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Important Design Criteria for Single Family Dwellings

March 21st, 2010

Before the first shovelful of dirt is moved, there are important code required design criteria which must be met for single family dwellings.  Chapter 3 of the International Residential Code addresses these and I will review them in this article.  I will save snow, wind, live and dead loads for another time.

 

Light and Ventilation

Habitable rooms (space for living, eating, sleeping or cooking) are required to have glazing not less than 8 % of the floor area of that room. That is; a 10’ X 10’ room needs 8 sq. ft. of windows.  Of those 8 square feet, 4(or half) have to open to the outside. Of course there are exceptions.  First, the windows don’t need to open if adequate mechanical ventilation is supplied.  You don’t need the windows at all if you have mechanical ventilation and artificial light.  Finally, sunrooms and enclosed patios are allowed to be used for natural ventilation if 40% or more of the exterior walls of the sunroom are screened.   You must take into account that emergency egress requirements  in bedrooms is maintained(This will be discussed later).

Bathrooms are required to have a minimum 3 sq ft of windows, half of which need to open unless you have the required ventilation.

Interior stairs have to have lighting which illuminates the entire stairway located near each landing.  The controls for the lighting must be at every floor level when the stairs have six or more risers. Exterior stairs are required to have lighting near the top landing and both the top and bottom landing if it leads to a basement.  The light switches are to be inside the dwelling.

Minimum room areas and ceiling heights.

One room per house need to be at least 120 sq ft and other habitable rooms can be no less than 70 sq ft.  One exception to this is the kitchen.  The minimum dimension of any habitable room is seven feet. Hallways are required to be a minimum of 3 feet. “Habitable rooms, hallways, bathrooms, laundry rooms and basements have to have ceiling no lower than 7 feet.  There are a number of exceptions for beams and girder, unhabitable basements, and bathrooms.

Sanitation

“Every dwelling unit” has to have a toilet, sink and tub or shower. They also need a kitchen with a sink, and water and sewage disposal.  Kitchen sinks, lavatories, bathtubs, showers, bidets, laundry tubs and washing machine outlets must have cold and hot water.

Shower and tub areas have to be made of a non-absorbent surface at least 6 feet from the floor. Water resistant drywall is no longer allowed to be used in tiled shower or tub areas (2006 IRC and IBC).

Glazing

The requirements for glazing address hazardous locations and the requirements for safety glazing which must be used in these locations.  For an excellent article which covers this subject in depth and gives you a historical and safety perspective about glazing go to the Code Check Web Site.  There are 11 areas considered by the IRC as hazardous locations.  There are also 10 exceptions to these locations.  Most importantly are doors, pool/sauna, hot tub, shower and tub enclosures/walls and fences,  large windows which are close to the ground, guardrails and glazing adjacent to stairways and ramps.  Section 308.4 of the 2006 IRC covers these locations along with the exceptions.  Skylights and greenhouse glass requirements are also covered.

Garages

A separation between the dwelling and a garage is a subject full of misconceptions.  “It’s a firewall….it has to have two layers of 5/8 gyp board on the garage side…., the door has to be a fire door with a closer are popular fallacies.   I can only speak for the last 20 years of CABO and BOCA requirements for separations,  but none of these have ever been required.  Here is what is required by the IRC 2006:

  1. You can’t have an opening into a garage from a bedroom.
  2. If you have duct work penetrating into the garage, it has to be made of a minimum of 26 ga sheet metal and cannot open into the garage.
  3. Other penetrations of the separation wall must be fireblocked.
  4. The garage shall be separated from the dwelling (including its attic) by ½ inch gyp board on the garage side (you could theoretically have open studs on the dwelling side).
  5. If there is a habitable room above the garage, the separation must be 5/8 gyp board (type X).
  6. The supporting structure of item 5 shall be protected by ½ gyp board.
  7. If there is a door in the separation wall, it must be either 1 3/8 inch solid wood, solid or honeycomb steel minimum 1 3/8 inch thick, or a 20-minute fire-rated door. (Wouldn’t a fire-rated door require a closer and positive latching?)

