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A
Guide to Building in Southwest Florida An
Outline for energy efficiency and sustainable building practices By
Rob Andrys A.I.A.
Building
in Southwest Florida in unlike building anywhere else in the continental
United States. We live
in the Subtropics where we average 50” of rainfall per year, rarely
use heat and cool our homes most of the year.
More
important than cooling the home is removing the humidity that damages
the interior finishes, propagates mold and mildew, leading to indoor
health problems. Removing
this moisture when the outside humidity is above 80% requires special
consideration in the design process.
By keeping the moisture out of the building through its design,
the air conditioner can be smaller and run less often. Other
considerations of living in the subtropics are the damaging effects
of hurricane winds, flooding, extreme ultraviolet sunrays, wood
eating insects and dry rot. The design and selection of a building’s materials and systems must ensure durability, low maintenance, and optimize indoor air quality, without compromising the planet’s future. The
overriding strategy for building in Southwest Florida is to: maintain
a dry interior; keep the rain away from your walls; hurricane strap
the structure; stop the termites from making your home their next
dinner; and become allies with the natural elements instead of fighting
them. The
following are suggested building component systems that, when combined
in a thoughtful design, allows your home to be energy efficient,
healthy and have a long life. General The
roof is the second most important component of your building (The
first being the footing and structural frame the roof sits on). Rainfall
striking the roof should be managed, that is, gutters and downspouts
are important ways of keeping water away from walls, thus reducing
dry rot and insect invasion. Choose
roofing that is in your budget that provides the longest life, the
easiest maintenance and serviceability.
Concrete tile roofs are the most durable and energy efficient,
followed by white standing seam metal roofing, and, lastly shingle
roofs. The
color of a roof is directly related to how much it will cost to
cool the building. The
closer to white, the more cost saving the building. Roof
Penetrations All
penetrations of the roof are potential leaks.
Keep penetrations to a minimum, and personally inspect all
penetration flashings before being covered up by the roofing.
If you plan on adding a component in the future which requires
roof penetrations, (such as a solar heater), install the lead sleeve
or flashed opening during the initial construction. If
solar panels will be added in the future (most probably), make accommodations
on the south side of the building.
Brace and/or block the trusses affected, provide penetration
boots. Do research
in planning ahead for the inclusion of these panels.
Hurricane
considerations Whatever
roof you pick, consider that this is hurricane country, and should
be tied down to the highest degree possible.
Tile roofs should be screwed down with stainless steel screws,
metal roofing should have the seams mechanically adhered and the
fasteners placed under the metal, not penetrating it.
Shingles (if used) should be the laminated type with the
first row set securely in mastic.
The plywood sheathing should be secured with twist nails
or screws. Finally,
the best shape for a roof is a hip roof with an average slope. Radiant
Barriers Radiant
barriers have proven to be very helpful in reducing the energy load
on a building. The
newest radiant barriers are now spray applied to the bottom of roof
sheathing; this allows complete coverage, ease of installation and
no damage to the barrier during construction.
The inclusion of a radiant barrier is dependent on the type
of roof you select. Sealed
Attic Space Research
from the Florida Solar Energy Center and Building Sciences corporation
has conclusively shown that an un-vented, sealed attic space with
the insulation placed below the roof sheathing is the most cost
effective and healthy way of building in Florida.
By sealing the attic, the air conditioning unit runs less
because it no longer draws the limitless supply of humid air through
the gypsum board ceiling or the holes in the light fixtures into
the house. Furthermore,
by having a warm, relatively dry attic space rather than a hot,
humid attic, it does not allow the mold and mildew to accumulate
on the gypsum board ceiling. It is also more forgiving in the possibility
of a/c duct leakage. Walls
built in SW Florida must resist hurricanes, termites and keep the
moisture from entering into the building. All
walls leak moisture through them.
Walls must be designed to have a drainage plane from top
to bottom to direct this moisture down and to the exterior. Wood
walls should be discouraged for the above reasons. (Cypress and
heart pine woods that historically had been used successfully are
no longer commercially available.) Metal
stud wall systems are available and solve the termite problem, but
must be engineered to resist hurricane winds and will rust if exposed
to water seeping into the walls. Masonry
walls or variations of them have preformed excellently when properly
designed and installed. They
are much stronger than wood or metal walls, they do not burn or
rot, and are not damaged by wood eating insects.
The following are various types of masonry wall systems currently
in use and commercially available. Hollow
Concrete Block-traditional.
The traditional SW Florida wall system consisted of concrete
block covered with stucco on the outside surface.
