Re-locating from London to the countryside is always challenging, especially when you aim to find a house which has good thermal comfort and is energy efficient along with the right location.
Marlen and Tony Godwin initial research was not very successful, therefore they eventually decided to buy a plot near their son school and to design their house with a minimalistic design and their specifications.
The location of the new house is Whitwell village in Rutland, a thriving village with a strong sense of community and a distinctive architectural appereance.
The brief was for a home with 3 bedrooms for the family, an additional guest bedroom and bathroom to host relatives and a working space as they both work remotely. They wanted the highest standard of energy efficiency and sustainability. When Tony walked into the Ecobuild exhibition in 2008 it was the first moment he started to hear about Passivhaus standard and its benefits and later on he became an enthusiast of the approach.
However, it was clear that achieving the standard with the proposed design of the house, was not easy and it would have involved more costs. As result the design was changed to aim for a more compact form with a lower form factor and South glazing rather than the inital North glazing orientation. Once the new design was ready, it was submitted for planning approval a second time. This was a lesson learnt from Tony, the owner as well as the architect of this house: Passivhaus principles had to be integrated in the design from the concept stage in order to make it cost effective.
The proposal for the house was on a slope with varied levels, which posed a few challenges as per envelope detailing, continuity of the insulation layer and the airtightness membrane, all very important requirements of a Passivhaus design.
Additionally, the plot was located within a conservation area, which required considerations as per the integration of the house within the surrounding area of farm type buildings with vernacular features and limestone facades. Hence, a quite compact design with limestone facade and pitched roof in line with the village appearance.
The external walls are of three types of superinsulated timber framed construction with 300 mm warmcel insulation between studs, with the main facade externally cladded with 110 mm Clipsham limestone. With this build-up the walls achieve an impressive U value as low as 0.099 W/m2K.
Warmcel is Recycled newspaper cellulose fibre with high levels of airtightness and good thermal confcuctivity in the range of 0.040 W/mK. It is characterized by a very low carbon footprint being the carbon sequestered into the building fabric
Ground Floor Strategy
The ground floor solution involves an exposed concrete slab sitting on the EPS insulation layer which insulates the floor from the outside. The exposed concrete floor provides themal mass which can absorb heat and store for longer.
The Roof Strategy
The main roof is a vaulted truss insulated with 550 mm glass mineral wool and a service void in the inner side. This robust strategy allows to achieve a U value as low as 0.074 W/m2K, which is quite impressive and indicates that the fabric has been pushed to the highest standard of energy efficiency.
The owners noted that the windows thermal bridging detailing and installation were critical especially for the ’tilt &lift’ and ‘slide’ windows, which are difficult to make totally airtight. As a matter of fact, after moving into the house, in very windy days the temperatures are slightly lower in the living room where the two sliding glazed doors were installed.
To reduce the overheating risk particularly in the South exposed rooms, the strategy involved the use of external aluminium horizontal louvres with electric control connected to sunlight sensors. Thanks to these, the results of the PHPP (passivhaus planning package software) assessed an overheating risk largely within the range of acceptance for Passivhaus, which allows for maximum 10% of yearly temperature above 25 degrees.
Another interesting fact is that the owners assessed that when the blinds are on, the maximum potential temperature achieved is 26 degrees and only for a few days per year, so it looks like the shading strategy is effective in mitigating peak temperatures.
Services wise the choice was of a standard condensing boiler connected to radiators nd towel rails with thermostat. The owners leave the boiler programmer mainly on at all times as they assessed it is more cost effective than having it turning on and off to reach the required comfort temperature.
Interestingly, the owners of Whitwell house commented that being accustomed to living in such comfortable home, they become more sensitive and demanding with the performance of buildings in general, could this be one of the downside of being ‘spoiled’ by the Passivhaus approach?
Passivhaus Issue 25 UK edition, Slope and Glory, pag 30-39