The short answer is often yes. New Jersey's residential code sets a height rule for chimneys that has nothing to do with how well a fireplace draws and everything to do with where the chimney sits relative to the roof and anything built near it. A second story addition, a dormer, or a raised roof section next to an existing chimney changes those measurements, and a flue that cleared the rule comfortably before the framing went up can come up short once the new wall is standing.
What the code requires
New Jersey's residential code, following the same model used across most of the country, asks a chimney to reach at least 3 feet above the point where it passes through the roof, and at least 2 feet higher than any part of a building within 10 feet of it, measured horizontally. The 3 foot figure is fixed, tied to the roof penetration, and it sets a floor height on its own. The 2 foot figure moves with whatever gets built nearby. A new second story wall, a dormer cheek, or a raised ridge within that 10 foot radius resets the number the chimney has to clear.
What a new wall or dormer does to an existing chimney
Many houses in Watchung and Green Brook were built in the 1950s and 1960s, decades when a masonry chimney serving a fireplace, a furnace, or an oil-fired water heater was standard construction, and plenty of those fireplaces and oil flues still work today. Those chimneys were built to clear the roofline of a one-story house, or a roof that sat at the original ridge height. When a homeowner adds a second story, builds a dormer, or raises a roof section within 10 feet of that chimney, the new framing often reaches higher than the chimney's old measurement allowed for, even when the chimney itself has not moved an inch.
Extending a masonry chimney
Bringing a masonry chimney up to the height the code now calls for falls under Chimney Repair, and it does not require rebuilding the stack from the footing up. The mason adds new courses of brick or block on top of the existing stack, ties the new work into the old with a matching bond pattern and mortar type, and pours a new crown once the final course is set. The flue liner inside has to travel the full new height as well, so the old liner either gets extended with matching sections or the whole run gets relined in one piece. A liner that stops short of the new crown leaves combustion byproducts able to reach the masonry around the extension instead of leaving through the top.
A flue serving a furnace or a water heater
The same height rule applies regardless of what the flue inside is connected to, and a flue that runs short changes more for a fuel-burning appliance than it does for an open fireplace. A furnace or water heater flue depends on steady draft to carry combustion byproducts out of the house, and an addition that traps the chimney top below the height the code calls for can weaken that draft enough to cause spillage at the appliance draft hood on a cold start or a windy day. Extending the chimney restores the height the appliance was designed around, and it is worth checking the liner size against the connected appliance at the same time, since an older oil-fired system paired with a replacement furnace sometimes calls for a different liner diameter than the original equipment used.
The airspace an enclosed chimney needs
Once framing wraps around three or four sides of an existing chimney, the new wall cannot touch the masonry. Code calls for a 2 inch airspace between combustible framing and the chimney, and that gap gets closed off with fireblocking material rather than solid framing, insulation, or anything that would bridge the space with wood or other combustible material. An addition that boxes in a chimney without leaving that airspace puts framing lumber against masonry that can reach high temperatures when the fireplace or furnace is running hard. The gap is straightforward to frame correctly the first time but awkward and disruptive to open back up once drywall and siding are finished.
Put the chimney in the addition's plans from the first drawing
A chimney extension is far easier to plan before the new roof framing goes up than after. Once the ridge is set and the roof is sheathed, a mason measuring the required 2 foot clearance against a chimney that is now too short has to work around finished framing, scaffolding placement gets harder, and matching old brick or block to new work means sourcing materials close to what is already on the house. Getting a chimney height check into the addition's plans from the first drawing lets the mason coordinate the extension with the framing schedule, so the new chimney courses go up around the same time as the new wall instead of as a separate project squeezed in after the roofers are gone.
What a visit looks like
A visit starts with measuring the chimney's current height against the roof penetration point and against any part of the planned addition that will sit within 10 feet of it, using the addition's framing plans where they exist. That measurement shows whether the chimney already falls short, or whether it will once the new framing reaches its final height. From there the liner gets checked for condition and size, especially on a flue serving a furnace or water heater, and Chimney Cleaning can confirm whether creosote or debris inside the flue should come out before an extension goes on top of it. The airspace plan around any section the addition will enclose gets confirmed against the framing drawings as well. All of that, along with the brick or block match for new courses and the crown replacement, goes on the written estimate before any work starts, whether the addition is already framed in Watchung or still on paper in Green Brook.