Vertical Extension Design in Salt Lake: Adding a Floor Properly

Vertical Extension Design in Salt Lake: Adding a Floor Properly

If you own one of the older houses in the Salt Lake blocks, a ground plus one or a ground plus two put up between the sixties and the nineties, with a terrace that has done very little for thirty years, then the idea of adding a floor has probably been in the house longer than any drawing for it. A son or daughter has married, the parents cannot manage three flights any more, somebody needs a room that works as an office through the day, and the plot itself is finished, because the neighbours on both sides have built right up to the boundary and there is nowhere left to go sideways.

A vertical extension gets described in small words, one floor, one slab, two rooms and a toilet, and that description is exactly what makes it go wrong. Another floor loads every column below it, so the frame and the footings have to be assessed before anybody picks up a pencil, and it moves the staircase, the overhead tank, the plumbing stacks, the electrical load and the rainwater path with it, which means the drawings for the top floor are really drawings for the whole house. The sanction file is a fresh file too, because what stands on the plot today has to be reconciled with what the municipal record says stands there.

This page sets out how we approach it at Studio Contour, working out of New Town across the Salt Lake, New Town and Rajarhat belt, in the order the answers actually arrive, which is the structural question first, the sanction question second, and which rooms go where third.

What the existing frame will carry decides everything else

Most of the older housing stock in these blocks is a reinforced concrete frame with brick infill, and the useful question is never whether reinforced concrete can carry another floor in principle, because very often it can, but whether these columns, with the reinforcement actually sitting inside them, standing on footings sized for a building planned decades ago, will carry what you want to put on top. That has to be read on site, with the frame opened at a few points and the structural picture reconstructed from what is found rather than assumed from the age of the house.

Once it has been read the options separate cleanly, and each one carries a number. You can keep the new floor light and smaller than the footprint below so the existing frame takes it as it stands, you can jacket columns and strengthen footings so the new level can be full sized, or you can build it as a lighter steel framed structure, which changes the cost of the slab and of the finishes with it. Those go in front of you with the cost consequence attached to each, because at the end of the day a client told the price only after choosing has not really been given a choice.

Reading the house you already own before anybody draws a line

Before any layout is drawn, two documents have to sit side by side, the plan that was sanctioned for your house and a fresh measured survey of what is actually standing. In this building stock they very often do not match, because a verandah got enclosed in the eighties, a toilet moved, a store room appeared on the terrace, and none of it reached the municipal record. The catch here is that a vertical extension forces the question, since the authority is being asked to approve a floor above lower floors that are on record in a particular form, and that is far better settled before you commit to a budget than after the steel is on site, which is why we have written the whole route up separately in Sanctioned Plan Deviation Regularisation Under Bidhannagar Municipal Corporation in Salt Lake: A Plot Owner's Guide. The survey also tells you what the new floor can be, because the column grid you already have sets where walls can land and which rooms can be the size you are imagining.

The sanction route runs through Bidhannagar Municipal Corporation

Salt Lake sits within Bidhannagar, and the building authority for the blocks and sectors here is the Bidhannagar Municipal Corporation, a different authority from the one that governs New Town, so anybody telling you the New Town rules apply to your plot is working from the wrong book. What you are permitted in ground coverage, in floor area, in height and in setbacks varies with the plot, the road width in front of it and the use of the building, so it has to be confirmed for your specific plot rather than quoted from a neighbour's project.

We prepare the drawings and documents and run them through the sanction process ourselves, which matters more on an extension than on a new build, because the file has to explain an existing building as well as a proposed one. The narrow plot case is its own subject, and Bidhannagar Municipal Corporation Building Plan Sanction for a Narrow Plot Under 3 Katha in Salt Lake covers it in depth. Sumana Kumar stays on the project through this stage and through site, so the person answering a query from the authority is the person who drew the thing being queried.

Where the new floor actually sits on a tight Salt Lake plot

Salt Lake is a planned grid, so your plot is regular, which sounds helpful until you notice that regular also means tight, and that the neighbours have usually built to their boundary lines already. That has one hard consequence for a new top floor, which is that light and air have to come from your own plot, from the front, the rear and whatever side gap or open shaft you can protect, because windows on the flanks will face a blank wall a few feet away for the life of the building.

So the new floor is not a repeat of the plan below. It is often worth pulling it back from one edge to keep a usable terrace and open a stair shaft that brings light down into the floor underneath, worth placing bedrooms where cross ventilation actually exists rather than where the lower floor happens to have walls, and worth deciding early whether the terrace you are giving up was doing real work. How that air movement gets planned is in Daylight and Cross Ventilation Planning for Salt Lake Houses, and it matters most on a top floor, which takes the sun. Meander House project in Salt Lake is an example of that category of work in the area.

