Concrete Slab Insulation

Schöck and Waterman meet structural challenges at NEO Bankside

Southwark has experienced significant regeneration in recent decades, with Bankside in particular home to such iconic developments as the Tate Modern, Shakespeare's Globe and the Millennium Bridge.   This year sees a new neighbour on the block, NEO Bankside.  This stunning 1.5 acre development of luxury apartments, penthouses and retail units, will provide 229 residential units in five separate buildings that range from six to 24 storeys.    The apartments vary in size from studios and one-bedroom to four-bedroom units, with larger duplex unit penthouses.  These are designed as independent pavilion structures and double-height living areas are made possible by the sloping roof plane.  Winter gardens are an additional feature, creating a ‘prow’ effect at the north and south end of each building.   Waterman is providing structural engineering and environmental consultancy on the project, which has been designed by project architect, Rogers Stirk Harbour + Partners (RSHP).    On this occasion it was Waterman who developed the structural system and final geometry, which comprises external stability bracing arranged on a six-storey staggered dia-grid.   Each building comprises a concrete frame of columns and flat slabs, but the frames are stabilised to resist lateral forces by a perimeter bracing system positioned just out-board of the cladding. For aesthetics, individual bracing members are steel oval-hollow sections, which actually provide greater structural efficiency under certain critical loading conditions. The bracing has a dual function, not only resisting lateral building loads but also supporting the triangular winter-gardens via a series of apex ‘nodes’. The entire construction presented significant structural challenges and this extended to the serious demands made on the requirement for protection against thermal bridging.  This is where Schöck Ltd played a major part with its Isokorb® thermal break modules. The modules offer outstanding thermal insulation properties and dramatically reduce thermal energy loss in connective areas by guaranteeing the homogeneity of the thermal envelope between cantilever structures and the internal slab.   They also transfer load and maintain full structural integrity, while at the same time enabling inner surface area temperatures to remain well in excess of those likely to cause mould formation and condensation.    For the NEO Bankside project, various configurations of the type K Isokorb®, for concrete-to-concrete construction were incorporated, plus the type KST. This is usually a steel-to-steel connection, but has been adapted on this occasion for concrete-to-steel connectivity.  The two main structural challenges involved the winter gardens and the level above, the penthouse mezzanine winter gardens. The winter gardens are triangular spaces between the columns and the hangers, which support the points at both ends of the building. These are essentially outside spaces, so the slab requires a thermal break between the winter gardens and the main slab.  Also, the hangers are not fire protected, so in the event of a fire, the winter garden slabs will need to safely cantilever from the rest of the building.  This meant the Schöck technical team had to resolve two load cases. In the first instance, where the winter gardens are supported by the hangers, this was relatively simple as only shear forces are involved and the standard type Q Isokorb® meets this requirement.   Structurally more challenging was the second load case.   Should a fire destroy the hangers, and as a consequence turn the winter garden slabs into cantilevers, then a high bending moment as well as shear force would result.  To meet this challenge Schöck designed and supplied bespoke thermal break connectors with a moment capacity of up to 200kNm/m.   It was also clear that the fire strategy would require the Isokorbs to provide two hour fire protection and to achieve this Schöck incorporated the patented HPC thrust bearing block into the units. The penthouse mezzanine winter gardens, which sit at the next level up, are steel structures with beams connected to the reinforced concrete slab.  Conventionally the Schöck Isokorb® type KS, for concrete-to-steel, would be used in this situation, but the high forces acting at the connection meant that an adapted KST (for steel-to-steel connectivity) was the chosen solution.    This involved the KST units being bolted to an endplate and then cast into the concrete. Schöck Isokorb® modules offer designers and engineers complete peace of mind, as all units meet full compliance with the relevant UK building regulations. The requirement described in BRE IP1/06 – a document cited in Building Regulations Approved Documents Part L1 and L2 and Section 6 in Scotland – that the temperature factor used to indicate condensation risk (fRSI) must be greater than, or equal, to 0.75 for dwellings and residential buildings, is easily met by incorporating the Isokorb®. There is also compliance with the Government Standard Assessment Procedure, SAP 2009, concerning CO2 emissions from buildings, and respectively heat losses through non-repeating thermal bridges. Here, the lambda values of the Schöck Isokorb® enables energy loss through balconies, canopies and other cantilever parts of buildings to be reduced by as much as 84% to 91%. A 20 page ‘Specifiers Handbook‘ is available which provides an overview and introduction to the Schöck Isokorb®., and there is a comprehensive 236 page ‘Technical Guide’ which displays in detail the complete range of thermal break applications for all construction types – concrete-to-concrete, concrete-to-steel, steel-to-steel and concrete-to-timber.

Insulation over a concrete slab on grade - DoItYourself.com ...

I'm converting my detached 20'x23' garage into a studio apartment (with permits for everything). It was built in the 1930's. My contractor is suggesting that we put a 6mil vapor barrier on the old 4" concrete slab, followed by 2x6's on-edge, then fill the cavities with R-21 kraft covered insulation batts and then plywood subfloor over that. The local city inspector says this will be fine. Also, the footprint of the building is being extended about 2 feet beyond the old concrete slab (in other words, the wall where the original garage door was is going to be 2' further out). He has poured a new foundation wall at that point but he wants to just leave the interior floor area with dirt and put 6 mil plastic over that section before installing his floor joists. You do not want to use kraft faced batts with plastic already down. The plastic is the vapor barrier and the kraft faced would add a second one. You never want two vapor barriers. That will result in trapped vapor. Plastic vapor barriers seems to be the common way to seal out moisture in crawl spaces with dirt floors. I don't see a problem with it. Make sure the plastic is sealed against the walls with acoustic sealant. Don't forget the seams as well. I thought there needed to be airspace underneath a floor but if I do it the way the contractor is suggesting, then it will be almost completely filled with fiberglass. He was telling me that "slab on grade" foundations don't have any airspace under the floor. I think they do usually have rigid foam boards put under the concrete though but as this is an existing old garage, we can't do that so we have to put insulation over the concrete instead. Its just hard to imagine that a thin sheet of 6 mil plastic will forever keep moisture out of that space. It will, of course, be overlapped ten inches or so and wrapped up the several inch foundation wall but it would be unreasonable to think it won't have holes or mice & insects chewing it or something in the future. Maybe the plastic will just degrade over time. I would think the overlaps would allow a bit of moisture inside the flooring joists. There won't be any ventilation of any kind so, if moisture ever does get inside, I would think its certainly going to create mildew issues.

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