Structural Exclusion in Brooklyn Heights

What does exclusion mean on a building that shares two of its walls?

It means treating the house as having two envelopes: an exterior one it controls and an interior one it shares.

On a detached house the argument is simple and complete. Close the exterior skin in materials that cannot be worked through and the animals outside stay outside. That logic runs cleanly on Long Island. It runs half of the way here and then stops, because a Brooklyn Heights rowhouse has two exterior walls, two party walls, and neighbors on either side who are not party to your scope of works.

So the work divides into two categories with different economics.

The exterior envelope — the front facade, the rear elevation, the roof, the areaway and the cellar line — is yours. You can survey it, price it and close it, and when it is closed it stays closed.

The shared envelope — the two party walls, with their joist pockets and every penetration made through them since 1845 — is only half yours. You can close what is accessible from your side, which is a great deal, but you cannot inspect the other side and you cannot control what the neighbor does. What you can do is remove the connection between the wall’s interior and your building’s interior, which is a different objective from removing the void.

That distinction is the whole of the method here, and it explains why two houses that look identical from the sidewalk can have completely different scopes. It also explains why the front facade — the surface everyone photographs, the one the historic district exists to protect, the one owners assume the work is about — is the least productive elevation on the building.

Where does the work actually happen, in order of what it achieves?

At the cellar first, then the areaway, then the party walls, then the roof, and only then the visible exterior.

The cellar ceiling line is the highest-value single intervention in most of these houses. Everything that lives below — in the cellar, in the drainage, under the yard, in the areaway — reaches the occupied floors through the openings where pipework, wiring and ductwork pass up through that ceiling. Standing in the cellar and looking up gives you the entire list in one view. Closing it separates the house from its own basement, and it can be done without disturbing anybody upstairs.

The cellar walls themselves. Nineteenth-century brick or stone laid in lime mortar, in contact with wet ground on the areaway side and the yard side. After a century and a half, a proportion of that mortar has crumbled at the face or fallen out entirely, and those open joints are not in predictable places. Closing them is repointing — raking out to a sound depth and repacking — not a bead of sealant across the face, which lasts one winter and comes away with the frost, taking loose mortar with it. The wall is also a moisture path, which matters twice over: damp mortar fails faster, and a damp cellar supports the insects that support everything else. Repointing and drainage correction are one project.

Service entries, live and abandoned. Water, gas and electrical entries, and every abandoned predecessor of each — a redundant lead water service, a disconnected oil fill and vent from a removed tank, the sleeve where an old feed came in, an old coal-era hatch or chute in a house that had one. On a building of this age the list of abandoned services is a substantial fraction of the whole scope, and every one of them is easy to close permanently once it has been found. They are also invisible on a walk-round, because they sit behind planting, behind stored goods, or above the line where anyone looks.

The areaway. Its drain has to run. The cellar door has to seat. The openings around service entries in the wall get mesh and mortar. Accumulated leaf litter and refuse comes out, because it is both harborage and the thing that blocks the drain.

The party walls, where accessible — see below.

The rear elevation and the yard line. Unwatched, unprotected and usually the most productive facade on the building. Rear extensions built at different dates create junctions between old and new construction, and every one of those junctions is a seam. A yard regraded upward over the decades so that it now falls toward the house, and a downspout discharging at the base of a rear wall, are both drainage repairs with a pest benefit.

The roof, parapet and cornice. Where animals arrive from above, and where the timber is softest.

The front facade, last, and mostly through repointing.

How do you close a joist pocket without opening the whole wall?

Opportunistically, from the side you can reach, and usually during work that is happening anyway.

This is the question owners ask as soon as they understand what a joist pocket is, and the honest answer is that you do not open a wall to get at them. You close them when the wall or the ceiling is already open.

During renovation. Any project that exposes a floor structure at the party wall — a ceiling down, a floor up, a wall stripped back to masonry — gives access to the pockets on that line. Closing them then is cheap, because somebody else has paid for the access. Closing them as a standalone project is expensive, because the access is the whole cost.

At the top and bottom of the wall. The most valuable closures are where the party wall meets the cellar and where it meets the roof structure. Closing the wall’s interior off from the cellar and from the roof void removes the two points at which the shared voids connect to the rest of the building. This is often achievable without opening anything.

Where services have been cut through. A pipe or cable passing through a party wall is a known, locatable opening, and it can be closed from either side without disturbing the wall.

Materials. Something an animal cannot bite, packed rather than sprayed: hardware cloth or stainless mesh set into the pocket and mortared, or sheet metal where the geometry allows. Mortar alone will not span a large void. Cured foam is not a barrier at all and does not go into the pocket in any supporting capacity either.

