we have damp patches appearing in random patches on roughcast - lot of snow in gutters in dec &the guttering and facias are fairly new - no probs previously

You may have had some slight cracks, previous to this winter, which may not have been noticable, with the zero temperatures we had water etc has got behind it froze and expanded, causing your render to blow. Get ladder up and if it sounds hollow when you tap it, hack it of and rerender, we normally use a sbr slurry before render/roughcast. Wait till good weather you dont really want to be doing this if any chance of frost.

Any moisture content behind render is bad news. It will freeze and expand and in turn "blow" or de laminate the render coat from the brick work. It can also quite easily enter into the internal walls of the house using rubble cought up in the cavity to wick across into the internal finishes. This is in the latter stages and when un checked. It would be a good idea to inspect the render fully to find any sign of it be de laminated or blown, and as already mentioned it will sound hollow. These areas will most definitly need removing. It is best not to assume any area's that don't seem too bad as not posing a problem, water has a habit of going places we assume it wouldn't. Remember, patching render or cast coats is a skilled art, unless you require blindingly obvious repairs and bright patches of paint etc. It would be a good opportunity to see the render as a job in it's entirity. An opportunity to repair, and restore. If it's done properly it was last forever, if kept in maintenance. Hire someone who is a specialist to patch in the render, and use a very high end external weather proof paint, and don't be shy with the coats. If the tin says 2 coats, give it four!! you may be maintenance free for ten years after this, with it only needing a spruce every now and then. Good luck

water is obviously penetrating somewhere ,any cracks visible,fix as soon as possible as this will extend and start to blow off wall