CLT Design and Construction short course

There are two CLT short courses on theWoodapp. This short course consists of three parts, architectural design of CLT buildings, CLT assembly and installation and finally some CLT connection technology. For more information on structural engineering of CLT please visit the course Structural Engineering of CLT in SA. Each part was prepared by a local topic expert. It is aimed at architects, engineers, builders and other built environment professionals in South Africa who want to explore the use of wood in building structures. We hope you will start your journey in wood here!

short course

How to complete this course

The course is open access and the content is available to anyone with internet access. This course should be completed in the sequence of the numbered sections. We make use of four components in our course (a) sections with text and illustrations, (b) video clips to explain some of the concepts, (c) a short online quiz after each section to test your acquired knowledge and (d) a test, available to learners who wish to obtain a certificate of completion. Please contact us at with the short course name to complete this test.

To make the course accessible to most people, we’ve tried to limit the time needed to complete it (an estimated 2.5 hours). This course will give you an overview of selected building materials impact and the environment, and design strategies to incorporate timber in a sustainable way. For in-depth knowledge on some topics you might require input from other sources such as national standards, material suppliers, selected textbooks, articles, etc.
If you have any questions or suggestions, please contact us at


1. Architectural Design in CLT Buildings

1.1 CLT – A brief definition
1.2 Outline of benefits: A South African Context
1.3 How is CLT different from timber frame building
1.4. Essential planning when designing with CLT
1.5. Final thoughts
1.6 Quiz 1

2. CLT Assembly and Installation

2.1 Pre-construction
2.1.1 Considerations
2.1.2 Methodology, technology and documentation
2.1.3 Planning, Scheduling and Material delivery
2.1.4 Site Prep
2.2 Moisture Control
2.2.1 Protection plan
2.2.2 Applied protection
2.2.3 Managing moisture on site
2.3 Installation Process
2.3.1 Site Considerations
2.3.2 Equipment
2.3.3 Safety
2.3.4 Transport, Unloading and Staging
2.3.5 Rigging
2.4 Finish
2.4.1 Protection during construction
2.4.2 Cleaning and repairing
2.4.3 Applying finishes
2.5 Quiz 2


3. CLT Connections

3.1 Angle brackets
3.2 Plate connectors
3.3 Slot connectors
3.4 Self-drilling screws
3.5 Pillar connectors
3.6 Spider Connectors
3.7 Soundproofing
3.8 Profiles
3.9 Quiz 3

In the compilation of this module, free use was made of published information such as text, figures, drawings, tables, graphs, etc. As the use of such material is subject to copyright considerations, and the suitability and relevance of this content is in the process of being assessed, the content of this module is only reserved for personal use and the purpose intended. To adhere to copyright regulations, any publication of the module or parts thereof considered, is subject to obtaining the necessary copyright agreement from the publishers by the author. Photographs taken and figures, drawings, tables and graphs generated by the author, are subject to copyright as well.

Whilst all and the utmost care has been taken to ensure the accuracy of the information contained in this module, no warranty can be given regarding the use, suitability, validity, accuracy, completeness or reliability of the information, including any opinion or advice.

1. Architectural Design in CLT Buildings (Alex McGee)


The driving force behind the development of cross-laminated timber (CLT) in Southern Africa is the need to provide alternative wood-based products and systems to architects, engineers, and contractors. Whilst we are not unfamiliar with the use of timber as a building product, it has lagged behind our more traditional building technologies and construction practices. Even though in countries similar to our own, timber has thrived and finds itself the overwhelming leader as a preferred building ma-terial. The reasons for its under-utilisation locally have generated debate, but it is clear to see that CLT offers a different solution that is not always associated with a timber building. And while this product is well established in Europe, work on the implementation of CLT products and systems has just begun in SA, with increasing interest.

