Construction (embodied) Energy Vs Operational Energy

My Summary / Conclusion

  • In 2007, 16% of CO2 equiv impact is construction of a building, 84% is operational / in-use.
  • Today the split is roughly 20% embodied and 80% operational.
  • The modelling shows that we are moving to a CO2eq (CO2 equivalent) of 38/62% for masonry construction, and 35/65% for timber-frame construction.
  • No significant differences emerged between masonry and timber construction in terms of overall CO2 impact over the 60- and 120-year study periods. The largest difference observed between comparable masonry and timber constructions was 4%.
  • No clear / significant impact of thermal mass.
  • Emissions are cumulative, so 1 tonne of CO2 equiv at the point of construction roughly equals a tonne of CO2 equiv during the 60 year life of a building.

Which aspects of a dwelling are responsible for the largest CO2 impact?

  • Space and water heating have the largest CO2 impact in dwellings.
  • Appliances also have a large operational CO2 impact.
  • In both masonry and timber constructions, the impact of foundations and ground floors dominates the embodied CO2eq impact.
  • In masonry construction, the external walls also have a major impact.
  • Other elements, such as windows/doors and floor finishes, have a relatively large impact because they are repeatedly replaced throughout the life of the dwelling.
    • Waste water heat recovery systems have a 60 year assumed life span (windows and doors – 40, MVHR 15, flooring 10 ….)
  • The embodied impact of services was found to be approximately 5% of impact at 60 years and 7% at 120 years.

Construction Vs Operational Energy

I’ve come across some interesting figures and links to research in an article in the Green Building Magazine (by

  • Embodied Energy – a ticking time bomb (Spring 2012)

In 2007, around 16% of the CO2 equivalence impact was constructing a building.
– This covers the manufacture of materials and components, transport and construction.

84% of the CO2 equivalence impact of a building was down in use emissions.

This data is from

That is why policy to date has been biased to making buildings more operationally efficient.

The article then makes the point that raises the importance of embodied (construction) emissions. Namely that since emissions are cumulative, 1 tonne of CO2 equivalence impact occurs for every year this “CO2” is in the atmosphere. So 1 tonne of CO2 at the start of a buildings 60 year life will have twice the impact of 1 tonne emitted during the building’s life.

The longer a tonne of CO2 hangs around in the atmosphere, the more damage it can do.

So it’s potentially dangerous to focus on carbon-intensive solutions that are installed at the point of construction, so that they reduce the operational emissions.

So, it is best to look for principles, materials, solutions etc. that will reduce both the construction (embodied) and operational energy of a building. So, as it’s often said, the general advice is still to optomise the fabric efficiency of a building before other measures.

October 2011 Update

The October 2011 report by the NHBC Foundation (“Housing Research in partnership with BRE Trust”) – Operational and embodied carbon in new build housing – A reappraisal:

Until now, focus has been almost entirely on the carbon emissions resulting from using homes, but clearly the balance between those operational carbon emissions and emissions from producing and installing the materials – the embodied carbon – needs to be considered.

This publication explores a subject which has to date lacked a strong and accessible evidence base. It looks at a range of carbon reduction scenarios as delivered through typical house types and estimates the likely impact both in terms of operational and embodied carbon – providing an insight into the contribution of different technical responses to the low carbon agenda, including the balance between operational and embodied carbon.

Evaluated Scenarios:

Twenty-four scenarios were appraised, using SAP software to determine operational CO2 emissions and BRE Global’s Environmental Profile methodology to analyse embodied CO2eq emissions.

The research considered the following variables:

  • two built forms (detached and mid-terraced)
  • two construction weights (masonry and timber frame)
  • three operational CO2 performance levels (25, 31 and 40% reductions over Part L1A 2010)
  • two dwelling lifespans (60- and 120-year study periods)
  • varying grid electricity CO2 intensity (to account for the expected impacts of grid decarbonisation).

Extracts from the report:

  • The modelling showed a typical percentage split between operational and embodied CO2eq (CO2 equivalent) of 62/38% for masonry construction, and 65/35% for timber-frame construction. These are averaged figures.
  • No significant differences emerged between masonry and timber construction in terms of overall CO2 impact over the 60- and 120-year study periods. The largest difference observed between comparable masonry and timber constructions was 4%.
  • The modelling showed that space and water heating, along with foundations, ground floors, windows/doors and floor coverings, were the largest contributors to overall lifetime CO2 impact. Appliances were also a significant contributor, but building designers have limited opportunity to reduce these emissions via their designs.
  • The typical split between operational and embodied CO2eq in new build housing has been taken as 80% operational, 20% embodied, a position largely confirmed by recent studies[1]. However, within the context of future Building Regulations requirements – which are expected to tighten to the point that new homes will be significantly lower in CO2 from 2016[2] – operational CO2 emissions are set to fall radically. This means that embodied CO2eq emissions will become increasingly significant in terms of the percentage they contribute to the overall CO2 impact of new build dwellings. In addition, typically the more energy efficient a given house type becomes, the greater the quantity of additional materials required to construct it (eg additional insulation, more services). There is also potential that such additional materials (eg renewable generation installations) may have particularly high embodied CO2eq levels. Both these considerations suggest that, as operational CO2 emissions reduce, embodied CO2eq emissions will increase.
  • The replacement of services and other building components has a direct bearing on both operational and embodied CO2eq emissions across the 60- and 120-year study periods.

