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Paju 2

16-Storey Office Building Facade Elements

Paju 2 16-storey timber concrete hybrid building in the centre of Tartu, Estonia. The office building is a Energy Class A building (LEED Gold) and will be home to many IT startups and tech companies.

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Client Profile

The project was led by a main-contractor consortium Rand & Tuulberg and Ehitustrust. The project team was very experienced yet the use of timber and pre- fab panelized solutions was new.

Goals

  • Site Logistics — since there was little room for stor- age on site, prefabrication lightened the load for logistics management considerably
  • Building quality — since the building is a LEED Gold certificate, the vapour barrier connections and win- dow joints were extra important
  • Health and Safety — because the building is quite high, prefabrication and the assembly of all the win- dows in the factory ensured increased onsite safety

Challenges

Since to building has 16-storeys high and the site was in the city centre there was little space for manuver- ing so the logisitcs was very important. Two main challanges were the tolerance management and critical path alignment which are covered in more detail below.

Challenge 1

Tolerance Difference

The tolerance difference is one of the key issues, that need to be addressed when dealing with hybrid structures.

The tolerance of a Weinmann CNC machines and our elements is 1-2 mm. The tolerance of insitu concrete works is 20-30mm depending on the country specific norms and contractual customs.

Unfortunatelly the reality is that 50+mm tolerances are not uncommon with concrete works and correct- ing this issue onsite can be very time consuming if not even impossible.

Recommendation: Since the main contractor is organising the site work and handling the contractual oblications of subcontractors, it is imporatant that the different tolerances are effectively communicated to different parties. More often than not, the concrete guys are not paying attention to some key ma- surements because they are simply unaware of the importance. As offsite construction is gaining more popularity, we reccommend assigning a dedicated Tolerance Manager (at least for bigger projects)

Challenge 2

Critical Path Alignment

Besides the environmental aspect, timber has many other advantages. It is robust, easly available, the work skills as well as tools are relatively easy to learn and use. Yet like any other material, it also has disad- vantages and the risks associated with moisture is one of them.

When dealing with a bigger project like a highrise office building the Critical Path is of course the concrete structure.

On the Paju project the post and slab concrete floor took 10 days but the prefab facade panel assembly took only 1-2 days.

Starting too early with the assembly of timber prefab elements, might give a feeling of progress but leav- ing them exposed to the weather without actually creating real value for the whole project life cycle can be risky.

Important consideration points for your next hybrid project:

  1. The main contractor should communicate to the subcontractors about the risk of moisture damag- es (for instance the concrete subcontractor should not bring any unneccessary water in the structure etc.)
  2. The prefab elements assembly should start as late as possible without compromizing the critical path, especially if closing the envelope in stages does not really open possibilities for other trades to start.
  3. Protecting the elements in the different assembly stages should be handled with a separate plan and in case moisture damages happen, it should be handled urgently.
  4. Also important is to know that mold does not form instantly and when the problematic places are allowed to dry out, there should not be any problems. In case there is a risk, special chemicals can be used to eliminate the mold.

Extra

Possible Extra Credits for LEED or Breeam

Having a green certificate for your building is becom- ing more and more important. Paju 2 will have a LEED Gold certificate and the client is considering going for the Platinum Certification. Using prefab timber elements can give valuble extra points for the mea- surement. We are not talking of course about double digits but when trying to get from Gold to Platinum, literally every point counts.

We have identified two main areas for potential additional points with the offsite facade solution:

Waste management/Innovation

With prefabrication, components are built offsite in controlled environments. LEED credits are given for the amount of waste that is diverted from landfills at construction sites. Prefabricated units constructed off-site need to account for the waste that is reduced at the manufacturing facility also, to satisfy LEED requirements. If it can be proven that similar waste management practices are being employed at manu- facturing facilities, innovation points may be available (Kobet 2009)

Materials gategory — FSC/PEFC timber etc.

The materials and resources category deals with efficient use of material resources, including building, component, and material recycling and reuse (Gorge- lewski 2009). This research presents the thesis that prefabricated building components, when implemented correctly, should aid in obtaining the LEED credits that the materials and resources category offers.

Source: Using Prefabricated Building Components to Obtain LEED Credits, Dominic Adams, Anoop Sattine- ni, and Jacqueline Thompson

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Lauri Tuulberg
CEO

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With prefabrication, the sooner you involve an offsite construction specialist, the smoother and cost-effective the whole process will be.

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