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Adaptive-reuse triage — keep, strip, demolish, priced in carbon

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A standing round barn, broken into the elements it is actually made of: foundation ring, cow-storey wall, mow floor and its post ring, studs, sill and plate hoops, roof frame, sheathing, covering, siding, silo, windows. Call each one KEEP, STRIP or DEMOLISH and watch the carbon move — keeping costs nothing, which is the entire argument for reuse; stripping buys a replacement; demolishing buys nothing back and loses whatever the element was doing, which the tool names. Then the comparison the whole thing is for: reuse + retrofit against demolish + rebuild, cumulative over a century on a decarbonizing grid, with the crossover year called. Reuse usually wins. It does not always win, and a tool that could not say so would not be measuring anything — so the numbers that decide it (how good the retrofit gets, how good the new build is, how fast the grid cleans up) are sliders on the front with their sources attached.

ft
ft
ft

Fraser's barn is a 9-ft brick cow storey with 20-ft studs on it — the plate lands 29 ft up.

ft

These are the numbers that decide whether reuse or rebuild wins. They are assumptions, not measurements, so they are on the front of the tool rather than buried in it.

kWh/m²·yr

How hard the retrofitted barn is to run. THE assumption that decides this comparison. An uninsulated barn is a poor thermal envelope; a deep retrofit improves it a long way but rarely to new-build levels. Move it and watch the crossover move.

kWh/m²·yr

How hard the replacement is to run. A new building to current standards. If you set this equal to the retrofit, rebuild can never catch up — which is exactly the assumption to be suspicious of.

kgCO₂e/m²

What it costs in carbon to make the kept fabric usable: insulation, glazing, linings, services. A deep retrofit typically lands well under a new build but is far from free — this is the number that decides how much of reuse's head start survives.

kgCO₂e/m²

A whole new building's product-stage carbon per square metre of floor. LETI/RIBA benchmarks put a new low-rise at roughly 350–600 kgCO₂e/m² upfront; the range is the point.

kgCO₂e/kWh

What a kilowatt-hour costs in carbon right now. US average grid intensity, ~0.371 kgCO₂e/kWh (EPA eGRID national mix).

× today

The share of today's grid intensity still there in 2050, then held flat. A decarbonization trajectory is a POLICY assumption, not a measurement. The faster the grid cleans, the less operational difference matters — and the more reuse wins.

kgCO₂e/kg

Taking a kilogram of building down: plant, cutting, handling. Module C1 only — carting it away and processing it (C2–C4) is NOT in here. RICS PS 2023 gives module C1 as a small fraction of A1–A3; 0.013 is the order of magnitude and is a slider because it varies with method.

The verdict

Reuse starts 109 t of CO₂e ahead, and the new building's lower running cost catches up in 11 years — 2037. Before then, reuse wins; after, rebuild does.

Standing in the barn
39.5 t
already spent
Reuse, upfront
104.0 t
94.6 t of it is the retrofit
Rebuild, upfront
213.2 t
3.1 t to take this one down
Crossover
2037
11 years

Cumulative carbon, 2026–2126

2026crossover 20372126

Reuse + retrofit · Demolish + rebuild · running at 23 t and 11 t a year to start. Past 2050 the grid is HELD at 25% of today's — an assumption, not a forecast.

The triage — 98% of the barn kept by weight

61% of what is standing sits in the substructure, frame and roof. That is the share people guess low, and it is the share you lose fastest.

Substructure
Foundation ring & footing
The footing and the ring wall under the cow storey — 18 in wide, 4 ft deep. 9.1 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
Fraser's 18-inch footing, 4 ft deep, round the full circumference.
Frame
Mow floor
2 × 12 joists on a post ring at the stanchions, ship-lap decked. 1.2 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
2 × 12 joists at 2'-6" at the wall (halving inboard, ≈0.55 of a full grid) plus 1-inch ship lap.
Mow-floor post ring
4 × 4 posts at the stanchion circle, carrying the mow floor's inner span. 0.1 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
34 4 × 4 posts on the stanchion circle, one per stall pair.
Mow studs
2 × 6s, 20 feet long, at 2'-6" centres, hooped every 5 feet. 0.3 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
75 studs at 2'-6" centres, 20 ft long.
Sill & plate rings
The built-up hoops — a 6 × 6 sill of 1 × 6s, a plate of five 1 × 4s. 0.2 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
A 6 × 6 built-up sill and a five-ply 1 × 4 plate, each closed round the barn.
Silo
The concrete-stave mast standing clear through the peak. 5.8 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
4-inch concrete staves, full height including the part that stands above the roof.
Envelope
Cow-storey wall
The 10-inch brick wall of the stable storey, with its 2-inch cavity. 10.3 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
10-inch masonry × the cow storey, priced on the concrete factor at 0.9 density (brick is not in the shared ICE set — stated, not hidden).
Siding
Vertical boards sprung round the hoops. 1.3 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
1-inch boards over the mow wall, the full circumference.
Windows & doors
12-light stable windows round the cow storey, and the big sliding driveway doors. 4.0 t as built · costs 4.0 t — Demolition plus a like-for-like replacement — the cheapest honest substitute.
16 stable windows at Fraser's own spacing (16 on 188½ ft) plus two 14-ft driveway doors; 20 mm glazed-equivalent.
Roof
Roof frame
64 framed 2 × 6 rafters, doubled to 128 below the gambrel break. 1.1 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
64 rafters over the full run, doubled below the break (≈1.6 × 64 stick-lengths).
Roof sheathing
1 × 2 sheathing laid to the shingle gauge. 0.7 t as built · costs nothing — Nothing. It is already there — that is the entire argument for reuse.
Spaced 1 × 2 sheathing — about 45% coverage, which is what shingle lath is.
Roof covering
The weathering layer — cedar shingles originally, steel on most survivors. 5.4 t as built · costs 5.4 t — Demolition plus a like-for-like replacement — the cheapest honest substitute.
Galvanized sheet at 5 kg/m² — the re-roof most standing round barns already have.

What this number does not see

Only carbon, and only some of it: product stage (A1–A3), demolition energy (C1) and operational energy (B6). Not transport to site (A4), not construction (A5), not replacement over the period (B4), not waste processing or disposal (C2–C4), not biogenic storage. And nothing that is not carbon at all — the embodied labour and skill in a hundred-year-old frame, what the building means to the place it stands in, or whether anyone wants the program you are putting in it.

v1 is sketch-only. The elements are derived from the barn's dimensions, not read out of a model you imported. Per-element triage needs to know that a thing is a rafter and what it is holding up — an imported mesh is triangles and carries none of that — so importing one and pretending it can be triaged is a feature this version deliberately does not have.

Factors are the platform's shared ICE v4.0 set (Circular Ecology), the same table Assayer, Footprinter and Detailer use. The professional tool for this job is the CARE Tool — free, and built for real reuse assessments.