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.


  1. Hi Shay,

    Interesting review, always good to read about passive houses taking place in Ireland.
    It was interesting the client choosing the “U” shaped house, with most people sticking to the rectangular option.

    It will be interesting to see if this house will achieve the passive house standard. The architect states in this video, it is going to be difficult to get this house the passive standard.

    Also the first builder which was on site, John Walsh is building his first passive house which may be difficult to get right at the first attempt. (Most builders state it takes three attempts before they get the first attempt right) After he went out of business the clients completed the project by direct labour.

    One would have to question the experience of these tradesmen in situations like this.
    Also the like you say the blower door test result may and probably would have been different if the MHRV system had been in place.

    It seems that passive houses are becoming more and more popular in Ireland.

    Good work Shay,

  2. Shay,
    Having seen that particular episode of about the house I was interested to read your blog on the Holden’s project in Carlow.
    What stuck out to me from this case study was the importance of planning at the design stage of the project. You mentioned about the 6 week delay caused from certain parts of the MHRV not being certified. This could have been avoided if more research was carried out at the design stage.
    Planning is essential with Passive houses and further delays were caused due to the cold weather last winter. Blocks cannot be laid if temperatures are below 40C. The blockwork should have been constructed earlier in the year or else timber frame construction should have been used.
    The client wanted his home concrete built and a lot of people building houses in Ireland would have this attitude. I think timber frame is a very beneficial construction type in Ireland due to its fast construction in Ireland’s unpredictable weather.
    Good review Shay which gave a good insight into all aspects of the project.


  3. Just to correct a typo in my above comment blocks cannot be laid if temperatures are below 4 degrees Celsius not 40.


  4. Kevin,

    I think the fact that the blower door test is well under the maximum allowed for passive is a good sign. Although the main builder ceased trading it says in the video that good continuity was achieved in terms of workforce on site. This means that some original site operatives must have been hired individually after the builder ceased trading.


  5. Hi Shay,

    I was just wondering about the MHRV system, if initially it was'nt passive certified, why was it installed? Also the issue of the experience of the tradesmen as kevin mentioned, I wonder how experienced they were...

    Anyways great post, Its good to see that passive houses are up in coming in this country, especially for ouselves!!

    keep up the good work!!


  6. Shay

    intresting blog, intresting to see a U shaped house built also. timber frame is a faster to erect over concrete but with the builders experience unknown would it be achieved first time round and would it reach the passive standard.
    good work


  7. Undertaking the construction of a new home can be very intimidating right from the start.

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