CLT assembly on a private residential project in Scarborough, Western Cape. The floors, walls and roofs were CLT elements.
Project: Seagull, Anima Homes


Cross-laminated timber is an innovative wood product and a relatively new building system, started in early 1990, and is helping to define a new class of timber products known as massive or “mass” timber. It is a potentially cost-competitive, wood-based solution that complements the existing light frame and heavy timber options and is a suitable candidate for some applications that currently use concrete, masonry, and steel. CLT panels are typically constructed by laminating three or more layers of timber sections together, with each layer oriented 90° relative to the neighboring layers (Figure 1). The timber most commonly adheres using a structural adhesive. Manufacturing methods and timber quality may have an impact on the final product properties but they do not affect the overall design strategy.

Figure 1: Standard composition of CLT panel,


Compared to traditional timber frame building, CLT offers many advantages in terms of both performance and design flexibility. Its load-bearing capabilities make it suitable for use in multi-story structures, while its excellent thermal properties mean that it is significantly more energy efficient than other materials. In a cost-oriented local market it also allows for greater freedom and higher-quality control when designing complex geometries or curved shapes, as well as unique patterns within the panel itself due to its ability to be cut off-site, via machining and table saws. This makes it an attractive option for those who seek an advantage in both complex modular and bespoke design. In addition, CLT has a low carbon footprint due to its sequestration properties, and renewable source material. It is also highly durable, with a lifespan of up to 70 years or more if properly considered in its detailing and if maintained. Finally, its light weight makes it easier to transport and install than other building materials such as concrete or steel.



When compared side-by-side, the advantages of CLT over traditional timber frame construction become clear. While both materials can offer similar performance when in good condition, CLT offers superior strength over an extended period of time. It also has a much lower risk of warping or shrinkage due to its greater dimensional stability. In addition, CLT does not, in most instances, require additional treatment for fire resistance like many timber frames do – the protection can be made up in the thickness of the timber panels. Meaning that it can often be used without requiring additional fire retardants.

Much like traditional timber frame structures, structures assembled from CLT require a deem-to-satisfy or rational design approach. The regulatory framework for CLT is set out in SANS 8892 of the building regulations, ‘Standard for performance-rated cross-laminate timber.’ Other certifications include;
SANS 1460: Laminated Timber (Glulam)
SANS 1738: Structural Lumber
SANS 10183-2: Adhesives for Wood
SANS 10096: Finger-jointed Structural Timber


It is essential to properly plan a CLT building and there are several important factors to consider. The wider use of off-site prefabrication to deliver efficiency gains in material usage and improve quality on construction sites: The use of off-site prefabrication is gaining traction in the construction industry. This process can help to reduce waste, save time and money, and improve the quality of a build by ensuring that each component is manufactured to the exact specifications. For CLT structures, this means individual panels or components can be made ahead of time, thus reducing the time it takes to assemble them on-site. It also means that individual components or panels can be tailored to suit specific designs, making it easier to create complex shapes and patterns without having to resort to potentially costly mistakes and delays on site.

The process of off-site prefabrication requires a more in-depth and thorough early-stage coordination exercise between the various design disciplines in order for the potential of increased quality to be realised. For example, it is not unimaginable that all electrical service runs can be routed into the panels before the materials reach the site, although this is not a necessity. It is essential that the structural requirements, connection details, sizes and lengths of panels, and openings are fully considered and finalised in order to maximise the benefits of the assembly process.

Robust detailing – the need for waterproofing and ways of dealing with moisture: CLT panels are not a cladding material and are not designed to be exposed to the exterior environment.

They are a moisture-sensitive structural assembly and required protection from the elements. This can be achieved through planning various techniques such as coating the panels in waterproof sealers or, the recommended, adding membranes to the building’s envelope.

It is advised that CLT panels are protected utilising a highly breathable membrane that envelopes the entire home. The membranes are water-resistant but vapour permeable which means that they can protect the building from water ingress while releasing any surplus moisture vapour from the timber back into the outside air. They optimise wind tightness by limiting the unconditional passage of air to protect the structure from the entry of cold draughts in winter or hot draughts in summer. Figure 2 gives a typical external wall build-up and illustrates the location of the waterproofing membrane. Overlaps and end-junctions are taped and sealed off in line with manufacturer’s recommendations and robust detailing.