On the inside ¾” pressure treated furring strips are fastened
to the block, ¾” fiberglass batt or rigid foam board is placed between
the furring and then covered with ½” gypsum board. Concrete blocks
are readily available and made from local resources.
Advantages:
Cheapest way of building a wall. Disadvantages:
Allows moisture to enter through the wall, has minimal insulation
value, and in areas exposed to the sun the block heats up and radiates
heat into the building even after the sun no longer is striking
the wall. The ¾” furring
requires that the concrete block be cut open where electrical outlets
and switches are located.
This allows moisture an easier way to migrate into the building,
especially if the concrete block is also penetrated on the outside
for the same reason. Hollow
Concrete Block-updated.
The updated method of using concrete block is to stucco the
outside surface. On the inside 1 ½” furring strips are fastened
to the block, then the walls and furring are sprayed with a water-based
semi-permeable coating, allowing the block to dry out somewhat,
but slowing down the transfer of water vapor into the home.
Between the furring, 1 ½” semi-rigid un-faced fiberglass
boards are installed and covered with ½” gypsum board. Advantages:
Varies only slightly from the traditional method, thus construction
prices are low, moisture barrier is continuous, and fills all holes
and cracks. The 1 ½”
furring allows electrical outlets and switches to be placed within
the furring space so that cutting the concrete block is not required. Disadvantages:
In areas exposed to the sun, the block heats up and radiates
heat into the building even after the sun no longer is striking
the wall. Requires
poured concrete tie beam at top of walls and large openings. Concrete lintels are needed above windows and doors.
Allows areas for insects to live in the hollow voids. c. Foam Insulated Concrete wall system (FIC).
This system uses hollow expanded polystyrene blocks or other
insulating materials that are used as concrete forms.
Steel reinforcing is added and ready mix concrete is then
pumped into the hollow cavities creating a solid concrete wall with
insulation on both sides.
The outside surface can be stuccoed, sided, or a brick veneer
installed. Depending
on the manufacturer, the inside surface is ready to receive gypsum
board, or must have additional wood-furring strips fasten to the
forms for attaching the gypsum board.
Advantages:
Much stronger than hollow concrete block walls.
In areas exposed to the sun, the block does not heat up and
radiate heat into the building because the insulation is on the
exterior. Does not require poured concrete tie-beams or lintels. Lower
infiltration of air because of solid concrete. The foam can be cut
to allow electrical outlets and switches to be placed within the
wall system. Can be
quicker to install than hollow concrete block or traditional poured-in-place
concrete walls. Disadvantages:
More expensive to install as a system than hollow concrete
block. The moisture
barrier must be placed on the outside of the wall by means of an
electrometric paint that needs to be repainted every 5-7 years. d. Aerated Concrete blocks.
This system uses solid aerated concrete blocks that are ‘glued’
together in the same fashion that a typical concrete block wall
is grouted together. The outside can then be stuccoed, sided, or
a brick veneer applied. On
the inside of the wall a water based semi-permeable coating is spray
applied, then a thin plaster coating is directly troweled onto the
aerated block. Advantages:
Higher ‘R’ value than hollow concrete block walls, or a FIC system. In areas exposed to the sun, the block does not heat up and
radiate heat into the building.
Low infiltration of air into the house because of solid construction.
The aerated concrete can be cut with a conventional saw to allow
electrical outlets and switches to be placed within the wall system.
Can be quicker to install than hollow concrete block. Disadvantages:
More expensive to install as a system than hollow concrete
block. Requires poured concrete tie beam at top of walls and large
openings. Requires
larger footings for ‘dead weight’ to resist hurricane wind loads. Floor
systems built in SW Florida began with raised wood floors built
above ground to allow air circulation under the house to cool it
and keep the house above periodic flooding and away from termites.
Today we raise the floor for many of the same reasons, except moist
air is no longer desired under the floor plane.
An un-vented crawl space is desired for the same reasons
an un-vented attic is advocated.
Concrete
slabs can be poured directly on the ground and the home built directly
on the slab. It is
recommended that the height of the floor be higher than your road
or flood stage. If
the home is desired to be raised above grade, a footing is poured
and a stem foundation wall is built up to the desired height of
the floor slab. The
inside area of the stem wall is then filled with sand, compacted,
the slab poured, and the remainder of the walls constructed. Raised
wood floors are still in use usually when higher elevations are
desired for parking below or for flood elevation requirements. The
structure is usually pressure treated wood, a system that is not
usually viewed as a permanent foundation. The
floor system must resist hurricanes, termites, and keep moisture
and radon gas from entering the building.
General Window
systems must resist hurricanes, termites and keep the rain and moisture
from entering into the building.
