-
To run ducts perpendicular to joists you must
have space between the ceiling and the bottom of the 'joist'. (Since light
wood solid framing occurs every 24" or less, there is no room to raise a
ceiling in between). Higher ceilings will require a special truss shape, higher
bearing wall and joist height, or Post and Beam framing. There is
also the possibility of:
-
Lowering the height inside a closet,
bathroom, or hall.
-
Provide chases around the perimeter
of rooms and above cabinets. (not common, too much trouble).
-
If raised joists are used, a common solution is to do a
10 or 11 foot floor to floor height. Lower the ceiling to 8 feet and use
the space between for your ducts, plumbing and electric runs. The smart
designer will organize the utilities so that some major rooms can have a 9
or 10 foot high ceiling.
-
A minor advantage of 'stick' floors is the ability to
cantilever a floor beyond the wall or beam supporting it. The building
codes once allowed a very meager 1 foot but with an architect's or
engineer's help getting out to 4 feet or more is doable. Sheltered porches,
balconies or sunrooms might be done like this although engineers don’t
like it.
-
A major advantage of stick ceilings/roofs construction
is allowing your main living rooms to 'soar' in height. There are only a
few limitations to get in your imaginations way. Sloping cathedral
ceilings or 2 story high rooms all are easy with sticks. Where with roof
truss your pitch is more limited and requires a special truss.
- Structural support at the limit of your span is discussed under Walls.
Your Budget Is
Really Tight
We discussed in the section "the 2x4
Eggshell---" solid light wood construction is generally the most
economical of all framing solutions . The same statement can be said of
solid light wood floor framing but not necessarily about it's use in
roofs. So, cost wise it is a mixed bag, (summarized below). The question
the designer must ask is do I want to accept the limitations of solid
lumber floor framing for the cost advantages? We listed the
basic limitations above. If you looked at them carefully you will see
compared to the other floor/roof framing large differences. (Keep in mind
those are conservative general numbers to give the Designer a working framework).
To summarize differences find the following:
Solid Framing vs Engineered Wood
-
Walls - less cost,
solid 2 x 4" studs allow only a 2
story high house.
-
Floors -Solid
joists are less cost, but
have significant span reductions and mechanical electric restrictions. (see footnote1).
-
Roofs -
Solid wood rafters usually cost more than light truss, and have
significant span limits.
Structural Walls
To say the obvious there
are (4) types of full height walls:
-
Exterior Load Bearing --
If your roof is to be sloped, the walls at the bottom of the slope are
load bearing. Openings in this wall are subject to either limits or
engineering. See the section on Shell Parts/Windows for more.
-
Exterior non Load Bearing -- Walls not carrying sloped roof loads
carry only wind loads. The limitations are less.
-
Interior Load Bearing --
These carry either roof or floor loads at the end of the structural
spans discussed previously.
-
Interior non Load Bearing (partitions)-- Carry no loads, have
fewer limits unless used as a stiffener for bounce and deflection.
Interior Load Bearing
Walls
These
are your items of concern inside your house. You have devised a
great floor plan and whole
bunch of walls separate your rooms. Which are load bearing and subject to
limitation and which are not? What are the limitations? All essential
questions.
Here is it as simply put:
-
Overlay on each floor of your plan a sheet of drawing tissue.
-
Diagrammatically sketch the joists or truss until they run their maximum
spans or until you have a wall that occurs below. If a wall is below
then it is Load Bearing.
- If
there is no wall below you must put one in or have a beam engineered
with end supports (posts or another wall).
-
Play with the direction of your spans until you find the best solution.
- For
an engineered beam go to the section "Framing for Construction
Drawings".
- For
a Load Bearing Wall see below.
Openings in Load Bearing
Walls
If your bearing wall
falls on the lowest floor your job as the designers is done except for
alerting the RT / construction drawer to its presence. This person will take
the loads 'to gound' on their foundation or framing plan. If your wall
falls lets say a floor above the lowest one then you must get the loads
down to the lowest floor in a manner that works for your hard earned floor
plan as well as satisfying the engineering. There are several solutions:
-
Work with the CD person to devise transferring loads by way of a 'flush
framing' solution. (see the Framing for Construction Drawings section
coming up).
- Run
a wall and puncture it with openings.
- Run
screaming out of the room and quit.
If a wall that has one or
more openings in it works with your design this is probably the simplest
way to go. There are though, as with everything, limitations as follows:
-
Openings 8 feet or less in width can be used without much concern. The
header can be made up of 2x10s or less. Openings greater than 8 feet
need engineering attention.
- The
designer's concern is making sure that the increase in loads created by
the opening also 'goes to ground' as discussed above and that any
support is accounted for in the floor plan below them. (If that did not make sense
then keep in mind the opening you made transfers the load to the
opening's sides and creates a 'concentrated load' or a 'point load' vs.
an evenly 'distributed load'. The point load must be engineered and
carried down. You the designer must account for this).
So there you designers
have it. You can have all the clear space you want within these limits.
And you can place walls where ever you wish without regard to supporting
anything (again within these limits). Also, if the spans above are too
restrictive an engineer, architect or experienced RD/RT (Residential
Designer) can find you some more.
Framing for
Construction Drawings
Once you get the hang of
what I have been saying in a very general manner the work will not seem
bad. In the mean time unless you have an engineering background (or other
technical fields) brace yourself. To engineer framing plans there are
steps that must be gone through and knowledge to be digested.
Unfortunately as I said these can not occur in this book. (Also forgive
me since I am about to do what will seem like a cop out). Instead this is
what you must do:
-
Study any number of books
on house construction and framing. There are several in our
bookstore as well as the
JLC Field Guide .
.
-
From these books and from your local Building Code acquire load and span
tables with their associated technical adjuncts. (see the eBook Appendix
for an example).
- Manufacturer's literature is an
invaluable resource. Trusses and engineered wood products are well
represented on the web and when
you dig into them your framing questions should be cleared up. Your
first framing plan then is only steps away.
- For roof truss basics go to
Alpine
Truss
- For floor truss and engineered
joists (I Joists)
refer to trulinetruss.com
- For
solid 2x lumber see
Southernpine
spantables
Samples
from the above links are in this book's appendix and provide an idea of
what you are looking for. Start with a book on wood framing. It is
imperative that the person doing construction documents understand this
subject. Here are where the bigger mistakes can occur during construction
and here is where significant liability lurks. Do not rely only on
the builder to catch mistakes. Remember they are often busy building other
houses as well. Imagine the problems if the experienced boss is off site
and his less experienced helper misses an error YOU made. It gets
built and one of two things may happen:
-
It has to be rebuilt at
considerable extra expense or, you never know,
-
a structural failure
might occur.
If you are doing framing
for the first time, the bottom line is study, study, study and then have a
PE review your final work. And remember you only have to get through this
once. After that it will be like riding a bike.
for
the remainder of this chapters topics as well graphics purchase this book.
|
graphic
courtesy of Alpine Truss.
plywood.
Can be used for floor or roofs (flat or sloped).
photo courtesy of Truline Truss