The staircase is the decision that sets the whole plan

The staircase is where most extension plans quietly fail. In this stock the existing flight usually ends at the terrace in a narrow mumty with low head height, built when nobody expected a floor above, so continuing it upward often means rebuilding the top flight entirely, and that eats into a room on the floor below. The alternatives are a new flight somewhere else in the plan, which costs you floor area on every level it passes, or an external flight in a side gap, which costs you the gap and the light that came through it.

That decision sets the circulation of the house for good, and it is also the right moment to ask whether a small home lift belongs in the plan, since the reason many families add a floor is that an elderly parent cannot manage the stairs, and adding a floor without solving that leaves the original problem where it was. If a lift is even a possibility in ten years, the shaft is cheap to provide now and expensive to retrofit later.

Making the new floor and the old house read as one building

A new floor on an old house announces itself, usually badly, because the parapet is a different thickness, the window proportions are wider, sill levels do not line up and the plaster reads as newer. Basically there are two honest ways to handle it, which are to continue the language of the existing elevation, matching opening widths, sill heights and the rhythm of the front, or to treat the new level as a clearly separate band with its own material and a deliberate line between old and new, which is often the better answer when the original facade has nothing worth repeating.

What does not work is the middle, where the new floor half matches and half does not, and that is what you get when the elevation is decided on site by whoever is laying the brick. The same discipline covers the things people forget, the railing on the retained terrace, the water tank now sitting in full view, and the stair box above the new roof, all of which end up in the front elevation whether they were drawn or not. Residential Building Project in Salt Lake is another example of that category of work.

Monsoon, waterproofing and the services that have to grow with the floor

Kolkata gets a long humid stretch and a serious monsoon, and a vertical extension creates the one condition that leaks most reliably, which is an old terrace slab that spent decades as a roof suddenly becoming an intermediate floor with a room sitting on it. Its waterproofing, its slope and its outlets were all made to throw water off the building, and if the new floor goes over that without being dealt with properly, the ceiling below will tell you about it in the first heavy spell.

The services need the same attention, because the overhead tank has to move and be supported, the stacks from the new toilets have to find a route down through a house that is already finished, and the electrical load and distribution board were sized for a smaller house. Settling the stack route before construction is what keeps a new bathroom from ending up directly above your drawing room ceiling, and it is close to impossible to correct neatly once the floor below is finished.

Living in the house while the floor goes up

Most families stay in the house while the floor goes up, which is workable, and far more bearable when the sequence is designed for it rather than discovered week by week. The strengthening work is the most disruptive, since it touches the lower floors, so all of it is worth grouping together, including the stack route and any lift shaft, and finishing before the new slab starts, after which the work moves upward and away from you.

This is also where keeping architecture, interiors and the sanction file with one team starts saving money rather than sounding like a slogan, because the new floor's interiors are decided while its structure is still open, so a kitchen stack, a wardrobe depth or a ceiling void for the air conditioning gets built into the shell instead of chased into it later. Our residential architecture and residential interior design run as one process for that reason, and if the extension is being fitted out immediately there is the wider picture of interior design across Salt Lake. An upper floor is often where a second sitting space finally fits, which is Family Room Design in Salt Lake: The Room Behind the Drawing Room, and where a more open kitchen becomes possible, which Island Kitchen Design in Salt Lake: When the Plan Allows It goes into.

When a different kind of provider suits you better

A vertical extension is not always an architect's job, and it is worth being plain about when it is not. If your terrace already has a structurally cleared provision for the floor above, the new layout is a straight repeat of the floor below, and all you need is those drawings turned into construction, then a competent contractor working with a draftsman will finish it faster and for less than we will, and that is the route you should take. For one extra room and a toilet on a terrace designed to take them, our process is heavier than the problem.

Where that stops being true is the moment the frame needs assessing, the staircase has to move, the standing building deviates from its sanctioned plan, or the new floor has to look like it belongs to the house underneath it, because the decisions then interlock and somebody has to hold all of them at once. Questions about the property itself, ownership, shares between siblings, or the tax treatment of the construction belong with your own lawyer or chartered accountant rather than with us.

Where to start

If you are weighing a floor on top of a Salt Lake house, the most useful first conversation is about the building you already have rather than the rooms you want, and that is where we would start. Bring whatever exists, the old sanctioned plan, photographs of the terrace and the mumty, and we will tell you what has to be checked before any budget means anything. There is more of our work around the belt on our Salt Lake area page, and when you are ready to have the building looked at properly, get in touch.