New A2 House Is Freezing!

What sort of heating system is in it? And how is heat distributed around the house? Who certified it? Are the draughts caused by the ventilation system or coming in around doors/ windows? 16% humidity must be wrong - sure you'd be getting desiccated with that. If the house is well sealed and insulated my non expert thinking would be pointing at the ventilation/ heat recovery system assuming one installed.

If you're close to Dublin the libraries have home energy monitoring kits. Try to get one to see if you can see any problems.

https://www.irishtimes.com/news/ireland/irish-news/dublin-libraries-to-stock-kits-to-test-home-energy-use-1.2990116

If the builders not acting on the issues then it could be time to get legal advice. A new A2 house shouldn't be freezing.

They have them in libraries outside Dublin too!

https://www.leitrimobserver.ie/news/local-news/293016/home-energy-saving-kits-available-to-borrow-in-local-libraries.html

I know I'm specifying mechanical heat recovery and ventilation across the board on one off larger builds yet alot of estates builds are still using wall vents.

Personally, I don't agree with the old style wall vent when dealing with an A rated house as the heating system typically isn't up to dealing with such uncontrolled airflows.

Mechanical ventilation is balanced, controlled and recovers heat as air is exchanged.

Another issue is that in housing developments, only a percentage of houses are required to be air tested while all one off houses are air tightness tested. This surely results in very poor standards of detailing and construction (thrown together).

If the heat can do the job when on, I'd suggest you problem is airtightness and uncontrolled ventilation.

I don't think another ber report is going to help you as that will just be based on the plans of what's supposed to have gone into your walls, thermal bridge details etc, I'm going to guess the house is timber frame so you should request the air tightness report from the builder, they have a legal requirement to achieve a minimum air tightness and if you can't get it consider getting your own one done.

Timber frames are very dependant on good workmanship and air tightness sealing or else your internal walls are venting directly to the external facade, less of an issue with older houses as you had block inside and out, hard to build an internal wall that stays standing with gaps in it!

Don't forget you have building control too, send your address to your local council dept and ask then to chase up that all the proper documents and test reports have been uploaded as part of BCMS, an engineer should have checked and signed off on the installation of insulation, etc