U-values - your opinions please

[dhaslam]

I don't think that air tightness is much of a problem  in a block built house.  Obviously a timber frame house   has much greater possibility of air leaks if the workmanship is poor.   Of course sealing up a building means there  has to be a reliable ventilation system.    Wall paint and other  household items do  require a certain amount  of  air circulation to make them safe.   

www.gasdetection.com/news2/health_news_digest129.html

[dan_aka_jack]

I don't know if this'll be appropriate on your build... and I have no experience of building an entire house... but the builders we've used for bits of our refurb really didn't understand some fairly basic things about insulation and airtightness.  Even when we explained things to the site manager, the information didn't seem to be passed on to the builders who are actually doing the construction...

If possible and appropriate, it might be worth having a site meeting before work starts with the site manager and as many of the actual builders as possible to quickly explain how important airtightness is, and that every little crack matters and will show up in the airtightness test.  This might be inappropriate for a number of reasons but might be worth considering.

[jwbellarby@gmail.com]

ive built and managed our own passiv haus and have a good understanding of airtightness.
unless contractors are specialists, they generally dont understand the importance no matter how many times you explain.
easy to get tested at inner wall membrane or plaster level and then for electrician or plumber to ruin it, hence always get 2 tests, wall membrane or plaster level then after second fix
ours was timber frame so quite different construction, a few points we took longer to get right included floor joists, always use joist hangers rather than fix on stud wall and round a load bearing steel beam. however perfectly possible with attention to detail

good luck

James