Wednesday, 7 December 2011

Blog Assignment no. 2 - Passive House construction in Carlow


The construction of this farmhouse style building commenced in 2010 in Tullow, Co.Carlow. The house was featured on RTE's program About the house on November 29th 2011 .
First and foremost, the clients wanted a beautifully designed home and if possible, that it be built to a passive standard to achieve low energy costs and avoid dependence on fossil fuels in the future.

House Details

The house plan ( 298m2 floor area) was U shaped with traditional farmhouse features. The client's preference was blockwork construction as they felt the area was windswept and open and that blockwork gave them better solidity than timber framed construction.

The foundation: On top of concrete ground beams, 400mm of insulation was laid under the concrete raft foundation. This separation of the wall from the ground eliminated thermal bridges.

The external walls: The external wall was made up of outer and inner blockwork leafs with a 300mm cavity. This cavity was filled with bonded polystyrene bead insulation. The outer blockwork received a breathable render while internally, an air tight plaster with a service cavity filled with insulation avoided the thermal envelope being disturbed. The wall ties were made from basalt as it has a low thermal conductivity. The U value achieved for the wall was 0.1W/m2K.

The windows: A-Rated passive standard windows including three seals on the window frame were used. Plywood boxes were attached to the internal blockwork allowing the windows to sit in the cavity area, which is the optimum position for a window in a passive house.

Air tightness: This was achieved by attaching an air tight membrane to the ceilings which formed a sealed envelope with plastered internal walls and floors. The passive standard three seal windows and attention to air tightness at joints around windows and doors meant that the result from the blower door test was 0.25 airchanges per hour which is well below the maximum level for certification of 0.6.
Below is a video of a typical blower door test.


There were several delays on the project - The MHRV system design initially wasn't certified, the harsh winter of 2010 meant construction came to a standstill and then the builder ceased trading. Building with a timber frame method of construction would have sped things up somewhat as components can be prefabricated (e.g. wall sections) and erected even in very cold weather.

I thought it was interesting to note that the MHRV system was installed after the blower door test and that there was no air test done on the pipework afterwards (the program didn't say this anyway). In our talk from David McHugh from pro air he told me that they usually expose the pipework to the blower door test to check for any leaks.

Other interesting information from the program was given by Jeff Colley of Construct Ireland (the only magazine dedicated to sustainable construction in Ireland).  He informed the viewers that:
  • FAS have commenced the world's first passive house training course for craftsmen
  • Ireland has the third highest number of certified passive house designers in the world
I think that this is some good publicity at last for the construction industry here instead of the culture we saw between 2000 and 2006, where the emphasis was on quantity and speed with quality losing out.


The client's are currently trying to complete the project by direct labour and have managed to maintain continuity in terms of craftsmen. The house is only nearing the end of its construction due to the delays that I mentioned earlier but I would be surprised after seeing the attention to detail in the construction methods if the house is not certified to a passive standard.