by Ronald Rovers
To make the consequence of (remaining ) CO2 budgets imaginable, the introduction of a basic calculation can show the scale of the transition required, for a industrialized country.
The Netherlands has 17 million inhabitants, if the CO2 budget is equally divided globally , The Netherlands can claim 17million out of 7 billion = 0,0025 part the budget (B), or 0,5 Gt CO2 under the 1,5 degree scenario (B1,5), and 2,2 Gt under the B2 degree scenario.. ( Which is optimistic, since global population is growing and the trend is for increasing demand , further reducing local and per capita budgets. ) If we assume that for the reform of society the attribution per sector remains the same, then 40% can be attributed for the building and housing sector, operations and investments , or B1,5 = 0,2 Gt CO2 and B2=0,8 Gton (- remaining to be emitted from the building and housing sector).
For only the housing sector, in The Netherlands its around 20% of total energy consumption.
Co2 budget Gt
NL eq share
Built env 40%
How does this relate to housing related emissions? Assume no new housing construction need, and all existing houses to be retrofitted to 0-energy ( 0-emissions from operational energy) To retrofit a house to 0-energy, requires materials, which have been produced with fossil fuel energy , so called Embodied energy. For a standard row-house retrofit , as currently practiced , this comes down to an estimated 3,4 Gj/m2-floor (near- passive house level, PV on roof for energy, in total “0” ) 
( this is a low estimate, including PV panels but not installations/equipment)
With a standard house in NL being around 100 m2, and 7,2 million houses, the investment will be estimated at 100 m2 x 7,2 miljoen x 3,4 GJ/m2 x 75 kg/GJ /1000 (ton) = 0,183 Gt
In the B1,5 scenario thats nearly the total Built env. budget, or twice the housing budget! In the B2 scenario this is nearly half the housing budget or 20% of the total Built environment budget .
While in that case still only part of society has become 0-CO2 :
All maintenance and replacement thereafter is not included, for which no CO2 is left. Like replacing for instance solar panels in 2041 (after 25 years of service) etc.
If we assume developing countries are entitled some more CO2 budget, the available budget becomes less , say half of that, implying the full budget is needed only to address the housing stock.
This is only existing houses. Not new houses, offices, or other buildings or infrastructure .
This is exclusive depletion of resources, or increased energy investments for same amount of material from ores.
From another point of view:
The current CO2 emissions per capita in The Netherlands (NL) are around 10 tons/year (everything included) . Adding up for a total for NL of 0,17 Gt/year. Following this scenario NL will run out of its total B1,5 CO2 budget in 3 years, in 2020 . Given that the budget is equally divided per capita, and developing countries do not get a larger share. However. Population by 2050 will be 10 billion. That will reduce the NL share even earlier. Its easy to see that if we wait a few years with transforming society, the budget has been used, and 1,5 degrees is definitely out of sight. For B2 it will be overall 13 years , still very short.
With a focus only at housing in NL , even if we retrofit all 7 million houses, and do that in the next 33 years,(until 2050) thats on average 3 % of current stock per year . Which implies that after the 1st year, 97 pct of stock still consumes considerable fossil fuel for operational energy, and after year 2: 94 %, and so forth etc. Knowing that the Dutch household energy demand is 450PJ fossil energy a year, or emitting 0,033 Gt per year, this leads to:
B1,5: Which implies that with a retrofit rate of 3% , after 6 years the “built environment budget” for 1,5 degrees will be used up, with only 18 % of houses retrofitted … To stay with B1,5 scenario, we have to retrofit 20% of houses a year, for the next 3 years, a impossible 1,45 million houses a year.
B2: In the 2 degrees scenario, if we do nothing, the Built environment budget is blown away after 25 years. ( this is because we use the whole budget for existing housing). With 3% of stock retrofitted each year, investments and savings balance somewhat, and by 2050 all houses are retrofitted, while by then the available (built environment -) budget is spend. The savings in operational energy en that speed scenario have provided just enough space for material investments , and delay budget spending to 2050. In B2 this is still 220.000 houses a year to be retrofitted for 0-energy. (of total 7,2 million) . The emissions for retrofitting houses go way over the ‘housing budget under 2 degrees.
If we do 6% of housing retrofits a year in B2 , it takes 17 years , And stays just within the B2 housing budget. Half the the Built Environment budget is left then, for all other building related use. Mind that with 6% it implies 450000 houses a year to be retrofitted..
