Insulating Historic Buildings: Lessons from Detroit Restoration

Detroit is in the middle of a multi-decade restoration wave. Pre-war commercial buildings that sat dark for thirty or forty years are being brought back online with modern HVAC, sprinkler systems, and domestic hot water loops. The mechanical scope on these projects looks deceptively similar to new construction — until the insulation crew shows up and runs into walls that have no cavity to route through, plenums that have no listed assembly, and pipe chases that were designed for a steam system that hasn't run since 1962. This post walks through the specific challenges of mechanical insulation on historic Detroit restorations and the strategy that keeps the work moving.

Why Historic Buildings Are Different

A new commercial building is designed around modern mechanical routing from day one. Pipe chases are sized for current insulated diameters. Plenums are continuous and accessible. Vapor barriers can be detailed at every penetration. Drywall partitions stand off from pipe runs by code-required clearances.

A 1920s commercial building was designed around point-source steam radiators, hand-fired boilers, and gravity ventilation. There are no chases for chilled water. There are no plenums above corridor ceilings. The exterior wall is solid brick — twelve to eighteen inches thick — with no cavity to insulate and no vapor barrier anywhere. Modern HVAC has to be threaded through structure that was never designed to receive it, and the insulation strategy has to follow.

Vapor Strategy at the Brick-Cavity Interface

The single biggest risk in adding modern HVAC to a historic masonry building is condensation behind the brick. Solid brick walls in Detroit's climate sit at outdoor temperature for most of the heating season. When a chilled water line or a cold supply duct is routed close to that wall, the dew point can drift inside the wall assembly. Moisture condenses, the brick saturates, and within a few winter freeze-thaw cycles the masonry begins to spall.

The strategy: keep cold piping and cold supply ductwork off the exterior wall whenever possible, and where it has to run there, build a real vapor retarder system. For chilled water lines in this configuration, RMI typically runs closed-cell flexible elastomeric (ASTM C534) — or fiberglass under a sealed, low-perm vapor-retarder jacket where cost is the driver — with every joint and seam sealed and the jacket properly lapped. The whole point is a continuous vapor retarder: on cold pipe the failure path is always at the joints, terminations, and penetrations, so the detailing matters more than the raw R-value.

For supply ductwork running through historic plenum space, the move is a closed-cell elastomeric foam with a factory-laminated vapor barrier facing, terminated cleanly at every register boot and damper. Open-cell duct wrap behind a historic plaster ceiling is asking for moisture problems.

Routing Through Original Pipe Chases

Many pre-war Detroit buildings have generous original chases that once carried steam risers, condensate returns, and waste stacks. Most of those chases are now half-full of conduit, low-voltage cabling, and abandoned utility runs from later renovations. Cleaning out a chase to receive new insulated piping is its own scope of work, and it's usually slower than people expect.

The practical rule we've found on restoration work: never assume an original chase has the dimensions called out on legacy drawings. Field-measure every chase before the insulated pipe size is committed. A 4" steel pipe with 1.5" of fiberglass and a jacket needs roughly 7.5" of chase width. If the chase measures 7", either the pipe gets downsized, the chase gets opened, or the insulation thickness gets reduced — and reducing insulation thickness has energy-code consequences that have to be re-checked against ASHRAE 90.1.

For a deeper look at how thickness, K-factor, and ASHRAE minimums interact, see our companion post on R-value for mechanical insulation.

Steam to Hot-Water System Conversions

A lot of Detroit restorations include converting a legacy two-pipe steam system to modern hot water. The pipe routing usually stays — the original risers and returns are reused as supply and return for the hot-water system. The insulation scope, however, is essentially a green-field install: the original asbestos pipe lagging (if any survived) has long since been abated, and the bare pipe needs new insulation specified for the new service temperature.

Two practical considerations on this kind of conversion:

• Old pipe surface condition. Decades-old steam pipe often has surface rust, pitting, or coating residue from prior abatement. Before insulation goes on, surface prep — wire brush, light cleaning, primer where needed — keeps the new system from sealing moisture against compromised metal.
• Operating temperature is lower. A modern hot-water system runs at 140–180°F, not 350°F. Insulation thickness can sometimes be reduced from the original spec — but verify against current ASHRAE 90.1 minimums, not the legacy 1950s minimum that's still pencilled into the drawings.

Working Inside Michigan Central Station

Michigan Central Station is the highest-profile restoration project in the region, and RMI's crews have worked on its mechanical insulation scope. Without revealing project-specific details, a few generalizable observations from the work apply to any large-scale historic restoration:

• Coordination with the preservation architect matters. Historic interior finishes drive routing decisions. Where insulated piping would be visible, the jacket finish, the band spacing, and the termination details all get reviewed. Plan that review into the schedule rather than the punch list.
• Mock-ups pay back. Building one bay of insulated piping with the proposed jacket and termination details — and getting it approved by the architect and owner — eliminates the "we didn't realize it would look like that" change order three months later.
• Material logistics are tighter. Historic buildings in downtown locations don't have lay-down yards. Just-in-time delivery of insulation material — and a working relationship with a local supply yard — keeps the production rate up.

Abatement and Mechanical Insulation Are Separate Scopes

A note that should be obvious but routinely gets confused on bid documents: removing asbestos lagging from legacy piping is an abatement scope, not a mechanical insulation scope. RMI does not perform abatement. We mobilize after a licensed abatement contractor has cleaned the pipe and a clearance test has cleared the area. Specifying abatement and new insulation as one combined line item on a restoration project creates bid confusion that ends up costing the owner.

Weather Protection on Roof Equipment

Historic Detroit buildings often have boiler stacks, exhaust ducts, and roof-mounted equipment that need weather-rated jacketing on insulated runs. Standard aluminum jacketing handles the climate, but the joint and termination details matter. Snow, ice loading, and the occasional 65 mph gust off the river are not edge cases in Southeast Michigan winters — they're December. Jacketing and lagging on outdoor runs gets the same finish-quality review as the visible interior work.

What to Ask at the Bid Phase

If you're scoping mechanical insulation on a historic restoration, three questions worth asking every bidder:

• How are you handling the brick-cavity vapor retarder on cold piping near the exterior wall?
• What's your strategy for routing through historic chases that may not match legacy drawings?
• How are you coordinating with the preservation architect on visible insulation finishes and mock-ups?

A bidder who can answer all three in a pre-bid conversation has thought about the work. A bidder who hasn't will find these problems in the field, on your dime.

RMI handles commercial piping insulation on historic restorations across Detroit, Hamtramck, and the broader Southeast Michigan corridor. Our PM team is comfortable with preservation-architect reviews, vapor strategy at masonry interfaces, and the logistics of downtown lay-down constraints.

Restoring a pre-war commercial building? Contact RMI at 248-379-5156 for a mechanical insulation scope tailored to historic constraints.