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The 2x4 Stud 'Eggshell'-- the
most economical shell
The analogy of an eggshell is pretty accurate. Simply
put the exterior of the typical American house is as thin as an eggshell
in relation to the volume of space within. The idea of an eggshell is
important to keep in mind when designing a house for three reasons.
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One is the shear efficiency of the ‘system’ of materials that
makes up the ‘shell’. This 'shell' has been refined since the 19th
century down to the barest of materials required to enclose the
space. Only the most minimum of materials go into this
‘shell’ and yet it is an extraordinarily strong membrane.
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The second and important
aspect a designer must understand is how this thin membrane gets it's
strength. Any individual material involved in of it's self
could not hold up an 'eggshell' house. The secret is in the whole
interaction of materials. The shell is truly without exaggeration a sum
larger than it's parts. The interaction falls into two groups; the
weight bearing and the bracing elements. Take away either group or any one
item in a group and you have a 'house of cards'. (See the
group list above). TIP:Building codes dictate how much can be taken
away and what must be added back.
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Third remember the function of our 'shell' is to
shelter us from the outdoors. If the 2x4 eggshell could get thinner it
would do less of a job in keeping in the tempered air we pay so dearly to
maintain. In fact thinner walls with unlimited openings could not
meet the Building Codes Energy Conservation laws. Not without the
invention of new and much better materials.
So what is so important? Simple, you can not ‘puncture’ the shell with doors and windows to an
unlimited degree before the house's thermal and structural integrity is jeopardized. Doors and
windows have no ability to brace the walls since they have no
strength and are designed to open (obviously the opposite of bracing). Some
openings can be tolerated but too many and you could weaken the house possibly to
the point of either failure under great stress (a hurricane for example)
or at very least deterioration of the shells integrity. Integrity is a
fancy way of saying cracks and cracks lead to water and air infiltration
(masonry cracks, unsealed doors and windows, etc.).
The structural bracing issue though is not the
critical one in 2x4 eggshell houses. In reality you would never get
as far as a reinforcement cost issue before you would encounter the
Energy Conservation Codes limitations on doors and windows. 2x4 walls are
just not thick enough to allow the insulation necessary for extensive
openings. The Section on "Windows" later in this chapter will go into
greater detail about windows and building codes.
TIP:
The bottom line for the 2x4 eggshell is; if you use 2x4s you can not do much
of what you as a designer wants to do. Which brings up the 2x6
eggshell.
the 2x6 Stud
'Eggshell'
This
'shell' is exactly the same as the 2 x 4" version discussed above with two
exceptions. Is it necessary to say the 2x4" studs are replaced by 2x6"
members? Also the spacing of these 2x6's is 16" rather than 24",
although you can space them at 24" as well.
So, larger structural
members in the walls and closer together. Why do it? Well although there
is more cost upfront in materials, the labor cost is minor and the
strength and long term energy savings is significant. Significant that is, if you take full
advantage of the 2 extra inches in wall thickness. How? Insulation;
you increase the amount of insulation by the same 2 " thereby gaining more
energy conservation. Also by spacing the 2x6's at 16 " you get a stronger
house. We are not going to go into the technicalities and details of this
cost and that cost or this strength or that because, although those are
important aspects they are not important to what we are after here:
namely design benefits and opportunities. But it isn’t fair to leave the
cost thing hanging is it? So let's be satisfied with one statement and
then go onto the design. The statement is; if you can afford $25
(2006 dollars) more in monthly mortgage you can afford 2x6's. (and It will be
paid back thru conservation I promise you).
Ok, what design
benefit? In short, you have gained significant flexibility in window
design for very little if any long term cost. Why? If you have
read the previous section on 2x4s you know you have some code related
window restrictions. You also know that the 2x4 frame is weak unless
reinforced and a 2x6 frame is inherently stronger.
Energy codes are assuming you are using the minimum insulation
for a 2x4 wall not the extra 2 inches from a 2x6. That added 2 " will go a long way in more windows. Just in thickness it’s
a 25% increase without getting into the technicalities of R values, whole
house energy calculations and without touching floor and ceiling
insulation upgrades. Add floor and ceiling upgrades as well and the
possibility of using insulated
wall sheathing your window design is becoming limited only by your
budget. As for the strength aspect, just put it this way; the
building codes do not allow 3 story houses out of 2x4s, but do for 2x6s.
(If you are saying to yourself 'what about the extra
heating/cooling costs of these 'unlimited' windows? Please read the
section on Window Walls.)