The strategic point about party walls is that a coordinated pair of neighbors achieves far more than two independent ones. Two houses that close their shared wall and coordinate their waste storage will outperform two houses that each buy a better service separately. If your neighbor is renovating, that is the moment to raise it — the access will not exist again for years, and once the plaster is back the conversation is theoretical.

What does a sidewalk vault add to the scope?

A permitted structure under the public sidewalk with a real void inside it, and a direct connection to your cellar.

Building vaults extend beneath the public sidewalk on many blocks in the city, particularly where there is ground-floor commercial use, and there are residential blocks with them too. They are not a curiosity: NYC DOT licenses them, sets live-load requirements for sidewalk doors, gratings and covers, and may order the owner of the premises to fill in an abandoned vault.

From an exclusion standpoint, three things matter about a vault that is still there and no longer used:

It is a large, dark, dry void that nobody enters, which is close to ideal harborage for a rat population through a winter.

It connects to the cellar, usually through a doorway or an opening that somebody closed decades ago with whatever was available.

It connects to the street, through gratings, hatches or a coal-hole cover.

The productive work is at the two connections rather than at the vault itself. Closing the vault-to-cellar opening in a real barrier removes the route into the building. Securing the gratings and hatches removes the route in from the sidewalk. Where the vault is genuinely abandoned and the owner wants it gone, filling it in is a permitting matter with DOT and a construction job, not something to improvise.

The same principle applies to any other void a house has acquired over a hundred and sixty years: a bricked-up former doorway between two houses, a filled stair to a garden level, a redundant light well, a former dumbwaiter shaft. Each is a void with two ends, and the ends are what get closed.

Which materials survive here, and which fail publicly?

The ones an animal cannot bite, chosen with an understanding of what the assembly is doing.

Barriers. Hardware cloth, stainless and copper mesh, sheet metal, mortar, hydraulic cement. These are what actually close an opening. Everything else supports them.

Repointing as an exclusion measure. This is the detail worth emphasizing in a historic district, because it is where the two disciplines agree completely: raking out a failed mortar joint and repacking it with an appropriate mortar is a preservation repair and a pest exclusion measure at the same time, and doing it properly serves both. Using an inappropriately hard modern mortar on soft nineteenth-century brick damages the masonry, which is a preservation failure and, eventually, a pest failure too as the brick faces spall.

Sealants as a finish over a barrier, or as an air seal, never as the barrier. Silicone and acrylic caulk have a genuine purpose on a building, and this is not it.

Screening, not sealing, where an opening has a function. A weep hole, a vent, a drainage path and a combustion air opening all exist for a reason. Closing them trades a rodent problem for a moisture or a safety problem, and it is got wrong more often than any other detail in this trade. Openings that must stay open get screened in a durable metal mesh.

What fails. Cured expanding foam is the standard error and fails twice: rodents chew straight through it, and because it looks like completed work an active opening gets recorded as closed and drops off the list. On a landmarked front it is also visible, discoloured and ugly within a season. Untreated steel wool corrodes within a winter and marks the masonry below it. Plasterboard patched over an opening with no barrier behind it lasts until something tests it. Anything an animal can bite through is not a barrier, however tidy it looks on the day it goes in.

The other material judgment specific to this stock concerns the brownstone itself. The Landmarks Preservation Commission’s rowhouse manual explains why these fronts fail: because veneer was commonly set with the stone’s grain running vertically rather than horizontally, water entering between the bedding layers freezes and forces the stone apart layer by layer. That spalling opens the wall, and an open wall holds water against whatever is behind it. Any exclusion work on a brownstone front is therefore downstream of a stone repair, and doing the sealing without the repair is a temporary measure by definition.

What does the historic district permit, and what does it slow down?

Nearly everything, and only the schedule.

This was the first historic district the city designated, in November 1965; the National Historic Landmark District designation came in January of the same year and the National Register listing in October 1966. The district runs from Atlantic Avenue to Fulton Street and from the East River to Court Street. Work altering the visible exterior of a building can require review.

Three things follow, and owners consistently overestimate the first and underestimate the third.

Most of an exclusion scope is invisible from the street. The cellar, the areaway floor and drain, the rear elevation, the party-wall pockets, the service penetrations, the roof bulkhead and the interior of a cornice return are not the protected streetscape in any meaningful sense. The overwhelming majority of the work on a house like this sits in those places.

Where the front is involved, material choice does the work. Repointing with an appropriate mortar, mesh set back and concealed within an opening rather than applied across it, and screening rather than sealing anything with a drainage function. A preservation-minded owner tends to grasp these distinctions immediately, because they are the same distinctions preservation practice already makes.

