And unfortunately, there will be some scammers who will try to take advantage of this situation no doubt.😒 Toodles.

Posted by: @jeff

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I expect a similar widespread failure as heat pumps ramp up

Agreed. Thousands of homeowners likely have average heat pump installations that they believe are good (we’re a prime example) until a few winters pass, and they realise their setup is subpar. A better installation could have been more efficient and cheaper to run, but by then it’s too late.

There is no end to the ingenuity of human beings when they see an opportunity to scam others.  Sadly this programme isn't unique and won't be the last.  There are times when I despair at the human race! 

It's all too easy to blame 'government' but no government can be everywhere (and we wouldn't want it it they could).  The real problem is unscrupulous people, all government can do is try to minimise the abuse, but inevitably some will get through.

I bet that a proportion of the installers that the government has vowed to force to fix their work have now disappeared, most likely into voluntary liquidation haven harvested the grants, not done the work, and not paid their taxes.

I think there's a sector of the energy efficiency retrofit industry that is well meaning, but simply incompetent. There are two passive retrofit measures that can have potentially disastrous results, and both for the same reason. One is external wall insulation [EWI] and the other is spray foam roof insulation.

Both fundamentally shift the natural balance of humidity and moisture vapour control in the fabric of the building. An older building may have solid walls, be naturally draughty, cold, at times uncomfortable, but thereby has controllable levels of internal moisture vapour. The building fabric can breathe. Preventing excess moisture vapour from escaping is never a good idea, and EWI and spray foam roof insulation can both do this when badly applied, trapping excess moisture in the fabric of the building and raising relative humidity of structural elements to levels that can promote the growth of mould, fungus and dry rot.

The building science isn't well enough understood by the retrofit co-ordinators who recommend and sign off energy efficiency measures, or the tradesmen who carry it out. New build modern homes can have problems with excess humidity, and overheating in summer, because they are built draught proof and well insulated, but often with inadequate natural or forced ventilation. 

Excess moisture vapour pressure in heated humid indoor air is compelled to find a colder surface upon which it will relieve itself of moisture to reach a lower enthalpy state, by means of condensation. At best that surface may be a wall or other somewhere visible, and controllable, at worst it is within the fabric of the wall, roof, floor or floor void, on a structural element.

Mechanical Ventilation Heat Recovery [MVHR] is a very energy efficient method of controlling indoor humidity levels and indoor air quality. But it is little used in the UK, and sadly when it is installed in new build or retrofit, it's often done badly and inefficiently, once again by incompetent and untrained tradesmen. The plumber, the electrician, anyone but a professional MVHR installation company gets the job, whoever can do it the cheapest. (Doesn't this sound depressingly familiar?)

@allyfish  Thats an interesting comment. 

The business of ventilation in retrofits seems to be a bit of a black art (sometimes literally).  I have looked several times but failed to find any literature which adequately describes how to go about it without either resorting to 'consult a professional' or giving advice that is so general as to be useless.

To the extent that I have been able to understand it there seems to be two major issues to be avoided:

• interstitial condensation caused by damp air from the house condensing in voids in the insulation/wall created by the process of insulating
• internal condensation caused by insufficient ventilation of the house 

The second can obviously be fixed retrospectively if necessary, the first appears more difficult but is it essentially solved by vapour barriers in the correct places and are these the only two major issues (other than the usual ones related to poor implementation as opposed to poor design)?

@jamespa it's seldom adequately understood even by us [so-called] engineering professionals. There was an excellent series of articles published in the ASHRAE Journal a few years ago about interstitial condensation risk and preventative measures in building fabric, authored by Dr Joseph Lstiburek. He put the subject matter in very accessible wording and diagrams, with simple cross-sectional 'do's' and 'don'ts' for housebuilding design. Crucially, where in the construction of the wall the vapour barrier membrane should go, which varies according to climate [who knew?] and where ventilation and air gaps in the wall structure can prevent risk of bridging. It was a series or articles largely for the North American market, so focussed on houses in their vernacular material - i.e.: wood framed. The States has a massive range of climatic conditions to build dwellings in, much more extreme at both ends that the UK, and things can go very wrong when a building design optimised for one end of the climate is used for the other end. Recently, wood framed housing has become much more common in the UK, quicker and cheaper than traditional inner course block and outer course brick cavity wall construction.  Brick and block are largely immune to structural decay when damp (setting frost spalling aside) but timber isn't. Are we building dwellings with latent defects that might cause homeowners problems a few decades from now?

It was only a few short years back energy retrofit companies were injecting hygroscopic moisture absorbent cavity wall insulation products into non-insulated walls. Bridging the air gap that was preventing moisture held by the external wall from migrating to the internal wall. A wall with moisture saturated cavity insulation product and no vapour barrier has a higher U value than the original non-insulated one with an air gap! Water is a much better conductor of heat than air. So the competence and knowledge level we were at in the UK was shamefully low. Given the unfolding horror stories of EWI, I don't see much evidence that things have improved.

One of the best defences against damp and mould is to keep a house heated above the dew point temperature of the internal air year-round, and with 'low and slow' heating, such as that provided by heat pumps, that's quite easy. Buildings like stability, ideally equilibrium, else slow & controllable changes of temperature and humidity. Rapid changes in the internal air temperature, such as caused by intermittent 'fast blast' home heating e.g.: morning and evening timed period, can cause problems, as warmer moisture laden air meets cooler internal surfaces that due to thermal lag, may be significantly colder than the air temperature. If the cold surface is non-insulated or the fabric is damp, things get worse. Cookers, bathrooms and showers need good intermittent mechanical ventilation to remove as much moisture vapour at source as practical. It's all basic, but very often lacking.

Some of these documents on moisture control 

SWEETS.CONSTRUCTION.COM "https://sweets.construction.com/swts_content_files/2109/676715.pdf"

https://images.finehomebuilding.com/app/uploads/2022/06/18004144/179404_1655527303_The-Perfect-Wall-BSI-001.pdf  

including his thesis https://utoronto.scholaris.ca/server/api/core/bitstreams/992d16ec-7c1e-489b-8b95-f2163a21e460/content

lots to read there!