Figure 2: Typical wall build-up in CLT construction,

Facade installation. Membrane and batterns in place to receive cladding
Project: Seagull, Anima Homes

Window and door openings and internal plumbing connections should be given paramount consideration and emphasis in their detailing. It is recommended that any openings are detailed according to windows and door frame material and sizes, and high-quality tapes and flashings are incorporated to ensure adequate protection against water ingress and thermal bridging around the frame.

Window treatments: Timber cover trims used over metal window and substructure to cover and protect waterproofing tapes and seals
Project: The Owlhouse, Anima Homes

Versatile cladding system

It is highly advisable that a durable cladding system, rain-screen drainage, and ventilation cavity is specified and installed on projects. Unlike traditional construction techniques, whereby the outer layer of a building is designed and specified to repel water and protect the structure from wind, the cladding in a CLT building has the primary function to protect the membrane behind from wear and degradation, and not to prevent water ingress. Water and ventilation behind the cladding enable moisture and condensation to escape from the surface of the membrane. It is important that membranes are sufficiently sealed and taped off and that the cladding substructure and insulation are aligned to maximise run-off and prevent water from being trapped behind the facade.

Due to the above, the selection of cladding material offers more flexibility compared to other types of construction. The choice of material is primarily based on aesthetic considerations, alignment with the site, and the user’s preferences in terms of appearance (see figure 3).

However, the material should also meet and assist the project requirements for thermal performance, energy reduction, fire protection, and cost. It is important that the selection assist the building in complying with National Building Regulations (NBR) and local municipal requirements, and this includes the regulation XA for Energy Usage in Buildings. Additional rigid insulation may be required in build-ups/instances whereby CLT wall and roof panel thicknesses do not satisfy required R and U values.

Figure 3: A selection of cladding types – various finishes require different substructure but options are open-ended in a rain-screen cladding system

Elevation and ground connections

To ensure the durability of timber construction, the ground-floor slabs should be supported above the natural ground to avoid moisture and insect damage. The selection of support options should be based on the size and spans of timber slabs, topographic and geotechnical conditions, climate, environment, and costs. It is crucial to seek advice from structural and geotechnical engineers to avoid costly errors resulting from incorrect selections.

Saligna glulam base frame/substructure with both reinforced concrete strip foundation at the rear and class 8 timber poles at front cantilever.
Project: The Owlhouse, Anima Homes

It is common for CLT to be used in conjunction with Glulam and/or steel when designing ground connections and ground floor slab support. Glulam often provides efficiency in the density of timber used and can elevate the softer pine timber further from the natural ground. Effectively coated and treated steel may offer longer lifespans than its timber counterparts when considering sub-terranean supporting structures and can mitigate the need for concrete completely. The careful leveling on a site and access to structures is an important design consideration, often overlooked, and can assist in creating buildings that integrate well into their landscapes.

Mass concrete strip foundations and base-frame in Scarborough.
Concrete was preferred to steel foundations due to the presence of saline in the ground water. Project: Seagull, Anima Homes

Low stone retaining wall used to create comfortable threshold into buildings. Providing sufficient space for water run-off and ventilation is paramount. Project: The Owlhouse, Anima Homes

Service strategy:

While it is not essential, it is highly advisable that an electrical and mechanical engineer is appointed to your CLT projects. The coordination and design of services on CLT projects can be integral to the performance and maximizing the benefits of the material on a project. The design services, such as plumbing and ventilation, must be considered from the earliest stages of a project in order to ensure that they run optimally alongside or through the CLT structure.

First-fix items can be installed off-site, in order to reduce time on site and should be in place prior to the completion of the taping off and installation of the membrane to ensure adequate water protection and air-tightness. The mechanical and electrical systems should also facilitate access for future maintenance without damaging other materials or components.

