Exterior retrofits are one of the best ways to improve the envelope of Canadian houses, but they require certain conditions to be successful. Some buildings will be better suited to an exterior retrofit than others. Essentially, it boils down to this: the simpler the style, regardless of the house type, the better.
Obviously, this means there are some ideal candidate houses out there, and all other houses have a lower ranking. That’s OK, because there’s more than one way to improve a house. But let’s talk about what an exterior energy retrofit is, what makes a house a good candidate for one, and what makes an ideal candidate.
Good candidates are found in the ‘sweet spot’ era, 1940 to 1980. You know these houses - they’re the bungalows, ranchers, two storey, and split entry houses that fill many Canadian neighbourhoods. They are blessed with very simple geometry.
What makes a house a good candidate for an exterior retrofit?
Here are seven key characteristics of a house that is a good candidate for an exterior retrofit. First of all, we’re going to assume that the cladding is in bad shape.
- Simple footprint (rectangular or square)
- Simple above grade geometries (minimal bump outs, cantilevers, dormers, turrets)
- Removable siding on all elevations
- 12-18 inch overhangs at the gable end as well as eave, or at all hip eaves
- Minimal or no permanent obstructions like concrete stoops or attached carports
- Room for a crew to move around the whole perimeter
- Ideally the windows are also due to be replaced
An ideal candidate house for an exterior insulated retrofit would have the complete list of characteristics. The proportion of ideal candidates in any region’s housing stock will be small, but there are likely to be many good candidates that meet some or most of these characteristics.
When is a house a good candidate for an exterior retrofit?
A good time to do an exterior insulation retrofit is when it’s time to replace the siding or cladding. The best time is to do it when it’s time to replace the siding AND the windows. The best time to replace windows is when the siding needs to be replaced.
Cladding, windows, roof. Replacement time means improvement time.
Timing is everything. Not just for deferred maintenance, but also for the owner’s monthly budget. What time of year the work happens can also be important for your client. Let’s say the retrofit takes place early in the spring. There will be a six-month lag before the owner sees the savings on their winter utility bills. Their repayment period starts as soon as they sign the loan or mortgage to start the work - that could put a lot of financial strain on a household.
The cost-effectiveness of energy conservation measures is inevitably higher when tied into capital improvements or deferred maintenance. Adding outboard insulation under new siding is a premium added to deferred maintenance. But it’s a premium that pays for itself over and over again through the years.
There are 3 (actually 4) Parts to an Exterior Insulation Retrofit
An exterior energy retrofit is a comprehensive process aimed at improving the energy efficiency, comfort, and overall performance of a home. The retrofit typically consists of three main components:
- upgrading insulation
- enhancing air sealing
- installing energy-efficient windows and doors
There’s a fourth component to check as the envelope is improved: ensuring that there’s adequate mechanical ventilation.
Increasing insulation - SURPRISE! - reduces heat transfer and leads to a more consistent indoor temperature. Various insulation materials, such as mineral wool, and rigid foam or spray foam insulation, can be used to reduce the home's carbon footprint while improving occupant comfort.
Obviously, upgrading insulation is a crucial aspect of an exterior energy retrofit. But you can’t just slap some insulation over the wall sheathing and walk away saying ‘job done’ - you need to consider how to tie the roof, and foundation assemblies into the new wall system.
You could easily argue that air sealing is the most important reason to carry out an exterior retrofit when it comes to energy conservation and occupant comfort, health, and safety.
Let’s toss in some numbers to support that statement.
A study of exterior insulation retrofits carried out in 2018 showed there were nearly ten thousand exterior wall retrofits in Natural Resources Canada’s database for the EnerGuide for Houses Rating Service. Why do we care? Well, those exterior wall retrofits as a single measure accounted for a 15% reduction in air change rate.
Now, a package of measures that addresses the whole house will always have a better outcome than a single measure. That’s true from an energy conservation standpoint and from a building science standpoint. For example, Peter Darlington, of Solar Homes Inc. in Calgary, did a Net Zero Renovation on his own house. Whole-house air sealing - not just at the walls - dropped the house from 4.55 to 1.27 ACH50 (air changes per hour at 50 Pascals). That’s a 3.5x reduction.
The fact is that when you’re working from the exterior, it’s way easier to get closer to a continuous air barrier install than it is on the interior. You have access to all the surfaces, there are fewer junctions to seal, and your client can actually be living in their house without a lot of inconvenience while you work.
Any time you strip the siding off a house, you’ve got the opportunity to fix a lot of problems and improve the durability, energy conservation, and comfort of the house. Installing energy-efficient windows and doors with low-emissivity coatings and insulated frames helps to reduce heat loss, but more importantly, improve comfort for the occupants.
Investing in airsealing and insulation for the win!
A study carried out for NRCan in 2019 by Gary Proskiw (Proskiw Engineering Ltd, Winnipeg) showed that adding insulation to the exterior of a house is a 15 to 20 percent premium on a recladding job.
What does that mean for the typical Canadian living in a typical house that would be a good candidate for insulation and air sealing?
Well, let’s do a back of the napkin calculation. We start with a reasonably typical house shape and size: a 1500 square foot 2 storey house, built in 1960 in Climate Zone 6. There are roughly 1600 square feet of wall surface after the door and window area has been accounted for. For simplicity, let’s assume it’s all-electric. Baseboards for heating, a storage tank for hot water. Average 2x4 construction and assemblies, average airtightness.
Next we create an energy model for our generic house in a generic location in Climate Zone 6 (cities in this zone: Halifax, Charlottetown, Ottawa, Medicine Hat, Lethbridge, Revelstoke, 100 Mile House, Williams Lake, Prince George) in HOT2000.
If all we do is add R12 to the outside of the main walls and drop the whole house airtightness by 50% we go from 23,260 kWh a year to 18,600 kWh a year.
That’s a 20% saving annually.
So, we save roughly 4660 kWh a year.
The average electricity rate in Canada comes in at just over 17 cents per kiloWatt hour, making the energy savings on our hypothetical house $800 a year. At that rate, it takes 6.4 years to recoup the cost of the insulation using simple payback.
If the siding lasts 25 years, the energy savings over the lifespan of the siding total $20,000. That’s worth more than 4 times the initial investment, and we haven’t accounted for increases in energy costs over that period.
That’s a pretty convincing sales pitch.
(It’s also why renovators should be working with a registered Energy Advisor who can help you crunch these numbers - you can’t manage what you don’t measure)