Emergency Escape and Rescue/Egress

A requirement for bedrooms in basement has now become a requirement for all basements with the exception of those under 200 square feet and used only for mechanical purposes.  An emergency window or door must be installed.  For basements with all sides partially or completely below grade, the emergency window is usually installed.  The sill height of such window cannot be more than 44 inches from the finished floor.  The minimum opening area has to be 5.7 square feet (820.8 square inches), with a minimum height of 24 inches and a minimum width of 20 inches. The well outside the window has to be at least 36 inches wide and 9 square feet in area. If a casement window is used, the well must accommodate it to fully open.  If the depth of the well is greater than 44 inches, a ladder or steps shall be installed.  The ladder or steps can impede into the required area of the well as long as the window can be fully opened. The rungs have to be 3 inches from the wall, 12 inches wide and not more than 18 inches

apart. Bars or grates can be placed over these openings but like the window itself-it must be operational from the inside without the use of a key or special knowledge.

Bedrooms must also have an opening, either a door or window meeting the above requirements.  If the bedroom or basement is at the grade level, the minimum opening is reduced to 5 square feet.

One exit door is required from the dwelling unit.  It has to be a minimum of 3’ wide and 80” high and should be side-hinged. No keyed locks are allowed on this door. There should be a landing (the width of the door and 36” in length) outside all exterior doors (there is an exception for non-egress doors).

Stairs, Handrails, Guard

Stairways and hallways shall be 36” wide minimum, with 80” of headroom at the stairs.  When a stair is enclosed, any walls, sofitts and the underside of the stairs have to be covered with ½ drywall.

Maximum stair rise is 7 ¾” and minimum tread depth is 10 inches.  These dimensions tend to vary by jurisdiction.  In 2003, The State of Michigan amended these to 8 ¼ and 9 inches.  The maximum deviation from the biggest rise to the smallest can be no more than 3/8 of an inch.  Landings are required at the top and bottom of each stairway (some exceptions) and a stair cannot exceed 12 feet in vertical rise.

Handrails are required on stairs exceeding three risers. Their height should be 34 to 38 inches measured perpendicular from the nosing to the top of the handrail.  They need to be terminated into the wall or into a newel post and a 1 ½ inch space (minimum) must be provided between the wall and the handrails.  Handrail grip size can either be circular between 1 ¼ and 2 inches in diameter, 4 to 6 ¼ inches perimeter dimension for non-circular(with a maximum cross section of 2 ¼ inches or on those with a perimeter dimension more than 6 ¼ inches it requires a finger recess on both sides of the profile.  This profile must meet certain dimensional requirements (Section R311.5.6.3).

Finally guards are required where a raised floor surface is more than 30” above the floor/grade below. They have to be 36” high (minimum).  Open stairs with a total vertical rise over 30” would also require a guard which would have to be 34” high (minimum).  Opening limitations for these guards are 4” and 4 3/8” for stair guards.  Please note that the forbidden “ladder effect’ was taken out of the IRC in 2003.

Smoke Alarms

Hard wired, interconnected smoke alarms are required in all sleeping rooms, outside the sleeping rooms, and on each story of the dwelling including the basement.  Exceptions are allowed for additions and renovations.

In Conclusion

I’ve only begun to scratch the surface of material covered in Chapter 3 of the International Residential Code. For those of you new to the Code, this is a great place to start and familiarize yourself with its requirements.  Those of you have been in the business for a while; this is a great chapter to frequently review because of the amount of information covered in it.  Unless otherwise noted, I have referenced the International Residential Code, 2006.

Articles, Residential Code

Guard Requirements in 2009 IRC

January 31st, 2010

2 important changes have been made for requirements for guards in the 2009 edition of The International Residential Code.

Previously, a guard was required when the walking surface was 30” or more from the floor or grade below.  I remember building decks on new houses and ripping the lattice skirting at 28”.  The landscapers could place topsoil to the bottom of the lattice and slope it away from the deck.  Since the grade immediately below the deck was 28”, we were exempt from guard

Deck with Fixed Seating

requirements.  This was particularly useful when installing bench seating around the perimeter of the deck and not wanting a guard to extend above the back of the seating.

2009 IRC requires a guard when the walking surface is more than 30”  “at any point within 36” horizontally from the edge of the open side”.  Using the 2006 IRC, a guard would not be required if the grade directly below the deck was 30”.  Take that same deck where the grade slopes 1” in every foot. At a point three feet from the deck; the grade would be 33”.  Using the 2009 IRC a guard would be required.

