I am a complete novice and looking for guidance on the best way to make some changes.
I have a 12 year old 3 bed room detached house with a large conservatory extension and converted garage.It already has UPVC glazing,fitted about 3/4 years ago.The insulation is as fitted when built-about 100mm in loft.No cellar etc.
It is costing huge amounts to heat and some parts of the house are always cold.
The boiler is due for renewal and we would like to do a loft conversion and open up living room into the converted garage space.Given the extent of the changes we plan i was hoping we could improve it's Green credentials at the same time.
I know little about it,but like the thought of wood burning stoves/heating,renewable solar energy,insulation and making the place airtight(how).I have concerns over cavity wall insulation as i thought the cavity had a purpose.

Brick with cavity to Breezeblock under a tile roof.Many internal walls are studded.

Yes.Some of internal walls on studding,rest i assume blobbed & dobbed onto walls.

Tony, you've highlighted this problem many times and I agree absolutely. If the cavity is empty (given the age of this house maybe it isn't), wouldn't simply fully filling the cavity with PU foam solve this problem? If this was done properly, I can't see how the draft would get from the outside to the void behind the plasterboard.

Also I think that we use U/F foam for cavity fillings. I would fill the cavity and replaster as my number one option.

Plastering in wire is OK. Best if they are fixed in some way first.

Yes do do cavity insulation as well as wet plastering.

More loft insulation is a good idea but may not be economic if you intend loft conversion in the near future.

Get structural changes out of the way first, then address air leakages ( read other threads for this too), Floor insulation if suspended floor?

Thermally isolate the conservatory.

Solar hot water, other things could include rain water recycling, grey water recycling, heat pump and eventually solar pv?

Make the conservatory an unheated area outside of the main house with double glazed doors and windows between you and it.

I think burning wood is polluting and adding CO2 to the atmosphere.

You can have foam (or fibres or beads) injected into masonry cavity walls. Indeed it is a good thing to do.

"Can i retro fit insulation into studded & dabbed plasterboard walls. i.e. inject anything???" If I under stand this question, you want to insulate your internal walls? to which I say no, only the external walls (and floor and loft floor) need be done.
From what I have read, cavity walls were the answer to prevent rain ingress through solid brick walls. They were always fully ventilated, so you were living in a single skin building as far as thermal considerations were concerned. There could be a downside to solid foam injection, if the cavity ties are sloping the wrong way - I have seen this in a 1970s bungalow - outer skin of the wall was re-built. But if you choose fibre or beads they are bulletproof against water. Any water finding its way into the cavity will go downwards not across, so keeping the inner skin dry. But both types can/will settle. You pays ya money. . . .
Frank