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Ross Barrett

Ross Barrett is a project architect with HLM architects working Passivhaus designs for Scotland's Housing Expo. Here he shares an ongoing diary of the construction process.


May 5th, 2010

Through 11 sets of road works up the A9 we finally made it to site for our second site visit to find that the weather had been a little kinder to our team at O'Brien Properties and, with all of our concrete strip founds in place and two thirds of our sub-structure walls complete, we could start to appreciate the scale of our terrace and its relationship to some of the other units on adjacent plots.


For the sub-structure, we are using an Aerated concrete block to help significantly with our U-Values and thermal bridging.  A common concrete block wall would not have provided us with sufficiently low thermal conductivity or indeed a suitable fixing base for the wide prefabricated timber panels which need to be anchored down to resist the significant wind loads experienced on such an exposed site.  We did consider importing a unique German foundation system called 'Isoquick' which uses modular foam blocks to create a foam 'tub' into which the concrete slab can then be poured.  It was ideal for Passive House construction but we couldn't satisfy ourselves that it could deal with the stepped profile of our terrace or more importantly the significant wind loads it had to withstand.  We have however decided to do some more research into this product for our next Passive House project as it would minimise many of the cold bridging issues we have come across.  In the end we went for the best solution available in the wide format Aerated blocks although I don't think we've been the brickie's best friends!

Blockwork on Plots 11/12

Given the stringent standards for thermal performance in Passive House construction we have had to accurately model every junction to understand and predict the heat loss of the buildings accurately.  This was done in conjunction with the Scottish Passive House Centre using the Passive House Planning Package (PHPP) software, a widely accepted energy design tool for Passive Houses which is frequently updated with numerous years of experience from built Passive House projects.  The tool itself is fairly complex but helped us to look at every heat loss and heat gain associated with thermal conductivity, thermal bridging, air-tightness, ventilation, solar gains and internal gains.  PHPP very simply establishes a number of rules and conventions against which we can test our design.  For us it simplifies the design process and the route towards the eventual Passive House certification.  It's far more advanced and relevant than the current UK norm, the standard assessment procedure (SAP).


RTC have more or less finalised the manufacture of the timber frame panels with only the roof panels to complete and it looks like they will be ready for delivery within a few weeks.  Whilst we were on site RTC made the first delivery of their patented Passive Wall Plates which act as wall plates for their Passive Wall system and help achieve significant air tightness in the wall panels. We have talked about the lead in times on the window delivery and have decided that the timber frame openings will need to be covered sufficiently to allow some first fix works internally to proceed.  We also think we can also get the triple glazed roof lights in, the profiled roof sheeting on and some of the external wall cladding framing commenced before we absolutely need the windows and doors!


It looks like the block work will be complete this week with drainage in place by early next week and our insulation and concrete slab in place awaiting the Passive Wall panels by mid Month.


Progress varies around the site with most ground works underway and even some timber frames complete.

Passive Plate Delivery for Plots 11/12


Rural Design + James McQueen Builders - Plot 17


Andrew Black + William Gray Construction - Plot 4.2


Warmcell insulation being blown in on David Blaikie Architects Plot 4.3


Since our site visit however, the snow has returned and the site looks as though it's the middle of winter again.  We can't believe the impact the weather has had on this project this year but everyone's still confident everything will be ready in time!  I wonder if there's some snowmen being built just out of picture?!

The Snow Returns!

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