Completed! Super energy efficient barn conversion
We were asked to survey this beautiful simple brick barn in late 2008 with the view to convert it into a family home.
The barn sits high on a north south axis with views down to fields and woods to the south and west. Built in the late 1800’s, the building was primarily used for storing straw and hay hence the unusually high eaves and narrow cross section. The layout and structure of the barn is simple but elegant, like many buildings of this era it is characterised by craftmanship. In particular, chamfered bricks have been used to detail all the external corners.
The plan is divided into three bays separated by two solid double skin brick walls, full height brick piers support the roof in the west bay. The barn is largely open to the north but has been filled in at different times to the south and east. The central bay housed a small two storey living space.
After completing the survey in early 2009 we were commissioned to develop a design to be submitted for planning permission. Our brief was to design a family home that is sensitive to the existing structure and surrounding agricultural area but forward thinking in approach and function. The key requirements of the client were to make full use of the incredible location and views to the south of the site and produce a highly energy efficient building.
Our aim was to maintain as many of the original external features as possible. You can see from the two plans the front door and windows are in the same position. We also felt that it was important to maintain the three bay rhythm to the layout, keeping the west bay open and making full use of the piers with full height glazing at both floors.
There is a fairly large amount of circulation space due to the narrow width of the barn, our intention was to open this out and allow many different views and spacial experiences as the user moves through the building or between floors. North facing roof lights have been positioned to allow better light into the bedrooms on the southern side.
Construction began on site in February 2010.
Although the existing barn walls were considered structurally sound they could not withstand the additional load of a second storey, so we designed a timber balloon frame to sit within the brick shell with a 50mm gap between the frame and the inside face of the brick. The new timber structure required some additional foundation support, which was achieved by pouring a reinforced slab into each bay of the barn. This initial ground work had to be done with enormous care so as not to undermine the existing brick foundations.
Initially Warmcell was specified to full fill the frame, however the brick
walls were more uneven than we had initially thought, in some places the 50mm gap between the frame and the brick wall was 300mm wide! So, to negate the risk of slumping the frame was full filled with rockwool insulation instead.
An 18 mm OSB board with taped seams was secured to the internal face of the frame to provide a moisture check and airtightness layer. 50mm polyurethane foam board insulation was then fixed to the inside face of the frame. A 25mm service void was then battened out from the insulation and finished with plasterboard and skim. The first floor was formed with TJI joists, supported by Kerto beams, very little steel was used in the build apart from to form lintels over new openings in the brick. As with all existing buildings it was important to respect the existing structure and accept that there would be some areas of thermal bridging and less insulation. We used the Passivehaus Planning Pack to inform the development of the design and materials specification. Overall the u-values are estimated to be 0.14 for the walls and floor and 0.10 for the roof, the annual heating demand is expected to be 24kW/m2.
Due to the high levels of airtightness mechanical ventilation and heat recovery or MVHR was installed throughout the building, this has been quite a learning curve for us as it is the first building of this scale that we have had such a system installed. Due to the size of the barn it was divided into two separate zones with an MVHR unit serving each. In addition the system features a summertime heat recovery bypass, this was vital to this project because of the large amount of south facing glazing. The units are housed in the roof space above the family bathroom, this is the only room at first floor with a flat ceiling.
Underfloor heating was installed throughout the building, we initially specified an air source heat pump as the primary heat source, supplemented by 2m2 of solar thermal. This system was chosen because of the low annual heating demand and the high levels of airtightness and insulation.
However, due to complications with EDF it became a logistical nightmare to get the air source heat pump connected so we opted for an LPG boiler with Solar thermal feed.
A rainwater harvesting system feeds the toilets and waste water is treated by a WPL Diamond system.
A number of different designs and systems were considered for the windows. Windows and doors are inherent weak points in the insulation and airtightness and it was important to ensure that the windows did not compromise the overall performance of the building.
In the end the windows were fabricated by a local joiner, who produced a high quality hard wood frame with double seals, argon filled double glazing was then installed into the frames on site.
Aesthetics and Finishes :
Externally the finish varies between brick and timber cladding. It is punctuated by intermittent glazing to the east and north which develops into full height glazed panels to the south and west. The window reveals are finished with render to match the brickwork in keeping with the agricultural history of the barn. A low brick wall runs along the north face of the East and West bays which is finished with lead detailing.
Internally the building is finished to a high standard. At ground floor the existing brick walls divide the space and lead the inhabitants through a series of different spaces, from the large open living room to the west through to the snug tucked away in the north east corner.
At first floor the ceiling runs up to the exposed ridge beam, this is an indulgent feature and allows a sense of space and height. The master bedroom sits above the living room with views out to the north, west and south. In the remaining rooms the views are framed by carefully placed windows.
… and finally :
This is the first completed domestic building that we have designed using the Passivhaus Planning Pack and it has been a huge learning curve for us as a practice. We have experienced first hand the changes that need to be made to the standard practice of construction in order to achieve airtightness and super insulation, fortunately our contractor had experience in this area and understood the importance of maintaining these standards throughout the entire build.