More and more, we’re seeing BC builders demonstrating that it is feasible to retrofit older homes to Net Zero or Near Zero. A Deep Energy Retrofit (DER) is an energy conservation upgrade to an existing home that leads to an overall improvement in the building’s performance. No standard-setting agency has established a legal definition of a deep-energy retrofit, but this approach can be defined as a whole-house analysis and construction process that aims at a reduction of on-site energy use by 50% or more.
Most projects begin with an energy audit. Energy audits typically include a blower door test, duct-blaster testing, thermal imaging with an infrared camera, and an assessment of the current insulation levels, windows and doors, HVAC and water heater systems, and the energy efficiency of appliances and lighting. The past year’s utility bills are evaluated, to establish performance objectives for the project. An energy monitoring device, like The Energy Detective, measures electricity usage and this can also be useful. Examining how the existing building envelope gets wet, and then dries out, can help pinpoint ways energy improvements can manage where the moisture goes.
In the energy retrofit plan are a set of defined client needs, design opportunities, goals and performance objectives that will be addressed in the remodel. Deep energy retrofits typically go beyond energy and cost savings, improving the functionality, thermal comfort, indoor air quality and noise levels.
Architectural designers make use of energy modelling tools to design their zero-energy retrofit plan. The plan typically includes the degree of airtightness required, the R-value of the insulation that will be installed, the U-value of the windows, the HVAC system (heating, ventilation and air conditioning), the energy efficiency of the appliances to be installed, and LED lighting fixtures that will be installed. The model includes the cost of each proposed solution, to arrive at the most cost-effective combination for achieving energy objectives.
Here are some of the primary energy considerations when planning the project.
Energy efficiency
A significant portion of a deep energy retrofit involves improving the sealing and insulation of the building envelope to reduce the annual energy consumption requirements.
Super-insulation
Super-insulating can dramatically improve the energy performance of an older house. Insulating and sealing all six ‘sides’ of the building envelope is a fundamental step in retrofitting to build an energy-efficient home. It is important to insulate the ceilings, floors and four walls with the type and thickness of insulating material that helps achieve the specific requirements of each exterior surface.
High-performance retrofit walls are usually constructed in one of two ways. The first is adding exterior rigid insulation on the existing single-frame wall to achieve the necessary insulating value. When adding an inch of low GWP rigid insulation to the outside of the structural sheathing, additional support is usually not required. Adding more than an inch of insulation thickness requires furring strips to hold the insulation in place.
The second approach is a double plate wall. An additional 2×4 wall is added to the outside, with studs placed on 24″ centres. The plates can be spaced up to 5″ apart to form a 12” thick wall cavity. Both systems can easily be adapted to match a specific R-value design target.
If the roof is poorly insulated, the house is going to lose heat in the winter, with potential ice dams and condensation problems, and it’s going to be very hot in the summer. There are two common retrofit ceiling or roof insulation solutions. The first is blown insulation on a flat ceiling. Most roof slopes provide up to 22 inches of vertical space, to achieve R-60 insulation.
The second solution is exterior rigid insulation. A four- to six-inch layer of low GWP rigid insulation is fastened to the roof deck. The sheets of rigid insulation are held in place with furring strips, which also create a ventilation channel. A second layer of roof sheathing and roofing material then cover the assembly. Additional insulation can be installed between the rafters using batts, dense-pack or low-density spray foam to achieve the desired R-value.
If air is allowed to leak in at the bottom, it leaks out the top, and you have a cold and drafty home in the winter. In new construction, a continuous layer of rigid foam insulation is typically installed under the concrete slab foundation for high-performance homes. The concrete’s thermal mass holds radiant energy and can keep the house dry and warm. But in a retrofit, the foundation has already been poured, so rigid foam is sandwiched between the existing concrete slab and new plywood or OSB sub-flooring. The rigid foam also reduces summertime condensation and mould accumulation, and any musty “basement smell”.
It is possible to retrofit rigid foam insulation outside the basement walls, but the more common and practical approach is applying a moisture barrier against the concrete wall, then adding an interior framed wall, with a focus on minimizing thermal bridging. The wall is insulated with thermal insulation like mineral wool and/or spray polyurethane foam and an interior vapour retarder is installed beneath the drywall. Warm, dry basements and crawl spaces can provide additional living and storage space if these were not considered “inside the house” before.
Homes that have undergone a deep-energy retrofit typically arrive at R-20 basement walls, R-40 above-grade walls, R-60 roofs, and U-0.20 windows.
