A DC storefront rowhouse with apartments above: which sprinkler system the building gets, where the line between shop and home falls, and who owns the riser

The corridors are full of them. H Street NE, 14th Street, Georgia Avenue, Barracks Row, Columbia Road, Rhode Island Avenue: a two or three story rowhouse with a shop at the sidewalk and one, two, or three apartments stacked above it. When one of these buildings changes hands or an owner finally turns the storage rooms upstairs into rentable units, the sprinkler question is harder than it is for a plain rowhouse, because two different kinds of occupancy share one roof and one water service. Here is how the District reads that building, which standard applies to each side, and the three decisions to make before anyone draws pipe.

Two occupancies, one building

The construction codes sort space by what happens in it. A shop or a cafe is a mercantile or business occupancy. The apartments above are residential, and the residential side is sorted again by how many dwelling units there are. One or two units above a shop is read the same way a two family rowhouse is read, which is the territory NFPA 13D was written for. Three or more units above a shop is a small apartment building and the dwelling side moves to NFPA 13R. The 13D, 13R, and 13 article covers the difference between those standards in full. What is new in a mixed use building is that the shop does not fit any of the three residential boxes, and the code answers that by asking whether the shop and the apartments are separated well enough to be treated as different fire areas.

The separation decides the design

In an old corridor rowhouse the floor between the shop and the first apartment is wood joists with plaster below, and the stair to the apartments often opens straight into the back of the shop. That is one fire area, and the sprinkler system has to cover the whole building. When the renovation adds a rated floor assembly and a rated, self closing door on the apartment stair, the shop becomes its own fire area, and a small shop under the mercantile sprinkler threshold may need no heads at all while the apartments get a 13D system. Which path the building takes is not the sprinkler contractor’s call. It belongs to the architect and to DOB plan review, and the right order is to settle it at a preliminary meeting before the sprinkler sheets exist. The permit steps article walks through where that meeting fits.

What changes on the shop side

A 13D system is designed around the two most demanding heads in a bedroom or a living room, because the point is to hold a fire until the family is out. A retail floor has racks of stock, a storage room, sometimes a cooking line, and the public walking through it, so the heads over that floor are designed to a higher hazard with more flow and a larger design area. That extra flow is the reason the hydraulic calculation for a mixed use building rarely passes on the domestic service that fed the old shop. The service sizing article explains the DC Water side of that, and in a corridor building the answer is more often a new service than it is in a plain rowhouse. The backflow device also changes. A system that feeds a commercial space is treated as a higher cross connection hazard than a house system, and the backflow testing article covers what that means for the annual test.

One riser, two tenants

Nearly every corridor rowhouse ends up with one riser, usually in the cellar under the shop, with a zone valve for the shop and a zone valve for the apartments. That layout is cheaper than two services and it keeps the inspection to one visit. It also means the shop tenant and the apartment tenants are standing on the same system, and the lease has to say so. The three things to settle are who holds the inspection contract, who may close a valve and when, and who pays when a head goes off in one tenant’s space and floods the other. The condo responsibility article works through the same questions for a unit owner, and the landlord article has the lease clause for the residential side. For the shop, add the hazard clause: the tenant may not change the use of the space, add a cooking line, or stack stock within the clearance below the heads without written consent, because any of those can void the design the heads were set to.

Inspection runs on the commercial calendar

A plain rowhouse gets inspected on the schedule in the inspection intervals article and nobody from the District asks to see the tag. A building with a shop in it is a commercial property to Fire and EMS, and the fire marshal’s office does walk the corridors. The riser gets an annual inspection by a licensed company, the tag hangs on the riser, the backflow test certificate goes to DC Water every year, and a lapse shows up as a violation on the building, not on the tenant. Owners who are used to a house system are often surprised by this, and it is the main reason we tell them to hold the inspection contract themselves rather than leave it to a shop tenant who may be gone next year.

What the install costs, and why the shop is a separate line

For the apartments, the published retrofit band on the cost page holds: $2 to $7 per sprinklered square foot, with the open ceilings of a gut job at the low end and finished plaster at the high end. The shop floor is priced on its own line because the hazard, the head count, and the exposed pipe runs are different, and a bid that spreads one per foot number across the whole building is a bid to question. The bid reading article says what the line items should look like. The new water service, when one is needed, is the other large number, and it sits with DC Water rather than with us.

The order of operations

Start with the occupancy letter. Ask the architect to request DOB’s reading of the building in writing: what the shop is classified as, how many units the residential side has, and whether the separation between them will be rated. With that letter the sprinkler design is a known quantity. Then the flow test and the service question, then the sprinkler sheets filed with the building permit, then the rough inspection before the ceilings close. A building that skips the first step usually finds out at plan review that the shop needs heads after all, and by then the service line and the riser location have been sized for the apartments alone.

Quick answers