MINNESOTA ENERGY CODE WORKAROUNDS
WHITE PAPER BY GARY TURPENING ARCHITECT Tuesday, March 8, 2022
Architecture Direct Duluth MN (612) 327-6725
MINNESOTA ENERGY CODE WORKAROUNDS
And caution concerning site foamed plastic insulation – see section G.
A. BACKGROUND ON RECENT CODES – CONSERVATION
In raising the code standard problems were created for several reasons:
1. The insulation required is above what normal building techniques can achieve.
2. Confusion has followed: many in the construction industry feel forced to use expensive foamed insulation. In an effort to stay within budgets, or to accommodate highly allergic customers, I find that they frequently use batts up against cold Rim Joists and other areas, a sure way to produce rot and mold.
3. Certain age-old rules were broken in the attempt to save energy, principally the concept of dry walls (breathable walls.) Recent codes, including International Residential Code (IRC), and the International Energy Conservation Code (IECC) instead of requiring breathable walls are advocating the use of non-permeable rigid insulation outside the frame walls, with spaces between studs filled with fiberglass batts or similar insulation. This is a perfect recipe for failure in cold climates due to mold and rot from trapped moisture in walls.
4. Minnesota and Wisconsin have made an exception the above rule and allow a frame wall with batt insulation of a higher insulation value.
B. PROBLEMS WITH THE CODE –‘so called’ PERFECT WALLS
1. FALSE REASONING #1-: Apparently the Code Councils only considered the ‘dew point’ without considering that walls must breathe to the outside air to dry.
2. FALSE REASONING #2: Part of the argument made by the Code Councils
is that walls can breathe to the inside of the exterior wall. This is NOT POSSIBLE in cold climates like Minnesota; what is needed on the inside of exterior walls of northern buildings is the opposite; a Vapor Barrier as close to perfect as you can get.
a. Even multiple coats of latex paint approach a perfect vapor barrier rating.
b. Consider that the moisture pressure at 70o F is 70 times that of 0 o F. (National Weather Service Calculator.)
C. VAPOR BARRIER SOLUTION: At the suggestion of a client, I have been using Vapor Barrier Primer Latex Primer for over 40 years.
1.TREATMENT BELONGS ON THE INSIDE OF THE EXTERIOR WALLS. (We use it on all walls including Bathrooms and Kitchens). Look for a perm rating of 0.06 or less).
2. DO NOT USE PLASTIC SHEETS: poly sheets attract water.
D. RIGID INSULATION ON INTERIOR SOLUTION:
1. A way favored by my firm and others locally to get a well-insulated but safe home, is to put the rigid Foamular XPS insulation on the INSIDE over the frame walls.
2.Along with batts in the stud spaces and some insulation value from breathable sheathing, a high 'R' value is achieved with a safe breathable wall.
3. To achieve an internal air barrier tape Foamular joints, including at the floor, with Owners Corning HomeSealIR.
E. EXTERIOR GYPSUM SHEATHING SOLUTION:
1. The idea of a ‘breathable wall’ is to place the vapor barrier on the interior paint surface, and then control the location and efficiency of the wall’s 'Perm Rating', which is the ability of materials to transmit liquid or gasses. Common sheathings such as plywood and OSB fail this test; they are so bad at breathing that they can be considered a vapor barrier.
2. A better sheathing: At Architecture Direct we have found an excellent product for a comparable price as plywood. Being sold in 1/2" and 5/8" in 4x8 and other sizes, durable ’glass faced exterior gypsum’ board has a fire rating, some insulation value, and an excellent perm rating. The only drawback is that it does not hold nails - so the carpenter must keep track of the stud locations and may require flat ‘X’ straps for wind bracing. Fill all joints using permanent caulk to complete exterior air barrier.
