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Windows
For me personally windows are the most important 'part'
of a house. North American history has presented them to the 20th Century
badly. Certainly it made sense for our forefathers/mothers in New England
to install the smallest windows. The climate and cost of glass being what
it was dictated such. Why some newer houses still have meager, thoughtless
windows has always perplexed me though. Certainly windows are expensive,
but in the overall cost of the house they come to only 5 to 8% +- for an
abundant number. And look what is sacrificed if you use the fewest windows
allowed. Windows are your contact with the outdoors, your moment to moment
outlet and ventilation. We could even bore you by citing psychology
studies in sensory deprivation but I suppose that would be pushing it. So
lets leave it saying how striking a house can be through its
window design or on the other hand how banal.
So, here we have a house 'part' that is involved
in your quality of life, in good design and in the ambiance of the house's
interior. The problem is windows are far from
restriction free since they are controlled by building codes for energy
conservation. Additionally it goes without saying they can be a bit expensive for many home owners.
So now we have a 'part' of the house that is not only very much involved in the successful design of your house
but is also critical in the house’s energy consumption and is expensive.
Obviously it is important to dwell on this subject and hopefully present a
practical design direction.
To do so let's divide, as we have before, the topic into 2 sections as follows:
windows in a economy house and those in more expensive ones.
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If you are designing the most economical (cheapest) house
Here the Building Codes reign supreme. Two
different codes are involved. The Building Code will dictate the minimum
sizes and the Energy Conservation Codes will limit the amount of windows
(and therefore energy loss). Limiting windows may by the predominate thought in your
mind. Rightfully so. Windows are certainly much more
expensive
than a solid 2x4 wall with basic insulation and siding. Windows are
also not very energy efficient especially if you are selecting the more
economical grades (no low E and minimal R factor).
Even so there are some tricks you can use to maximize your views,
sunlight and design impact.
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Start by placing the windows required by code where they must go.
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Subtract these from the total windows allowed by the Energy Code.
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Take the window area
remaining and design these in groups.
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Then place the groups in places where they have the most lifestyle benefit (see the complete
book for more on the building code & process).
(The above
statement will make sense once you study the energy conservation
portion of your building code. If studying the code is not your cup of tea
then an engineer or RT who is willing to work by
the hour is probably your best bet. Also there is an
abbreviated method I use below. To purchase a copy of the "2006
International Energy Conservation Code" (the basis for most state codes)
click here.
Here are some rules of 'thumb' for
placing windows in an economy
house.
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Unless views absolutely dictate
otherwise. The south side is the easiest to protect with shading
devices.
See Chapter 5 for more on compass
direction and shading.
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The north side is prone in some
regions obviously to winter wind stress and therefore not a recommended
side for major windows. The exception for the
north side is in hotter climates where you want ample windows north and
south for cross ventilation.
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Every
room should have minimum natural light and ventilation from windows or
doors unless compensating mechanical means are provided. 8% of a room's
floor area is cited (verify with your local codes) as the minimum
aggregate per room size. The operable area must be at least half of
this.
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Every
inhabited room must have at least 2 exits. Windows of a minimum size and
type are allowed for one of the exits in most States. You should be ok
if your clear opening of an operable window is at least 2 ft wide and
2'-6" tall and no higher than 24" from the floor. This window can also
count toward the light / air requirement above. Awning windows are often
disallowed as exits.
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Windows
(and doors) should not be closer than 4 ft from an outside corner of the
house. The IBC (International Building Code) dictates this but once
again check that your local code has not been revised. Why no closer
than this? The 4 ft. closest to a corner is critical for bracing a
house. The wall sheathing that is secured to the studs in these
locations creates a rigid 'shear' wall which resists an amazing amount
of wind load. Any closer and reinforcement must be added,
otherwise the wall might rack.
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With the same reasoning as the corner 4 ft, the IBC also wants
significant rigid wall between corners. A rule of thumb is 2 times the
amount of punctured openings. So if you have a 4 ft window, 8ft of
solid wall should be present around it. This is not to say you can not
violate these rules, but if you do an engineer or architect may be
asked for by the building department. There would also be the cost of the extra reinforcement work.
