IRC Question & Answer
IRC Question & Answer
For the past several months BIAW has partnered with Washington Association of Building
Officials (WABO) and our 15 local associations to offer classes on the transition
to the International Residential Code. Attended by nearly 800 members, BIAW's class
offered answers to many questions, but there were bound to be others as builders
began using the new code. This site is designed to answer those questions.
Do you have a question that you would like to ask about the new IRC Codes? Just
click the link below and type in your question. Check back to see the answer to
your question posted here. IRC Code Question
Regulations on septic tanks
We live right on the shore and are concerned about the drainage and septic system.
Any regulations on septic tanks would be helpful as well.
Assuming the question relates to drainage around the foundation and from the roof,
the following code sections from the International Residential Code apply to the
question:
R401.3 Drainage. Surface drainage shall be diverted to a storm sewer conveyance
or other approved point of collection so as to not create a hazard. Lots shall be
graded to drain surface water away from foundation walls. The grade shall fall a
minimum of 6 inches (152 mm)within the first 10 feet (3048 mm).
Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6
inches (152 mm) of fall within 10 feet (3048 mm), the final grade shall slope away
from the foundation at a minimum slope of 5 percent and the water shall be directed
to drains or swales to ensure drainage away from the structure. Swales shall be
sloped a minimum of 2 percent when located within 10 feet (3048 mm) of the building
foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation
shall be sloped a minimum of 2 percent away from the building.
R403.3.3 Drainage. Final grade shall be sloped in accordance with Section R401.3.
In other than Group I Soils, as detailed in Table R405.1, gravel or crushed stone
beneath horizontal insulation belowground shall drain to daylight or into an approved
sewer system.
R405.1 Concrete or masonry foundations. Drains shall be provided around all concrete
or masonry foundations that retain earth and enclose habitable or usable spaces
located below grade. Drainage tiles, gravel or crushed stone drains, perforated
pipe or other approved systems or materials shall be installed at or below the area
to be protected and shall discharge by gravity or mechanical means into an approved
drainage system. Gravel or crushed stone drains shall extend at least 1 foot (305
mm) beyond the outside edge of the footing and 6 inches (152 mm) above the top of
the footing and be covered with an approved filter membrane material.
The top of open joints of drain tiles shall be protected with strips of building
paper, and the drainage tiles or perforated pipe shall be placed on a minimum of
2 inches (51 mm) of washed gravel or crushed rock at least one sieve size larger
than the tile joint opening or perforation and covered with not less than 6 inches
(152 mm) of the same material.
Exception: A drainage system is not required when the foundation is installed on
well-drained ground or sand-gravel mixture soils according to the Unified Soil Classification
System, Group I Soils, as detailed in Table R405.1.
R801.3 Roof drainage. In areas where expansive or collapsible soils are known to
exist, all dwellings shall have a controlled method of water disposal from roofs
that will collect and discharge roof drainage to the ground surface at least 5 feet
(1524 mm) from foundation walls or to an approved drainage system.
Further, the Uniform Plumbing Code, as adopted by the State of Washington, requires
foundation drainage systems to be installed on all new houses. You can refer to
UPC Chapter 11, Storm Drainage.
Four Story Residential
Construction of a 4 story residential seems to be in a gray area. The IRC governs
single family and townhomes with a maximum height of 3 stores. Recently we encountered
a project which, due to slope of the property, will be a 4 story single-family residence.
However, upon review IRC does not seem to govern it and IBC does not seem to have
an answer for single residential structures. Which is the correct code to follow
for this project?
You are correct that the IRC does not govern a 4-sotry building, so the only code
to use is the IBC. IBC Section 1018 regulates the number of exits and their continuity,
as follows:
1018.1 Minimum number of exits. All rooms and spaces within each story shall be provided
with and have access to the minimum number of approved independent exits as required
by Table 1018.1 based on the occupant load, except as modified in Section 1014.1
or 1018.2. For the purposes of this chapter, occupied roofs shall be provided with
exits as required for stories. The required number of exits from any story, basement
or individual space shall be maintained until arrival at grade of the public way.
