Flat, and no more than 30 cm off the roof
Longueuil's zoning bylaw 01-4501 sets three conditions on a roof-mounted solar collector: it must be installed flat, it must project no more than 30 cm from the roof, and it must integrate harmoniously with the building's existing architectural style. Two of those are measurable and one is a judgement, and it is worth treating them differently when you talk to an installer.
The flat requirement is the one with real design consequences. On a pitched roof it is barely a constraint, because panels normally sit parallel to the slope anyway. On a flat or very shallow roof it is a significant one: the usual approach there is a ballasted tilt frame that angles panels up toward the sun, and a frame like that is not flat to the roof and will usually breach the 30 cm limit as well. If your roof is flat, raise this with the city before anyone quotes you a system, because the answer changes both the layout and the output.
The harmonious integration clause is the soft one, and soft clauses are where projects lose time. Ask the borough what it has accepted on buildings like yours, and ask whether anything about your roof colour, your street frontage or your building's style is likely to attract comment. Getting that conversation done at the design stage costs a phone call; getting it after the panels are ordered costs a redesign.
One bylaw, three boroughs administering it
Longueuil applies bylaw 01-4501 separately in each of its three boroughs: Vieux-Longueuil, Saint-Hubert and Greenfield Park. The text is the city's, but the counter, the queue and the person reading your application are the borough's. That has a practical effect worth knowing about in advance: an answer a neighbour got, or a precedent an installer cites from a job across the city, may have come from a different borough office than the one handling your file.
So ask your questions of your own borough, and ask them by address rather than in general. The two that matter are whether your roof is treated as flat for the purposes of the bylaw, and what the borough considers harmonious integration on a building of your type. Write down who told you and when.
This also gives you a fair test of an installer. Someone who works in Longueuil regularly will know which borough you are in before you tell them and will have submitted there before. Someone who cannot name the three boroughs is quoting your roof from a satellite image.
Hydro-Quebec, the two approvals, and the 24 month reset
Hydro-Quebec is Longueuil's distributor, and connecting a solar array means enrolling in the option d'autoproduction. You do not file that yourself: a licensed CMEQ electrician submits the installation request, and Hydro-Quebec evaluates whether the local network has the capacity to accept your generation before issuing a conditional acceptance. Approval is tied to your circuit rather than to the province in general, so it is not automatic.
That process sits between a signed contract and a system permitted to export, and it runs alongside the municipal side rather than after it. A Longueuil project therefore has two separate approval tracks, the borough's and the distributor's, and they should be drawn on one timeline before equipment is ordered. Ask which electrician will sign the request and whether they are on the installer's staff or subcontracted.
Once running, surplus energy banks as a credit measured in kilowatt hours and offsets later consumption at parity, which is what carries a July surplus into January. The bank resets every 24 months, and a balance left in it at that point is settled well below the retail price you pay to buy electricity back. Capacity is not the constraint, since the option is capped at 1,000 kW, far above any house. Your own consumption is the constraint, so size the array to twelve months of your own kilowatt hour totals rather than to the roof area available.
Grants and financing
Hydro-Quebec's LogisVert residential solar grant pays 1,000 $ per kW of installed capacity and covers up to 40 percent of eligible project costs, typically landing around 5,000 $ to 6,000 $ on a residential system. Installations must be completed on or after June 30, 2025, and the claim is filed through the LogisVert portal within 9 months of the installation date. Hydro-Quebec's own projection is that this brings a typical residential payback from 25 to 30 years down to roughly 10 to 12 years.
Because the grant pays per kilowatt installed, anything that shrinks an approved array shrinks the grant with it. In Longueuil that is a live risk rather than a theoretical one: if the flat-mounting rule limits what you can put on a shallow roof, it limits the grant too. Settle the municipal question before signing a contract for a specific system size, not after.
Federally the picture has narrowed. The Canada Greener Homes Loan, interest-free up to 40,000 $, stopped accepting new applications on October 2, 2025, and only previously approved loans are still being funded. The Canada Greener Homes Affordability Program replaced it in September 2025, delivering no-cost retrofits through provincial partners for low- to median-income households, with solar PV federally eligible but each province setting its own technology list. Canada has no federal investment tax credit for residential solar, so a Longueuil household works with the provincial grant and ordinary financing.