The Rectory for St James the Less, Penicuik was built in 1963, from a Canadian timber kit, but without any of the insulation you might expect from a Canadian timber house!
The walls were constructed of one internal layer of plasterboard, some retrospectively added blown paper insulation in a 50mm gap, with external board and a mixture of timber weatherboard and shingles, to ward off the elements. The Rectory is at 200m above sea level, and definitely above the snow line.
The challenge was to design a system to insulate the Rectory which was compounded by the fact that the vertical struts in the external walls were just about suitable for the existing load. Our architect (Euan Millar of Icosis) came up with a scheme, to apply insulation to the outside of the external walls, rather than reduce the internal dimensions of the rooms by putting the insulation on the inside.
The specification requested the use of insulation products that were of natural materials rather than predominantly chemical formulae, to be kinder to the environment and aid a healthy environment in the Rectory. Also, using natural materials would store carbon in the insulating material.
After competitive tender, the contract was awarded to RPO Joinery. It took five weeks to complete the main aspects of the work:
- taking off the old weatherboards (these were sent to a timber recycling facility);
- removing the blown paper ‘insulation’;
- adding new battens;
- fitting the first layer of insulation (Steico 60mm Flexible wood fibre);
- applying a breathable membrane;
- fitting a second layer of insultation (Steico 100mm Flexible wood fibre board);
- applying a second membrane;
- applying new battens and finally fitting new weatherboards.
All that remains to be done is to apply a protective layer of Osmo Wood Oil to the wood and replace a badly fitting external door to the side of the Rectory.
For the technically minded the Rectory’s U value prior to the work being undertaken was at least three times worse than the current building regulations, and now the U value of the walls is better than 0.24 (the thermal insulation properties of the two layers of insulation).
Current building regulations require a new build to have a external walls with a U value of 0.18. The solution has got us as close to that specification as possible given the constraints of the original construction of the Rectory.
Whereas before the work commenced the use of the dining room and living room was curtailed during the winter because the costs of heating it were too great and it took a long while to heat up yet quickly cooled down, now these rooms can be utilised.
Also, the study, kitchen, bathroom and main bedroom which were the rooms normally heated now remain warm for much of the day on a lower thermostatic radiator valve setting. These rooms also maintain their temperature for far longer once the target temperature is reached.
It will be interesting to see how much energy is saved by this insulation work. What I can attest to is that it is a much more pleasant home to live and work in, and will be a great asset to the church going forward.
This work could not have been completed without the grateful financial support of the Benefact Trust and the Scottish Episcopal Church.
Rev Nick Bowry, Rector of St James the Less, Penicuik