Traditional
wood windows are beautiful but do not hold up in Florida, as evidenced
by their failure in older homes. Newer aluminum clad windows have
solved much of this problem. Aluminum
frame windows are popular because of their durability and ease of
maintenance. Since
we do not have the long duration of cold weather that creates large
temperature differences between indoors and outdoors, thermal conductivity
and the resulting condensation problems are viewed as minor deficiencies
in the selection of an aluminum window.
Vinyl
windows solve the thermal conductivity losses and corrosion problems
associated with aluminum windows.
They are becoming more durable with the advancements of UV
blocks that stop the vinyl from becoming brittle.
However, field-testing is still years away from a final answer
on durability. Solid vinyl windows have also experienced problems with losing
their shape as the horizontal dimension has increased. Vinyl
clad wood windows have the same dependence on a good UV block, but
they also tend to keep their shape better than an all-vinyl windows
and have the advantage of a wood look on the inside and no thermal
conductance loss. Glazing Window
glazing is typically only single pane in SW Florida, again due to
the low number of days where there is a large temperature difference
between indoors and outdoors. The
glazing is usually clear or slightly tinted.
If there is no physical solar control on the east or west
sides of the building such as awnings or trees, a reflective, tinted
or spectrally selective glazing is highly recommended.
Controlling the solar heat gain through windows is important
not just for cooling concerns, but for damage to the home’s interior
finish. Skylight
and Light tubes Skylights
deliver expansive amounts of daylight into a space by virtue of
their location high in the ceiling and positioning to the sky.
Along with “free” light, they permit a view to the sky, but
can also become noisy in a heavy rain.
There are disadvantages: they have a history of leakage problems,
it is imperative they be covered in a hurricane, and the day light
can be hard to control contributing to large amounts of solar heat
gain and damage to interior finishes of homes. Light
tubes require smaller roof penetrations, deliver smaller but more
controlled daylight to the space, but do not give a view to the
sky. Mechanical
systems in SW Florida are primarily used for cooling and dehumidifying.
They usually come with an electric heat strip that tempers
the air during our days of cold weather. Removing humidity is the
top priority from an indoor air quality assessment.
Second is to make sure the building is under a positive pressure;
the mechanical system should not create a building that sucks moisture
into the house. If
the system is not designed correctly, you can have a cool house,
but still have humidity problems from a bad design or leaky ductwork.
Humidity allows molds to grow in the ductwork, carpet, drapes,
etc.; molds are the number one air pollution in a home. Along with the issue of humidity, there is the need for correct ventilation. As the building is ‘tightened’ up and allows less air to infiltrate through leaky doors, windows and cracks in the wall, the indoor air becomes stale and polluted by our everyday activities. The air inside must be exchanged with fresh outdoor air, but that air is usually very humid and must be conditioned before entering the building. Cooling The
most popular systems and most affordable systems are Direct EXchange
air conditioning units, (DX units).
A DX unit is comprised of two components, an indoor air handler
and an outdoor condensing unit.
The indoor unit removes heat from the home and in the process
condenses humidity on the coil that collects in a pan and runs outside.
The outdoor unit condenses the refrigerant gas by drawing
air across the coils, expelling the heat to the outside air.
When the ambient outside air is hot and humid it takes much
longer to remove the heat and more coils are needed, thus bigger
outdoor units are also more efficient.
The more heat that can be removed from the refrigerant gas,
the more efficient the system runs. That is why water is used on large commercial systems, because
it usually has a lower ambient temperature and can remove heat easier.
Variable
speed A/C units are an excellent way of removing humidity using
a modified DX machine. The
inside air handler has a variable speed fan that start up at slow
speed and gradually comes up to full speed.
This allows for the coils to become very cold at first, then
as the fan speeds up, the coil is warmed to normal operating temperature.
Thus more moisture condensates on the coil and is subsequently
removed from the home than a conventional DX system. New
systems include heat pipe technology, heat pumps and combinations
of DX and dehumidifying units.
Heat pipe technology has the most promise since it removes
more humidity using the same amount of energy as a DX system, this
is especially important if higher levels of fresh air and, or low
humidity levels are desired.
The placement of the ducting should occur within the air-conditioned part of the house. It has been estimated that duct leakage accounts for 1/3 of the total Florida residential cooling and heating consumption. To reduce the amount of dust and mold in the ductwork, metal or plastic-lined ducts should be used. Ductwork with fiberglass exposed to the air stream should be avoided. Ventilation Air
to air heat exchangers or heat recovery units are used to remove
humidity from incoming air and cool it down by exchanging the heat
from the outgoing stale but conditioned air.