Furthermore, facilitating adequate service entries into the building is essential to ensure that all construction elements are correctly positioned and sealed off.

First fix installation being coordinated in prototyping.
Timber frame walls used as non-load bearing, high-traffic service walls.

Spherical back-boxes were designed to allow for electrical fittings to be cut on site with a hole saw rather than square box cut-outs.
Images courtesy of Anima Homes.

Timber frames should be considered for internal walls and areas of high-traffic services, like bathrooms and kitchens which have access requirements and require depth for connections. The ventilation cavity between the membrane and the rear of the cladding, when spaced sufficiently can offer a route for most services to pass and be accessible in future maintenance and configurations. Similarly, if installing a finished, ‘floated’ floor the void between the batterns and the floor is effective for electrical runs.

Carbon neutrality and supply
Mass timber typically has a net positive environmental impact due to its sequestration properties. An optimally designed CLT structure may be up to seven times more carbon-efficient than traditional construction methods, but it should still be utilised responsibly in a building design and take into account the long growing cycles of wood. The demand for timber needs to be in proportion to the supply, and thus hybrid designs utilising both CLT and frame construction for wall systems should be considered. Responsible sourcing of timber materials is essential to achieving the environmental gain. Using locally grown and certified or recycled sources is integral to tipping projects to the positive. Know where your materials are grown and derived.

Range of expressed joints used on roof, beam and wall plates.
Beams and walls were created as separate panels. The timber lamellas reveal this internally.
Project: The Owlhouse, Anima Homes

Pine CLT panels (Industrial Visual Quality) with white-tinted, water-based sealer. Images courtesy of Anima Homes.

Timber finishes and selecting the right species

In a South African manufacturing context, the dominant timber used for CLT panels is South African Pine. Although the lamination process significantly improves the structural performance of the material and there are different visual grades that suppliers will offer you on consultation, it needn’t be your only choice. Although it is predominantly a structural element, CLT has the added advantage of providing a finished surface to the interior of your project. Whether this is a floor or a wall surface, this can offer considerable savings in both time and cost at a later stage of the project and your selection of timber finish should reflect these decisions.

For example, a more durable hardwood species could be specified for the top floor layer to offer a suitable longer-lasting floor finish. It’s crucial to plan and choose the right species of timber that fits your project needs.If using the pine CLT panel as your interior finish, consider specifying a sealer with a UV protective coating and a white tint that will prevent the timber from yellowing and sun degradation. It is equally worth considering the timber lamella (the direction of the timbers on the outer face of the panel) and the edge detail of the panels, when two or more panels come into contact. The lamella direction can positively reinforce the structural strategy of the building, while small chamfers and rounds on the edges of panels can visually be more forgiving on tolerances and possible inconsistencies in assembly.


– Cross-laminated timber (CLT) offers numerous advantages to developers of South African projects,
helping to create a more sustainable and durable building system. While CLT projects can save an
enormous amount of time and cost on-site, this is slightly offset by the time and early
stage project expertise required to effectively plan for this benefit. It is hoped that this article
shines a light on the level of detailed planning and considerations required in order for these bene-fits
to be realised.

– It is a misconception that mass timber and CLT construction is cheaper than traditional bricks and
mortar or timber frame construction due to its quick assembly and reduced time on site. However, this
is not currently the case. While it is hoped that in its adoption and expansion of mass timber
construction will become more cost-effective in the future, it is important to communicate the facts to
prospective clients early on. If the benefits of the building system are still unclear, it is worth
communicating that in traditional buildings the percentage cost split between labour and material is
generally 55/45 when taking into account professional services (and that is on the conservative side).
This ratio reduces significantly to 40/60 in CLT design. Effectively meaning that even though you have
higher building costs, developers are purchasing one and half the amount/quality of materials in CLT
buildings. This has a direct bearing on the quality of the building and its performance and livability.

