The last few weeks have been pretty frenetic with some good and some less great results. On the plus side, the ground works are now done (yay!) and, as the TV says, “you can’t really plan until you are out of the ground”. Another big relief is Storm Eunice seems to have let us off with the site remaining intact. Getting to this point has not been without some challenges on the energy standard front though.
As mentioned previously we are building to the EnerPhit standard which allows us to have a total heating demand of no more than 25kW hours per m2 per year. This is calculated using fiendishly complicated software which models the energy performance of the house down to minute detail. Every little change has an impact. For example, a thicker window frame will reduce the amount of solar gain you get through the window and therefore increase our heating bill over the year. To give us a margin of error our original design included a healthy ‘energy buffer’ and predicted our overall demand of around 21kWh/m2/year so well within the standard. Then the build started.
As the design was tweaked to reflect changes on the ground, modelled performance of the building also changes and the results of the energy model fluctuate. This became a significant problem with the isoquick raft for the Stone Barn slab. Unfortunately what no one knew, was that the old stone wall we are keeping was considerably wider at the base, this fact alas hidden underground. Digging the foundations revealed we couldn’t get the insulation as close to the wall as planned – not a huge problem we thought, the internal wall will just come in slightly. Unfortunately this has the effect of slightly reducing the internal volume of the house and therefore increasing the relative heating demand for the available space in the energy model putting us above the Enerphitt standard!
Fortunately things like this are apparently normal and the model always bounces up and down. Even better for us the Architects sensibly don’t tell us every time there’s a fluctuation and this one has now been sorted with a change in internal insulation to a higher performing and cheaper (hurrah!) product.
Our energy buffer is back in the model and all is good. Until the next time …