You'd need ~120mm of aerogel at ~£300/m^2, and anything else is going to need at least twice the thickness, ie at least 1/4 metre depth, though should be cheaper, for the same effect.

Rgds

Damon

have a play with http://www.vesma.com/tutorial/uvalue01/uvalue01.htm
200mm Phenolic might do it.
remember the first 50mm of insulation does most of the work
very approx for phenolic
no insulation U=2.10 Wm2K
50mm U= 0.34
100mm U=0.18 , thats far better than current regs.
200mm U=0.10

Also hows your wall going to react to being cold and damp when its used to heat travelling through it for the last 100 years

If you want a 'green' material 400mm of warmcell (recycled new paper) might get it to U=0.1

I think all insulation could be considered quite 'green' , as even with the petrochemicial derived products the posistives in energy saving quickly out way the embodied energy and environmental damage caused in manifacturering and end of life disposal.
Better to make insulation out of it to reduced the need to burn it for heating

As for the condensation problem, if you insulate internally, and there is no gap between the wall and insulation (glued in place), would that not be similar to just dropping the internal temperature down as far as the wall is concerned?
If there is a point within the wall that hits the dewpoint, that point will just move inward. As long as it does not affect the materials used I cannot see that it is a problem in normal operating temperatures, extremes are always different and dificult.

As you want to insulate soon, this is an idea tile to improve the airtightness as well.

If you go too far, could you risk condensation on the first floor joist ends?
There would also be a thermal bridge there which would have to be included - were you planning to insulate the gap between ground floor ceiling and first floor?
Assuming two storey of course...

Brian.

I am hoping the external walls have no damp.

I do have a problem with damp issues on internal walls and a builder thinks the last owner may have unwittingly caused this. A rotten wooden floor was replaced with a solid floor and DPC. This may be causing damp to migrate up the walls. All the external walls were dampproofed, I think with an injection into the brickwork.

The U-value of your wall may not be as bad as you think! I would guess that the actual U-value is closer to 1 than 2 W/m.K. We've lately tended to not insulate existing walls but have concentrated on the roof, floor and windows. In order to conpensate for heat-lost through the walls we've started using Solar Roof's with Solar Slab heat stores.

The existing wall U value of your solid brick wall is taken as is 2.1W/m2K. BRE convention and all that. That means it has a thermal resistance of 1/2.1 = 0.476 m2K/W.
For a U value of 0.1W/m2K you will need a total resistance of 1/0.1 = 10m2W/K. So its a simple (!) matter of making up that shortfall of 9.524m2K/W resistance with insulation plus a bit of plasterboard although the gypsum will contribute little.
To get the thickness of insulation you multiply the resistance required, here 9.524 by the thermal conductivity of the insulation of choice.
So as Damon says you will need 125mm Aerogel Spaceloft or 210mm phenolic or 300mm graphite enhanced EPS or 275mm XPS or 230mm PIR or 600mm Sempatap.
If you read "Breaking the Mould" by Joseph Little, the Dublin based architect, you will see that the guidance for insulating older properties, and this is gaining favour, is obvioulsy not to ignore the wall insulation but rather don't overinsulate for the reasons that Wookey refers to in his posting. The school of thought is that a U value of 0.5W/m2k will possibly prove safer to the building fabric in the long run than insulating excessively

Sempatap has long been recommended by the Energy Saving Trust. But it's recently been joined by another product; 'Marmox'

http://www.energysavingtrust.org.uk/Find-Energy-Saving-Trust-Recommended-Products/browse/insulation/internal-wall-insulation

What kind of process is required to gain EST recommendation?

This Historic Scotland document suggests that the actual U-value of Victorian brick sold wall construction is closer to 1W/m.K.
http://www.historic-scotland.gov.uk/technicalpaper10.pdf#xml=http://web1:10700/texis/webinator/pubssearch/pdfhi.txt?pr=publications&prox=page&rorder=500&rprox=500&rdfreq=500&rwfreq=500&rlead=500&rdepth=0&sufs=0&order=r&id=4e51aaec7

That's a well known report and shows principally that the in situ U values for massive walls of sandstone, granite, rubble are typically better than calculated. Many of them are 600mm thick and so you'd expect a better U value than for 9" brickwork.
I'm not aware that they even measured a 9" solid brick wall.
Its easy to estimate the U value for a solid brick wall, the thermal conductivity of the brickwork is around 0.7W/mK so the R is around 0.3 add on a bit for air resistances and plaster say 0.18 gives 0.48m2K/W so the U value is around 2.0W/m2K

I would look to insulate no better than 0.5 W/m2K and make damn sure that my Victorian

DPCs
Brickwork pointing
Gutters
Cills
Flashings

were routinely maintained to ensure the brick wall fabric did not also absorb undue amounts of rain water penetration.

Posted By: SaintThe school of thought is that a U value of 0.5W/m2k will possibly prove safer to the building fabric in the long run than insulating excessively

Actually quoting myself posted before Sinnerboy, this is where real life experience counters (political) good intent. Yes 0.30W/m2K is the Part L requirement if you renovate more than 25% of your existing walls. In Ireland the requirement has been 0.27W/m2K and they are already seeing issues with this

From the article;

"But there is another problem with interior insulation of this magnitude: heat loss through the exterior walls will be virtually eliminated. A little bit of heat loss through old brick walls drives out moisture; if you get rid of it completely, there is the possibility of freeze-thaw cycles causing the brick to deteriorate. Fortunately London doesn't get too many of these."

Well I think that pretty much answers any concerns about IWI.