There are however a few caveats in all cases: : This is only housing, while all other buildings and infrastructure are not covered , offices, new houses, etc. Plus, there is no budget left/included for maintenance and replacement;: If after 25 years Solar panels have to be replaced, that is impossible. And the first that will have to be replaced will be in 2041.
In the case case we focus at the B1,5 scenario, and only use the ‘housing budget’ for housing, things get very difficult: in B1,5 with 3% houses retrofitted, its 3 years before we run out. We have to retrofit 33% of all houses a year, thats 2,8 million/year, impossible.
Left the 3 % retrofit scenarios, right the 6% scenarios. (See larger graphs below)
3 extrapolate beyond NL : EU and OECD .
These data count for the Netherlands. We are hardly growing, The Netherlands could do without too much new construction. For many other countries the data will be worse , new construction demands more embodied energy, assuming they are constructed as 0-energy houses. If not, its impossible by definition to stay within any budget.
The EU has 255 + million houses, which partly are under a colder climate conditions, partly warmer, with cooling. If we assume the total resembles the average , since the Netherlands is in a moderate climate, in that case under the 6 % scenario, in the EU 15 million houses a year have to be retrofitted for 0-energy .
If we look at the OECD data, as comparable industrialized countries , we find that CO2 emission per capita are higher as in the Netherlands or Europe, while housing sizes are comparable ( data available in rooms per capita: NL 1,9, OECD average 1,8 ) . The situation for OECD therefor looks at least the same if not worse.
Overall we could conclude that B1,5 is impossible for the building sectors part, and B2 requires immediate and broad action, to keep the target in sight. That counts for most industrialized countries. For developing countries there might be some more maneuvering space, but only if 0-energy is targeted for operational energy as well . Otherwise a lock in is created while still emitting considerable amounts of CO2. It must be said that 0-energy does not mean by definition to invest that much (embodied) energy : here its was used in calculations assuming the prevailing comfort levels are maintained: In Industrialized countries that is to have the whole house 24 hours a day acclimatised (In the Netherlands: 21 degrees, expressed as “21/24” ) .
It can be concluded that to stay within the B1,5 scenario seems unrealistic, and to stay within the B2 scenario requires immediate and immense action to reduce CO2 to within budget limits.
Even then, it requires to invest a lot of materials to reduce fossil energy demand, especially in the housing sector . ( by insulating and PV production) . Which is the main burden to the remaining CO2 budget, assuming that retrofit leads to 0-(operational) energy housing. If not, CO2 targets are impossible to meet.
Even the B2 and 6% scenario is a challenge for which reasonable doubt is in its place if the construction industry can upscale fast enough to that level, even is supported by policies. Therefore efforts should go to direct reduction by limiting the direct demand of energy by behavior related measures. For example: Scale down housing sizes, in any case limit heated or cooled areas. Reduced comfort is unavoidable, its impossible to maintain current comfort levels, and have innovation provide new technologies to do this within current budget levels, before budget limits have long been passed.
Before starting to retrofit and insulate these (limited) indoor areas and invest indirect CO2 emissions via materials and technologies (embodied energy) , its seems more wise to focus at reforming the industry first, and make industry produce 0-Embodied energy/ 0-CO2 materials and products. In that case retrofits require far less embodied energy, and the industry has to transform anyway as well. Better start there so that the application is not so critical anymore.
To reduce embodied energy in building industry and products manufacturing fast and large will require the application of low impact materials and processes, or a move away from abiotic materials towards biotic materials, and a greater input of labor. Its a similar transition as for food: away from high impact food ( meat), and large scale bio-vegetarian diets . Which brings me to summarize the built environment transition required as one towards: vegetarian building, plant based.
In general: : this explorations shows that its highly required to add a a CO2/embodied energy value to every action in society, not holistic approaches, but direct information on CO2 impacts of every single action/ product, to reduce CO2 levels absolutely and fast. To have a 66% chance to stay at least below the 2 degree scenario.
Ronald Rovers oktober 2016
 Ritzen,M., Haagen T., Rovers R., Vroon Z., Geurts C., Environmental impact evaluation of energy saving and energy generation: Case study for two Dutch dwelling types Building and Environment, Volume 108, 1 November 2016, Pages 73–84 http://dx.doi.org/10.1016/j.buildenv.2016.07.020
 OECD, accessed January 1 2016: http://www.oecdbetterlifeindex.org/topics/housing/