Subsection 1018.2 gives the requirements for a Group R-3 occupancy through Exception
2:1018.2 Buildings with one exit.
Only one exit shall be required in buildings as described below:
1. Buildings described in Table 1018.2, provided that the building has not more
than one level below the first story above grade plane.
2. Buildings of Group R-3 occupancy.
So, an R-3 occupancy only requires a single stairway from each floor.
Sill Plates
A sill plate rests on the top of a concrete foundation wall which projects 9 inches
above the adjacent grade. Is the wood sill plate required to be preservative-treated
or naturally decay resistant in accordance with the 2003 International Residential
Code or the 2003 International Building Code?.
No. Section R319.1 of the 2003 International Residential Code and Section R2304.11.2.2
of the 2003 International Building Code only require wood sill plates to be pressure
treated or decay-resistant when they are located less than 8 inches from grade.
Roofing
Many roofing companies are changing over to coil nails as a primary fastener. Has
the code for approved fasteners been changed to nails only? Are staples still considered
an approved fastener?.
IRC Chapter 9, Roofing Assemblies refers only to nails. There is no longer any specific
reference to staples. Further, the manufacturer's installation details on either
their web sites or on the bundles of roofing materials refers only to nails.
Height Restrictions of Buildings
The UBC, section 209H, gave two ways to establish the datum for height restrictions.
I do not see anything in the IRC for this. The only reference I found is under definitions
(pg. 15) and this is a very general definition without any consideration for steeply
sloped lots or establishing where the grade is measured from.
I am designing a house for a lot which has 17-18% slopes. Establishing a datum higher
than the lowest grade is critical.
HEIGHT, BUILDING. The vertical distance from grade plane to the overage height
of the highest roof surface.
STORY ABOVE GRADE. Any story having its finished floor surface entirely above
grade, except that a basement shall be considered as a story above grade where the
finished surface of the floor above the basement is:
1. More than 6 feet (1829 mm) above grade plane.
2. More than 6 feet (1829 mm) above the finished ground level for more than 50 percent
of the total building perimeter.
3. More that 6 feet (1829 mm) above the finished ground level at any point.
GRADE PLANE. A reference plane representing the average of the finished ground
level adjoining the building at all exterior walls. Where the finished ground level
slopes away from the exterior walls, the reference plane shall be establsihed by
the lowest points within the area between the building and the lot line or, where
the lot line is more that 6 ft (1829 mm) from the building between the structure
and a point 6 ft (1829 mm) from the building.
So, this is a lot like the UBC definition for "height of building"
in Section 209, as you noted. This new definition of grade plane allows you to take
the average from all corners of the building, with the slight modification if the
lot slopes away from the building at the lower side. So I'm sure the IRC requirements
are the same as the UBC, just worded differently.
Seismic Design Categories
In Reference to R404.1.4, Seismic Design Categories D1 and D2, and table R404.1.1(2),
we are clear on the vertical reinforcement required, but not on the horizontal.
We will have a 9'0 high and 8" thick basement foundation wall with #6 bars
at 24" o.c. In the past we have specified #4 bars at 10" o.c. horizontally.
As we read the code (R404.1.1(4)), it seems to only require 2 horizontal #4 bars
located in the upper 12" of the wall.
Your application of R404.1.4 is correct. The IRC (R404.1.2), constructs your concrete
foundation in accordance with either Table R404.1.1(1), (2), (3) or (4). Once you
know the type of soil you have at a particular site, and know the height of the
unbalanced fill, you can then decide what Table you want to use. It appears that
you decided to use Table R404.1.1(2), with the middle column of soil types, and
using 9 feet of unbalanced fill. Based on that, you are correct that the vertical
rebar is #6 at 24"o.c. And you are also correct that the only horizontal bars
required are two #4 located in the upper 12" of the wall, as shown in the last
sentence of R404.1.4
Now--non-code: remember this is just the MINIMUM code. Do what makes you feel comfortable
with your design. If you still want the #4 at 10" o.c., do so.