The second important change requires the height of a guard to be 36” above any adjacent fixed seating.  If the deck requires a guard it would have to extend a minimum of 36” above the seating surface.  The concern here is with children climbing on the seat and falling over the guard.  The code language does not require a guard in instances where the deck (walking surface) is less than 30” above grade (at 36” form the face of the deck) and the seating is more than 30” above grade (as in the picture above).  Anyone who has observed small children might say that the backless seats, like those on the deck above, ARE walking surfaces for unattended children.  Just a thought for 2012.

New Guard Requirements

Also, a change in location for guard height requirements clarifies that height and openings requirements for guards do not apply for guards that are installed in non-required locations.  The 34” wrought iron rails with the 6” openings you find at the big box stores can be used if a guard is not required.

New in 2009

Single Family Garage Separation

November 16th, 2009

garage separation 003A separation between the dwelling and a garage is a subject full of misconceptions.  “It’s a firewall….it has to have two layers of 5/8 gyp board on the garage side…., the door has to be a fire door with a closer are popular fallacies.   I can only speak for the last 20 years of CABO and BOCA requirements for separations,  but none of these have ever been required.  Here is what is required by the IRC 2006:

  1. You can’t have an opening into a garage from a bedroom.
  2. If you have duct work penetrating into the garage, it has to be made of a minimum of 26 ga sheet metal and cannot open into the garage.
  3. Other penetrations of the separation wall must be fireblocked.
  4. The garage shall be separated from the dwelling (including its attic) by ½ inch gyp board on the garage side (you could theoretically have open studs on the dwelling side).
  5. If there is a habitable room above the garage, the separation must be 5/8 gyp board (type X).
  6. The supporting structure of item 5 shall be protected by ½ gyp board.
  7. If there is a door in the separation wall, it must be either 1 3/8 inch solid wood, solid or honeycomb steel minimum 1 3/8 inch thick, or a 20-minute fire-rated door. (Wouldn’t a fire-rated door require a closer and positive latching?)

Myths & Legends, Residential Code

Separation between dwelling units and non-residential occupancies

September 10th, 2009

As you may remember, in the 2006 edition of The IBC section 419 was a new addition which provided scoping requirements for horizontal and vertical separations between dwelling or sleeping units in I-1, R-1, R-2 and R-3 Occupancy classifications.  The one-hour separation requirement had always been in Chapter 7 of the IBC but now there was a directive to send you to Chapter 7 when checking on special requirements for the occupancies in question.

Now in 2009, the IBC has added that the same “between-unit” requirements be met between these occupancies and others.  Why is this important?  In some instances, the previous versions of the code would allow you to have no fire-resistance-rated separation between say a manager’s office and the apartment next to it.  Let me give you an example:

7000 sq ft, Type 3B Construction

7000 sq ft, Type 3B Construction PLAN VIEW

Let’s take a 7000 sf building, with 5000 sf of 1st floor area and 2000 sf on the second floor.  The second floor contains 2 apartments.  In 2006, section 419 sends you to 719(fire partitions) and 711(horizontal assemblies).  Both of these sections talk about ratings for walls or floors separating dwelling units (or sleeping units).  It did not require any separation between dwelling units and other occupancies other than the requirements for separated occupancies in Table 508.3. Now, we’ll say we are going to put in a BBQ restaurant in our building with solid fuel grilles.  The Code allows us to have non-separated occupancies if the building does not exceed the most restrictive building area and height limitations (from Table 503) for the occupancies in question.  We have an R-2 which is allowed to be 16,000 sf and 4 stories and an A2, which is allowed to be 9500 sf and 2 stories.  Since the A2 is the most restrictive and our building has not exceeded this, no separation is required under 2006 IBC.

2006 IBC only required 1-hr separation between dwg units

ELEVATION

We could have an open ceiling with open floor joist between the restaurant and the apartments. (The requirements for the Sound Transmission Class requirements, oddly enough, have always required a “sound” separation (STC 50) between dwelling units and “public or other service areas”.)

All this changes in 2009.  Language has been added to require the 1-hr rating between dwelling or sleeping units and “other occupancies contiguous to them in the same building”. Now a minimum 1-hr rated floor ceiling assembly would be required between the restaurant and the apartments.

2009 IBC now requires at least a 1-hr horizontal separation between the lower level bar and the second floor apartments

2009 IBC now requires at least a 1-hr horizontal separation between the lower level bar and the second floor apartments

As before, in Types 2B, 3B and 5B, these separations can be reduced to ½ hr in buildings equipped with an NFPA 13 sprinkler system. (Has anybody figured out a ½ hour wall yet?)

Frank Bayer

New in 2009 , ,