THE CODE TRAP –BREATHABLE WALLS in northern climates
A WHITE PAPER ON IBC AND IRC CODES
By GARY TURPENING, ALA ARCHITECT
February 8, 2017
Recent International Building Code (IBC Commercial) and International Residential Code (IRC) codes have included as a base standard Table C402.2 ‘Opaque Thermal Envelope Requirements from the 2012 International Energy Conservation Code (IECC).
COMMERCIAL WALLS: IECC and IBC requires mandatory use of rigid insulation on the exterior walls of IBC commercial buildings in the colder Climate Zones 5-8.
RESIDENTIAL WALLS: IECC and IRC requires mandatory use of rigid insulation on the exterior walls residential buildings in the colder Climate Zones 5-8, and Marine areas of Zone 4.
Although the code allows a time consuming method for figuring approved amounts to energy through walls using the ‘U’ method instead of the more easily understood ‘R’ method, many professionals and code officials assume that the ‘continuous insulation’ is required.
SERIOUS FLAWS IN THE CODES
Dew point calculations: The IECC is apparently based on the average winter condition of a wall in northern climates.
For Duluth MN that would be +20 ºF, when it can actually be below 0 ºF for nearly a month. In these conditions the vapor pressure in the building interior can be 45 times (4,500%) the outside, and that moisture will always try to get out can resulting in wet sheathing and wood frame members. In summer conditions the vapor pressure differential only varies from 22% to 60% over the inside conditions by comparison. See Footnote
This creates a situation where moisture sits on the outside of any sheathing, like plywood or OSB, which does not adequately breathe to the outside and creates a condition perfect for rotting.
I have observed the above condition on projects with forensic engineers where you can literally dig out the plywood and OSB sheathing with your bare hands.
Breathability of INTERIOR WALL surfaces: The code speaks of excess moisture escaping to the inside space in the summer months: (i.e. drying out). This does not work for the following reasons.
Several coats of latex or oil paint creates a very good vapor barrier, trapping moisture in the wall.
A very good vapor barrier is required for winter months in cold climates, which makes the summer reverse flow of moisture a moot issue.
At Architecture Direct we have found the best vapor barrier is one coat of Vapor Barrier Paint (Benjamin Moore’s product is typical with a perm rating of 0.6) plus an overcoat.
Inadequate Breathability of EXTERIOR WALL sheathing and surfaces:
Plywood and OSB act as vapor barriers, as well as foam insulation.
Some insulations such as Georgia Pacific DensElement do have adequate Perm Ratings of around 26, but has an insulating value of R=0.67 which is far below the code required values of R=5 to R=15.
In addition to moisture from inside winter conditions, provision must be made for inevitable leaks from windows, etc.
Care must be used to choose and install sidings that result in adequate breathability. (Caulking joints should sometimes be avoided.)
THE GREAT GAMBLE
Inadequate breathability of exterior walls will inevitably cause rot accompanied by mold in many structures in the north, and possibly in most of the moderate areas of the United States.
Architects, including myself, and forensic engineers that I know are all dismayed by the continuous insulation requirements in the code for walls, and some have retired because of it. My personal concern is not just a good product, but liability. I do disagree with what the code says, as it goes against my best judgment, and I will not put it on the drawings or defend it. The architect or builder is the one that will get sued for failure because of the wall construction, not the building official.
Traditionally many architects and contractors used code approved Structural Fiberboard Sheathing, with an ‘R’=2.06 (at 25/32” thick) making it an excellent continuous insulation. This is a ‘smart’ material with a Perm Rating of 26 when dry, and higher if it gets wet; i.e. it promotes the movement of moisture. With the application of Grade ‘D’ felt, which also breathes, and traditional sidings walls were assured of drying out in almost every cold climate situation.
REASONABLE STATE EXCEPTIONS
Some states, such as Minnesota and Wisconsin have avoided the problem of the improper code references by revising the residential charts, but still leave the original table in their codes which adds to confusion and improper construction and extra work for the designer (usually unpaid.)
The industry and the public deserve better vetting of ideas for more insulation. There have to be tests of the logic, and cost benefit, of all items included in the codes.
EFFECT OF BAD CODES
ROTTEN WALLS WITH MOLD.
Total misunderstanding of the rules for building walls among the press, the public, the design profession, and code officials.
GOOD PRODUCTS NO LONGER MADE
Manufactures such as International Buildrite Corp. (BuildRite) have discontinued manufacturing of non-foam products that have always provided the best option for breathable walls.
The codes should specifically allow these proven products.
WORK TO BE DONE
ELIMINATE RISKY CODE LANGUAGE
Eliminate Continuous Insulation requirement for small wood frame commercial building.
Encourage good products such as structural insulating fiberboard sheathing.
More research on new methods such as foil faced bubble wrap.
Codes should have approved assemblies resembling the UL ratings.
Gary Turpening ALA Registered Architect phone 612) 327-6725
Architecture Direct 1820 East 7th Street Duluth MN 55812