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As said the
energy codes limit the amount of windows and openings. This
limitation becomes the maximum for the entire room or house depending on
the code. There are a couple of ways to calculate it. The most flexible
way requires an engineer and their PE stamp. The other you
can do yourself
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Once again you must refer to your code. As an alternate the following
rule of thumb can be used and checked by your builder prior to beginning
construction.
TIP:
An Abbreviated Method to Determine
Window Quantity
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Aggregate windows which are ‘mulled’ (attached together) in the factory
need to be checked for a seal between windows for energy conservation. Those field mulled under normal
labor conditions can have ample amount applied.
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Larger windows are more energy efficient than smaller
ones. There is more solid glass area and less edges and joints to seal
than a comparable area made up of smaller windows.
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Windows come in a range of stock sizes and
companys varies the increments they provide. You can feel
comfortable with designing the house with windows ranging from 1ft 6in.
x 1 ft. 6in. up to 6ft x 4 ft in increments of around 4". The larger
sizes will have limited to no operability (picture windows) and should
be checked with a name brand manufacturer.
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An
important restraint on window size is the opening size width (see framing
topic). It usually is not a problem by code or engineering to
have a 6 ft to 8 ft clear opening in the wall unless you have heavier
than normal loads above or 3 stories of house. However designing an aggregate
group of windows larger than 8 ft wide should have a caution
button attached. Check with your codes, an engineer and the window company if
you are over 8ft.
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Casement and Awning windows are more
energy efficient than other types. Picture windows are the most efficient of all. (note--
awning windows are not allowed for fire exits in many states)
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2. Windows in houses with bigger
budgets are another animal all together.
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In these houses we can spend a
little more on the walls to get a lot more in windows. If you read the
previous topic on the 2x6 'Eggshell' you know to use
2x6 walls rather that 2x4s and increase the thickness of insulation
accordingly. In this manner you are allowed in most codes
significantly greater window area.
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Next, you upgrade to better windows (with low E and
the highest R values). Now the energy implications of more windows is
reduced. In fact, in a temperate climate, a north east
living room wall which is designed and well sealed
can be 80% glass without adding to the overall energy consumption of the
house, assuming you have more minimal windows elsewhere in the house.
It will also be comfortable. The photo shows such a ‘window wall’ in the great room of a house in
western North Carolina. The owners report no discomfort and much
lower electric bills than expected. This example also had significant
winter winds against it (and if not for the views would not have been
advisable).
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When you begin adding more windows than the code
prescribes see the economy house above for a TIP
strategy.
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Many of the solid wall rules
mentioned under the economy house should also be used. They are
much less critical in the 2x6 walled house but will help cut costs.
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Houses where there is an abundance
of windows concentrated in one room such as the house pictured have
a very special and critical situation. These larger aggregates of
windows are referred to as Window Walls and should be discussed at length.
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Where you are doing large window walls such as
pictured, an engineer or architect will be required to add back necessary
reinforcement. These folks can then do your energy tabulation for you.
Window Walls are discussed at length next.
Window
Walls
Once
windows are aggregated beyond let's say 8 ft wide and 10 ft high the
reinforcement necessary becomes the providence of the Architect, the
Structural Engineer and the window manufacturer. After all, houses where
there is an abundance of windows concentrated in one room such as the
house pictured remove nearly all of the bracing from that
entire area. The walls would be unstable under normal wind
conditions.
The extent of
the opening will define the need for who is to be involved. Look at this way;
the larger the aggregate area the more 'players' there need to be.
Where that point of adding all of this 'expertise' occurs will be a
combination of a prudent judgment call and once again your building
code. I will though try to help establish these points below.
Let it be said for now that the code official if attentive and
knowledgeable will certainly 'pull the trigger' on bringing in a licensed
Architect or Engineer but this same official will probably not advise
anyone to bring in all 3 (Architect, STRUCTURAL Engineer, and window
manufacturer). It will be the conscientious and careful designer who sees
the need for all of these big guns.
All of this professional help then brings up
another question. If you are the home owner as designer how do you know
with confidence all this extra expense in fees is necessary? Or if you are
a Residential Designer what do you say to the owner to explain the
expenses? See if a description of the parties strengths and
weakness' help this make sense.
