I used a small braising torch and wire brush to burn off the Ivy remnants on my house and it worked very well. Obviously there is a lot of care and attention that needs to be taken using a flame but it is the best way to completely remove the stuff.
My house is a bungalow so I just needed steps but if your talking about a 2 story house it may be a bad idea for your situation. If your palster finish is quite rough as you say then chances are you will not notice any marks under the paint.
I found out that the exterior of the house is made from Terolene (sp?).
A friend has a small torch used for roofing that can be used on a ladder - only thing is I have PVC windows...is there a danger of window frames getting damaged by the heat?