwater. This means that the roof structure must be designed
to carry the additional weight. You should not plan to hang
a suspended ceiling from the roof structure because it can move
up and down as the weight decreases and increases with the weight
of the water. The flexing of the roof can cause ceiling panels
to fall out and cause damage to the roofing membrane. The only
way to overcome this problem is to over-design the roof so it
won’t move at all, which is not economical.
The roof drainage system should also be increased
in size, and should be designed so that there are no tight turns
in the drain lines, otherwise soil that washes into the system
will eventually clog it. In addition, the roofing system must
be extremely well-designed and expertly installed, because finding
leaks and making repairs will require excavation.
The vegetation requires a lot more maintenance
than a standard roof. Many green roofs are nothing more than
grass, but even that must be watered, fertilized and mowed.
It seems strange to me that a movement that is against watering
and fertilizing lawns and doesn’t like using electric or gasoline
mowers would want to create a situation where there would be
more of it than less.
All of this is not to say that I am opposed
to green roofing. However, anyone considering this system should
be willing to balance and accept the additional costs and risks
that come with it.
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