Review changes the timeline, and the timeline is the real constraint. If a scope touches the visible exterior, the review period becomes part of the program, and a job that could have been done in October gets done in March — which is to say, after the winter it was meant to prevent. The response is to survey early rather than waiting for evidence to become undeniable, and to do the concealed work, which needs no review at all, while any exterior element is in process.

One further point about the fabric. The district covers Federal, Greek Revival, Italianate, Second Empire, Victorian Gothic, Romanesque, Neo-Grec and Classical Revival houses, including a small number of two-and-a-half story late Federal houses on the Fruit Streets, and adjoining buildings frequently come from different decades and different builders. A single blockfront can hold five different wall assemblies with five different failure patterns. A pair of houses that match from the street can differ completely in cellar construction, in what has been built onto the back, and in what has been cut through the front wall over a century and a half. That is why this work is not priced from a template or from a photograph.

Why does the sequence matter more than the scope?

Because closing an occupied house with animals inside it produces a worse outcome than not closing it at all.

The order is reduce, then close, then verify.

Reduction first. Sealing a house with an established interior population removes the animals’ way out. In a rowhouse they concentrate in wall voids and party-wall pockets, and anything that dies inside masonry and plaster is very difficult to reach and impossible to ignore for several weeks. Reduction in an occupied house means trapping placed on the evidence — following rub marks and droppings rather than convenient corners — checked frequently, over a period, before sealing begins. Devices placed where animals are not already traveling get avoided and ignored, so placement follows the survey rather than the floor plan.

Closing second, and comprehensively rather than conveniently. The productive openings on a house of this age are behind planting that has been there for fifty years, under a stoop, behind stored goods in a cellar corner, at the back of an areaway, or on a roofline that needs a ladder set on an awkward surface. The comfortable openings get closed and the awkward ones get described as inaccessible. A perimeter that is ninety per cent closed is not ninety per cent effective; the animals need only the remaining ten.

Verification third, and it is the step everybody skips. Openings get closed and nobody returns after a freeze-thaw cycle, after settlement, or after a wet autumn to see what has moved. On a hundred-and-sixty-year-old masonry building that check is part of the work rather than an extra, and it is why a closure log matters: location, date, material, photograph, and who did it. Without one, the same openings get quoted repeatedly and nobody can tell what was actually done.

The calendar shapes all of it. Late summer into autumn is the window for the cellar and the service penetrations, because a house closed in September never acquires the population that arrives as nights cool. Winter makes the openings findable — a cold, still morning shows where warm air is escaping, and air leaks and animal entries are largely the same openings viewed with a different instrument. Spring is the masonry season, when a winter of freeze-thaw has left its record on brownstone fronts, parapets, sills and cornices. Summer is for the yard and areaway work: regrading a yard that now falls toward the house, clearing areaway drains, rebuilding waste storage.

What does it cost a house to skip this?

A recurring bill with a flat outcome, and a set of second-order costs nobody attributes to it.

An owner comparing a correction project against a recurring service is comparing a lump sum against a small monthly number. The lump sum requires a decision. The small number requires nothing at all. It is entirely rational for the small number to win, and that is exactly how a house ends up with a permanent low-level population and a decade of invoices.

The second-order costs are real. The same openings carry sound between attached houses, carry odors, and carry air — which in a house with a hundred-and-sixty-year-old envelope is a heating cost every winter. The same water that opened the joints is rotting concealed timber, which is a structural repair deferred rather than avoided, and which is what carpenter ants excavate when they find it. And where the building is a multiple dwelling, Local Law 55 requires remediation by integrated pest management — physically removing debris, sealing openings, eliminating water sources — and states plainly that pesticide use does not substitute for those measures. A file showing applications and no closures is a service history, not a compliance record. The reading is at NYC Local Law 55 and the Housing Maintenance Code and pests, with the questions worth asking before comparing bids at choosing a pest control contractor.

For the discipline in general, see structural exclusion. What this stock generates across the rest of the services is set out at pest control in Brooklyn Heights, with the New York City hub for the shape of the city work. The two services that depend on this most directly are rodent control in Brooklyn Heights and wildlife management in Brooklyn Heights. Across the river, structural exclusion on the Upper East Side is the same discipline applied to riser chases in apartment houses; on Long Island, structural exclusion in Great Neck is the detached-envelope version.

If a renovation is about to start, or a neighbor’s is, that is the moment to have this scoped. Get in touch before the plaster goes back on.

Related

• Structural Exclusion — how we approach it
• All pest control in Brooklyn Heights
• Rodent Control in Brooklyn Heights
• Cockroach Control in Brooklyn Heights
• Bed Bug Treatment in Brooklyn Heights