Exploring the synergy between structural engineering design solutions and life cycle carbon footprint of cross-laminated timber in multi-storey buildings

Figures & data

Figure 1. Illustration of the explored synergies between engineering design and carbon footprint of CLT building.

Figure 2. Illustrations of the west facade and a floor plan of the studied CLT multi-storey building.

Figure 3. Schematic representation of the different CLT walls [(a) exterior wall, (b) apartment separating wall, (c) other interior load bearing wall (within apartment)] and floor constructions of the studied building.

Table 1. Mass of CLT in different parts of the studied CLT multi-storey building.

Structural component	Amount of CLT (air-dried metric tons)
Floors	180.8
Exterior and interior walls	135.1
Balconies	51.6
Stairwells	2.4
Total	369.9

Figure 4. System boundary of activities in the study. The dash borders show what is covered in the analysis.

Table 2. Structural engineering aspects and their implications for the life cycle carbon footprint modelling.

Engineering aspect	Life cycle phase influenced	Description of influence
Optimised material utilisation	Production, end-of-life stage and post-use benefits	Amount of CLT used and recovered for post-use management
Efficient connection and construction	Production, construction, end-of-life stage and post-use benefits	Amount of fasteners used, assemble and disassemble of CLT, amount of CLT recovered for reuse
Service life risk management	Service life	Early identification of repairs and maintenance needs, thereby avoiding major structural replacements

Figure 5. Material production (A1–3) carbon footprint for the reference building.

Figure 6. Relative distributions of materials of the reference building in terms of mass and carbon footprint.

Table 3. Material production carbon footprint (kgCO_2eqv/m²) broken into CLT and non-CLT structural components.

Structural component	Reference	Optimised material utilisation	Efficient connection and construction
CLT structures:	107.5	104.5	106.3
Floors	41.3	40.0	41.3
Exterior and interior walls	55.2	54.0	54.1
Stairwells	0.6	0.6	0.6
Balconies	10.3	9.9	10.2
Non-CLT structures:	95.9	95.9	95.7
Foundation and ground floor	64.0	64.0	64.0
Windows and doors	10.1	10.1	10.1
Interior finishes	16.9	16.9	16.9
Roof	4.9	4.9	4.7
CLT + non CLT structures	203.4	200.4	201.9

Table 4. Reductions of carbon footprint for the structural engineering aspects compared to the building in the reference case. Negative values denote increased benefit, while positive values denote reduced benefit.

Building module and stage	Optimised material utilisation	Efficient connection and construction	Service life risk management
Production (A1–3)	−1.5%	−0.7%	-
Construction (A4–5)	–	–	–
Service life (B2–4)	–	–	−25.8%
End-of-life (C1–3)	–	–	–
Post-use benefits of CLT (D)	7.5%	−27.9%	–

Figure 7. Relative distribution and net balance of the carbon footprint for the reference building and the synergy effect of structural engineering design.

Table 5. Carbon footprint and life cycle GHG balances for the reference building and the synergy effect of structural engineering design.

Building module and stage	Carbon flow (kgCO2eqv/m^2)		GHG savings
	Reference	Synergy	kgCO2eqv/m^2	%
Production and construction stage:
Module A1–3	203.4	199.2	4.1	2.0
Module A4–5	40.4	40.4	–	–
Service life stage:
Module B2–4	32.2	23.9	8.3	25.8
End-of-life stage:
Module C1–3	4.5	4.5	–	–
Potential benefits and burden:
Module D			-
CLT/wood recovery of energy	−152.4	−181.3	28.9	19.0
Concrete & steel recycling	−35.7	−34.3	−1.4	−3.9
Life cycle balance (With Module D)	92.4	52.4	39.9	43.3
Life cycle balance (Without Module D)	280.5	268.0	12.4	4.4

Table A1. Quantities of inventoried materials (air-dry) contained in the reference building and data sources for the life cycle inventories analysis. RER and CH are short names for Europe and Switzerland in Ecoinvent.

Material	Mass (tonne)	Names of used dataset in the Ecoinvent database (v3.7.1)
CLT	369.9	Cross-laminated timber//[RER] cross-laminated timber production
Sawn timber	116.0	Structural timber//[RER] structural timber production
Plywood	1.2	Plywood//[RER] plywood production
Particleboard	12.6	Particleboard, uncoated//[RER] particleboard production, uncoated, average glue mix
Plasterboard	231.7	Gypsum plasterboard//[CH] gypsum plasterboard production
Rock wool	69.9	Stone wool, packed//[CH] stone wool production, packed
Concrete	1518.4	Concrete, high exacting requirements//[CH] concrete production, for building construction, with cement CEM II/A
Crushed stone	145.8	Gravel, crushed//[CH] gravel production, crushed
Rebars	49.6	Reinforcing steel//[Europe without Austria] reinforcing steel production
Steel sheets	21.6	Metal working, average for metal product manufacturing//[RER] metal working, average for metal product manufacturing
Aluminium	1.4	Aluminium alloy, AlMg3//[RER] aluminium alloy production, AlMg3
Plastics	5.7	Polystyrene, extruded//[RER] polystyrene production, extruded (average for CO2 blown, HFC-134a blown & HFC-152a blown)
Paints	4.7	Alkyd paint, white, without water, in 60% solution state//[RER] alkyd paint production, white, water-based, product in 60% solution state
Mortars	56.4	Cement mortar//[CH] cement mortar production
Sealants	9.5	Light mortar//[CH] light mortar production
Glue	0.4	Adhesive, for metal//[RER] market for adhesive, for metal
Asphalt	0.1	Synthetic rubber//[RER] synthetic rubber production
Roofing felt	2.6	Bitumen seal//[RER] bitumen seal production
Rubber	0.1	Latex//[RER] latex production
Glass	29.3	Flat glass, coated//[RER] flat glass production, coated
Ceramics	22.2	Ceramic tile//[CH] ceramic tile production
Porcelain	1.4	Sanitary ceramics//[CH] sanitary ceramics production