– We still do not have clarity from suppliers on compliant treatment in South Africa. CLT currently
manufactured in South Africa (or globally) does not comply with the standard for pressurised treat-
ment of softwoods required by South African building regulations SANS10005. Referring to pressure
treatment, with minimum penetration and retention requirements as per the hazard class – H2. It
is on a project-by-project basis that this is being dealt with, often as a rational design and placing
a large responsibility on us, as designers. It is important that you are aware of this and constantly
refer to the requirements and liaise with your suppliers to understand how this is being managed.

– For those starting a CLT project, it’s crucial to work with an experienced team of consultants
and contractors, especially structural engineers and installers. Although CLT design is relatively
straightforward, successful execution requires a team that is familiar with handling panels, and
connection details, and has experience with the minimal tolerances within the materials. Early engagement
with these professionals can define the success of your project.

1.6 Quiz 1

1. Name three very important design considerations when it comes to CLT
Field is required!
Field is required!

Congrats, you nailed it!

Try again.

2.      CLT Assembly and Installation (Jamie Smiley)


The use of mass timber and specifically Cross Laminated Timber (CLT) in the construction industry is fairly new, with the material becoming commercially available in Austria and Germany in the 1990’s. Since then the use of CLT has become wide spread in Europe and is also gaining popularity around the world, due to the benefits it offers in speed, accuracy, cost and green credentials.
With this rapid increase in mass timber construction, the demand for knowledgeable and skilled installers has also increased. While CLT installation is not difficult, it does require a variety of skills from general carpentry, rigging, logistics planning and basic CAD knowledge.
This module will run through the process and essential knowledge required.

2.1      Pre-construction

Mass timber and CLT construction requires a more sophisticated workflow then traditional construction. Early engagement with the architects, engineer and mass timber manufacturer is essential.

2.1.1 Considerations

The following checklist is not intended to be exhaustive and items may not apply to every project. Where relevant, detailed information is included elsewhere in this manual. Co-ordination between the key players in the installation is essential. The site needs to be ready for the CLT installation, logistics for delivery needs to be in place, crane needs to be onsite to unload and install. Pre-planning is the key to mass timber installation.

Figure 2.1 Builder input and engagement is essential during the design phase.

2.1.2 Methodology, technology and documentation

One of the benefits of mass timber construction is found in the workflow of the documentation. Mass timber construction takes advantage of a Building Information Model (BIM) workflow. BIM is a modeling system that condenses and coordinates all project details in one location. Architects, engineers, contractors and subcontractors can interface within the model and share information. Mass timber fabricators use BIM to extract data and communicate with the CNC manufacturing equipment to create customized panels.


Figure 2.2 Shop drawing example, source Timberlab.

2.1.3 Planning, Scheduling and Material delivery

With the correct planning of a mass timber project the construction schedule of the project can be significantly reduced, but in order to capitalize on these time savings detailed planning is needed. A site logistics plan (as shown below) is a great tool in this planning and helps co-ordinate the delivery of materials with the crane and site constraints.

Figure 2.3 Site logistics plan for mass timber project site, source Anderson Construction.

2.1.4 Site prep considerations

Framing with structural steel and cast-inplace concrete offers multiple opportunities to “auto-correct” as construction progresses. The manufacturing tolerances of mass timber are precise, and the foundation must be “plumb, level and square” or have tolerances built into the initial connection interfaces for smooth installation. Check the following as part of site prep and adjust where needed:

Individual anchor bolt locations

  • Line and grade conditions
  • Cleanliness of existing anchor bolts; elevations set
  • Plumbness of existing anchor bolts
  • Required modification of anchor bolts if any
  • Layout of post-drilled anchors

Concrete cast-in-place, masonry and embed work

  • Line and grade of embeds
  • Level of embeds
  • Cleanliness of embeds
  • Compressive strength of concrete in footings, walls, piers and walls, and mortar in masonary piers and walls

If construction discrepancies are discovered on site, including anchor bolts and/or cast-in-place embeds, evaluate the schedule and cost impacts of modification in the field vs. manufacturing facility. If on-site modifications are required, ensure they are completed, certified, inspected and approved prior to the mass timber installation. The GC/CM should provide a report of the completed modifications. A building survey conducted prior to installation can prevent having an install crew on site waiting on corrective actions by preceding trades.

