PART 1 – RENOVATE OR REBUILD?
Late in 2016 we were approached by client’s who had just bought a typical 1970’s 2 storey semi-detached house in North Kildare. Their initial thoughts were that they would like to modernise and do a deep energy up-grade before moving in. Our discussions soon moved to “Passive House Retrofit” which is a really high standard of energy performance certified by the Passive House Institute in Germany. Everything about the building made it unsuitable to be renovated to this very high standard and so after much toing and froing we decided that the best option would be to knock the building all the way back to its foundations and start again.
Normally a new build is no problem but in this case, we had the small matter of it being a semi-detached house and also the client’s requirements for it to be to the Passive Standard. The house was originally about 100M2 in size and as part of the process, permission was granted for a large 2 storey extension to both the side and rear elevations, bring it to about 170M2 in size. With all that was involved in the planning application, re-design and layouts it wasn’t until May 2017 that the work on site began and the first task to be undertaken was to knock the original house without any disturbance to the attached neighbouring house.
The original house was your typical three up and two down layout with small sized rooms and lots of doors. The layout for the new house would be open plan with four bedrooms upstairs, a spacious dining room and a kitchen/living room which is more than 60M2 in size and south facing. By the end of June 2017, the old house was completely knocked with no disturbance to the neighbour, other than noise and dust, then work on the new build commenced in earnest.
TO BE CONTINUED……
PART 2 – THE PASSIVE RETROFIT STANDARD
As previously stated, we had decided to build the new house to the Passive House Retrofit Standard and now came the time to make all the decisions on how to deal with things like, insulation, air-tightness, thermal bridges, ventilation, quality of windows, type of heating and many more. Luckily the Passive House Institute publish very detailed guidelines on how to meet their standard but we still had to make the final decisions on the materials to use and most importantly, make sure they were fitted or installed correctly so that we not only met the rigorous standard but also got the benefits of its aim.
The overall aim of the passive standard is to build the house to such a high standard of energy performance that the annual costs for heating, cooling and ventilation will be very low. Although the passive standard and the Building Energy Rating (BER) scheme in Irish Building Regulations are not the same, we can loosely say that a passive house would have a better energy performance than a house that was rated A1 in the BER scheme. In real terms, we would have to achieve a performance of less than 25Kw/M2 per year for primary energy use and in our case, that means a maximum of 4,250Kw of energy could be used or we would not meet the standard. In monetary terms, we were planning to spend no more than €400 per year on primary energy costs. In addition to the benefits of low energy costs it is also worth stating that two other aims of the passive standard are that the house will have a year-round temperature of 20 degrees Celsius and it would have a guaranteed supply of managed fresh air.
Before we commenced rebuilding in July 2017 we had to make decisions on some of the important elements like, how to insulate, achieve air-tightness, eliminate thermal bridges and where to locate the services. We opted for block-work walls and 150mm of external insulation which would help greatly in the effort to eliminate thermal bridges. On the insides of the external walls and ceilings we would add a small amount of extra insulation, a battened area for first-fix services, an airtight layer using a breathable membrane and finally the plasterboard and skimcoat. We also made many of the decisions on location of services and most importantly the position of the windows and doors in the insulated layer.
With these decisions made, rebuilding began and within weeks the external walls were up to wall plate level, the roof was then rebuilt but this time we used an external breathable membrane under the tiles instead of the problematic bituminous felt used on most roofs. High performance insulation was placed between the rafters and it is intended that an additional layer of insulation will be fitted to the underside of the rafters at a later stage of construction. The attic area will be used as a guest bedroom or home office so we designed for a warm attic and all insulation and airtightness was fitted at rafter level. To help with day-lighting, high energy performing windows were fitted on the south facing slope of the roof. At time of writing this element of the article, the roof, internal floors, and all the structural elements were completed. The building is also watertight and ready for internal first-fixing.
TO BE CONTINUED……