CPB says:

''If you are going to go with EWI I think it really helps that you are going with one of the class leading solutions. I have to say I really cringe when I see people mention that they will DIY their EWI, I really think it is a job that should be left only to the professionals.''

Hmm....

I think I would add to that ''if the professionals are actually good at insulation''.

I still find EWI contractors who simply do not understand insulation. They understand pretty cladding, and the finish is often great, but things go on behind the finish which are questionable or wholly unacceptable. Add to that a continued uncertainty about whether it is acceptable to render down over the dpc - and bear in mind that many retrofit dpcs are at, or above, floor level anyway - and you may already have a big fat built-in cold bridge.

Many DIY jobs may be better than some of those professional jobs I have come across.

The whole thing saddens me because in my work I generally have at least one contractor for various forms of energy-related improvement who I would heartily recommend to clients. The best I can do at the moment with EWI is to point towards a contractor who was OK in the end.

I generally agree with the sentiment about best left to professionals.

In this case there are a couple of confounding factors.

First, contractors we have had to have a look at it have not been keen. The façades are complex with tricky detailing around windows, string courses etc.

Secondly, we have a lot to do, potentially 3 x large 3 story buildings, 2 stone cottages, 2 brick cottages

The stone cottages may be getting some form of cladding to help with the damp, we currently have a test panel underway to see if the damp issues are due to penetration, rising or condensing damp. If the test shows a reduction in damp, the next phase is to try the cladding with insulation behind, both ventilated (with a tyvek membrane) and unventilated (i.e wool against back of cement cladding). Cement cladding board is our first guess as it is easier to apply than a render, no danger of cracking, is breathable (via the joints), repairable, removable for inspection and access. Colour wise it can match the current victorian cement render.

We have access to a small labour pool and small but steady cash flow, so a small scale system that can be put up slowly and in sections i.e. north elevation one year, west the next, half the south the year after and so on is attractive to us rather than blowing a large wad of cash in one go.

This isn't our first rodeo so to speak, we've been maintaining and upgrading these houses as a family business for over 150 years so are familiar with the building's quirks and history.

Currently the system is on the drawing board and tests panels are in place to check what is causing the damp, or at least what % is caused by penetration vs rising etc.

The 'new' (2000/2001) building at Heeley City Farm, Sheffield (designed by Eco Arc) had 250 or maybe even 300 cavity, fully filled with rockwool.

isn't alli a good heat conductor ? why not ply/stud Larsen truss?