VTT TECHNICAL RESEARCH CENTRE OF FINLAND Quality of

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Quality of timber construction - Guidance document for buildings and load bearing structures • A printed RIL report published at the end of 2006 • The work in the QA working group has been actively industry driven Jouni Hakkarainen, Metsäliitto Osuuskunta/Puutuoteteollisuus, pj. Juha Elomaa, Ramboll Oy Unto Hyytiä, Versowood Oy Antero Järvenpää, Late-Rakenteet Oy Ari Kevarinmäki, VTT Veijo Lehtonen, Late-Rakenteet Oy Mikko Mäkinen, SPU Systems Oy Alpo Ranta-Maunus, VTT Gunnar Åstrom, RIL Tomi Toratti, VTT, siht. • 15 working group meetings in 2 years • Has been well received by the building designers • The city of Helsinki mentioned they will be using the proposed quality ensurance practices 1

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Definition of building quality A. The process quality is made up of the design and building processes as well as the communication and co-operation between these parties B. The quality of the end-product on the other hand may be divided to visual, functionality, ecological and technical quality. The service-life perspective is an essential part of the end-product quality 2

VTT TECHNICAL RESEARCH CENTRE OF FINLAND A. Indicators of a good quality process are: • The objectives of the building project are well defined and clear • The schedule is realistic • The staging and decision making processes function • The responsibilities and tasks of the building partners as well as the related scheduling is agreed • The competences of the persons involved is adequate • The building partners form a positive atmosphere and a desire to cooperate • Sufficient resources are allocated to the design and building processes • The security measures are taken care of • The critical stages are identified and these are emphasized 3

VTT TECHNICAL RESEARCH CENTRE OF FINLAND B. End-product quality • Visual quality is composed of the appearance of the visible structures, the rooms and building volumes, the environment and the combinations of the above. • The functionality quality is determined on how the building performs its intended functions, eg. logistics and ergonomics or in other ways efficiently and comfortably. • The technical quality is made up of durability, strength, safety and healthiness. • The ecological quality is first effected when the building materials are chosen in the initial stages of the project, however the major part is determined on the building use. The main issues are the energy efficiency of the building, long service life, good maintenance procedures and modifiability of the building. 4

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Considering timber the following should receive special attention • Handling of information and communication between the building project partners • Bracing of load bearing structures • Considerations on performance of connections and how these are effected by variable humidity conditions • Swelling and shrinking of timber elements • Cracks caused by shrinkage of moist wood • Orthotropic strength of wood • Fire safety 5

VTT TECHNICAL RESEARCH CENTRE OF FINLAND The scope of this report is on the quality assurance of the endproduct quality, which is achieved by a functional cooperation among the project partners, sufficient coverage and quality of design and on the documentation to be produced in a building project. This report describes the following means for quality assurance: 1. Building process – Moisture control plan, assembly plan, tolerances 2. Design – initial risk analysis, design process, following the design in the site, information and feedback flow between engineer and building site 3. Fabrication of elements - Approved methods for design, fabrication and quality control (templates given) 4. Maintenance – Contents of the maintenance manual 6

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Documentation needed for decisions on quality and information transfer among building project partners • Project description template : a) all technical information on project b) all decisions recorded c) a tabulated form is provided, when and what decisions should be done • Moisture control plan template: a) moisture of wood through the building process from factory to ready building. b) moisture protection levels. • Assembly plan template • Tolerances in timber construction a) Fabrication tolerances for materials (CEN standards) b) Assembly tolerances (Finnish building codes) c) Tolerances for connections 7

