[gerdesj]

I'm a bit wary about filling the external wall with polystyrene balls or whatever. I need to determine whether there are enough brick ties installed and that they are working. Brick ties are basically bits of heavy wire that should be laid in the mortar that hold the two rows of bricks together.

The idea of filling the cavities of a fairly old brick built building with some form of insulation is sound but does need care. In the UK (and elsewhere too) we generally go for "sticks and bricks" construction. The external "box" is often a double skin of brickwork. My house is roughly six meters by 12 meters (20' x 40') in plan. Each storey is about 2.5m high - that's why you see wood in 2.4m lengths (allow for bits above and below).

So let's look at the structural components: Take a wall 12m long x 5m high. The wall is constructed of two skins of brickwork. Brickwork is very good in compression but not so good in response to a lateral force. If wind is allowed to whistle inside our brickwork it will basically raise the pressure inside the gap between the two skins of brick. If you pump something into the gap that will also exert a lateral force. To stop your walls collapsing outwards, you should have brick ties installed and they should be in reasonable condition and the mortar should be gripping them effectively.

You can go for external or internal insulation instead. External means cladding of some sort and internal means you will lose some internal floor space.

The biggest gain of all is insulating the loft - heat rises. You should aim for a good 250mm of "wooley" or equivalent.

In general I'd suggest looking for draughts and plugging them. Do be careful that ventilation is still maintained.