Climate change mitigation potential in building preservation: comparing the CO₂ performance of four refurbishment alternatives to new construction

Figures & data

Figure 1. Korso school, perspective drawing and facades 1:750. Photo courtesy of Kimmo Nekkula.

Table 1. Structures used in the scenarios.

Building part	Existing case building	R1 Delayed refurbishment	R2 Refurbishment	R3 Energy refurbishment and R4 Extensive energy refurbishment	N1 New concrete school	N2 New wooden school
Frame / exterior walls	Concrete, expanded clay aggregate brick	Sealing	–	–	Precast concrete elements, concrete beams and columns	CLT structure, glulam beams and columns
Facades	Plaster 30 mm	Plastering, 30 mm, renewed partly	Plastering, 30 mm, renewed completely	R3: as in R2 R4: Adjustment screed 10 mm, additional insulation 50 mm, thin-coat plaster 10 mm	Brick-tiled and painted concrete elements, glass walls and steel grilles	Wood-clad solid 280 mm CLT elements, glass walls and steel grilles
Roofing	Tinned roof	Renewed partly 1/10	Renewed completely	Renewed completely with bitumen roofing	Bitumen membrane coating	Bitumen membrane coating
Roof	Concrete slabs, wooden truss, with wood wool insulation, 150 mm, in between	Sealing	New mineral wool insulation 300 mm	New wood construction and mineral wool insulation 500 mm	Hollow-core slabs, wooden truss, mineral wool insulation	Glulam beams, wood fibre insulation 480 mm, mineral wool insulation 40 mm
Windows/doors	Double glazed windows, wooden doors	Conserved	Renewed, better than typical solutions	Renewed, energy efficient solutions	Typical solutions for new construction	Typical solutions for new construction
Intermediate floors	Beam and slab floor	–	Additional gypsum board and mineral wool	Additional gypsum board and mineral wool	Hollow-core slabs 370 mm	CLT floor slabs 260 mm
Walls against ground	Concrete, inner lining of calcium silicate bricks	Sealing	Additional mineral wool, external moisture barrier	Calcium silicate bricks removed, additional mineral wool, external moisture barrier	Precast concrete elements, external moisture barrier	Precast concrete elements, external moisture barrier
Base floor	Two in-situ cast concrete slabs with insulation in between	Sealing	Concrete slab on ground with thermal insulation	Concrete slab on ground with thermal insulation	Concrete slab on ground with thermal insulation	Concrete slab on ground with thermal insulation
Partition walls	Wood-framed, calcium silicate brick and concrete partition walls	–	–	–	Steel-framed, calcium silicate brick and concrete partition walls	CLT partition walls 120 mm, calcium silicate brick and concrete partition walls
Toilets & bathrooms	Original tiled floor	New moisture barrier and tiles	New moisture barrier and tiles	New moisture barrier and tiles	Typical solutions for new construction	Typical solutions for new construction
Building systems	Typical building systems	–	Typical building systems, renewed completely	Typical building systems, renewed completely	Typical building systems, no sprinklers	Typical building systems, sprinklers
Ventilation	Mechanical extract ventilation system	–	New mechanical ventilation with heat recovery	New mechanical ventilation with heat recovery	New mechanical ventilation with heat recovery	New mechanical ventilation with heat recovery

Figure 2. Tesoma school, perspective drawing and facades 1:750. Photo courtesy of the authors.

Table 2. Input data for energy calculation.

Property	Unit	R1 Delayed refurbishment	R2 Refurbishment	R3 Energy refurbishment and R4 Extensive energy refurbishment	N1 New concrete school	N2 New wooden school
Net heated area	m²	2412	2412	2412	2412	2412
U-VALUES OF STRUCTURES
Exterior wall 1, basic	W/(m²K)	0.996	0.996	R3: 0.996 R4: 0.44	0.190	0.390
Exterior wall 2, basement	W/(m²K)	0.43	0.16	0.23*	0.17	0.17
Roof	W/(m²K)	0.27	0.10	0.07	0.09	0.10
Base floor with earth thermal resistance	W/(m²K)	0.41	0.15	0.15	0.14	0.14
Doors	W/(m²K)	1.80	0.80**	0.60**	1.00	1.00
Windows	W/(m²K)	2.81	0.80**	0.60**	1.00	1.00
STRUCTURE PROPERTIES
Air tightness (q50)		2.00	2.00	1.00	2.00	2.00
WINDOW PROPERTIES
U-value of glass	W/(m²K)	2.90	0.67	0.45	0.90	0.90
U-value of frame	W/(m²K)	2.00	2.00	2.00	2.00	2.00
g-value of windows		0.76	0.54	0.32	0.54	0.54
EQUIPMENT, VENTILATION
Annual efficiency of air supply unit’s heat recovery	%	–	55	70	55	55
Specific fan power/SFP	kW/m³/s	0.9***	1.8	1.5	1.8	1.8
Type of heating		District heating	District heating	District heating	District heating	District heating

*The value is weaker than in R2 because in R3 and R4, the inner lining of masonry is removed from the basement wall to reduce mould risk.

**The value is better than in N1 and N2 because in refurbishment, the options to improve energy efficiency are more limited than in new build; thus, more efficient doors and windows are often chosen.

***Exhaust air only.

Figure 3. Scope of LCA. Source: See note 13.

Figure 4. Energy simulation results.

Figure 5. Life cycle phases, data sources and tabulated values used. Notes: A5 or C values are not available for refurbishment works in the MoE method. Thus, the method’s A5 value for new construction was used for R2–R4. This is likely an exaggeration, so it was assumed that the value compensates for C_B5 as well, and a value for C_B5 was not estimated separately.

Figure 6. Accumulation of emissions during different life cycle stages.

Figure 7. Accumulation of emissions in the different refurbishment and replacement scenarios.

Figure 8. Accumulation of emissions when +10% to electricity consumption and +50% to district heating consumption is assumed. Compare to Figure 7.

Figure 9. Accumulation of emissions when no decarbonization is assumed for energy production. Compare to Figure 7.

Data availability statement

The data that support the findings of this study are available in the tables and figures of the article, the supplementary data file, and Open Access sources (emissions coefficients and tabulated values in the MoE method or the CO2data.fi database).