The
Builder:
Certainly the heart of the team. They usually have good understanding of the code and
when the code requires extra help. The builder may or may not have
experience in large residential window walls but the designer and owner
should not look to this party to engineer and warrant the wall. The
Builder does
not have the training nor the industry liability in anything outside of
the building code. They do have some liability in advising the owner of
problems and expertise needs.
The Window
Manufacture and Installer:
These folks are the second tier of liability and
expertise. The manufacturer will know how strong their units are and when
reinforcement must be added. They also know what reinforcement they can
and can not add. Beyond a certain point in the 'mulling' (attaching
together) the manufacturer does not want legal responsibility for
designing the reinforcement. They should though be reviewing the design of
larger walls to assure themselves that their assemblies are not being
installed in a weak wall that may end up in a law suite. As such they act
as good advisers and 'policemen' to the builder, owner and designer.
The
Structural Engineer (PE):
The
Structural Engineer basically designs the frame in which the window
assemblies fit. All the exact forces going on in a
multistory house are analyzed on how they transmit or 'come to
ground' through the window wall. Stress is determined and the structural
intervention necessary is designed. The diagram of the window wall used in
the example house above shows the intricacy of the structural needs of
that particular wall (see the complete eBook). Determining what is
needed, how large, and how it all fastens together is the providence of
the engineer.
All engineers
are not equal though. Same for Architects. This means that just because an
engineer has a PE license (Professional Engineer) does not mean they are
qualified in the design of large residential window walls. Many PE's have
a general training and then specialize in Civil areas of utility design
and site engineering. For a window wall the engineer needs a special
education.
The
Architect:
Here are the ones who have the role to coordinate our
team of 4 parties. Also the Architect will look at the results with a
discriminating eye to the elegant and more tasteful. (In other words
they assure all the work is done and it does not come out looking like an
armored tank). A good designer after some solid experience with window
walls should be able to fill this position but chances are the code
official will require someone with a stamp to be involved.
The complete
eBook will go more into Window Wall design. But let's stop here with a few rules of thumb on when to sign up
all those 'guns' above.
Aggregate
Windows 8' wide by 10' tall or less;
The builder and Building Code should be able to provide what is necessary.
The window manufacturer should be provided drawings and requested to
submit 'shop drawings' depicting any reinforcement they are adding. More
importantly the drawings show that the 'expert' has reviewed the
conditions and is standing behind their warrantee. (If you have a heavy
wind condition be sure to do this).
Aggregate
Windows wider than 8' and less than 16'. Height same as above 10 ';
An engineer should be brought in to design a support
beam above the 10 ft and spanning the 16 ft opening. The window
manufacture MUST submit a shop drawing showing their intermediate
reinforcement. An Architect is an over kill unless you want to be
assured others have not 'over designed' in a less than elegant manner.
Window
Walls Higher than 10' and wider than 16';
Since this size is made up of multiple aggregate window areas (such
as in the photo). This wall condition requires the full participation of
all players.
Warning: If you the designer
are not prepared to do what
is described above do not design anything over 8'x 10' and without solid
wall in both directions between window areas.
Window Views
Other than ventilation what else are they for? The
eBook has some valuable design info on how to maximize your window views.
But in the mean time to repeat something said above; Larger windows are more energy efficient than smaller
ones and they allow more unobstructed view (just don't break it).
Exterior Doors
Doors have made significant progress
in recent years. There are numerous designs on the marketplace of
different materials; wood, fiberglass and steel. All are insulated and
weather sealed if bought as pre-hung packages. There are a handful of
design issues involving privacy and security but the industry has
responded to these enough to skip them here. However there is one
condition that
deserves attention. Namely a hinged exterior door that swings in and a
sliding patio door that has
the active door on the inside track. Neither of these doors are desirable
for wind. Obviously if the wind is blowing against a door you want the
door to be blown against its weather seals not away from. You would
be surprised at the leakage possible.
TIP: Buy a sliding door that
has the slider in the outside track and a swing door that swings out. (For
the swing door you might have to either sacrifice a screen door or design
the entrance so the door is sheltered from the wind). Both
should be prehung.
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