These units are not as popular here as in colder climates
where the temperature difference is more extreme, however studies
are now showing how important is it to pressurize a building in
the humid south regions. If
a home does have air leaks then moist humid air is not drawn through
that opening in to the building.
This creates a spot where the building is moist and causes
mold to grow and a place for termites to feast. Windows
should be operable to allow natural ventilation. Paddle fans are still one of the best ways to circulate air efficiently. New high efficiency fans shaped like air plane propellers are now available. Water
Heating In
SW Florida it is just plain wasteful to heat water using electricity. It is estimated that in a home containing 4 or more people
that 30% of the average electrical bill is spent on heating water.
Solar panels are most effective way to heat water, the payback is
immediate when amortized over the life of the mortgage.
The other method of heating water is to use a heat exchanger
in conjunction with the air conditioning unit.
However, this heats water only when you are using the air
conditioner. Efficient
lighting systems employ as much fluorescent lighting fixtures as
possible. Compact fluorescent
technology now allows fluorescent lighting to be used in regular
incandescent fixtures. These
compacts use 60% less electricity and add 30% less heat load to
the A/C equipment. This constitutes tremendous comparable cost savings.
Further advancements in fluorescent now add a full spectrum light
source, eliminating the garish yellow hue.
Halogen
light bulbs should be used where brighter light levels or dimmable
lighting is desired, rather than incandescent bulbs due to their
higher efficiency. Recessed
can lights should be insulated and used sparingly considering you
are punching a hole in your ceiling, allowing attic air to enter
your house. Irrigation Grey
water treatment systems are relatively new to the market in SW Florida,
but have been fulfilling water conservation needs elsewhere for
quite some time. The use of domestic drinking water for irrigation of plants
is expensive and wasteful.
These systems reuse water that is put down the drain of tubs
and lavatory sinks of the home. Efficient use of water saves money
and allows the use of irrigation water during the “water restriction”
dry months of the year. Water
catchment systems utilize collecting rainwater from the roof, filtering
it, storing it in underground cisterns, and then pumping it out
as irrigation water when needed. Drinking
water Drinking
water that is usually purchased in a supermarket is not only costly
and wasteful, but also inconvenient.
The manufacturing of pure, clean water at the home without
excessive amounts of water needed to back flush the unit is now
available. The purity
of the initial water source will determine how many and what kinds
of components are necessary. Swimming
Pool The
typical chlorine systems used in most homes are now being questioned
as to its healthiness. New
bromide systems are less expensive to operate and maintain, have
less health risks for the users, and are less corrosive to the various
metals used in the pool system, thus prolonging their life. Wall
Coverings The
most common and dangerously unhealthy practice is to install vinyl
wall coverings on an exterior wall.
This creates a vapor barrier on the wrong side of the wall,
allowing moisture and fungi to accumulate on the backside of the
vinyl. Oil
based paint have the same results as vinyl wallpaper on an exterior
wall, use latex paint. Oil
based paints release VOCs that are not whisked away magically after
they are applied. They
are absorbed by other soft materials in the house and then released
slowly over time, making the air unhealthy.
Sherwin-Williams offers no VOC paints. Natural fiber wall coverings should not be used in rooms with frequent exposure to high humidity; the fibers become a breeding ground for mold. Floor
Coverings Carpets
should be used sparingly, as they can become breeding a ground for
mold if not cleaned often with a powerful vacuum cleaner.
Dirt is the medium that molds grow in, not carpet, but dirt
can hide better in carpet than tile. There
are more sustainable products on the market than real wood flooring
such as bamboo, cork and linoleum. This
list will be added to, amended and edited in coming months.
If you have any comments, please address them to Rob Andrys
Architects, at AndrysR@ix.netcom.com Priorities
for energy efficiency for new residential construction in Florida.
By D. Parker/R. Vieira, Florida Solar Energy Center
The options are listed in order of importance: Proper
window orientation Windows
should be maximized on North and South walls and minimized on east
and particularly on the west and northwest. Window
shading. By
use of exterior shading devises such as porches, awning shutters,
trellises. This reduces cooling costs while preserving daylight.
Trees can also be very effective and increase a homes value
as they grow. Light
colored surfaces on exterior. Low
cost to implement yet has high energy efficiency. Low
energy use appliances and lighting. Keeping
internal heat generated loads low will save on A/C costs.
An efficient refrigerator is particularly important along
with using as much fluorescent lamps as possible. High
SEER A/C systems Use
at least a 14 SEER with a variable speed indoor fan unit.
Unit should be sized using “Manual J” (a/c design manual)
with the 97.5% summer design temperature for the location and a
75 degree indoor temperature. |
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