Southeastern Ontario Phased Retrofit

This case study about a deep retrofit of a wartime bungalow is an excellent example of a phased retrofit done right.

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Southeastern, Ontario


We were looking for an affordable home in southeastern Ontario with deep energy retrofit potential when we found this charming wartime bungalow. We wanted to do the job right in order to avoid costly rework in the future, but our budget would not allow us to undertake the entire project at once. Working with a deep retrofit expert, we have developed a manageable, staged approach where each of the stages took into account the other work that would need to be done.

First Steps

Building Condition Assessment

When we first looked at the house, we found it was in good shape overall, but had a very old furnace and air conditioning unit, minimal insulation, and old windows. Aesthetically, it was outdated but had original wood floors and other charming features. We thought it had great potential for both a retrofit to make it energy efficient and DIY renovation work to make it more liveable and attractive. It was appealing that not a lot had been done to it, meaning that we wouldn’t have to pay for or redo piecemeal upgrades that had been done before. 

After moving in, we tested the vermiculite attic insulation and learned it contained asbestos, which would require remediation before we could add new insulation. We also noticed that the basement was quite cold in the winter and had some moisture issues, leading us to prioritize the foundation phase of the retrofit.

Energy Audit

Next, we hired Homesol Building Solutions to perform an energy audit. The audit showed where the biggest savings could be achieved. Because we were determined to get to net zero and are on a limited budget, we knew we had to get everything we did right - on the first try and as efficiently as possible. Our adviser used the energy audit to dial in the best set of net zero-ready energy specifications for the whole house that also took into account how the house was when we started. (See Before and After specs). 

Planning the Deep Retrofit Stages

The next step was to develop a plan where we could retrofit our house in affordable stages while meeting the net-zero specifications. The advisor helped us come up with a plan that accounts for later stages so that we will never have to undo or take apart previous work. Stage 2 - The Attic (below) shows the kind of thinking that’s needed.

Since we were eager to address the basement moisture issues as soon as possible, we decided to tackle the foundation insulation first and add a waterproofing membrane and weeping tile as part of the same excavation project.

The original plan was to make the house as efficient as possible before adding a heat pump. We would do most of the upgrades, the foundation, the attic, and then upgrade the exterior wall insulation and windows before doing the mechanical needed to electrify the home.

However, because our air conditioning died in late 2023, we decided to do the mechanical after completing the basement walls and attic, because these were the largest sources of heat loss.

Because the cold climate heat pump is sized for the full retrofit, we may have some issues in the very coldest weather. So until we do the exterior walls and windows, we will keep a couple of electric heaters handy.

Finally, at stage five, we will add rooftop solar.  

This staged approach allowed us to address immediate issues with the structure and was flexible enough to account for unforeseen developments like the air conditioning unit giving out. Most importantly, it provided a clear, practical order of operations that will get us to net-zero.

Project Stages

Stage 1: Foundation (Completed Fall 2023)

It made sense to do the basement first. The basement accounted for the biggest portion of the building’s annual heat loss (around 30%). It was cold and uncomfortable. (We work from home and spend a lot of time in our basement office.) It also leaked in two places. The steps in this phase included:

Stage 1 Steps

1 Excavating to the footings, inspecting the foundation,sealing any cracks, and applying new waterproofing.

2 Installing new weeping tile and sump.

3 Installing low global warming potential (GWP) styrofoam insulation to R24.

4 Replacing basement windows with triple-glazed, LOW‑E Argon-filled windows, and adding window wells so the grade could be raised for better drainage.

5 Providing for an air-tight connection to the wall air barrier to be installed in Phase 3.
6 Adding temporary flashing over the new insulation to keep the water out until after the upper walls could be done.

7 Removing the old, asphalt driveway. To be replaced with a small driveway later, reclaiming more space for the backyard.
8 Regrading around the entire foundation (will be completed in Spring 2024, after the ground has had a chance to settle)

Stage 1 lessons learned:

