The Residential Building Code - Test Your
Understanding of Some Common Issues
Below you’ll find an assortment of common
code issues confronting residential builders. Do you know what call
to make? Test yourself and see how well you know the code. We’ll use
the International Residential Code as our answer guide.
by Paul Fisette - © 2006
Understanding and satisfying the building code can
be confusing. To be fair, it is difficult to write one set of
regulations that addresses every building condition. But having a
reasonable level of code consistency would be helpful. Building
codes are written as national models, but they are enforced locally.
Recently, a director at the National Conference of States on
Building Codes and Standards, informed me that there are more than
2000 different code interpretations in our country. It’s
mind-boggling. To make matters worse, inspectors interpret the same
code differently – even in states that have statewide codes. There
is hope. The International Code Council is pitching its
International Residential Code (IRC) as a national standard. And
many communities are adopting this model. While many building
professionals doubt that we will ever have a uniform code, many
building code officials respect the IRC as a good code model. It
provides a common language. So, using the IRC, let’s test our
understanding of some common code issues.
1. True or False --- Small holes and gaps
around ductwork and plumbing penetrations are OK as long as they are
not in an exterior wall.
Very few plumbers fill the holes they run pipes
through. However, they are required to seal the holes, spaces and
pathways as a fire-blocking requirement. Standard practice is to cut
oversized holes to accommodate ductwork and piping runs. Section R
602.8 of the IRC outlines this code requirement. It states, “Fire
blocking shall be provided to cut off all concealed draft openings
(both vertical and horizontal) and to form an effective fire barrier
between stories, and between a top story and roof space.” The IRC
goes on to prescribe sealing 6 specific locations. Number 4 on the
list is: “At openings around vents, pipes, and ducts at ceiling and
floor level, with an approved material to resist the free passage of
flame and products of combustion.” This issue also involves energy
conservation and indoor-air quality.
2. True or False --- Metal roof-framing
connections are required only in high-wind zones.
The traditional practice of toe-nailing
trusses to a wall’s top plate does not satisfy basic
code requirements. Section 802.10.5 states that “Trusses
shall be connected to wall plates by the use of approved
connectors having a resistance to uplift of not less
than 175 pounds and shall be installed in accordance
with the manufacturer’s specifications.” Section
802.11.1 imposes further requirements for roof
assemblies subject to wind uplift pressures of 20 psf or
greater. An interesting side note is that the code does
allow toe-nailing of roof rafters, but this is a
complicated issue. It’s complicated because you must
consider location, roof pitch, natural topography,
building height, and constructed features of a building
site to craft an adequate roof-fastening strategy.
However, toe-nailing rafters is inadequate based on
recently conducted research. Jim Cheng, Senior Research
Analyst with State Farms Insurance Companies, concludes
in his April 2004 Forest Products Journal article that
toe-nailed connections fail at 90 mph wind loads found
in most of the country. Cheng states, “Toe-nailed
connections for the roof-to-wall system are not
appropriate in wood-framed structures, and stronger
connection methods for the uplift load resistance should
be recommended.”
3. True or False --- Steel reinforcement
(rebar) isn’t required in continuous concrete footings and
poured-concrete walls.
In general, steel reinforcement is not
required in residential foundations. IRC subsections
under R 403.1 outline footing requirements and those
under R 404.1 deal with foundation walls. Tables R
404.1.1(1) – R 404.1.1(4) provide design guidelines that
list a wide range of options for designing un-reinforced
concrete foundation wall systems. While not all designs
are exempt from rebar, the design guidelines are clearly
written and chances are you will not need to use rebar.
There are notable exceptions to this “Free Pass”, so you
do have to review this code section carefully. And if
you live on the West coast, all bets are off. You need
rebar because of seismic exposure. In fact the seismic
map [Figure R301.2(2)] reveals that most areas in the
western US and a significant region in the Southeastern
US require seismic reinforcing described in section
R403.1.3.
4. True or False --- Manufacturers’ span charts
are suitable for designing engineered-floor frames.
I-joists and floor trusses are similar
to roof trusses with regard to the code approval
process. Sizes, spans, and performance values for
specific products are not found in the building code.
Builders must submit a drawing to the Building Official
with the set of plans. IRC sections R502.1.4 and R502.11
provide clear guidance about what is required when
engineered I-joists are used in a design. Some of the
relevant code language states that “The truss design
drawings shall be prepared by a registered
professional…” and “Truss design drawings … shall be
provided to the building official and approved prior to
installation.” The design drawings must address
including: span, spacing, bearing widths, design loads,
connections and deflection ratios for live and dead
loads. There is a list of 12 issues in all. While these
requirements might be satisfied by a Faxed document,
many inspectors will not accept a Faxed copy and require
the submittal of plans that are “Wet Stamped” by an
engineer.
5. True or False --- Connecting roof-gutter
downspouts to foundation perimeter drains is OK.
Section R903.4 prescribes drainage requirements
only for those roofs that do not “… drain over roof edges.”
