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On
November 21st & 22nd, 2005 three Energy Star certified modular houses
were delivered and lifted into place on their sites just south of the
10th & Page St. intersection in Charlottesville. The houses are the
culmination of a pilot program led by the Charlottesville Community
Design Center and the Piedmont Housing Alliance (PHA) to bring increased affordability, energy efficiency and quality to PHA's clients.
Each
house was built to exacting standards at the Mod-U-Kraf factory in
Rocky Mount, Virginia before being delivered to the site in
Charlottesville. Over the next two months workers will complete the
finishing details on the homes, which will be ready for their future
owners in early 2006.
WHAT IS MODULAR?
Modular
houses are composed of multiple factory-built units called modules that
are up to 90% finished when shipped from the factory to the house site.
Walls, floors, ceilings, stairs, and certain interior work (as
contracted) are all in place. Actual construction time for a
single-family modular house takes approximately one to two weeks. The
modules are individually shipped on flat-bed trailers to the site where
permanent foundations have already been built to receive the modular
assembly. After the each module is craned into place, all connections
to the foundation and between the modules are sealed and
weatherproofed.
On-site contractors hook up utilities and
complete exterior siding. Roofs are often only partially
factory-finished with rafter sections folded for secure transport from
the factory. Roofing installation is completed on site when the rafters
have been fully extended and sheathed. Depending on the percentage of
factory completion, on-site work after the delivery of modules takes
one to three more weeks to finish. The coordination of factory and
on-site tasks requires careful communication and planning. Every
modular house is built to comply with the same state, county and local
codes that would apply if it were built on site. Each phase of
construction is factory-inspected by an approved third-party that
issues a State or inspection agency label of approval.
Modular
houses have the potential to be more affordable through decreased
construction costs, decreased management oversight and a much shorter
financing period. The controlled construction environment of a modular
factory creates less waste of construction materials, less risk of mold
contamination during construction and overall higher quality through
strict measurement tolerances.
DESIGN CONCEPT
CCDC
design consultant Alan Wong worked on the design for the three houses,
researched potential modular factory partners and established the
relationship with Mod-U-Kraf. Each of the three narrow lots only
measures about 2600sf, and necessitated a long and narrow house shape.
The concept called for houses that would mesh with the rest of the
neighborhood, as well as the previous 20+ site-built houses already
constructed by PHA. The floorspace was limited to 1200sf to keep
overall costs low, and also to fit within design guidelines for Habitat
for Humanity houses, with the hope that in the future Habitat might be
able to benefit from project findings as well.
ENERGY EFFICIENCY
Energy
efficiency ranks high on the list of design requirements for PHA
houses. PHA's low-income clients often spend 15% or more of their
incomes to heat, cool and power their homes before moving into PHA's Energy Star
certified homes. Energy Star houses are at least 30% more efficient
than houses built to standard specifications. Energy Star homeowners
typically save $50-$100 a month on their utility bills, money which can
go towards their mortgage payment or into a savings account. Over a
30-year mortgage, this can add up to over $30,000!
The
Mod-U-Kraf factory already had an Energy Star option for their houses,
so they were an obvious choice for the Modular Pilot Program. Attention to detail in caulking joints and sealing
vents also yields tremendous energy savings. The efficient building
envelope allowed for a smaller heating and cooling system, which
allowed PHA to specify a more efficient model, thereby allowing for
increased savings for PHA's clients.
SITEWORK & FOUNDATION
The position of the site at the bottom of a steep hillside, along with a good amount of non-pourous surfaces in developments on top of the hill required some creative solutions in terms of sitework and foundations. Much of the stormwater from the surrounding area filters through the site, and in the past has lead to standing water after heavy rains. Consulting engineers from McKee Carson generously assisted in designing a solution. The foundations consist of prefabricated insulated concrete walls manufactured by Superior Walls, which rest atop three feet of compacted gravel. The compacted gravel allows stormwater to flow beneath the foundations, preventing flooding and foundation damage. The stormwater eventually flows to a bioswale that was created at the rear of the site. The bioswale is able to filter most of the stormwater pollutants and lets most of the stormwater percolate down to the water table, instead of sending the water into the city's stormwater sewers.
TESTING
Through
the partnership with Mod-U-Kraf, CCDC and PHA will be conducting
testing of three different insulation materials (standard fiberglass,
blown cellulose and icynene foam) in order get real world data on the
costs and benefits for future projects. Check back for the results of
this testing in the second half of 2006.
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