Garage Code
I have a downslope house with the Garage above the living area. It has a 3" thick
concrete floor. What are the fire code requirements for the floor? Also are there
any waterproofing code requirements for the floor?
International Residential Code, Section R309.3 Floor surface. Garage floor surfaces
shall be of approved noncombustible material. The area of floor used for parking
of automobiles or other vehicles shall be sloped to facilitate the movement of liquids
to a drain or toward the main vehicle entry doorway.
Here is something else that needs to be observed:
Table R301.5 Minimum Uniformly Distributed Live Loads, Footnote a: Elevated garage
floors shall be capable of supporting a 2,000-pound load applied over a 20-square-inch
area.
I'm in the process of buying a home and during the inspection a question came up
related to building codes for Bremerton, Kitsap County, Washington. The house was
built in 2003 and the garage is not finished. Is there a building code regarding
the ceiling of the garage having to be finished? I know the walls don't have to
be finished but I heard that it is written in the code that the ceiling has to be
sheetrocked. Is this true?
The home, built in 2003, would have been built under the 1997 Uniform Building Code.
The answer depends on whether the home is a one-story rambler, or a two-story home
with living quarters above the garage. Based on the question, I would assume this
is a rambler. If that is the case, the common wall between the garage and the house
would have been required to have been sheetrocked. To meet that requirement, the
builder could have either (1) installed the sheetrock straight up the common wall
to the bottom of the roof sheathing, or (2) installed sheetrock on the common wall
up as far as the ceiling line, and then sheetrocked across the ceiling. But, if
option (2) was chosen, the two walls supporting the trusses would be required to
be sheetrocked as well. The only wall not required to be sheetrocked would be the
one non-bearing wall.
Any future work in the garage would now be under the provisions of the 2003 International
Residential Code. The wording in the IRC (Section R309.2), while saying essentially
the same thing, is clearer. It requires "the garage shall be separated from
the residence and its attic area by not less than 1/2" gypsum board applied
to the garage side. Garages beneath habitable rooms shall be separated from all
habitable rooms above by not less than 5/8" Type X gypsum board. Where the
separation is a floor-ceiling, the structure supporting the separation (the bearing
walls) shall also be protected by not less than 1/2" gypsum board."
Exterior Sidewall Flashings
I have a question regarding IRC code for Flashing 703.8. We have tried
to explain to the local code official that when it states "approved" he
can make the determination. Is this printed anywhere to help us?
R703.8 Flashing. Approved corrosion-resistive flashing shall be provided in the
exterior wall envelope in such a manner as to prevent entry of water into the wall
cavity. . . .
R202, Definitions: APPROVED. Approved refers to approval by the
building official as the result of investigation and tests conducted
by him or her, or by reason of accepted principles or tests by nationally recognized
organizations.
Every product used in construction is required to be "approved" prior to use.
That does mean "approval by the building official." As the definition states,
that approval is typically based on a national test standard and subsequent testing
by an recognized testing agency. For example: Underwriters Laboratories
(UL), or the International Evaluation Service (IES) "list" products after testing
and determination of compliance with national test standards. They, as the
testing laboratories, do not "approve." A building official uses the listing
as the basis of her/his approval. When a product does not have a national
standard, a building official may base their approval on their own knowledge, compliance
with Architectural Graphic Standards, or whatever other source she/he feels comfortable
with using. But ultimately, it is only the building official that can approve
any product or installation.
The new IRC doesn’t list a gauge thickness required on exterior sidewall flashings.
The old UBC stated 26 gauge. Is 26 still the minimum?
The IRC, in Section R703.8 (exterior wall flashing) only states that "Approved
corrosion-resistive flashing shall be provided in the exterior wall envelope in
such a manner as to prevent entry of water into the wall cavity or penetration of
water to the building structural framing components." However, Section R905.3.8,
Roof Assembly Flashing, requires that all flashing, when of metal, be 26 gauge.