Windows and doors
An upgrade to triple-pane windows and doors with exceptional thermal performance is part of most deep retrofits. Triple-glazed windows have the space between glazing filled with argon or krypton. Doors offer the airtightness and insulation levels required, are thermally broken, and triple-glazed as applicable. U-values of 0.80 W/(m²K) [0.139 BTU/hr.ft2.F] or less, with g-values around 50% are possible.
Heating, ventilation, air conditioning and hot water
Heat pumps used in net zero homes transfer indoor and outdoor heat by circulating a refrigerant through an evaporation and condensation cycle. During the winter, heat pumps move heat from the outdoor air inside; during the summer, they move heat to the outdoor air.
Regular thermostats allow you to adjust the temperature with a control panel on the wall somewhere in your home. Smart thermostats allow you to manage the home’s temperature remotely, or on a schedule. In addition, smart thermostats provide usage data, allowing you to compare energy needs across different seasons, as well as discover patterns.
Low-flow shower heads and faucets will reduce hot water use. Old inefficient water heaters are usually replaced with an Energy Star®, or better, high-efficiency heater.
BC Hydro offers seasonal rebates for products that improve the energy efficiency of your home.
Energy-efficient appliances and lighting
Energy Star®, or better, appliances and lighting meet strict energy efficiency guidelines. Energy retrofits usually include an upgrade of all of the appliances and lighting in the home, for better performance and lower operating costs.
Sustainable energy
When your energy consumption has been reduced significantly, producing enough energy to cover your needs becomes possible. The most common clean energy solution is an on-site renewable energy system. Roof-mounted solar photovoltaic (PV) systems – also known as solar panels – are the most common solution. Solar panels are very reliable and require little in the way of ongoing maintenance. It’s easy to predict the amount of electricity they will generate in a year.
Energy can be stored in a battery system, or sent directly to the utility grid, with a power credit process agreement with the utility known as “net metering”. With net metering, a net zero home can offset its energy consumption, breaking even over the year.
Moisture control and air quality
In a deep retrofit, moisture should be evaluated and carefully managed. Perimeter drains in the basement can remove any moisture that accumulates, helping to prevent mould in your home. Exhaust fans in the kitchen and bathrooms, with timed shutoff, can balance moisture removal with energy consumption.
The air quality inside average Canadian homes is roughly five times more contaminated/polluted than outdoors, and most of us spend 90 percent of our daily lives indoors. The average household stores and uses more chemicals than an average chemical plant did a century ago; with everything from fragrances to personal care and cleaning products.
In conventional homes, most fresh air enters accidentally, through leaks. When retrofitting to a zero-energy home, your building must be made as airtight as possible. A typical airtightness goal, as determined by a blower-door test, is 1.2 AcH (air changes per hour) at 50 pascals. Whole-house air filtration ERV systems can remove stale and polluted indoor air, replacing it around the clock with fresh, clean air delivered to every room and living space.
If trees are too close to the house, they may block access to the sun, contributing to a damp environment.
Does a deep retrofit make sense for you?
The big rewards homeowners are pursuing from a deep energy retrofit are savings, functionality, comfort, durability and knowing they’re part of the carbon solution; not the problem.
The biggest consequence of a DER is the reduction in your energy bills; at least a 50% reduction in energy usage. Net zero homes produce as much energy as they consume and are up to 80% more energy efficient.
It takes a while to recover the investment of a deep retrofit in energy savings. The cost-effectiveness of a deep energy retrofit can be achieved when the annual energy cost savings equal or exceed the annual loan costs. That perfect balance is referred to as the neutral net-monthly cost.
A deep retrofit is not just about reducing your carbon footprint and saving money on energy costs. The primary reason people remodel is to get their home working the way they want it to. The energy upgrades are usually part of a larger redesign that improves the overall functionality of the home. Perhaps a bedroom needs to be converted into an office, or you want to make the kitchen larger.
For many families, it’s less about saving money on energy for heating and cooling and more about improving the comfort of their home. Airtight and super-insulated houses are wonderfully quiet. The air is fresh, dry and free of pollen and pollution. When they are sealed from the elements, manage moisture effectively and are well-ventilated, homes are not just healthier to live in, but more durable.
Example project: Squamish Deep Energy Retrofit
This project was a high-performance renovation; taking an early 1980’s home, and remodelling it with modern architecture into a Near Zero energy building.
Coast Essential provided all the architectural design for this deep energy retrofit, the construction management and services. Under the Zebx Near Zero Emissions and Retrofit categories, this unique renovation took an approach to achieve Green Built Canada Platinum Certification.
It was a complete remodel and restructure, designed to improve the views and entertainment spaces while hitting deep energy efficiency targets. The home employed sustainable solar energy and drain water recovery systems. The project won two Georgie awards and two Havan awards.
