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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthordsewell
    • CommentTimeJun 17th 2017
    Hello all, just looking to see if anybody has any advice on reducing thermal bridges where steel columns are taken below ground level to foundation.

    We are building a new passivhaus and are trying to design a robust detail to reduce local thermal bridging for two columns. The main wall structure is a 215mm AAC block with 280mm EWI / Render. The floor is a 150mm slab on 300mm XPS. For the columns, our current design is to use a thermal break (farrat) where the column meets the foundation. Because this is all below ground, we will encase the column in c.100mm concrete to form a plinth, and the plinth will be painted with liquid dpc as with the other area of the wall. We are then planning to wrap the plinth in 100mm insulation up to the same level as the floor insulation to provide thermal continuity. See attached drawing.

    This feels like an ok solution. An alternative we are considering is to again use a thermal break but move the insulation in so that it wraps the steel with the plinth then around that. Again, with DPM etc around the plinth.

    In both cases, we will then RIW damp-proof products and apoxy mastic / similar around the column at the top of the plinth.

    Does anybody have any experience with either or the above suggested methods? Or, can anybody recommended other ways to reduce thermal bridging for columns below ground level?

    We obviously need a solution that can take the structural loads, but also needs to be robust to stop corrosion and condensation. Any tips / solutions that have worked would be greatly appreciated.

    Best regards,

      C1 column_Thermal break FINAL.jpg
    Hi dsewell, we've developed solutions to similar issues for the Passive Slab, I can email you some details. How many kN loading is coming down through the column?
    • CommentAuthordsewell
    • CommentTimeJun 18th 2017
    That would be fantastic. Thank you very much.

    * The higher of the two columns has an unfactored loading of 91Kn (131kn Factored).
    * The second column has 21.6Km and 31Kn unfactored and factored respectively.
    * The Tie Angle has no compressive loading (this is tension only).

    The foundations are existing, so we are looking for a solution that we can add to the foundations. And, obviously we need to ensure good corrosion prevention of the solution whilst designing out the cold bride. Any thing you are able to provide would be greatly appreciated.


    ''....we need to ensure good corrosion prevention of the solution whilst designing out the cold bride.''

    Summer wedding. You've chosen the right time of year.
    • CommentTimeJun 19th 2017 edited
    • CommentTimeJun 19th 2017
    Not really, one is steel columns, the other is timber.
    • CommentTimeJun 19th 2017
    But both about column bases which don't bridge the insulation
    Hi Dean, the 21kN load can be taken onto the thickened edge slab, the 91kN load needs more detailing, can it be spread out higher up and be taken down through a wall instead of a pillar? Another option may be to wrap the pillar in an AeroGel blanket and fill it with foam to stop convection currents.
      TwinStud Notation.jpg
    • CommentTimeJun 19th 2017
    There's no shortage of space. Why would you use aerogel?
    Posted By: djhThere's no shortage of space. Why would you use aerogel?
    Seems to be only 20mm between the pillar and the inner surface of the block but I suppose you could move the pillar towards the outside and wrap it in 50mm EPS.
    • CommentAuthordsewell
    • CommentTimeJun 20th 2017
    Thank you for comments so far.

    There are similarities between this and the other post suggested by fostertom, but as also stated there are differences as this is a steel dropping to trench foundations the other is timber to concrete pads.

    I think the main question is should we keep the insulation outside of the plinth (as shown) or bring internally to wrap the column up to the blue blocks (which are a continuous layer of Marmox Thermoblock)?
    Posted By: dsewellShould we keep the insulation outside of the plinth (as shown) or bring internally to wrap the column up to the blue blocks (which are a continuous layer of Marmox Thermoblock)?
    Or as I suggested earlier (but maybe it wasn't clear so I've attached an image) wrap the column completely where it comes up through the slab and all the way up til it meets the middle floor or roof. So it stays as a 15 degree element inside the wall but its no longer a condensation risk as its outside the airtight plaster layer. I suggested wrapping it in Aerogel because its a more concentrated form of insulation and useful for tricky areas like your pillar. Your detail shows the pillar coming from a 10 degree plinth into a 19 degree wall so it would probably show at 13 degrees at the skirting, wrapping it completely with Aerogel would improve the surface temperature at the skirting by about 5 degrees.

    I've built some Aircrete block Passive Houses in the past with mixed success, you have to wait til the plastering is complete to test them for airtightness and its too late to do anything about it at that stage. The blocks are hard to plaster and some walls cracked after building which didn't help matters. Its easy to fall between a rock and a hard patch which is a super-insulated house with an average air-tightness. You end up doubling the size of the heating system to keep the house warm when the wind blows. 20mm of extra EWI with a normal block we found was a simpler build with the same U-value. EWI houses we've built don't wear as well as cement board and block clad houses and often looked tatty after a few years.
      Aerogel pillar.jpeg
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