Kitchen renovation and external wall insulation requirements - Approved Document

During the kitchen renovation of our Victorian property we have revealed a large area ( about 30-35% ) of an external wall that was dry lined. There was once a chimney breast there that was removed over 20 years ago. Before we owned it and I assume the dry lining was a 'make good' following the removal of the breast. In this dry lined area the internal brickwork is about 2 inches back from the surrounding internal plasterwork which is mostly good. Whilst removing the wall tiles to that dry lined wall area resulting damage was done to the plasterboard to which the tiles were attached. The plasterboard was slightly damp through penetrating damp - pointing and roof verge tiles at roof level soon to be attended to. Due to this dampness I thought I'd remove all the plasterboard on the dry lined part of the wall and renew the dry lining with new plasterboard.
Then I read Building regulations regarding insulation to external walls that are to be re-plastered or part re-plastered.
Do I need to dry line the whole of this wall and install Kingspan etc to the parts that are currently good. I have difficulty interpreting the Approved Document for material changes and have no previous experience of this.
We are on a strictly limited budget and this could be an unexpected expense we were not aware of or prepared for.
How does a building inspector view this sort of situation.
We will be removing a small load bearing wall during the renovation of the kitchen so a buildings inspector will need to be involved during that job and I'm sure he would notice a large area of this external wall that had been replastered.
What are my options re the dry lined wall. Do I really have to renew and insulate all.
Thanks in advance for any replies.
ABC123

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Given that a) you have exposed some of the wall already (and hence have already suffered the inconvenience); b) the price of energy, and its likely future trajectory, I would /strongly/ recommend you invest the extra money in properly dry-lining this bit of wall. (and while you are doing it, try for at least 100mm of insulation).
http://www.secondsandco.co.uk/page_show/read_plasterboard/index.html has what look like reasonable prices on Kingspan. It's easy to do yourself (so you don't need to pay a builder to do it).

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Going from nothing to 25mm will get you a large energy saving. The extra you get on top by going to 50mm or 100mm will be very low in comparison, and unless the rest of the room is similarly well insulated, it will make no difference to the overall heat loss. (Building regs may still require it though - don't know off-hand what it says here.)
You might find you can get the kingspan with a plasterboard face in the right thickness to dot-n-dab to the wall, and have the face flush enough with the original wall to just plaster across. I've not used this myself, but there have been one or two times when I came close to doing so.

On Aug 8, 2:46 pm, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:
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Yes. 25mm will (I think) halve the energy loss through that wall.
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If I'm right about 25mm having the same insulative properties as 13" brickwork, 25mm will save 50%, 50mm an additional 16%, and 100mm a final 14%
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"no" difference is overstating somewhat.
My argument is that the additional cost of 100mm over 25mm is low(ish), and then you have "done" that wall. It makes it more worthwhile to put in the underfloor insulation and the insulation on the other wall and ...
... but I agree, if you are in a /really/ tight budget, the first 25mm gives you the most benefit.
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Me neither (but Building control will probably be happy to explain).