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Table of contents • • • • Preface 1 1. 2 2 3 3. 1 3. 2 4 4. 1 4. 2 4. 3 4. 4 4. 5 • 4. 6 • 4. 7 • • • 5 5. 1 5. 2 5. 3 6 6. 1 6. 2 6. 3 6. 4 6. 5 7 3 Introduction 4 Scope 4 Partners in a building project 4 Plans and documents 6 Project description 7 Introduction 7 The content of the project description 8 Quality assurance of the structural design 13 Introduction 13 Main requirements of the structural design 13 Documents to be drafted 14 Quality control 14 Following the structural design during construction work 15 Structural risk analysis 15 Information transfer and control of updates on the plans 16 Materials 17 Wood materials and product standards 17 Durability of wood 19 Corrosion of fasteners 19 Industrially fabricated elements and building components and quality control 21 Introduction 21 The control of the process 21 Storage and transportation 21 Connection techniques 22 Specific guidelines 23 Quality assurance of the building process 24 • • • • • • 7. 1 7. 2 7. 3 7. 4 7. 5 7. 6 8 8. 1 8. 2 8. 3 8. 4 8. 5 8. 6 9 10 11 General requirements Supervision on building site Moisture control plan Assembly plan Inspections, testing and repair Tolerances Stability of structures Introduction Design and execution Responsibilities for stabilization Stability of a building and bracing Stability of the whole building Bracing Special Risks Maintenance Manual References Appendix A. Durability of wood Introduction Mould and rot in wood Structural protection Chemical protection Appendix B. Checklist for the structural design Appendix C. Checklist for the assembly plan • Appendix D. Example of a project description 8 24 25 25 28 29 29 35 35 35 36 37 37 39

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Tasks for the Decision on project building Organisation of design developer Initial project plan, Main phases Organisation of construction Prep. Of design Assess. Of needs Project plan. Main documents Counselling and supervision of construction Construction Prep. of construction Draft plan Project description draft Bidding and negotiation of contracts Building use Construction design Project description version III Initial risk analysis Construction design External inspection Moisture control plan Assembly plan Maintenance manual 9

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Table 3. 1 The content of the project description, where a recommendation of the partner responsible to deliver the content is given using the following abbreviations: Building developer (or representative): BD, Main designer: MD, Architectural designer: AD, Structural designer: SD Responsible Building developer Who delivers: The building developer or by his commission the main designer, the structural designer, element designer or any other consultant Who verifies: The main designer, the building officials and the contractors before initiation of building work Who follows: All partners, especially the contractors and element producers. Content: Cover page Version I, II or III (a recommendation at which latest stage a decision has to be done) Name and address of building project location The name of the main author of the project description The name of the contact person of the partners: - the building developer - The building supervisor (if not the same as above) - The main designer - The main structural designer - The architect designer - Other designers Update version and date (of last update) List of updates: - What updates are done compared to last version, and date 10

VTT TECHNICAL RESEARCH CENTRE OF FINLAND A. Basic information 1. A description of the end-use of the building and the its consequence class, I MD 2. The designed in-service life period of the building and the service intervals, I BD 3. Climatic conditions of the building (exterior and interior) , I AD 4. The loads applied on the building and other special conditions (snow, wind etc. ), I SD 5. The initial survey of building condition report, in cases where the project is a reparation or restoration assignment, I MD 6. The fire class of the building, and other fire requirements set for the building, I AD 7. Other known requirements set for the building, I AD 8. The initial schedule of the building project, which involves the timing of the following main tasks, I BD (This schedule is initial and not binding, it is updated as needed): 8. 1 Project plan 8. 2 Preparation of the design work 8. 3 Preparation of the building and call for bids 8. 4 Timing of the decision on the method of building 8. 5 Design work period 8. 6 Construction of elements, assembly and the period of building 9. A Brief description on the organisation of the building project, II BD 9. 1 The chosen contract organisation 9. 2 The contract limits of design and building. 10. Design procedure and the responsibilities of the designer, II MD 10. 1 The tasks of the main designer and the skills/experience required 10. 2 The approval method of subcontracting design work 11. The exchange of information and contact methods used in the building project, II MD 11. 1 The exchange of information and cooperation among the designers 11. 2 Filing method used and delivery methods for the documents 11. 3 File formats used 11. 4 The method how alterations on the building site are delivered for the designers approval. 11

VTT TECHNICAL RESEARCH CENTRE OF FINLAND B. Materials and construction products used 1. The construction materials used in the building project. It may be possible to deliver a list of essential materials to be used in a specific building project (wood materials, connectors etc. ), in which case the price, the required technical specifications and the availability are considered. If necessary, the requirements on the façade or the roof materials may also be set by the building officials or the building owner and these are then listed here. I SD 2. The method how the use of alternative materials is approved in case there is a list of materials to be used. I MD C. Quality requirements on the structural design This is a verbal description on the technical information on the design and requirements 1. The loads, the duration classes and the service classes to be used in the design, I SD 2. Schedule, II MD 2. 1 Timing of the design work, in comparison to the building on site. 2. 2 Inspections to be done on the design 2. 3 The timing of an external evaluator of the design work. 3. The standards and guides to be used in the design and construction (eurocodes), II SD 4. A brief description on the requirements set on the structures by the fire class and how these are implemented on the construction, II SD 5. A brief description on the structural design, II SD 5. 1 Foundation conditions and foundation method 5. 2 The load-bearing frame system of the building 5. 3 The method of stabilizing the structure, during construction and final 5. 4 The most critical structural connections 5. 5 The requirements set on the outer walls of the structure 5. 6 Building conditions and any other requirements 6. Requirements set by the main designer, III MD on the moisture control plan and assembly plan (which are described later), as: 6. 1 Tolerances of the structures 6. 2 The stability of the structure in different phases of the construction. 12

