Posted By: CWatersI'm not sure the Building Regs allow you to insulate an existing wall that badly :-)

I think the worst it can be is around 0.3 but I haven't been back to check Part L.

Your right CW -

http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1B_2010.pdf

Table 3 Page 18 looks for 0.3 W/m2K .

It does footnote to state (paraphrase) that the U Value may be reduced where floor areas are affected by +5% reduction . And Item 1.7 page 2 states "the adoption of any particular energy efficiency measure should not involve unacceptable technical risk of for instance excessive condensation" . Page 23 refers to BR 262 Thermal insulation: avoiding risks (2002 edition) for guidance on risk assessment . Anyone have a copy ? ( I don't) . No mention of EN 15026:2007 Hygrothermal Performance Of Building Components And Building Elements - Assessment Of Moisture Transfer By Numerical Simulation - the method (using WUFI software ) that Joseph Little used to prepare his report.

Something JL stressed in his report is that " even the closest attention paid to micro issues, such as insulation type and membranes, are not enough if macro issues like driving rain, substrate type & U-value haven’t been dealt with"

So as in the case of the OP with a Victorian brick house - I would at the very least approach my local BCO with my concerns about the 0.3 W/m2K value.

Or find someone expert in WUFI to run a simulation based on local climate data. Last time I checked there aren't so many such folks around.

Posted By: seanieWell I think that pretty much answers any concerns about IWI.

Couldn't agree less seanie ( no offence )

Posted By: seanieFrom 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."

1. The UK does not start and finish in London.
2. The most substantial risk with IWI is the accumulation of condensation immediately behind the insulation. This will happen even in the absence of freeze/thaw cycles which impact the outer face. And - London's housing stock is old - very old , and very attractive too visually. Taking such time spans into account how many freeze thaw cycles do we responsibly subject this brickwork to ?

I thought U=0.35 for the walls was acceptable for refurb, or has it changed since I worked mine out?

Posted By: seanie

Couldn't agree less seanie ( no offence )

I was being sarcastic.

Looking at that project website it's very impressive. And it shows how challenging the goal was. Look at how they dealt with the issue of joist ends;

"As well as the thermal bridge issue, there is an additional concern - that the joist ends will be exposed to dew point temperatures. Wet joist ends are worrying because the wood can rot and, ultimately, break.

Addressing this issue is one of the major engineering challenges of our project, one that we have spent a great deal of time considering and one to which we are applying an extremely innovative solution. In brief, it involves cutting the floor joists away from the external wall, hanging a steel beam off the party walls, insulating outside the steel beam and then hanging the floor joists off the steel beam; i.e. now entirely within the thermal and airtight envelope. As with pretty much everything on this build, there is an enormous amount of fine detail that I haven’t covered here "

Posted By: seanieLooking at that project website it's very impressive. And it shows how challenging the goal was. Look at how they dealt with the issue of joist ends;

"As well as the thermal bridge issue, there is an additional concern - that the joist ends will be exposed to dew point temperatures. Wet joist ends are worrying because the wood can rot and, ultimately, break.

Addressing this issue is one of the major engineering challenges of our project, one that we have spent a great deal of time considering and one to which we are applying an extremely innovative solution. In brief, it involves cutting the floor joists away from the external wall, hanging a steel beam off the party walls, insulating outside the steel beam and then hanging the floor joists off the steel beam; i.e. now entirely within the thermal and airtight envelope. As with pretty much everything on this build, there is an enormous amount of fine detail that I haven’t covered here "

That is impressive alright. It's akin to constructing a timber framed house within the existing walls. I wonder if they left ventilated cavity at the interface ?

Shoebox in't middle o't road

Luxury !

Posted By: SaintWookey they actually say they used an additional 50mm Kooltherm so 180mm in total. Even so there must be an airspace included as well unless Kingspan is claiming a TC of 0.019W/mK for Kooltherm.......nah they wouldn't

Where do they say that, Saint? I can't find it.

The beam across the front taking the joist ends is sat on foamglass bearing blocks to stop it being a thermal bridge itself (and the whole end covered in tescon tape). Impressive attention to detail. I'm actually rather surprised that a couple of foamglass blocks will take that loading but I assume someone's done the sums.

It is a thoroughly impressive project, and it will be most interesting to know whether it really does have a problem with facade deterioration or not over the next few decades. I hope it does work, and I'm glad someone is trying it, but there are good reasons to worry.