2.2      Moisture Control

Moisture control and a defined strategy for dealing with moisture is very important with mass timber construction. Moisture on the site is unavoidable whether from rainfall, vapor and the equilibrium of moisture content of the timber once it arrives on site. These can have negative impacts on the wood materials and can result in:
Staining and dirt
Shrinking and swelling
Water damage from prolonged exposure.

Mass timber can get wet—and it will get wet on most projects. That is not a problem, provided an effective moisture management plan is in place.

2.2.1 Moisture protection plan

Planning a moisture management plan at an early stage is important. Techniques will vary depending on the location, and it is common for a moisture protection plan to be a requirement from the contractor. Expectations and responsibilities should be determined.

Figure 2.4 Typical moisture protection plan.

2.2.2 Applied protection

There are many types of applied protection. These can be in the form of plastic wrap to water-resistant and waterproof membranes, moisture resistant sealants, and coatings to minimize water absorption. Note that membranes can refer to a spray-applied product, sheet product (non or self-adhesive) or board/sheathing products. These can be applied on-site or in the factory.

2.2.3 Managing moisture on site

It is strongly advised to cover CLT that has been delivered to site in a staging area waiting to be installed. These temporary covers can be removed just before installation.
Panels that have been installed should be protected as much as possible from water ingress. This is more important for horizontal surfaces were water could stand, than for vertical surfaces. There are a number of protective covers, coatings and sealers that can be used but it is important to allow the timber to dry after it got wet. Covers may need to be removed and natural or mechanical ventilation will aid in drying.
ations and responsibilities should be determined.

Table 2.1 Production types and example products, source RDH Building Science.

2.3      Installation Process

Mass timber construction is unique in that it draws installation techniques from other construction types, making it a mix of skills found in timber framing, pre-cast concrete and tilt up construction, and steel installation. This makes it a relatively easy process to learn for tradesmen who have some of these skills.

2.3.1 Site Considerations

Each site will need to be considered for its own particular challenges but some basic requirements for all sites will be:
Review site conditions, including construction progress, access roads, perimeter control and security, and staging areas.
Determine what materials (e.g., anchor bolts, plates, angles, columns, beams, panels) require pre-installation work and ensure that all connection material is available.
Confirm that all equipment has been procured and deliveries scheduled.
Ensure an Operations health and safety plan is in place.

2.3.2 Equipment

The equipment required for installing CLT consists of typical carpentry tools and some specialized props and ratchet clamps. While the panels are designed and manufactured to fit together easily, there are occasionally site conditions which require panels to be altered.
When installing panels you will also need props and rachets clamps to position the panels correctly. Surprisingly a sledgehammer does come in useful to move panels that final few millimetres, just be careful not to damage the edges of the panels. It is advised to place a block of wood between the panel and the sledgehammer when knocking them.

Figure 2.5 CLT equipment.

2.3.3 Safety

Cross laminated timber panels are large and heavy items that are often lifted high overhead and installed at height. A detailed Health and Safety plan is essential.

  • Identify the risks and hazards
  • Determine who is at risk
  • Evaluate and protect
  • Record, plan and train
  • Review, review, review

It is very important for harnesses to be used when installing items at height as the panels can easily knock someone over when they are being moved.

Also key to safe and successful installation is to check all equipment, ensuring that straps are in good condition, tools have safe electrical connections, and installers are wearing the correct PPE.

Figure 2.6 CLT rigging.

2.3.4 Transport, Unloading and staging

CLT Panels are typically delivered to site on 8m, 13m or super link trucks. The CLT panels should be loaded on the truck in an order that is co-ordinated with the installation process. The less you can move the CLT panels the better, and ideally you want the panels to arrive just in time (JIT) for the installation. This JIT process will allow panels to be lifted directly from the delivery truck to the position in the building.