VTT TECHNICAL RESEARCH CENTRE OF FINLAND D. Quality requirements on the construction work 1. The method how alterations from the design and quality disputes are dealt with, I MD 2. Guidance on how alterations in structural design are dealt with, I MD 3. The main tasks of the building developer in the project, II BD 4. A statement on how the partners are able to fulfil the requirements set on the project description, II BD 4. 1 Competence requirements on the contractor and the management 4. 2 Assurance of sufficient resources in line with the project size 4. 3 Earlier experience and references 5. Construction methods to be followed: , III SD 5. 1 General work guides 5. 2 Guidance given from the structural designer 5. 3 Guidance for the production of structural parts and elements – external inspections 5. 4 Requirements on tolerances 5. 5 Specific instructions to be followed in the assembly plan 6. Inspection and test plan on the construction work, III MD 6. 1 Inspection of the main modular network positions, 6. 2 Foundation, frame and final inspections (possibly other inspections) 6. 3 Persons responsible for the different inspections 13

VTT TECHNICAL RESEARCH CENTRE OF FINLAND F. The requirements set on the moisture control plan The moisture control plan is done as described in section 7. 3. In the project description, the following are drafted: 1. The schedule of the realisation of the moisture control plan, I BD 2. The person responsible for drafting the moisture control plan, I BD 3. The inspection of the moisture control plan, who carries it out and when, I BD 4. The protection level used in the construction, I SD (Protection level PL 0: no protection, ST 1: mobile covering used, ST 2: temporary roof , ST 3: indoor conditions or a full tent protection with heating) 5. The target moisture content of the wood and wooden elements in the different phases of construction, II SD: 5. 1 Fabrication phase of elements, 5. 2 When delivered to construction site, 5. 3 When stored at the construction site 5. 4 At the assembly and building phase and the final (during use) 6. Methods of drying wood, if necessary, II SD G. The requirements set on the assembly plan The assembly plan is require in construction methods where prefabricated building parts are used. The assembly plan is done as described in section 7. 4. In the project description, the following are drafted: 1. The schedule of the realisation of the assembly plan, II BD 2. The person responsible for the drafting of the assembly plan (for instance Element producer or contractor carrying out the assembly), II BD 3. The inspection of the assembly plan, who carries it out and when, I BD 14

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Moisture protection levels Protection level 0, ST 0, no protection - moisture content depends on the climate and may not be assigned, to be used only in winter climates and in short durations Protection level 1, ST 1, plastic covering - moisture content below 20 % Protection level 2, ST 2, sheltered - moisture content below 20%, more reliable than ST 1 Protection level 3, ST 3, internal conditions or a tent with heating - moisture content below 15 % 15

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Moisture control plan This covers the whole production and building process of the timber structure This plan is communicated to the personnel on site. • Responsible Building developer • Who delivers: The building developer and by his commission the main designer, the structural designer, element designer or any other consultant • Who verifies: The building officials, the structural designers and the contractors • Who follows: The producers of building components and the contractors operating on site. • Content: The moisture control plan is drafted for building projects that are carried out at least partly in external conditions. 1. Basic information of the building project (address and other coordinates of the building site, the person responsible for the construction on site, the main author of the moisture control plan) 2. List of wood products to be used in the construction site 3. The target moisture content of wood and wooden elements at different stages of the industrial production. 4. The target moisture content of wood and wooden elements when delivered to the building site, during assembly and when the building is finalised. 5. Inspections and the person responsible for these. 6. Possible sources of moisture e in the building site (for instance, rain, snow, ground water etc. ) 7. The protection level (ST 0 -ST 3) chosen for the building phase and an estimate on the necessary protection duration. 8. The protection of wood and wooden elements on the building site: - storage method and protection of storage - protection during assemble (as determined by the protection level), - drying methods applied for wood that has gained moisture 9. Risk assessment of moisture in the building project - Sensitivity of the project to unfavourable weather - Needs on drying duration and how drying conditions are realised - Effects on the overall schedule of work on site 10. Moisture measurement plan (measurement method, timetable, documentation and person responsible) 16

