| Buildings
and leads to a lot more problems
as rainfall hits the insides, runs
down & drips off the base corner
and it feels like it is raining in. The
base of any upstand should
always be at a minimum 50mm (2”
inch) back from the top of the roof
sheet, this is so any water/rainfall
that hits the inside of the upright
flashing can then drain away.
Let’s be honest, it is very rare
that rainfall comes straight down, it
nearly always comes down on an
angle so then it will hit the inside of
any upturned flashing, run down to
the bottom edge and as long as
that edge is back from the top of
the sheet it will run down the roof
to the gutter.
If you double the volume of air
in a building then realistically you
need to double the size of the
openings at the eaves and ridge.
People often have one side of a
building open and think that will be
fine, there is plenty of space for the
Farmplus has thirty
years experience in the
design and supply of
timber framed farm
buildings and shelters
air to get out. After buying a
smoke machine for testing
buildings a few years ago, it really
opened my eyes to how ill-
informed most of us are regarding
air flows. The best I saw was in an
old building that I could barely
stand up in, it had a small gap
under the gutter and an open
ridge. Within 30 seconds the
smoke had gone completely. Yet in
a single slope open shed it took
approximately 5 minutes to go and
when it did the smoke went out
through the low side.
The wider buildings become a
greater problem arises with stale
air, the air has to travel much
further to get to the ridge and often
the stale air cools and comes back
down again.
From my experience, lower
buildings are much easier to get
natural air flow working. You need
to design your buildings for the
animals that use them, not the big
machines you like to play with.
Let’s face reality, we have been
constructing bigger, taller
buildings for the last 10 years and
now nearly all the farmers have
had to buy fans to try and get air
to move. Most of these fans are
only trying to move the air, they
aren’t blowing clean air in or
extracting stale air out. This must
be simple truth that volume of air is
not enough in itself. Air exchange
is what is needed, simply clean air
in and stale air out.
Think of what you would like to use the building for and
design it for that specific purpose to get the best value
overall.
hen we look at
buildings we need
to stick to the
basic principles of
nature. All animals
want shelter from
the wind and rain, shade from the
sun and plenty of fresh air. Air
movements should be above
animal height so as not to create a
draft.
Animals left to nature always try
to find shelter in the basic form,
they use hedges, walls & natural
hollows to get out of or reduce the
impact of the winds. Likewise, they
use trees for shade.
Ideally animals need a shelter
wall to be able to lie behind with a
decent air gap above for air to
pass over. Depending on the
height of the wall, the gap above
may need some wind break
material to break wind speed on
W
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bad days.
The best and cheapest form of
ventilation is and always will be
natural ventilation using the stack
effect with gaps at the low eaves
and open ridges. No fans using
electricity, no moving parts &
nothing to go wrong. In high
rainfall areas, special caps can be
supplied. The best is still simple,
upturned flashing to make the
outside air lift over the ridge of the
roof. The base of any upstand
should always be at a minimum
50mm (2” inch) back from the top
of the roof sheet, so any
water/rainfall that hits the inside of
the upright flashing can then drain
away.
Ventilation is not the volume of
air in a building, it is the rate of air
exchange, simply clean air in and
stale air out.
August 2018 | Farming Monthly | 33