It appears that the writers of the IRC recognized that there are other materials
that can be used on exterior walls, such as the vinyl flashings that come with vinyl
siding assemblies. But, that leaves the builder with the word "approved"
which means "approved by the local building official." I would suggest
that metal flashings on a building, both roof and wall, meet the same requirement--26
gauge. That gauge, as the requirement for roof flashings would certainly be approved
for walls as well.
In the IRC it appears to state that building paper is not required behind vinyl
& wood siding (that’s frightening).
This is another example, of "what the Code giveth, the Exceptions taketh away."
IRC Section R703.2 requires weather-resistant sheathing paper to be applied over
studs or sheathing of all exterior walls as required by Table R703.4. That Table
requires sheathing paper under brick veneer, vertical hardboard panel siding (see
exceptions), horizontal hardboard lap siding, stone veneer, plywood panels--if the
joints are treated, fiber cement panel siding (see exceptions), and fiber cement
lap siding (see exceptions).
The Exceptions to those noted: The sheathing paper is allowed to be omitted under
panel siding applied as required in R703.3.1 and R703.3.2; and under paper-backed
stucco lath. Sections R703.3,1 and .2 are very specific about the joints, laps and
caulking and/or flashing.
So--while it seems "worse," if installed absolutely correctly, the end
result will be the same.
Misc
Can new state codes tighten up these areas?
The State Building Code Council has the ability
to review code changes that are proposed. Look at the Council's web site for the
code change proposal forms.
When does the state make its amendments to the IRC?
The web site noted immediately above has the entire schedule of code amendments.
Typically, all code change proposals have to be into the State by March 1st, with
hearings after that, and then a final vote in November. However, remember that the
State is limited in what it can consider to a nationally-accepted model code. The
issue to be amended must be "unique to the State of Washington.
What is the rule on grade line for four story floors?
As I understand the question, the elevation difference between the front and back
of the house is 21 feet. There will be a "basement" and a "sub-basement" to make
up the elevation difference, so the main floor level can be entered from the front,
and have the basement, and sub-basement exposed at the rear of the house. And, as
I understand it, the "sub-basement" is basically a crawl space--albeit tall-that
will have no finished floor, no heat or cooling, and be ventilated to the outside
just like any other crawl space. And, I assume that there is a story above the main
floor. If all of that is correct, my analysis will work.
The Scope of the IRC is, "R101.2 Scope. The provisions of the International residential
Code for One- and Two-Family Dweelings shall apply to the construction, alteration,
movement, enlargement, replacement, repair, equipment, use and occupancy, location,
removal and demolition of detached one- and two-family dweelings and multiple single-family
dwellings (townhouses) not more than three stories in height with a separate means
of egress and their accessory structures."
The definition of a "story above grade" is, "[B]STORY ABOVE GRADE. Any story having
its finished floor surface entirely above grade, except that a basement shall be
considered as a story above grade where the finished surface of the floor above
the basement is: The definition of a "story above grade" is, "[B] STORY ABOVE GRADE.
Any story having its finished floor surface entirely above grade, except that a
basement shall be considered as a story above grade where the finished surface of
the floor above the basement is: 1. More than 6 feet (1829 mm) above grade plane.
2. More than 6 feet (1829 mm) above the finished ground level for more than 50 percent
of the total building perimeter. 3. More than 12 feet (3658 mm) above the finished
ground level at any point. So--the question is what portion(s) of this house qualify
as a "story?" Obviously, the main floor and top floor are stories. The "basement"
would also be a story since its "finished floor" is more than 12 feet above the
finished ground level. So it is now a three story, guaranteed. The only question
that remains is if the sub-basement qualifies as a story. I would say that it does
not, for the following reasons: 1. The definition of a story above ground is very
precise in its wording, "any story having its finished floor surface entirely above
grade, except. . . ." There is no finished floor. 2. The definition of "story" is
also very precise in its wording, "that portion of a building included between the
upper surface of a floor and the upper surface of the floor or roof next above."
Again, there is no floor. 3. The Scope of the IRC is very clear that it applies
to ". . . detached one- and two-family dwellings. . . not more than three stories
in height . . . " "