We have been very fortunate with the weather this year. Lots of warm weather, dry weather, and even a mild autumn so far. However, there was a week at the end of July when it was very, very, wet. On the 25th, water started collecting around the Peerie Hoose, so S called our groundworks contractor who came and dug a dry well. This was a hole two metres wide on both sides and two metres deep, which was then filled with stones to give the water somewhere to drain. Sorted! Or so we thought…
To prevent moisture rising from the ground and up into our walls, it was necessary to lay a damp proof course (DPC) after a few layers of brick and stone. These days this is typically accomplished by using a plastic membrane, but as our materials brief stated:
We want to avoid synthetic materials wherever possible. The ideal house would biodegrade over a couple of hundred years of non-use.
We therefore went with one of the traditional methods of damp proofing which is to lay a double layer of slate (the second layer offset from the first and so covering the cracks between slate pieces). The slate we used is second-hand Welsh slate. As you can see in the final image below, after the DPC was laid, further courses of brick and stone were put on top to complete the plinth walls.
Our structural engineer specified MOT Type 1 Sub-Base aggregate for the foundations. It’s a highly-specified aggregate in terms of particle sizes with well understood compression rates and characteristics. While it may have been possible to get by with aggregate of a more random composition (for instance a 6F2), it was important that we were certain the foundations would work – obviously they can’t be changed later on and have a significant impact on whether the house stays up properly. By using Type 1 Sub-Base, our engineer was certain that the (very heavy) cob walls will be properly supported.