I wrote to CIGA explaining that the 25 year guarantee certificate does not mention anything about the how having a cavity full of wool changes the mode of failure in terms of water ingress compared ot the original empty cavity. It's a well accepted fact that cavity walls were designed to keep the water away from the inner leaf and problems arise when anything other than air sits in the cavity providing a bridge that could result in water ingress. If you have cracks in the render then it may cause some water to enter to the inner surface of the external wall just as with wind driven rain. However the presence of insulation material can lead to bridging and penetration into the inner leaf, particularly if it there are gaps.  In the case of wool it can become saturated and never dry out leading to an obvious damp mass which readily transfers to the inner leaf. I argue that with cavity full of wool, the mode of failure when presented with severe weather, or cracks in the mortar is c...

While awaiting the CIGA inspector number 2. I thought I would try to grow some microherbs on the wool, since my tests have shown that it seems to hold water from evaporating rather well. Rock wool is used in hydroponics because the structure can hold large amounts of water and air for developing roots and provided a good 3d structure to support them. For simple cress, it works marvellously. With just one initial watering of the insulation the cress was able to grow and complete it's life cycle on a 30degree day. From what I understand rock wool for hydroponics has been treated to bring the pH to a foliage friendly range. Not sure about glass wool. Egg and cress roll anyone?