  • Contractors
    We initially struggled to find contractors in our area who were open to the project because many viewed it as unnecessarily complicated and did not value energy efficiency. Through asking around in our neighbourhood, we eventually found a great general contractor. He was open to trying new things, willing to listen, and focused on doing things right. While liaising with our Alberta-based deep retrofit expert and the general contractor in Ontario, we learned the importance of good drawings, constructive dialogue, and flexibility in service of the overall vision.
  • Excavation
    Despite some rainy weather, the excavation went smoothly. We were pleasantly surprised that the foundation was in good shape, so it required minimal repair, and the original backfill was not rocky (like in some parts of the neighbourhood) so we were able to reuse it. The house is also quite close to its neighbour on the north side, which posed some challenges during the excavation phase
  • Waterproofing
    We did not plan for the waterproofing contractors to use the pink fibreglass insulation you can see in some of the photos, but it was part of their “Tuff-n-Dri” system so we let them go ahead. We asked them to add more of it — all the way to the bottom of the siding — to create an even base for our GPS insulation.
  • Insulation
    We had planned to install the 4’x’8’ boards vertically, but the excavators suggested installing them horizontally in two rows so they could partially backfill. This was a good idea because it minimized how long the trench was open to rain and made it easier for contractors to work on the window buck and strapping for the upper row of insulation and cement board.
  • Windows
    Windows were installed in pressure-treated ‘bucks’ affixed to the outside of the foundation so that the windows could be installed in the most efficient location- in the middle of the new insulation layer. It made the air sealing a little more complicated but simplified the problem of making it waterproof. As an added bonus, we now have deep window sills on the interior, which is a great design feature. We used Sikaflex caulking and Fentrim tape to air seal on the inside. There was some extra labour involved in enlarging the rough openings to allow the window returns to sit level.
  • Coldroom
    We wanted to preserve the passive cooling function of the existing cold room, which required special planning during stage 1.

Stage 1 Costs
Excavation and Waterproofing


Subterra low-GWP GPS Insulation
This was hard to source in Ontario and includes a fairly steep delivery fee. We have about 10 sheets left over, which we’ll use in the upstairs phase


Basement Windows (1 Hopper, 4 fixed, 1 casement)




Additional labour and materials:
Materials - fasteners, strapping, flashing, wood, tape, caulking, new hose bib, etc…
Labour - upper row of insulation, cement board, new windows, removing old windows, temporary flashing, plumbers installing new sump pump and battery backup, electrical work to restore connection to garage




Stage 2: Attic (Spring 2024)

The Energuide Report showed the heat loss through the attic was about 15% of the total  - not including attic air leakage. There is about 5” of old vermiculite insulation which testing shows contains some asbestos and a few scattered fibreglass insulation batts. The attic is also very likely to be responsible for a lot of the air leakage. (We were unable to test the actual air leakage for fear of sucking vermiculite into the house.) The steps in the phase:

  • Vacuum out the old vermiculite
  • Removing upper chimney section (above mainl level ceiling)
  • Install the ERV stale air exhaust ducting needed for Phase 3 in the old chimney chase, including the exhaust ducts from the bathroom and kitchen. (see drawings)
  • Install conduit for the PV system that will be installed in Phase 5
  • Replace the attic hatch with one that is airtight
  • Air seal the attic with 50mm or more of low GWP spray foam taking care to seal in the ERV ducting. Detail the perimeter so that the new exterior wall air barrier in Phase 4 can be tied to it.
  • Conducting blower door test after abatement for more accurate mid-project energy audit
  • Add enough blown in cellulose insulation to get to a total R value of 60.

Stage 3: Mechanical (Summer 2024)

Before efficiency upgrades, space heating alone accounted for 54% of the house’s estimated annual energy use and water heating for 21%. The steps in this phase, which was moved up because the home’s air conditioning unit died, will include: 

  • Upgrading the electrical service if it turns out be necessary
  • Installing a cold climate air source heat pump for heating and cooling
  • Installing an energy recovery ventilator ERV and tying it into the exhaust ducting from the bathroom and kitchen installed in the attic in Phase 2
  • Installing drain water heat recovery pipe
  • Installing electrical load share interlocks if necessary to avoid upgrading the electrical service

Stage 4: Main Floor Walls and Windows (Summer 2025)

The main walls account for over 20% of the building’s annual heat loss. The steps in this phase will include: 

  • Remove and recycle existing aluminium siding
  • Replacing windows with new triple-glazed high-performance windows, possibly enlarging a few
  • Install new air barrier sealed to new windows, to the top of the foundation, to the attic spray foam and at all electrical and mechanical penetrations. 
  • Add exterior insulation to R26
  • Install new siding over a continuous vented rain screen.
  • Install new eavestroughs

Stage 5: Solar (Tentative - Summer 2025)

  • Trenching power lines to the garage for connection
  • Replacing asphalt tile roof with metal roofing
  • Installing solar panels

Before & After



Drafty, inconsistent temperatures between floors
Good condition with expected maintenance requirements for a 73-year-old building. Moisture issues in the basement.
WAll Insulation
Ceiling Insulation
Foundation Insulation
Mix of single pane wood and double-pained vinyl windows (R1.1 to R2.9)
Natural Gas, 10 kW, 34500 BTU/h
Central Air, 2.24 kW, 8000 BTU/h
Hot Water
Natural Gas
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