Figure 2.7 Transportation of CLT panels.

On certain projects the panels will need to be unloaded and stored on site in a staging area before they can be installed. In these cases it is important to make sure the panels are stored in an order that makes sense for the installation, and that they are kept dry and clean. They should also be covered to protect them from any bad weather.

Figure 2.8 Storage of CLT at construction site.

2.3.5 Rigging

Moving large mass timber elements is similar in principle to moving precast concrete or structural steelwork. There are similar techniques used to lift the elements, and include the use of rigging, slings and spreader bars. It is essential that experienced rigging teams are used to move the mass timber panels.
There are a number of material specific lifting devices used to lift mass timber elements, with the most common being:

– Drilled holes through panels with a lifting strap looped through.
– Lifting hooks
– Lifting plates

Mass timber differs from other materials in the wide variety proprietary and generalized hoisting devices and lifting anchors that can be used. This is because wood is relatively lightweight; mass timber buildings are approximately one fifth the weight of comparable concrete buildings. This is a benefit for overall construction but must be accounted for when planning hoisting operations. Construction sites are dynamic places and subject to every possible environmental effect. Understanding how a large mass timber panel will respond to a strong gust of wind (or other conditions) on a tight site—and planning for it is important.

Using tag lines is an easy way to prevent problems in the middle of a lift.

Figure 2.9 CLT rigging equipment.

Panels will require specific rigging depending on where they are situated in the building. Slabs are typically lifted horizontally and walls vertically.

2.4      Finish

Cross laminated timber is typically used as a ‘rough carpentry’ structural element. This implies that the material will be covered with some form of finishing material. On the external (weather) face of the building this is essential as the CLT is not meant to be exposed to the elements. Typically some form of cladding or a plastered finish is used.

Internally the CLT can be left exposed but this requires specifications of a visible surface during the design process. Panels will need to be finished and protected during the construction phase.

2.4.1 Protection during construction

The installer should be aware of potential risks that can damage the panels. While majority of this damage can be rectified quite easily, it is advisable to have plans in place to avoid any of these issues:
Water, mud, rust and other substances can all stain mass timber. Even hot-dipped galvanized nails can bleed metal stain as the coating is damaged when they are driven into the wood.

Unprotected elements may be vulnerable to dings and dents.

UV discoloration will occur to any wood exposed to the sun. There will likely be differences under flags, banners or signs hung during installation, but UV discoloration does fade over time.

Best practice also includes:

Adding a protective barrier to prevent water from pooling on the CLT. A hard covering (such as hard board) can also stop damage that may occur on floor slabs due to typical construction work.

Removing metal shavings and nails which can rust and stain the timber.

Make sure metal grinding is done away from the timber.

Painting a protective sealer onto the timber.

While these steps are not required it is normally cheaper and less time consuming to protect the timber rather then having to take corrective measures after the fact.

2.4.2 Cleaning mass timber

Some stains can be removed using simple methods and some may require assistance from a company that specializes in this work. The decision on how to proceed should be made with the Architect of Record and/or owner.

Options for removing stains include sanding, cleaning solutions and dry ice blasting. Cleaning solutions such as hydrogen peroxide, wood bleach or oxalic acid may require experimentation to determine the correct concentration and length of application. Consultation with the supplier or installer is always advisable. Note that there may be aesthetic implications beyond the member being corrected—e.g., a wood column that is freshly sanded toward the end of construction may be a different colour than one that has been exposed to UV for the duration of the job.

2.4.3 Applying finishes.

Finishes are often applied to exposed mass timber elements to maintain its appearance long term. Similar to prefabricated penetrations, shop- applied coatings are an option with many suppliers and can limit field work to minor touch- ups to repair dings and scrapes that occur during installation. However, some exposed applications will have multi-layer finishes that are applied
in the field. For detailed instructions, refer to the design requirements and manufacturer’s installation instructions.

