Empirical
design & permits...
What
is Empirical Design
Empirical building design refers to the tried and proven methods of
building with concrete, concrete blocks, and bricks for home construction.
Most building codes recognize these decades old building methods as
accepted in lieu of specific design engineering. The only requirement
is that your project meet minimum design criteria as specified by
the code. The book has an entire Chapter devoted to this topic.
This is very good
news if you want to design in dry-stacked block construction. As long
as your building complies with these minimal requirements, then expensive
engineering studies may not be required for building permit approval.
Terminology
Understanding the industry terminology is a must to expedite code
research. I will point out a few of these terms in this section. When
searching for these code items, look in the masonry chapters of your
code for concrete block reinforcement requirements. Below is an example
of one of the many home construction block data tables that can be
found in code books. I have added explanation comments at the bottom
of the table.
Some of the terms
you will be looking for are continuous bond beam span openings, bond
beams combined with lintels, vertical wall reinforcement, shear walls,
and roof framing connection to bond-beam or bolted top plate.
You will have
to find out what the minimal requirements are in your region, but
the Florida requirements for 100-mph winds are discussed below as
a representative example. Even if you are in Florida, you must still
contact your permit office to see what building code is in current
use, since the code changes from time to time.
Example Empirical
Requirements
Examples of empirical design requirements for dry-stacked CMU, and
condensed into lay man terms are listed below. These requirements
are representative only and must be confirmed by your local permit
office:
One and two family
home construction in areas with a basic wind speed of 100-mph or less,
shall comply with the following:
a.
Exterior walls shall be not less than 8" thick for a multi-floor
structure, nor less than 6" thick for a
single floor structure.
b.
A reinforced bond-beam shall be placed around the perimeter at the
top and bottom of each multi-
floor wall with at least one
#5 bar. A number 5 rebar refers to a rebar diameter of 5/8-inch. A number
4 rebar refers to a diameter
of 4/8-inch, etc. For the first floor of a dry-stacked structure,
the
(foundation/monolithic slab) attachment
meets the bottom wall reinforcement requirement.
c.
Wall area cannot exceed 240-sq. ft. without approved vertical and
horizontal support. If your walls
are 8-feet high, then the
maximum wall length without a corner or outcrop is 30-feet. If your
wall is 9
feet high, then the maximum
wall section length is about 26-feet. If your wall height is 10-feet,
then
the maximum wall section
length is 24-feet.
d.
#5 rebar reinforced wall cell grouted with concrete at each corner.
General Block
Construction Requirements
The above list is the minimums to be considered for Empirical design
rules. There are additional requirements specified under concrete
block construction aspects of the code which consists of but are not
limited to:
a.
#5 rebar reinforced grouted wall cell on each side of all doors and
windows.
b.
Two #5 rebar in the bond-beam (to meet combined lintel/bond-beam requirements).
c.
Two #5 rebar in all foundation footers
d.
Header rebar requirements are specified in header tables within the
code.
Once again, check
your local code for exact requirements. For example, you may not need
2 each #5 rebars in the entire bond-beam, but I did it anyway for
added strength. My window and door headers were much taller than required
(about 24") but that solved many forming issues and window/door
framing issues by making the headers higher than required. The code
is only the minimums. You can build beyond the code requirements when
you feel the need to do so.
There are also
general rules relating to a ratio called the Maximum Span to Width
Ratio of Floor and Roof Diaphragms. This simply means the length to
width ratio of the floor plan and roof plan. For a wood stick structure
this ratio is limited to 2:1, but a block structure can be 5:1. This
means that if your floor plan is 40-feet deep, then it could be up
to 200-feet wide (5:1 ratio). Of course, you still have the 240-sq.
ft. rule to contend with, so a wall this long would need outcroppings
or lateral reinforcement to break it into smaller sections for stronger
home construction.
Lateral Wall
Reinforcement
Typical lateral wall reinforcement refers to shear walls or some other
engineered reinforcement method. Shear walls are parallel to the lateral
forces, and work just like an outcropping. They brace the wall just
like a 90-degree corner braces the wall. In other chapters I mention
an inside load bearing wall. This could also be a shear wall, and
could be used to exceed the 240-sq. ft. rule.
As you can see,
complying with Empirical design rules is relatively easy with most
home designs. Just keep these issues in mind as you plan your home
design. This pretty much sums up your requirements to build under
the Empirical design rules. As stated earlier, check with your permit
office to confirm their current requirements.
