The Rural Voice, 1998-07, Page 45Advice
Renovation of the
older two-storey barn
By John W. Johnson
P. Eng. Engineer
Structure Design, Komoka Office
How many times have you
renovated your older two-storey
barn? These barns are proven to be
versatile structures, often enduring
renovation for several different
livestock types. In my work, I often
see renovation projects where major
structural changes have occurred
without consideration for important
aspects of engineering. People
commonly ask me for information
pertaining to the following situations:
Attaching an addition to an
existing building - if you are adding
a lean-to or an addition to an older
building, consider supporting the
new structure so that it does not rely
on the older building for bracing or
support. Assuming that the older
building can carry large additional
loading is common. This is not
always the case. Where possible,
place a row of posts and footings as
close to the existing building as
possible. Include sufficient wind
bracing in the new structure to
support itself. The attachment to the
older building should be non-
structural. Often, a gable roof is
preferable to a lean-to.
Removal of the hay mow/granary
floor — commonly, farmers decide to
remove the barn floor to a two-storey
building to allow more headroom for
a workshop, machinery storage, seed
cleaning operation, etc. The barn
floor provides stability for the walls
of the building. As well, the floor
assists in transferring wind Toads to
the corners of the building. When
removed, the stiffening effect of the
floor must be replaced. Since each
circumstance will be different,
engineering assistance is necessary to
ensure that the integrity of the
building is maintained.
Pouring a new concrete floor on
top of the hay mow floor -
frequently, farmers wish to consider
using the second storey of a two-
storey barn for livestock production.
Pouring concrete onto an existing
floor is quite possible. If the floor
originally carried a mow full of hay
or straw, it is likely that it can
support a slab of concrete, 4-6 inches
in thickness. A six-inch thickness of
concrete weighs approximately 75
pounds per square foot. By contrast,
20 feet of hay or straw can weigh 160
pounds per square foot or more. It is
a concern if the owner should once
again use the floor for hay or straw
storage at some point in the future.
The additional 75 pound per square
foot weight of the concrete can
reduce the overall carrying capacity
of the floor. Reinforced concrete
floors must be properly engineered.
Jacking up a barn to replace a wall
or beam — when replacing a section
of wall or a beam in a two-storey
barn, jacks must be used to
temporarily carry the weight of part
of the structure. To do this,
temporary beams must be located as
close as practical to the beam that
will be moved. Temporary beams are
commonly needed on both sides of
the existing beam. Jacks can be used
either at the top or base of temporary
posts.
Care should be taken to place the
posts or jacks on several layers of
planking. This will distribute the
weight carried by the posts so that
they will not punch through the
concrete floor or sink into a soil base
when lifting begins. Temporary
bracing should be used when lifting
the structure. If instability occurs at a
time when the permanent support
system has been removed, structural
collapse can result.
In Ontario, for new construction
and for structural renovation, the
Ontario Building Code requires that
you obtain a building permit. When
you discuss the project with the
municipal building official, he or she
will indicate what critical design
information they will require (if any)
before issuing a building permit. In
some circumstances you will need to
contact an engineer to obtain a design
for some or all building components.
Therefore, applying for a building
permit well before starting
construction is wise.
With proper planning, a well
designed renovation project can
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JULY 1998 41