Rob Dumont’s Recipe for High Performance Residential Design
Rob Dumont is a building scientist who is a “guru” in developing practical cost effective fully integrated high performance building solutions. An abundance thinker that is willing to share “his special recipe” that is based upon a life long journey of research and innovation.
Rob’s solutions are always based upon passive house principles, proven technologies, air tightness and an investment in his favorite low tech solution “high levels of insulation”.
The following blog is a summary of Rob’s more detailed article published in the September 2013 issue of Solplan Review
1. Do not scrimp on design. Design fees are a small part of the overall cost of a new home. Be prepared to pay 5 to 10% of the construction cost for a good design.
“The bitter taste of poor quality lingers much longer than the initial sweetness of a low price.” So wrote John Stanhope.
For most people, their largest single investment will be their house, and it pays to get the design right.
2. Select a piece of land that has good solar access. The lot should have unobstructed access to the direct sun from about 8 am to 4 pm each day of the year. A wide lot facing south is definitely preferable to a narrow lot facing south.
3. Choose a shape for the house that is roughly rectangular with the long axis of the house running east and west. Avoid house plan shapes that are L shaped, T shaped or U shaped or trailer- shaped houses as they have more surface area and heat loss for the volume that they enclose.
4. Design for flexibility: A well designed house should last for centuries, and over that length of time many different uses will be made of the space in the home. By providing separate entrances to the basement and/or a second story the dwelling can accommodate suites, which can help to make the home more affordable as well as, increase the density of the neighborhood a key component of sustainable communities.
5. If you want a garage and have the space on the property, a detached garage is preferable compared with an attached garage for safety reasons. People have died in homes with attached garages from car motors running and producing carbon monoxide which drifts into the living space.
6. Choose a contractor with experience in building energy efficient construction such as R-2000 Houses and Energy Star Houses. Make sure that the contractor has input on the design.
7. Choose windows with great care. On the south side, put windows with an area equal to about 5 to 8% of the floor area of the house. Fixed windows are preferable to operable windows and are usually less expensive and have narrower frames and admit more light and solar energy. For egress and summer ventilation incorporate operable windows.
On the south side, choose windows with a solar heat gain factor of 0.55 or higher. To control unwanted solar gains on south windows in the cooling season, provide a roof overhang or awning that will shade the south windows. On the east and west sides, limit the window area, as windows in these orientations provide little passive solar heating in the heating season and yet contribute to overheating the house in the cooling season. Windows on the north side contribute little to useful space heating, and for this reason should be limited in area. On the east, west, and north walls, choose windows with a high R-value.
8. Place inexpensive thermal mass in the home. A simple way to do this is to place scrap gypsum board in the hollow wall cavities of interior wood stud wall partitions. This technique will also reduce the amount of landfill waste during construction and save on tipping fees.
9. Insulation levels: The author is a great believer in high insulation levels. For cold climates a minimum of R40 walls, R60 Roof and R30 in the basement floor is recommended. Because wall insulation is more expensive due to additional framing or more expensive insulation materials, the above-grade and below-grade walls usually should have R-values about 70% of those in the attic.
If you are building Net 0 it is less costly to install better windows and more insulation than buying PV panels!
10. Build tight and ventilate right. The R-2000 air leakage standard of 1.5 air changes per hour at 50 pascals is now readily achievable by many Canadian builders, and some commenters called for an air leakage rate as low as 0.5 air changes per hour at 50 pascals. Have the house tested for air leakage. Select a heat recovery ventilator (air to air heat exchanger) that has a low electrical consumption. HVI has a web site with detailed information on the effectiveness and electricity consumption values of commonly available HRVs in North America.
11. Water efficiency: Domestic Hot Water. The domestic hot water (DHW) load is usually the second largest energy load in houses after space heating.
To reduce Hot Water use:
- Low flow showerheads that use less 2.0 US gallons per minute (7.6 litres per minute) Try to find a showerhead that allows you to save water while you are soaping yourself. They are sometimes called “Navy Showers”.