Note that the heartwood of most softwood species contain tannins (which are water soluble) or pitches and resins (which are not water soluble) that can bleed through paint or stains, especially lighter colored shades. If painting or staining is specified, understanding the type of wood being used and paying special attention to exposed knots can avoid problems later. Proper surface preparation that leaves the wood dry and free of any dirt, oils or waxes will have a better final result.

Figure 2.10 CLT floor underlay protection.

2.5 Quiz 2

1. Name four important processes for correct CLT assembly and installation:
Field is required!
Field is required!

Congrats, you nailed it!

Try again.

3      CLT connections (Mark O’Connor)


This section introduces a few connection systems that are available to complement mass timber and CLT development. For more technical detail – visit Rothoblaas or any other specialised hardware supplier.

Figure 3.1 Rothoblaas Headquarters Building (20m high and fully automated), Italy. Specialist in CLT connections,

Figure 3.2 Angle brackets.

3.1      Angle Brackets

The WHT angle bracket is ideal for the construction of timber-to-concrete and timber-to-timber tensile joints for CLT panels and beams, framed structure, timber-based panels, LVL, solid timber and glulam.

TITAN PLATE C is the metal plate for shear loads that can be used for CLT panels and framed panels continuous connection to the substructure. It is ideal for making added stories and flat joints. In general, between elements in concrete or masonry and CLT panels. Also, for creating continuous shear connections.

TITAN S is the angle bracket for timber that guarantees exceptional shear and tensile strength values.
Angle brackets is ideal for making both timber-to-timber and timber-to-concrete joints for timber panels. It is typically used together with plate screws such as HBS Plate Screw.

Figure 3.3 Plate connectors.

3.2      Plate Connectors

TITAN PLATE T is the series of metal plates for shear forces that are ideal for creating timber-to-timber joints, such as flat connection of the timber platform beams to load-bearing timber panels.

SHARP METAL steel hooked plates have a multitude of small hooks spread all over the surface. The joint between the two timber elements is made by the mechanical engagement of the metal hooks in the timber. The system is non-invasive and can be uninstalled.

Figure 3.4 Slot connectors.

3.3      Slot Connectors

SLOT is a connector for structural panels that allows very high stiff joints and can transfer exceptional shear stresses between the panels.
Its ideal for walls and floors, as it is used to reconstitute monolithic panels of large dimensions, previously cut for transport needs.

Figure 3.5 CLT self-drilling screws,

3.4      Self Drilling Screws

Numerous specialised screws and fixings exist, that can be used to connect CLT panels or to install a range of CLT connectors – such as angle brackets or plate connectors.

Figure 3.6 Pillar connectors.

3.5      Pillar Connectors

PILLAR is the revolutionary connection system that allows to build structures with column-to-floor system that until now were impossible to build, with a distance between the columns up to 3.5 x 7.0 meters. It allows the transfer of more than 5000 kN of vertical force between the pillars.

Figure 3.7 Spider connectors.

3.6      Spider Connectors

The SPIDER connection and reinforcement system allows the construction of multi-storey buildings with column-to-floor structure.
Until now, these were impossible to build, with a distance between the columns of more than 7.0 x 7.0 meters of structural mesh. It allows to transfer more than 5000 kN of vertical force between the pillars.

Figure 3.8 XYLOFON profiles.

3.7      Soundproofing

High performance resilient profiles that ensures, acoustic comfort, in timber structures and houses, through its ability to solve the problem of structure-borne noise.

An example of such a profile is XYLOFON in the pictures above.

Figure 3.9 ALU START profiles.

3.8      Profiles

Profiles can be used for connections to the ground to transfer shear, tensile and compressive forces into the foundation. As example see the ALU START profile in the picture above.

The rise from the foundation and the use of aluminium ensure the support base protection against capillary rising damp.

3.9 Quiz 3

1. Name three different CLT connections:
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