Insulation/heat questions - cavity insulation etc

Our 1930's semi is rendered on the back and sides, with stone cladding on the front. The downstairs seems to get cold quite quickly in the evenings when the heating goes off (and is almost suffocating when its been on for a few hours!). There's an old extension/conservatory off the back which has a single skinned dwarf wall with old metal double glazing (which gets a lot of condensation on). The roof is a flat, felted roof. This extension goes directly into the kitchen, whilst the living room entrance to it has metal patio doors which does a good job at keeping the warmth into the living room.
I can't easily think of a neat/clean/easy way of keeping the kitchen separated from the extension except by having a large heavy curtain between the two - and we like having it open as it currently is. Putting in a door would be difficult and we don't like that idea (due to us many reasons such as liking it being open, and the layout of the extension's side door being close).
Also, the old metal double glazing in the living room is badly fitting so does have a small draught - though this isn't noticeable with the curtains pulled.
Anyway - I was wondering whether cavity insulation would be wise, though I'm also thinking that the coldness of the extension is possibly the largest heat loss for the kitchen (which has an exterior wall), and in the living room, there's actually little wall to insulate (as the window takes up a significant amount of the exterior wall). Also, my concern with cavity insulation is that the render is in good condition and we don't want lots of unsightly holes drilled in it. Same with the cladding on the front (though I assume you could drill between the stones, as long as the mortar gap was larger than the hole needed).
Any suggestions? Secondary double glazing is a possibility for the living room (can't afford to replace the double glazing at present). Any idea of approximate costs of this (100 a window, 500, 1k)?
Basically, cost is very important to us - but I'd like to try and improve things a little.
BTW - we have insulation up to the height of the joists in the loft - and at some point we'll board the loft out, and possibly raise the floor and add extra insulation whilst we're at it - but the upstairs isn't too bad on temp I think.
Thanks
D
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Firstly, you need to sort out your heating controls. One room (per heating zone, usually only one) should have a room thermostat and radiators with no controls on (i.e. lockshields both ends). Other rooms should have thermostatic radiator valves on. They need to be replaced every five years or so. These should not be treated like on/off valves, but should be set about midway. Some valves can be physically limited to a particular setting (i.e. 21C) to prevent uninformed persons turning them higher just because they are cold and don't realise that they set a temperature and not a power rating.

Secondary glazing is cheap and easy to DIY, provided you can live with the appearance and inconvenience.
Insulation is always an excellent idea. If you have no cavity, but can lose a few centimetres inside the house without affecting period cornicing, then insulation boards (i.e. Celotex) can be clad on the internal walls.

at
temp
You should still ensure that the loft insulation is very thick. Heat rises.
Christian.
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no
setting
power
I'm planning on fitting TRV's to all rads (except hallway which has the thermostat) once the cold spell has gone. I balanced the radiators last weekend becase the huge living room one (and a couple of others) just didn't heat up if the upstairs ones were on and now they all work nicely. But I don't want to drain down and fit TRVs at the moment. I've not done plumbing before, and I'd like to take it slowly - which means at least a day without heating - something we can't do at the moment!

living
of
I had thought about DIYing it - but wondered what the cost would be of parts (specifically for a large bay, with a single pane about 6'ish square and 2 smaller 1.5' by 6' panes). I'd not want to do an openable one (at least, during the winter we don't open it!). What sort of thickness glass would I need for a 6' square pane? and what cost? What sort of frame could I use/make? What sort of cost of pre-made ones (which could open in the summer). It would be useful to have secondary glazing for the front bedroom for noise reasons (even during the summer), but these would need to be openable during very hot periods, and I'd prefer not to have to have to add/remove 6' panes too often.

lose
then
The main house has cavity walls - its just the small extension's dwarf wall which doesn't - but then I think most heat goes through the windows. As for insulation boards - this would require a redecoration (skirting off etc) which I think isn't feasable at present. Its not too bad, not enough to do major work over. ;)

rises.
Yup - will do that when we board it out.
Thanks
D
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