Net metering settles per connection, so an array on the common area meter offsets only the common area bill. What that means for sizing, for the committee's decision and for how the cost is shared.
Somebody on the management committee has done the arithmetic. The building has forty flats, the roof is empty, the sun is free, and a quotation has arrived for a plant sized to cover the roof. Before that quotation is discussed at the next meeting, the committee needs one fact that changes the whole conversation: in Bangladesh, net metering settles per electricity connection, and a residential building has many.
Each flat has its own meter and its own account with the distribution utility. The building normally has one more, the common area or service connection, in the name of the society or the owners' association. Generation is credited against the connection it is wired into and against no other.
So an array tied to the common area meter reduces the common area bill and nothing else. It does not reduce the bill of flat 5B, even though 5B's owner paid a share of the plant. There is no group netting, no virtual netting and no mechanism to allocate one meter's export across forty accounts. Any proposal that assumes otherwise is proposing something the guidelines do not offer.
That leads directly to the sizing rule for a housing society, and it is a smaller number than most committees expect: size the plant to the common area daytime load, and stop there. Everything above that ceiling generates units the building cannot consume, which are exported and settled on the terms in the agreement rather than displacing the retail tariff the society is trying to avoid.
The common load in a Dhaka apartment building is real but modest. Lifts, the water pump and any booster pump, corridor and stairwell lighting, compound and gate lighting, the security post, the intercom system, the sewage treatment plant if the building has one, the car park fans and lighting, and the standing draw of the common generator's charger and control panel.
Two of those are worth measuring rather than estimating. Lift consumption is bursty and depends on traffic, so a monthly bill tells you more than a nameplate rating. Pumping is often the largest single item and is usually scheduled, which means it can be moved. A pump that fills the overhead tank at eleven in the morning instead of five in the morning converts an imported unit into a self consumed one, and it costs nothing to change the timer.
Bring a clamp meter and log the common panel over a full week before anyone sizes anything. On several buildings the honest answer after logging is that the plant worth building is a fraction of the one that was quoted.
There is one configuration where the arithmetic changes completely. Some larger residential complexes take a single bulk supply, own the substation, and sub meter the flats internally for their own billing. In that case the utility sees one consumer, one meter and one sanctioned load, and generation nets against the whole building's consumption rather than against the corridor lights.
If your complex is built that way, the plant that makes sense is much larger and the case is much stronger. If it is not, converting is a serious undertaking involving a substation, internal distribution, an internal billing system and the agreement of every owner, and it is not something to do for the sake of a solar project. It is worth knowing which of the two you are, because the answer decides the size of everything that follows.
Residential roofs are busier than commercial ones. Before measuring the area, count the overhead water tanks and their shadows, the lift machine room, the stair head, the solar water heaters if any, the dish antennae, the clothes lines, the common area used for gatherings and children, and the parapet setback the building code requires.
Then ask the harder question: does the deed treat the roof as common property, and has anybody sold or promised the roof rights to the top floor owner or to the developer? That question has stopped more society projects than any technical issue. Settle it in writing before a survey is commissioned.
In a dense city the surrounding buildings matter more than the roof does. A ten storey block going up on the south side of your six storey building will remove most of the winter afternoon, and in Dhaka's development pattern the plot next door is always a candidate.
A shading survey should include the plots around you, their permitted heights and anything visibly under construction, not only what casts a shadow today. Where partial shading cannot be avoided, module level electronics or a larger number of shorter strings will limit the damage, but neither of them recovers energy that is not falling on the roof. Sometimes the right recommendation is a smaller array placed where it will still be in sun in five years.
The technical work on a society project is usually simpler than the governance around it. A plant is a shared asset with a life measured in decades, bought by a group of owners whose membership changes.
The net metering application is made by the holder of the connection. For a society plant that is the society or the owners' association as it appears on the common area bill, and the applicant needs the authority to sign, which is why the resolution matters. The plant is capped against that connection's sanctioned load, so check the sanctioned load on the bill before sizing, because on many buildings the common connection is smaller than the committee assumes.
Expect the utility to ask for the single line diagram, module and inverter datasheets with test certificates, the earthing and protection arrangement, and details of the installer. Expect also that the file will be checked for consistency between the sanctioned load, the proposed capacity and the drawing, and that any mismatch sends it back. A society application is not technically difficult. It fails on incompleteness.