Step 4: Dial in the plan to get to net-zero-ready

The objective is to use the energy model to dial in the most practical, cost-effective, near-net-zero version of the building while taking into account the findings of the building condition assessment and the owner’s goals.

The optimization process

Start by dialing the envelope component specifications in the energy model — walls, windows, roof, etc. — to near net-zero performance levels, much as if it were a new net-zero building, but taking into account what’s practical considering how the building is now. For example, if the wall R-value is not far below optimal and the walls are in good shape, you would probably look for savings elsewhere because the cost of the new siding that would be needed to cover the added insulation would be too high in relation to the energy benefit. The objective is to find the optimum combination of envelope and mechanical upgrades where the marginal cost to save a kilowatt-hour per year for each upgrade is close to the same for all components of the envelope (foundation, walls, roof windows, airtightness, and mechanical) and where that marginal cost is a low as possible while still meeting the net-zero target. In other words, finding the point of diminishing returns where additional insulation is getting too expensive relative to the additional energy savings.

Many considerations

There are many things to consider when choosing the best set of measures and upgrades for any particular retrofit. They include the following:

Adding insulation to existing assemblies increases the risk of dangerous moisture buildup in walls that previously dried out just fine because the existing walls were built from vapour-open materials and there was lots of heat and air movement to dry them out. Someone, preferably multiple people on the team — a qualified building scientist, the designer, and contractor — needs to understand the risks involved in adding insulation and airtightness and make sure that the solutions are included in the optimization process. It is critical to use a house-as-a-system approach and sound building science to make sure that any interventions address the risks to the four control layers: water, air, vapour, and thermal.

The earlier in the planning process that these are considered, the more practical they are likely to be.

Capturing the Potential Co-benefits

When looking at the options and levels of possible envelope improvements, it is important to evaluate and capture the co-benefits of the upgrade measures in the optimization process. Some co-benefits, like healthier indoor air as a result of controlled filtered ventilation from HRVs or ERVs and the luxurious comfort that comes from better-insulated, more airtight walls and high-performance windows, involve no additional cost. They follow from the measure if done right. Others, like enhanced durability and lower ongoing maintenance costs that result from vapour-open assemblies, rain screens, and better flashing detailing, will have some costs associated with them. The same is true for measures that provide better resilience in the face of climate risks like hail, wind, fire, and flooding. 

Service upgrades

In most cases, deep retrofits aim to prepare the building for the electrification of heating and hot water and end dependence on fossil fuels. This will immediately raise the question of whether the existing electrical service has the capacity for these additional loads without requiring an upgrade. Service upgrades are expensive. In most areas, only a limited number are possible before requiring major utility capacity expansion. Smaller electrical loads from more aggressive envelope upgrades and more efficient heating and cooling from higher performing mechanical systems like geothermal heat pumps can reduce the need for service upgrades. 

Minimizing disruption

Moving people out of their homes during a retrofit is rarely an option. It is expensive and, for multifamily buildings, usually impossible. Choosing solutions that minimize disruption will be part of the optimization process. It is the big driver for exterior rather than interior insulation and airtightness solutions.

Maintaining heritage value

Preserving the character and charm of older buildings can be difficult and expensive, particularly so for buildings with historic designations.

The future cost of dispatchable emissions neutral energy

The economics of net-zero emissions retrofits are as dependent on the future cost of dispatchable, emissions-neutral energy as they are on the construction costs, whether we know what that cost will be or not. If the cost of the emissions-neutral energy needed to heat buildings in January is high because of peak demand, then we can afford to spend more on insulation and other measures to reduce future energy use. Typically, retrofit paybacks are based on the current cost of fossil energy, based on historical prices, and adjusted using an inflation escalator and an allowance for carbon pricing. Those costs may be all we have at the moment, but that should not prevent us from using our best judgment to make predictions based on foreseeable probabilities.

This can all be pretty complicated, especially when you consider the immense diversity of buildings, ages, and construction types that are out there, and the many changes that have been made to them in the different eras since they were built. Dialing in the best solution set often requires an interdisciplinary team of energy advisors, building scientists, engineers, and contractors working together to come up with the right mix of solutions and evaluate their cost-effectiveness. This should and must get easier if we are going to achieve the scale that is needed. Fortunately, there are some shortcuts and workarounds that can simplify some of this work. And more coming — we’re learning fast.

Shortcuts and workarounds

Envelope First: Dialing in the right insulation levels

There are good reasons to tackle the envelope upgrade first in the optimization process.

The mechanical system can then be right-sized, saving upfront cost while providing better comfort. The resultant smaller equipment size lets you electrify without an electrical service upgrade, or at least a smaller upgrade if one is still necessary. Finally, the envelope upgrades are where most of the co-benefits are to be had: luxurious comfort, healthier indoor air quality, enhanced durability, better resilience, and higher resale value. 

The question is how much insulation to add. Finding that optimal insulation level can be complicated, but a study by RDH Building Science for the North American Insulation Manufacturers Association (NAIMA), has already worked out an optimum range for wall insulation for near net-zero building for every climate zone in the country. The values from the NAIMA/RDH study are consistent with several other sources and our own long-hand calculations. This is a lot easier than doing the cost-benefit analysis yourself. 

In most cases, this insulation will be added to the exterior because of lower overall cost, the opportunity to improve airtightness, and lower disturbance for the occupants. 

The new cladding required to cover the new insulation is the expensive part. The insulation cost difference to get to an optimum level is relatively small. And the recladding could be needed in the short term anyway, or be desired for appearance reasons. The fact that the next recladding may not occur for 50 or more years makes it compelling to insulate to the high end of the optimum range and not to waste this once-in-a-lifetime opportunity to add enough insulation. A lot of the cost of any upgrade is getting ready to do it. The same is true for attic and foundation insulation.

Retrofit Canada Repository and Case Study Library

The Retrofit Canada Case Study Library is another time saver. It has many useful examples (with more being added all the time) of projects where someone has already done the hard work of optimizing solutions. They may not always be perfect solutions, but the lessons from them can help you avoid expensive mistakes. Retrofit Canada is now hard at work mining the solutions from the Case Study Library.

Retrofit Types

Determining the most appropriate retrofit type early in the optimization can narrow the scope that needs to be considered and save a lot of legwork. Retrofit types range from mechanical only for buildings that have envelopes that are good enough already, or at least too good to be worth upgrading, to retrofits where the heavy lifting is on the envelope. This can be useful even though most retrofits are likely to fall on a spectrum with some of each. 

Many possible upgrades can be ruled out early because of the prohibitive costs of the measures needed to execute them. This will be the case with many newer buildings that have exteriors with a lot of remaining life. The existing assemblies in newer buildings also tend to have higher R values that leave less room for performance improvement. In those cases, it makes more sense to look for mechanical solutions or renewable energy sources as the primary measures.

Phased Retrofits 

While a deep retrofit as a single project is usually more efficient and less expensive, this may be financially out of reach for some homeowners. If this is the case, a phased retrofit with a clear plan to become net-zero-ready is an excellent option. READ MORE ABOUT PHASED DEEP RETROFITS