Why didn’t we realize this before… Since a year or two there has been a working group of a number of collaborating researchers in Europe, under the wings of an international NGO (iiSBE) who are investigating what the ‘carbon budget’ implies for the construction sector or the built environment. The carbon budget is the amount of CO2 calculated by the IPCC that maximum can be emitted to (keep a chance of) staying below 1.5 or 2 degrees of warming.  It turns out that the remaining budget is entirely needed to cover current continuing emissions from the existing stock, together with the retrofit investments to reduce the emissions to zero by 2050.
For example: insulating 250,000 houses per year to zero energy or energy neutral means that it will take 30 years ( in the Netherlands) before they all have been retrofitted. In the meantime, the still un-insulated homes will cause CO2 emissions, upto 30 years on! The CO2 budget that is involved in this approach exceeds (a fairly by sector distributed ) proportion by the construction sector for 1.5 global heating , and could maybe stay just within the 2 degrees budget.  The same reasoning also applies to other sectors.
But that implies that new construction, extra additions to the stock, be it houses, or other buildings, may not cause any emissions anymore, otherwise this will be at the expense of the budget for the already existing buildings and houses, and the entire operation will in any case become unfeasible. De facto this means that new construction must already meet the construction standards that will apply from 2050 on, when CO2 neutral is a basic requirement. Only if buildings already comply with the 2050 standards they will not increase our current problem. Society is already struggling to achieve those current goals in existing buildings, let alone if new buildings care added to magnify that problem.
In fact, the current regulations in many countries are outdated: they still allow emissions, which is at the expense of the budget for the existing stock, and already undermines the objectives in advance.
It is not just about operational energy, to heat and ventilate the buildings. The materials used to build or renovate also cause significant CO2 emissions in their production. And these emissions are not spread over a 30 or 50 year lifespan, but directly, and immediately, during production. 
Of course, the national energy mix supplied for production will change and will have a larger share of renewables, thus reducing the CO2 emissions embodied in products, but in fact the emissions from constructing the renewable energy installations must then be added to that. What is clear is that the Embodied energy will play an increasing role. It is already half of all energy calculated over the lifetime of a building , but will even far exceed operational energy as the energy mix changes, as Danish research shows. 
New construction should therefore not only be 0-energy (operational) but also 0-CO2 in terms of material emissions. This virtually excludes traditional Western building methods, because they require at least about 6 GJ / m2 of fossil energy per m2, with associated emissions. (excluding installations or PV panels) Building with materials with a very low energy content, and even with negative emissions, is then the only option not to increase the emissions due to new construction. Think in particular of biobased materials. That was also confirmed by a recent lecture from the IPCC’s Vice-Chair Working Group 3, Dr. Urge-Vorsatz, who stated that construction should be zero energy operational anyway, that materials that capture CO2 should be used, and that concrete and steel must be phased out in construction. ( see previous article) .
The Buildings-carbon budget working group  will publish a number of papers on this subject in a special issue of the scientific journal Buildings and Cities in the coming year.  In the meantime, it is also being explored what those building rules could look like in 2050, which we should in fact already comply with. I here pose a few rules, as a first attempt , which gives some impression where it might be going:
1. The building, insofar as energy is needed for the use of the buildings, will have to come exclusively from renewable energy.
(renewable energy is energy not depleting stocks and produced without causing CO2 emissions. The CO2 emissions related to the materials required for capture and converting renewable energy must be included in 2.)
2. The building must be net 0-CO2 with regard to all materials used. (ie the CO2 (or Carbon) recorded in the building must be at least as large as the emissions caused by the construction. *
3. the building permit is only granted if materials have been used that have a certified origin. (ie are available through biobased production, with no effect on biodiversity or food production, or which do not deplete stocks in any way. An exemption is required for any other materials) *
Well, this is not yet watertight, only a first attempt, but it gives an idea of the challenges that have to be met.
In fact , already from now on, actually, for new construction ….
* fundamentally speaking, it goes one step further, since biobased sources are also a limited resource, that is to say maximized in production. In other words, we can no longer use these unless stocks are restored. See also the Trias Exergetica http://ronaldrovers.nl/de-trias-exergetica-22/
 carbon budget:
See strugis and Rics publications http://www.targetingzero.co.uk/publications.html
 SBI 2017:08 Bygningers indlejrede energi og miljøpåvirkninger
Vurderet for hele bygningens livscyklus
 buildings carbon budgte workgroup http://www.buildingscarbonbudget.org/