4 February 2011

AECB London at Temple Yard

ATA hosted the AECB London group's first gathering of the year at their offices in Temple Yard this Wednesday. The theme was 'delicious details', and a great turn out of about 30 people stretched our drinks and nibbles to the limit, but kept our meeting room toasty warm with all the watts we were collectively emitting!

Many thanks to all who attended and contributed to the debate.

Click below for a summary of the evening, please feel free to comment below, and see you at the next AECB london meet....

Cavity Conundrums
Fran Bradshaw of ATA kicked the evenings discussion off presenting the construction detail issue of how to address the positioning of windows in super-wide cavity walls, whilst still aiming to bring in light by tapering reveals - the detail is from a housing project about to go on site in West Hendon.

Discussion from the room touched on topics which included:

  • Bill Butcher's ply box detail at Denby Dale
  • Durability of ply box in terms of moisture protection
  • AECB member site experience of building in ply frames on site - retrofitting preferred
  • Ideal location of window within cavity
  • Cold bridging possibilities of steel window brackets
  • Reducing cavity size using rigid insulation (ATA policy not to specify phenolic foam)
  • Development of resin wall ties
  • Window head position at ceiling level to give better quality of light
  • Advantages of increased thermal mass to thin-joint internal blockwork cavity with 18mm lime plaster finish
  • Concerns of wind-driven moisture into mineral wool cavities
  • Moisture in : Moisture out! (i'll be using this in the future!)

Sit Lightly
Jon Broom then presented his thoughtfully simple detailed Green Homes for Green Oak Housing Ass. Screw piles foundations and no ground beams meant that the foundations of these 2-storey houses were minimised, and saved a truck load of concrete being poured into the earth.  PVC, and now cement has been eradicated from the build.
The build was designed and detailed so as to be packaged into simplified phases. The roofline was also the insulation line, so room-in-the-roof could be taken advantage of for additional storage.

The first floor structure was open web joists supported on the ground floor walls, but Jon commented that this created a fiddly air-tight detail to wrap the membrane around the first floor joist, so a simpler revision would be a balloon frame shell to the house with the first floor hung from this to allow the membrane to carry straight up.
The open joists also allow services to be taken through the void, so no service penetrations are needed in the roof or ground floor.

Jon warned against over-engineered timber design as he'd experienced form the timber frame company on the project, with the addition of timber members that create unwanted thermal bridging.

Insulate Right
Next up was Tanya, an AECB member and psychologist, with her proposal to externally insulate her solid-walled house, and the issues of connected to a new external porch.
There was great contributions  from the group on the importance of choosing the insulation materials with the right properties to deal with existing moisture within the walls (the house has been heated using LPG oil, so potential for alot of moisture).
External woodfibre (Heraklith, Pavatex & Udi boards were all mentioned) and breathable render systems were proposed, along with removing internal gypsum plaster and applying internal natural fibre insulations (a product called Woolcool was mentioned) that can absorb and release moisture and heat.
Also seen as very important was removing the external cement render as a barrier to letting the wall breathe.
There was concern amongst the group that External Wall Insulation companies were not addressing issues of moisture and future fabric problems, instead just wanting to sell a product.

'Almost' Passivhaus
Last up was Ralph Swallow of Fluid Structures, who had brought along a 3-storey scheme in development for student housing that the university client requires to be a flagship low energy scheme, with energy demand targets near, but above passivhaus standard.
Ralph was at the important stage of deciding which structural route to take - cavity wall, concrete frame, solid timber, etc. The project has not yet gone for planning.

Discussion centred around whether going just above passivhaus was wise, as the additional heating system, etc. required would be an additional cost and not an economical move to make.
The use of modelling the building in the passsivhaus planning package PHPP seemed vital to produce a truly coherent low energy project.

Ralph was concerned about the depth of the wall construction to reach U-values of 0.1 W/m2K - the passivhaus institute recommends that your wall depth should be no more than 450-500mm, as going over this depth is expensive and shouldn't be required if the building has been designed correctly in PHPP.
Modelling the building in PHPP may also affect thoughts of the orientation of the building so that living area faces South rather than North.

Examples of built Passivhaus student accommodation were also raised, designed by the belgian passivhaus architect (Sebastian Moreno?).

1 comment:

  1. Looks like a great evening I wish I could have been there. The issues with externally insulating and wall thickness came up at Neil Mays talk to the AECB group in Brighton this week.

    Jo Saady