Permit Process
First of all, differing regions of the USA use one of three different
building code standards. Here in Florida we use the SBCCI standard.
Your region could use one of the other two standards. The examples
described here will reflect the SBCCI standard. When you first visit
the permit office, the office will provide you with a permit application
package, which contains forms for the application of all the required
permits for your home construction.
Meeting with
the Inspector
When you submit your building permit application, they expect certain
plans to be included as specified in the permit application package
they provided to you. This is where the rub comes. You can take a
shot in the dark and just submit your application, or you can arrange
a meeting with the inspector to discuss your project plans. At this
meeting is when you want to ask semi-intelligent questions about your
proposed plans and how they will be accepted. For example, you might
briefly describe your intention to use the dry-stacked block construction
method. Because dry-stacking is not yet popular, your building permit
office may not be familiar with the process. The will certainly know
about it because it is in the building code, but they may have no
direct experience with it. Fortunately the code treats building with
dry-stacked blocks about the same as building with mortared blocks.
If you take with
you the "ASTM C-946-91 (change 91 to current version) Standard
Practice for Construction of Dry-Stacked, Surface-Bonded Walls"
which can be purchased on the Internet, by searching for the title
name; you will impress the inspector and establish a better relationship
with that office. It also wouldn't hurt to include the Quikrete product
data sheet for QuikWall, or any other surface-bonding product you
intend to use. These can also be downloaded from the Internet or mailed
from the manufacturer. Once again, you will demonstrate to the inspector
that you intend to do a competent job, and you will also provide facts,
which should help dismiss any early inspector doubts about the process.
After all, the inspector is an engineering type, and specifications
are what appeal to him/her.
Don't try to cover
every detail at this first meeting. It would be helpful to mention
that you are seeking reference standards which describe concrete block
construction rebar requirements for wall cells, door and window poured
headers, and bond-beams.
That's it, bail
out of the meeting with these small tasks accomplished. Now you must
review the appropriate standards and the application package you received,
and then determine any questions you may have about your proposed
plans and the code. I'm not suggesting that you have to learn the
building code in detail. I am just suggesting that you read through
the building code chapters, which apply to your home construction
details.
Your next meetings
will be informal and hopefully conducted during the morning questions
availability time. Most offices make the inspectors available for
building permit questions during the first hour of office operations.
This gives all builders a time when they can call or visit an inspector
for technical questions about their project. For the remainder of
the day; the inspectors will be out of the office, unavailable, and
conducting inspections. Once again, only ask a few questions during
each call. Space your calls a couple of days apart so you don't appear
to be a burden to the inspector. Try to limit your questions to topics
you can't find in the building code, or to topics you have found,
but you still require further clarification. The inspectors will be
much more helpful when they realize that you are reading the code.
Owner-Builder
Electrical & Plumbing
In many regions, the owner-builder can also perform all the Electrical
and Plumbing work without a license. Of course your work must pass
code inspections, but it can certainly save you a ton of money by
doing it yourself. Many library books are available on these code
requirements, which aren't all that complicated.
Progress
Inspections
The building permit office will provide a list of what inspections
are required as the project progresses. Make sure you understand what
each inspection means. Sometimes the inspection name wording does
not relate to conventional naming terms. There is also the problem
where most inspection lists are developed for stick built homes. Concrete
block construction will have some differences. When you are given
the list of inspection requirements, make sure that you clarify the
differences for concrete block home construction.
Inspections are
typically scheduled when you call an answering machine and request
a particular inspection. In my region, if you call before 8AM, Monday
through Friday, then the inspection will be conducted on that same
day. I usually call the evening before to avoid busy signals. While
working on a specific task, when in doubt always make that phone call
to the inspector for clarification. It is much better than doing it
wrong, failing an inspection, and then having to do it right. I have
never failed an inspection to date, but I do my research and ask questions
when in doubt.
Abandonment
Rules
Last but not least, find out what the timetable is for home construction
permit abandonment in your region. Do not ask the inspector (don't
wake a sleeping dog…or make the inspector suspicious of your
determination), but find the answer in the building code, or County/State
law books. Go to your library and start there. Florida has this topic
in the State Building Code which is available on the Internet This
is important if you are an owner-builder.
The State of Florida considers a building permit abandoned if six
months passes without
any approved inspections. Your region may vary. I don't know how
lenient building permit offices are with this requirement, but abandonment
should not be taken lightly. The consequences are usually extreme.
Make sure you understand this aspect of the building permit process.
I always keep something I could easily get inspected on the back burner
for emergency abandonment prevention.
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