F. USE GOOD FOAM (BOARDS) and PAINT: Examples follow.
1. Rigid foam insulation manufactured under controlled factory conditions can offer a good economical product without worry about health problems, long or short term. A good example is Extruded Polystyrene (XPS) Formular by Owens Corning.
a. There is minimal outgassing, and it is easy to work with. Normal installation is covered over by finished products like drywall - see Rigid XPS on Inside Walls above.
2.NOTE ABOUT PAINT: By using vapor barrier primer paint on all walls the possibility of outgassing problems such as formaldehyde is further minimized.
G. AVOID BAD FOAM – SITE MIXED AND SPRAYED:
1. If the foaming process on the job goes wrong for any reason, outgassing can be serious and long term, especially for asthmatic and allergy sensitive people.
2. These disasters happen frequently and are not acceptable, making site foamed plastics a bad choice for human occupied buildings. At Architecture Direct we search for alternatives.
3.STRUCTURAL LONG-TERM EFFECTS: Site foamed plastics are not dimensionally stable over the long term due to shrinkage, so there is a good chance that moisture will go around to the cold side of the foam, causing the rim and floor joist ends to rot and cause mold.
H. RIM JOIST REMEDY - DESIGN #1: SITE MADE INSULATED: Back a dozen years ago the code required R-11 at rim joists, which was perfect using factory made Insulated Rim, which even came with waxed surfaces creating a vapor barrier making every part of the code a one-step operation. The higher ‘R” value caused the discontinuing of this product nationwide. At Architecture Direct we designed a similar detail so this superior method can be site built meeting the code. This will eliminate the need for expensive foamed plastics at the rim joist.
(see illustration below).
I. RIM JOIST REMEDY - DESIGN #2: NO RIM JOIST: After thorough study of steel hanger technology, we found that using 'off-set’ joist hangers allow the placement of the hangers on top of a wood framed or concrete wall, holding the joist ends off the wall up to 1 1/2 inches. This allows rigid insulation or wall finishes behind the hangers and batts up to the top of the wall, up to the top plates. This creates walls that are totally insulated without a rim joist. (see illustration below).
J. ATTIC EDGE REMEDY - ICE DAM ALTERNATE: It is important to differentiate between vapor flow and air flow; Where old roofs pass over exterior walls, especially those with low slopes, the thickness of insulation becomes too small. The walls and ceiling should be painted with vapor barrier primer which should stop moisture flow. Using rigid insulation in attics will insulate without causing a vapor problem. Use XPS or other rigid board, cut to the slope and pushed to the wall line. Maintain 1-2 inches of air space between the insulation and the roof deck to vent and keep the attic dry.
K. BASEMENT WALL REMEDY – CAUTION: Be careful on that basement wall - first cure it of dampness.
1. Often homeowners put standard framing lumber next to the wall (and published material shows this). Do not use wood next to a cold wall, unless it is treated, or it may develop rot and mold.
2. SUCESSFUL BASEMENT EXPERIMENT: I have had an unusual success here in Duluth where the block walls are very cold, but not wet. We used 1 1/2" rigid insulation temporarily glued up onto the wall. Around the windows and doors we used treated wood backing for trim. Then we secured moisture resistant 'paperless drywall' with 8 shot nails per board. After plastering, we used vapor barrier primer paint on the walls and rim joist, and ceramic tile as a base.
L. MATERIALS MENTIONED
note: I have used all these products personally on my own properties and have no financial interest in any of them.
exterior gypsum Georgia Pacific Densglass
Insulated Rim Joists Structural Wood Company R-11 Rim Joists
Joist hanger Simpson Strong tie
paperless drywall Dens Armor Plus by GP
permanent caulk Prosoco R Guard STPE Joint and Seam Filler
*Available at Heritage Windows, Superior WI
rigid XPS Insulation 3/4" Formular by Owners Corning. (R-4.)
shot nails Remington Nail Gun
Vapor Barrier Primer Latex Primer Sherwin Williams and Benjamin Moore
X wind bracing Simpson Strong-tie WBC
· United States Environmental Protection Agency