Hi. Need some help on this. I live on quite a slope. My house is lower and at ground level than my neighbours. They are thinking of having an extension on the rear of their house but as they are higher than us it will not be built on ground level. If you follow me, their house has steps of probably 1.5m from the rear of their back door to the ground. Do they need to apply for planning for this ? I'm really struggling with any info on elevated extension