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Second storey additions: what your house has to carry.

A second storey is the addition people want most and the one their house is least ready for. The deciding factor sits under the building, not on top of it.

Last reviewed September 2026

Rear elevation of a two-storey custom home at dusk with dark blue and beige stucco, large black-framed windows, a covered patio and a stamped concrete terrace — The upper floor of an Icon build seen from the rear. On an addition, every load in a wall like this has to find a path down through a foundation that was poured before the storey existed.

The short answer

A second storey addition is a structural project before it is an architectural one. The new floor adds load that has to travel down through the existing bearing walls, foundation walls and footings, none of which were sized for it. Where they cannot carry it, they get reinforced or replaced, and that is also the point where the legal classification can change. BC Housing Regulatory Bulletin No. 6, Scenario 2, sets a lower threshold for exactly this case: where the foundation is new, 50% or more of new above-foundation structure makes the home substantially reconstructed, and therefore a new home under the Homeowner Protection Act. The bulletin's own worked example is an existing first storey on a new foundation with a new second storey and roof structure added.

What gets checked, and in what order

The sequence matters, because each answer changes what the next question is worth asking. There is no point drawing an upper floor plan before anyone knows what the footings can hold.

Check 1

The footings and foundation wall

The load from a new floor lands on the footings. An engineer needs to know their width, depth and condition, which usually means digging a test hole rather than trusting the original drawings. Undersized footings can sometimes be widened. Where they cannot, the foundation gets replaced, and the project moves into Scenario 2 territory where the 50% threshold applies.

Check 2

The bearing walls below

Load travels down through walls that are already carrying the roof. Adding a floor between them and the roof increases what they carry. Older Burnaby houses often have bearing walls that were adequate for one storey and are not for two, especially where previous renovations removed structure to open up a plan.

Check 3

The soil

Footings transfer load to soil, so the soil's bearing capacity is part of the answer. On Burnaby's slope neighbourhoods this is where a geotechnical engineer gets involved, and it is the reason a second storey that works on one street may not work three blocks uphill.

Check 4

The height limit against grade

Burnaby Zoning Bylaw No. 14815 allows a front principal building 10 m to the midpoint of a sloping roof or 9.5 m to the top of a flat roof in the R1 district. On level ground that is generous for two storeys. On a slope, where grade is measured decides whether the second storey fits under the limit or has to lose ceiling height.

The threshold that catches second storeys

BC Housing's general test for substantial reconstruction asks whether 75% or more of the reconstructed home is new, or whether 25% or less of the original structure above the foundation remains. Scenario 2 of Regulatory Bulletin No. 6 covers the case where the foundation itself is new, and there the bar drops. Fifty per cent or more of new above-foundation structure, on top of a new foundation, is enough.

That combination is common in second storey work. A house that needs its foundation replaced to carry a new floor, and then receives a new floor and a new roof, has replaced most of what holds it up. The bulletin treats the result as a new home, which means a New Home Registration Form, and either a licensed residential builder who has arranged home warranty insurance or a formal exemption such as an Owner Builder Authorization.

The determination is not yours to make. Bulletin No. 6 states that each case is examined on its own merits and that BC Housing makes the final call. Run their Substantial Reconstruction Online Query while the design is still moveable, because the answer can change which builder you are allowed to hire.

Energy requirements on the new floor

New construction is held to a higher standard than altered existing areas, and a second storey is new construction. Abbotsford's Building Division publishes the split in table form: an addition portion needs an effective RSI of 3.08 in walls and 8.67 in ceilings below attics, where renovation of an existing home is held to 2.78 and 6.91. New windows and doors in an addition area are capped at a U-Value of 1.22, against 1.84 for newly installed windows in an altered existing area.

Those numbers are Abbotsford's own schedule, and the bulletin says so on its face. Energy requirements for renovations and additions are set per municipality under the BC Building Code's provision for existing buildings, Division A, Sentence 1.1.1.2.(1). Confirm the schedule with the city your lot sits in before a designer specifies assemblies.

