Hi, slayer,
Is the pebbledash old or new? If it's new, it may be just drying out. The crack can be filled with sand/cement and made to match the rest with a few small pebbles if need. If it's old, then it could be a problem. Trouble is with pebble dash, like all external wall coatings, it covers up all sorts of problems in the brickwork. It could be subsidence where the foundations are moving, partciularly if your house is on a clay subsoil which has dried out through lack of rain or swollen due to too much water. This could be due to a large tree that's been taken down near your house. A large tree can drink gallons of water each day. If the tree has gone, then the ground can have too much water that has nowhere to go. It sits in the ground making it swell and causing cracks in your wall. You haven't been doing any alterations inside where you've taken walls down, have you? You have to be careful here as taking the wrong wall down could cause problems. Any building work going on nearby creating vibrations in the ground? If you have a clay subsoil, then a small crack is allowable due to seasonal movement of the clay. The crack generally opens in the summer when the clay is dry then closes in the winter when the clay is wet and swells. It's a question of degree. A crack of up to about 5mm may be acceptable in this situation. I would suggest calling in a building surveyor who will probably fix what's called a telltale across the crack. It may be a small bit of glass stuck to the wall which he will watch over a week or two to see if it cracks. This will tell him if the crack is getting bigger. Sometimes a small gauge is fixed which will show the degree of movement. If the crack widens and increases in length, then there could be serious problems. Get someone in soon to have it looked at before it gets worse and possibly more expensive to repair.
Denis Langley, April 2011