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Table 7. 3 Assembly tolerance on timber structures (main reference: Finnish general construction quality requirements RYL 2000 ). Maximum deviation allowed Tolerance class 1 2 3 Dimension or location Wall structure Side location of wall ± 3 mm ± 5 mm ± 10 mm Spacing of wall studs ± 3 mm ± 5 mm ± 10 mm Size of windows and doors ± 3 mm ± 5 mm ± 10 mm Location of windows and doors ± 3 mm ± 5 mm ± 10 mm Distance between two adjacent walls ± 3 mm ± 5 mm ± 10 mm Straightness of walls 1 ± 1, 5 ‰ Deviation of the wall frame from a perfect vertical line - height max. 3 m - height over 3 m ± 1, 5 ‰ ± 5 mm ± 8 mm 17

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VTT TECHNICAL RESEARCH CENTRE OF FINLAND Dowel connection Location of connector 4) Simultaneous drilling Location of hole 4) Separate drilling + 3 mm + 1 mm 6) Length of dowel in wood member t - max(2 mm; 0, 05 t) 7) Gap of contact < min(3 mm; 0, 25 tt) 8) Grooved or battened members Incline screw connections Angle of screw + 5° Glued-in rod Location of rod Position at wood surface + 5 mm Glued-screw connections Skewness of holes Drilling length La + La/50 Contact connections Gap Contact required Skewed gap max. 3 mm 1) In the direction of grain, the nails have to be at least d out of line from each other, if a 1 < 14 d. 2) Drilling once through all members or using one drilled member as a template 3) When wood members have 1 mm oversize holes and metal parts have 1, 5. . 2 mm oversized holes. 4) In both surfaces of all wood members 5) In the grain direction, the row may be out of line max. 5 mm from each other 6) When in wood-metal connections have 1 mm oversized holes in metal parts 7) t is the design smooth length in a wood member 8) Gap between wood surface and metal plate, where t is the metal plate thickness t 9) For example the distance of a supporting L-plate from the wood-wood contact surface 19

VTT TECHNICAL RESEARCH CENTRE OF FINLAND Table 7. 5 The tolerance of holes for connectors, if no other information is given in the structural design. D is the hole diameter , d is the connector nominal diameter, Lp is the depth of the hole measured from the designed connector head location and L is the nominal length of the connector. Wood here signifies all wood and wood-based panel products. Connector Drilled material Recommended D Allowed D Lp Nail, screw Metal d + 1 mm d + 0, 2. . 1, 0 mm through Pre-drilled nail 1) Wood 0, 7 d 0, 5. . 0, 8 d L - 0. . 5 mm Pre-drilled wood screw 2) Wood 0, 7 d 0, 5. . 0, 7 d L - 0. . d mm d d + 0. . 1 mm 3) 0, 4 L + 5 mm 0, 7 d 0, 60. . 0, 75 d 4) L - 0. . d Lag screw 5) Dowel 6) Wood d 0, 95. . 1, 00 d L + 0. . 5 mm Dowel 6) metal d + 1 mm < 1, 1 d d + 0, 5. . 1, 0 mm < 1, 1 d through Bolt, threaded rod Wood d + 1 mm d + 0. . 1 mm through Bolt Metal d + 1 mm < 1, 1 d d + 0, 5. . 2, 0 mm < 1, 1 d through Glued-in rod Wood 1, 2 d 1, 15. . 1, 25 d L + 0. . 5 mm Glued lag screw Smooth part in wood d + 1 mm d + 0, 5. . 1, 0 mm Ls + 5 mm 7) 0, 85 d 0, 8. . 0, 9 d L - 0. . d Threaded part in wood 20

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VTT TECHNICAL RESEARCH CENTRE OF FINLAND Further ideas for the future • The guideline should be made into European level • Production of a CEN standard • Performing a risk analysis on a demanding building project 22