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Moravian College • Preservation Master Plan
with no further method of draining away from the
building. Site drainage can also become problematic
through alteration of the original design intent, such
as when increased water runoff is directed to a part
of the system that was not designed to handle the
extra flow or when planting beds are introduced
that build up the soil level and change topography.
Lack of maintenance or improper maintenance will
cause site drainage failure. When drains become
clogged, the entire site drainage system can back
up and overflow, causing problems at building
foundations. Over time, the mulching of planting
beds can lead to mounded beds that direct water
against the foundation.
Site drainage systems are often subtle features in the
landscape, or even underground. It is easy to forget
about them. Often, building owners of historic
buildings do not even know where underground
drain lines are located. Old underground drain lines
can break, become clogged with tree roots, and fill
with sediment and debris. These unseen problems
may go unnoticed until they create obvious water
problems within buildings.
Site Drainage Improvements
Open site drainage systems, including swales,
surface and channel drains, and culverts, must
remain properly sloped to effectively drain water
runoff from buildings and circulation surfaces.
At downspout ends, where downspouts drain to
grade, try to direct runoff so that it empties at least
four feet away from the building foundation where
it will drain away from the building, using ground
leaders or splash blocks. Keep swales and surface
drains free of debris, vegetation, and utilities.
Regrade areas where water runoff has eroded the
site drainage system. Excessive soil erosion may
indicate a need to redesign the open drainage
system.
Closed site drainage systems, such as underground
drains and catch basins that may lead to a storm
sewer, can be costly to upgrade. Replacement
of underground drainage systems involves soil
disturbance and may trigger archeological oversight.
It is important to flush out underground drains
annually. Snaking out drains may remove small
clogs in the system. When underground drainage
systems must be replaced, it is worth replacing the
entire system with high quality materials if possible.
Install cleanouts at downspouts and at underground
drains for easier maintenance. Replace old terracotta
pipes as part of site drainage improvements.
It is important to keep a record of where all new
underground drains are installed and to document
the new system.
A French drain is essentially a pit or trench filled
with gravel that is sloped to direct water to a
well-drained location. The gravel may be wrapped
with a geotextile fabric to keep out silt and the
trench may have a pipe at the base. The drain can be
left open or can be covered with topsoil. A French
drain is appropriate in areas with slow moving
water, not in areas with storm runoff. French drains
can be helpful in areas where ponding water,
underground springs, or boggy soil conditions are
noted, near building foundations, and adjacent to
roads and walkways.
9.2 Concrete
Cast-in-place concrete is a common material used
for building foundations, porch flooring, access
ramps, areaway structures, and entrance steps.
At Moravian College, cast-in-place concrete has
been used primarily at later additions and changes
around existing historic buildings, such as new
entrance areas. Concrete used in visible locations,
such as entrance porch flooring, is finished with an
exposed aggregate finish. Cast-in-place concrete
is vulnerable to deterioration from site drainage
problems, freeze/thaw cycling, salt damage, and
structural stresses.
Cast-in-place concrete is a conglomerate material
composed of a cement matrix that has hardened
around an interior matrix of coarse and fine
aggregate and metal reinforcement. In contrast to
pre-cast concrete, it is poured into formwork, cured,
and finished on-site. Its compressive strength is
acquired from the hydration of the cement which
forms a binding paste around the aggregates. Metal
reinforcement gives concrete tensile strength.
The alkalinity of sound concrete protects the
reinforcement from corrosion by stabilizing an
oxide film over the steel. Corrosion will be inhibited
as long as the oxide film over the reinforcement is
not impaired.
Typical Concrete Conditions
Concrete work that predates ca. 1950, when
concrete was poorly-understood as a building
material, is prone to failure from design or
installation flaws. Expansion joints were typically
John Milner Associates • October 2009 • Chapter 9 • Building Guidelines • 281