Can loft insulation be used in cavities?
You will have difficulty placing it in the cavities owing to (hopefully) the presence of wall ties. Using the wrong insulation can cause damage to the older galvanised types of ties btw and then you are in trouble – and it will not be very effective if it holds moisture. You could use the additional in your loft on top of what you have got – warm air rises and the most effective place to put it is there. You should be able to calculate the U value. I would be looking for a bit of a vaopour barrier somewhere in this loft to avoid any risk of interstitial condensation.
