Gary Turpening, ALA Architect
Minnesota Registered Architect # 13584
Wisconsin Registered Architect # 5826-005
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WHITE PAPER - ENERGY OPTIONS FOR DULUTH AREA HOMES
14 December 2013
By Gary Turpening, Architect 14 December 2013
Every several years I re-evaluate my assumptions on the energy options available. I have designed and built homes since before my architect registration in 1972, and have always embraced the latest trends. However, my experience has largely been with small and mid-sized projects where I have had to evaluate all options on a 'cost benefit' basis. The comments enclosed are based on a detailed effort of counting BTUs and comparing systems based on yearly performance.
The result of the above study is that the Minnesota Energy Code is very hard to improve on based on yearly energy cost. There are new items in the code relating to radon and ventilation that need further study and refinement, but the basic R-values are close to optimal.
ASSUMPTIONS OF CURRENT STUDY
These comments are based on using a 1 1/2 story house in Duluth with a full basement. The footprint is 1200 square feet. Walls are made of 2x6 at 16" o.c. with fiberglass insulation. Siding is cement board.
I recommend the following construction practices for reasons other than energy savings:
WALL SHEATHING: Structural Fiberboard allows the wall to breathe to the outside air, and is less expensive than plywood which does not have proper permeability rates to qualify as a breathable material.
ROOF SHEATHING: Use Plywood instead of OSB. When OSB is exposed to moisture repeatedly it continues to grow and finally fail.
SIDING: Care should be taken to use materials that allow moisture in the wall to escape. Cement board has many advantages: it allows moisture to escape at the joints; it is a man-made product that will remain stable without rotting; and it can be ordered primed or pre-finished in many colors and textures. This is a 50-year product.
VAPOR BARRIER: Vapor Barrier paint (by Benjamin Moore and others) on inside surfaces of exterior wall surfaces works better that any other method.
This method must be combined with good practices for sealing electrical and other openings, and an air barrier must be created per code.
I recommend this for the first paint coat on all drywall surfaces, because it creates an excellent surface for final finishes and seals in any mold or formaldehyde gasses.
HEAT UNDER THE BASEMENT FLOOR: This is for comfort, and to keep the basement dry.
PAPERLESS DRYWALL: Use on all outside walls, especially in cool basements and cabins where they are allowed to cool for long periods. This gypsum board material will not grow mold and is about 50% heavier than normal gypsum board creating a 'thermal mass' allowing your furnace to cycle less frequently and absorb any solar heat. This material is also good as a plaster veneer or ceramic tile base.
RESULTS OF ENERGY STUDY
FOOTINGS AND RADON
Radon requirements are required by code, but one interesting way to solve the problem with other benefits is to use Form-a-Drain by Certainteed, a hollow plastic box, forming the footing, that conducts water and radon gas to a central point for removal. These measures also keep a basement dryer.
The code now has many requirements for block foundations making ICF (Hollow Insulation blocks with the ceneter poured concrete) the easier way to build. A durable surface, like thin stone or plastic sheet, must cover the exposed Styrofoam (after which point, the interior will be ready for drywall to be installed).
WIND SCREEN: 2 layers of building paper is still the best method for several reasons including its longevity and breathability.
AIR BARRIER: Careful attention to details is the best approach. It is recommended to spray cracks of certain wood frame joints on the inside of the house with a rubber mixture or flexible caulking before placing fiberglass insulation.
INSULATION: Unfaced fiberglass is our preferred method to avoid trapping moisture. Spray foams may contain irritants for some people, and is frequently misused. Rigid insulation (such as Dow Blue Board or Styrofoam) is acceptable in special conditions.
RIM JOIST: Structural Wood Corp. has a product that solves many problems. It is a composite of OSB on the outside and inside for strength with Styrofoam in the center for a rating of R=11. The surfaces are treated to make them vapor barriers. When the product is laid, top and bottom, in a bed of caulking that part of the wall is finished for both air and vapor barriers.
RAIN SCREEN: The concept here is to increase the drying of the wall by creating an air space between the building paper and the siding. This can be done by applying a fluted material like Home Slicker, or creating a 3/4" air space with 1x3 boards nailed to the studs. This is a good idea, but not really necessary and not cost effective for the extra R of 2.37. The total wall with this system is R=28.54, instead of R=26.17, and cost thousands of dollars extra.
WINDOW STUDY - 3 PANES VS. STANDARD 2 PANE
Using Pella windows as a guide, it is hard to improve on a modern window. The inexpensive Proline (available at Menards and Pella) has E-glass coating and argon gas, for a composite R rating of 3.3.
Triple pane has an R rating of only 3.45, but has an up-charge of 50%. This change would only return a savings of $8.00 per year (for all the windows).
Triple panes also come with shades, which doubles the cost with a cost savings of only $25.00 (for all the windows).
I spoke with a major Duluth installer of geothermal systems, and with architect colleagues who have installed systems in their own homes.
The cost of a system is between $30,000 and $40,000.
The cost of the system may be offset by the following:
Lowering the cost of a hydronic heat system (radiators) or under-slab heat.
Federal tax breaks of 30% are available (i.e. $11,000 on a $33,000 system). Caution - on a limited income you may not receive this credit.
Some areas may get an additional credit from their electric company.
In a typical installation costing $35,000 the total savings per year comes to $690, while the interest on the investment after taxes and heat saving is $975.00 at 5%.
ENERGY RELATED RECOMMENDATIONS
HEAT RECOVERY UNITS: Avoid because the yearly maintenance is up to $800, and it takes electric to run. With improper maintenance you may be creating conditions favorable to growing mold and then pumping it throughout your house.
NATURAL VENTILATION: This is always the best, and the simplest to accomplish. Provide plenty of fresh air to your basement, especially in any area with combustion appliances.
SMALL CONTINUOUS EXHAUST FANS: These are now required by the code, and are simple and easy to maintain.
SOLAR PANEL - WET: Use as a 'Passive System' to preheat hot water in an extra tank, or to pre-heat concrete slabs.
SOLAR PANEL - ELECTRIC: Photovoltaic only if it pays. Check your electric company to see if you can sell back power.
SOLAR PANEL - PASSIVE AIR - This can be used to pre-heat fresh air to your house.
BEST CASE FOR SOLAR - South facing windows and skylights. East and West facing windows can also work well under certain conditions.
Comments are invited. Gary Turpening (612) 327-6725 firstname.lastname@example.org