- Energy Star clothes washer, dishwasher
- Drain water heat exchanger
- Extra insulation on the water heater storage tank and pipe insulation on the hot water line.
- Locating the water heater close to the end uses in the kitchen and bathrooms
- High efficiency water heater.
- In larger houses with a bathroom or en-suite some distance from the water heater, it may be desirable to install a small (cottage-style) booster water heater that is well insulated in the remote location so hot water is available in seconds (rather than minutes).
To reduce Cold Water use:
- Toilets are usually the single largest interior water users. Choose low water use toilets. Some toilets use a dual flush mechanism with either 3 or 6 litres per flush. One single flush toilet on the market is so well designed that it can provide a good flush with only 3 litres of water.
- For extra water saving, consider a Japanese style combined sink and toilet. These units have a sink on the back of the toilet. Wastewater from the sink flows into the toilet tank and is used for flushing the toilet.
- Choose low water use vegetation on the outside of the house using native plant materials.
- Use water collected on the roof for irrigation. A rain barrel is an inexpensive technology.
12. High Efficiency Lighting: Use natural lighting, light the task rather than the whole room, and use light coloured walls and ceilings. LED lamps are preferred as they typically have a longer life than CFLs and do not contain any mercury. Most LED lamps are dimmable.
13. Energy Star White Appliances (refrigerator, freezer, dishwasher, and clothes washer) are recommended. Look for Tier 3 Energy Star Appliances for the best efficiency. Consider a drying rack in addition to a regular clothes dryer. An outdoor clothesline is also an option for part of the year. A conventional clothes dryer is usually the largest consumer of electrical energy of all the appliances in a house. To conserve space, use a stacked washer and dryer combination.
14. Keep the space heating and water heating systems simple: While there may be a temptation to use every thermodynamic opportunity to maximize performance, the reality is that complex mechanical systems almost always prove to be problematic, expensive and far too unreliable.
15. Plan for the use of renewable energy technology devices such as solar water heaters and photovoltaic panels by orienting a roof surface toward the south at a tilt angle roughly equal to the latitude angle plus or minus 20 degrees at your geographic location. (Example: Saskatoon is at a latitude of 52 degrees North. Given Saskatchewan’s current electricity price of 12.9 cents per kilowatt hour including GST, a low maintenance, high quality solar photovoltaic system amortized on a mortgage is now competitive with grid supplied electricity.
16. Safety. If you have any combustion appliances in the home or if you have an attached garage, install a carbon monoxide sensor in the living space. Placing smoke detectors in each bedroom is also a good idea.
17. Durability. In coastal and higher rainfall areas, make sure that your walls are of a rain screen design. Don’t buy the cheapest asphalt shingles for your roof. A lot of energy is required to replace short-lived building materials.
18. Reduce phantom energy loads (the electrical loads that draw power even though the device is nominally off) by having a separate electrical switch and outlet to control devices like your cable box, internet router, and TV.
19. Think multiple uses when designing. As mentioned above, orient the roof surface for future solar devices. A roof overhang can also serve as an exterior shade for the windows on the south side. The noted architect Frank Lloyd Wright stated that you should never put anything in a dwelling that serves only one purpose. Concrete floor toppings provide both thermal mass and a finished floor surface with a polished surface.
In summary, a good house design should make use of strong energy and water conservation measures, use passive solar heating, be adaptable in space use, and plan for the eventual use of more renewable energy devices such as photovoltaic panels and solar water heaters.
Thank you Rob, we really appreciate your passion and commitment to developing a truly sustainable building industry and for sharing your recipe that we have used for the Prefab Green Net 0 duplex that we are currently building.
Builders’ Manual, Canadian Home Builders Association, 150 Laurier Avenue West5J4, Suite 500, Ottawa, ON, K1P
Tap the Sun, Canada Mortgage and Housing Corporation, Ottawa, ON
A Pattern Language, Towns, Buildings, Construction, Christopher Alexander, Sara Ishikawa, Murray Silverstein and Max Jacobson,1977 (Warning: Fairly theoretical)
Not So Big House, Sarah Susanka