Here is a recap of benefits:
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More Insulation
= better energy conservation = long term cost savings.
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More Insulation
= better energy conservation = more windows allowed.
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Thicker walls = stronger
house = less bracing = cost savings.
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Thicker walls = stronger
house = more windows allowed.
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Taller walls without
increasing the sheathing thickness. 9 & 10 ft walls are fine.
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3 stories possible
instead of two (with 2x4 framing only 2 floors are allowed).
- Homes in wind
stress areas are more secure from deterioration.
TIP: Fear not about
loss of strength, the amazing versatility of the 'eggshell' can easily regain lost strength. The
regaining is a technical subject unto itself so leave it here to say; a
broad range of strengthening and reinforcing devices have been compiled by
the housing industry over time. Which brings up the bottom design line;
the more you puncture the 'eggshell' the more reinforcement you must add;
the more reinforcement the more cost. If you are designing an
economy house this issue is important to you. If not, then
don’t worry too much, at worst you will end up with a post and beam shell.
And as said in chapter 2 going the whole way in puncturing until you get
to a true post and beam structure
will add lets guess 20 % to the cost (before windows).
If you would like to get a feel for some of the
reinforcing devices mentioned go to
http://www.simpsonstrong-tie.com/
Post and
Beam Framing and its Cousin the Hybrid
The Post and Beam house; what a way to wow
your neighbors. What space, what feelings of the pioneer, country
spirit! And no Architect necessary! (just an engineer or P&B kit. You know
those prefab packages that have been pre designed and engineered and made
ready to go).
Must we describe the P&B? Did I hear a young couple in the
audience say please? Ok, so be it. Tongue in cheek aside, the P& B 'shell'
has a lot going for it (and some warning caveats). Unfortunately as
said at the beginning of this chapter I can not do the subject
thorough justice in this book. So please forgive me while I will
only 'skim' the surface here.
Take some large timbers (timber = larger than 4"
in the thinnest dimension), stand some uprights spaced according to----(lots
of things). Call them posts, columns or whatever you wish to call
them. Next place another timber across 2 of these. Continue the same
thing all the way around what ever it is you want to be P&B framed. Put in
some sloping rafters and brace them with 'check' braces every 2 to 3
spaces. Cover your rafters with a T&G roof topped with rigid insulation
and shingles and bingo, you have a P&B framed house,
or room. Simple---yes. Simple until you get into the methods of making all
those intersecting joints rigid and braced. Then it gets more intricate
and becomes the providence of either a professional architect, engineer or
a P&B kit!
So what does it all mean? A lot
actually. Here you get a completely 'puncturable' shell with windows
restrained only by your imagination, your budget and how much insulation
you can get into the rest of the house. Not simple engineering tasks by
any means but one which can be done by any PE or architect experienced in
Post and Beam framing. (Or by a 'Kit' provider). Plus you get the
ambiance and spatial wonder of a P&B design!
So after that' s said what does it
really mean. Here are some points before we move on .
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As said in Chapter 2 the Post and
Beam will cost significantly more than a standard 'stud' shell. How
much? Good question. There are so many variables that you need to talk to some kit providers
or builders and
compare their number to the standards for the caliber house you want if
done in 2x4 or 2x6 studs. Remember the % allotted to framing in Chapter
2. There is where you compare apples to apples.
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If you do not like the 'Kits'
and get a local builder to quote a budget remember an architect or
engineer will need to be added to the equation (Chapter 3).
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If you are fond of unusual shaped
rooms or roof lines keep in mind that the essence of P&B is straight and
90 degree angles. Anything else catapults complexity and price. In other
words; keep it rectilinear and simple!
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P&B is almost synonymous with big
open ceilings. While these are liberating spaces they are in need of
added HVAC engineering and cost. Without these the room may end up being
an uncomfortable space you have spent a lot of money not to use.
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Not all builders are qualified to
deliver everything necessary (such as the HVAC above) to assure a great
livable P&B home. Check them out well.
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Timber frames made of natural
versus engineered wood has old growth Green issues. Five years from now
your social pride may be in for some bruises.
TIP: The whole house does not need to be P&B. If you only do your key
living area and do the rest in 2x4 shell construction your costs will come
way down. This is called a Hybrid P&B house.
(If these sections made no sense to you, some study of
house construction is in order. Since a complete explanation is
beyond the scope of this one book, the reader would be well advised to
locate a house which is just beginning construction. Follow it closely and
the mystery should disappear. Also our complete eBook will offer more information and
graphics on this subject).
Click here.
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