Is building up the right call?

Best for

Lots already at or near their lot coverage limit, where building out is not available
Houses with a sound, adequately sized foundation confirmed by an engineer
Owners who want more bedrooms without losing yard
Level lots, where the height limit is measured against a consistent grade

Fails when

Footings or foundation walls cannot carry the new load without replacement
The house has to be vacated for longer than the family can absorb
Grade on a sloped lot pushes the new roof past the height limit
Previous renovations removed bearing structure that now has to be rebuilt anyway

Verify before acting

Have an engineer expose and measure the existing footings, not read the old drawings
Run BC Housing's Substantial Reconstruction Online Query before finalising the design
Confirm how height is measured against grade on your specific survey
Ask your city for its own energy schedule for addition versus renovation areas

Frequently asked questions

Can any house take a second storey?

No house takes a second storey automatically. The existing foundation, footings and load paths were sized for the loads the house carries today, and a new floor adds weight that has to reach the ground through them. An engineer checks the footing size, the foundation wall, the bearing walls below and the soil. Where those cannot carry the new load, they get reinforced or replaced, which changes both the scope and the legal classification of the project.

Does a second storey addition need engineering?

A second storey addition needs structural engineering because it changes how load travels to the ground. The City of Burnaby's addition permit application also marks an Engineering Pre-Application as required on the form itself. Beyond the City's process, the structural design has to demonstrate that the existing foundation and bearing walls can carry the new floor, or specify what has to change so they can.

When does a second storey addition become a new home in BC?

A second storey addition becomes a new home when the project is substantially reconstructed. BC Housing Regulatory Bulletin No. 6, Scenario 2, sets a lower bar than usual for this case: where the foundation is new, 50% or more of new above-foundation structure makes the home substantially reconstructed. The bulletin's worked example is an existing first storey given a new foundation with a new second storey and roof structure added.

Why is the threshold lower when the foundation is new?

The threshold drops to 50% in Scenario 2 because a new foundation plus a new upper storey leaves only the original first storey doing structural work. BC Housing's general test asks whether 75% or more of the reconstructed home is new. When the foundation has already been replaced, the remaining original first storey is a smaller share of the whole, so a lower proportion of new above-foundation structure reaches the same place.

Do I have to remove the roof to add a second storey?

Adding a full second storey means removing the existing roof structure, because the roof has to move to the top of the new floor. That is the reason second storey work is harder to live through than a rear addition. The house is open to weather between roof removal and the new structure being made weather-tight, so the schedule is built around closing that window as fast as the framing and roofing sequence allows.

Does a second storey addition need to meet current energy code?

The new storey is held to the standard for new construction rather than the lower standard applied to altered existing areas. Abbotsford's Building Division bulletin on the BC Energy Code for renovations and additions gives the split: an addition portion needs an effective RSI of 3.08 in walls and 8.67 in ceilings below attics, against 2.78 and 6.91 for renovation of an existing home. Energy requirements are set per municipality, so confirm the schedule with your own city.

Is it cheaper to build up or build out?

Building up avoids using more of the lot, which matters when coverage or setbacks are already tight, but it puts new load on an existing foundation and removes the roof. Building out spreads load onto new footings and leaves the existing roof alone, but consumes lot coverage and permeable surface. Which one costs less depends entirely on what your foundation can carry and how much zoning room the lot has left, so both get priced against your actual house.

Can I add a second storey to a house on a sloped lot?

A sloped lot changes how the height limit lands, because height is measured against grade and grade is not one number on a slope. Burnaby Zoning Bylaw No. 14815 allows a front principal building 10 metres to the midpoint of a sloping roof or 9.5 metres to the top of a flat roof in the R1 district. On a slope, the point at which those metres are measured decides whether a full second storey fits, so the survey comes before the design.

Official sources