Traditional pitched roofs do not need gutters and downspouts to
satisfy code. On the other hand, section R405.1 does require
foundation drainage and provides fairly elaborate direction due to
the importance of keeping basements dry. Surprisingly, there is
nothing in the code that prevents you from connecting downspouts to
a foundation’s perimeter drainage system. The logical question
stands: Why introduce all that roof water into such a sensitive
location? To my mind, it makes no sense to inject water below grade
to an area you are trying to drain. As a side note, you can’t
discharge this drain water into either a septic system or municipal
waste system. Downspouts and foundation perimeter drains must be
connected to a separate storm sewer system.
6. True or False --- Vented rain screens
violate fire-blocking requirements.
In this case, the answer is not straightforward.
Typically strips of furring are attached vertically over the
wall sheathing and left open at the top and bottom. Siding is
nailed to the furring strips. This creates an air space between
the back of the siding and the face of the house-wrapped
sheathing that drains and dries readily. It is highly effective,
but there is 1 code issue to consider. Section R602.8 requires
fire blocking to cut off all concealed draft openings “including
furred spaces.” Cross blocks must be placed at the bottom,
between stories, every 10 feet, and at the top near the roof.
Installing all this cross blocking reduces airflow, drainage and
drying. Many builders and building code officials think the
spirit and intent of this code provision is not directed at
vented rain screens, but rather at furred interior spaces.
However, some inspectors disagree and think the code section
holds as written. The code is not clear and the decision will be
at the discretion of your local building inspector. So run your
rain screen design past the inspector before building the walls.
7. True or False --- Unvented “Hot Roof”
designs for energy efficient cathedral roofs are illegal.
The code is clear. You need to ventilate roofs.
This goes for both attic and cathedral roof frames. Section
R806.1 states “…enclosed rafter spaces formed where ceilings are
applied directly to the underside of the roof rafters shall have
cross ventilation for each separate space…” Subsections under
R806 provide specific guidance regarding the minimum vent area
and clearance required. There are no exceptions provided in this
section of the code, but this may not mean the case is closed.
Building scientists have demonstrated that combining high levels
of insulation with airtight detailing can provide superior, dry,
durable cathedral roof construction without roof venting. Roof
cavities filled with expanding foams or dense-packed cellulose
have a winning track record for keeping roof cavities dry and
functional. Call section R104.11 to the rescue. This section
states, “An alternative material, design or methods of
construction shall be approved where the building official finds
the proposed design is satisfactory and complies with the intent
and provisions of the code.” So the challenge is to convince the
building inspector that your hot roof design works. Submit
thoughtful details and copies of research reports that
demonstrate hot-roof designs satisfy the intent of the code.
This is a case-by-case and inspector-by-inspector decision so
have a cooperative attitude and be prepared to answer questions
about performance.
8. True or False --- Code allows no more than
15% of wall area to be windows.
The code is flexible in this case. Section
N1101.2.1 provides you with options. It prescribes code compliance
by stating that buildings are limited to a glazing area that does
not exceed 15% of the gross area of the exterior walls. However,
this section also provides you with the opportunity to use
performance-based solutions through the International Energy
Conservation Code (IECC) for detached one- and two-family dwellings.
The IECC performance-based approach is more complicated, but far
more powerful regarding design choices. It allows you to consider
the total building performance and energy tradeoffs are permitted.
For example, you can compensate for extra glazing by using more
insulation or other energy-saving design strategy to compensate for
the energy lost by the additional glazing.
9. True or False --- Vapor Barriers are
required.
Moisture control is required in all
framed walls, floors, and roof/ceilings of the building
thermal envelope. IRC section R318.1 states, “…a vapor
retarder shall be installed on the warm-in-winter side
of the insulation.” However exceptions to the code are
noted:
1) In construction where moisture or freezing
will not damage the materials.
2) Where the framed cavity or space is ventilated to allow
moisture to escape.
3) In counties identified with footnote in Table N1101.2
Language in section 502.1.1 of the IECC also talks
about “…other approved means to avoid condensation in unventilated
walls…” The intent of the code is abundantly clear: To control
moisture and prevent damage to materials. Obviously, trapping
moisture between the foundation wall and a plastic wall membrane is
not a good building strategy. While there are several smart ways to
design a basement makeover (see FHB # ??), the point here is you are
not restricted by the code. You do need to demonstrate to the code
official that your design approach is sensible.
10. True or False --- Crawlspaces must be
vented.
The building code treats crawlspaces as
a special case, and they are subject to a different set
of regulations than basements. Section R408.1 of the IRC
regulates the ventilation of under-floor space.
According to the IRC “The under-floor space between the
bottom of the floor joists and the earth under any
building (except space occupied by a basement or cellar)
shall be provided with ventilation openings through
foundation walls or exterior walls.” However, section
R408.2 lists 5 exceptions. In general, building a
code-accepted un-vented crawlspace is straightforward.
For example, crawlspace vents are not required when
continuously operated mechanical ventilation is provided
in the crawlspace; nor are they required when you
install a vapor-retarding groundcover, supply
conditioned air to the crawlspace and insulate
crawlspace walls according to the prescribed levels
listed in section N1102.1.7.
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