The airtightness issue that you flag up is worthy of more discussion. Leakyness may be ‘useful’ in reducing condensation and stuffiness in some poorly vented buildings but has no benefit in buildings with proper controlled ventilation, eg MEV or MVHR. Leaky buildings are cold and draughty and warm moist air leaking into the insulation can cause structural damage. However people continue to confuse uncontrolled leakyness with proper ventilation.

Ironically Passivhaus certification requires a maximum leakage of 0.6 ac/h at 50 Pa because airtightness is actually a very cost effective way to save energy. However it requires a step change in design to make such a tight (by UK standards) target routinely achievable.

As with all other aspects of PH, airtightness can’t be bolted on as a contractual requirement but has to be designed in.

The fact that airtighness, building form, orientation, insulation etc are hard or impossible to retrofit is a really good reason for focussing on the core design rather than blowing the budget on toy renewable that could be added later – if they are ever proved to work.

Sorry my comments as long as your post.

Nick

I see three challenges for PassivHaus – on construction quality, on end users & lifestyle and on addressing existing homes and the whole commercial industrial and public building stock.

I will post in more detail over on my isite blog at http://www.fairsnape.wordpress.com