Assumed lifespan of construction elements:

  • The proportion of embodied CO2eq in masonry construction was found to be higher than that in timber construction. However, this difference was relatively marginal, the maximum difference being 4%. This is because, other than the walls, the majority of building elements were similar in both the masonry and timber constructions modelled.

Which aspects of the dwelling are responsible for the largest CO2 impact?

  • Space and water heating have the largest CO2 impact in dwellings; this remains significant in all scenarios despite diminishing slightly as designs move from 25 to 40% CO2 reduction.
  • Appliances also have a large operational CO2 impact, although dwelling designers have limited ability to help achieve reductions in this area.
  • In both masonry and timber constructions, the impact of foundations and ground floors dominates the embodied CO2eq impact.
  • In masonry construction, the external walls also have a major impact.
  • Because both of these areas will last the lifetime of the dwelling, they should be considered at the design stage when seeking to reduce the overall dwelling CO2 impact.
  • Other elements, such as windows/doors and floor finishes, have a relatively large impact because they are repeatedly replaced throughout the life of the dwelling.
  • The embodied impact of services was found to be approximately 5% of impact at 60 years and 7% at 120 years. However, these results should be treated with caution as some aspects, such as controls, had to be omitted due to lack of available data, and the services were not studied in depth during this project.

Did the varying thermal mass levels have a significant impact on cooling?

  • No clear trend was identified from the modelling carried out, with minimal impact from space cooling in both masonry and timber designs.

UK Solar Hot Water Trial Findings

The Energy Saving Trust did a survery on a large number of UK and Republic of Ireland solar hot water systems.

PDF report on the survey >>

Key Points

  • There were 54 flat-plate systems in the trial.
  • There were 34 evacuated-tube systems in the trial.
    • There was no difference in the annual solar energy yield observed between solar installations using flat-plate solar collectors and those using evacuated-tube solar collectors. This may be because although evacuated-tube collectors have higher insulation, flat-plate solar collectors generally have a larger working area as a proportion of the collector size.
So there are none of the “new” Thermodynamic Panels in the survey. These do appear to be different and better. Providing 24 hour hot water.

Distribution of the surveyed / trial locations:

So for Silver Spray in Cornwall, should get better results as more sunshine:

The solar energy input to the hot water cylinder is at a maximum in summer, with back-up heating providing more energy in the winter months.

It’s key to set the backup (non solar) heating system to run so that the solar heating can be most effective and the house occupants have hot water when desired.

How to improve the performance of a solar water heating system:

  • Using boiler timers and/or solar controllers to ensure that water is only heated by the back-up heating sources after the water has been heated to the maximum extent possible by the sun.
    • Timing of back-up heating and hot water use. Systems
      provided more energy when the back-up heating was
      used just before the main hot water use or at the end of
      the day. This provides a better opportunity for the solar
      collector to heat the water rather than using the back-up.
  • Having an adequately sized dedicated solar volume (that is, a portion that can only be heated by the solar water heating system). Where a dedicated solar volume is not used (for example in systems that do not require the existing cylinder to be changed), the timing of back-up heating has a particularly important impact on performance.
  • Insulation is a vital part of this, as systems with poorly insulated storage cylinders can suffer from inadequate hot water provision in the mornings.

Key Findings:

  • Well installed and properly used systems can provide around 60% of the years hot water.
    • Across the whole trial, the proportion of domestic hot water energy provided by solar power ranged between 9 per cent and 98 per cent (with a median of 39 per cent).
  • Plenty of other findings, see the report.

Customer / Consumer Advice

What to expect from your installer:

  • All MCS installers should be able to provide a detailed breakdown of the specification and costs of their proposed system. They should:
    • Complete a technical survey.
    • Explain how they calculated the size of the system to be appropriate for your hot water usage.
    • Provide an estimate of how much heat will be produced by any proposed system.
    • Supply clear, easy-to-understand and detailed information and advice on how best to use the system and operating instructions.
    • Explain how the system will be installed and if there will be any disruption to your property.
    • Install and set controls and settings to ensure you get the most out of your solar water heating system.
    • Provide clear and easy-to-understand information on product and workmanship warranties.

Ecobuild: Grey Water Harvesting

Notes from Ecobuild expo talks on Grey Water use:

  • Greywater is waste water from showers, baths, washbasins, washing machines and kitchen sinks.
  • Greywater reuse is the use of untreated greywater.
  • Greywater recycling is the use of treated greywater.

Key technical issues to overcome using Grey Water:

  • The age of the water..
  • Stagnant water generates bioforms leading to unpleasant odours.
  • User interaction.
  • Anticipating users bathing habits.
  • Low level of maintenance.

Ecobuild: An “air tight” building

A principal of modern buildings to achieve thermal efficiency and improved health is to make an “air tight” building .

The aim is to head towards and perhaps meat the Passivhaus standard of air change rate of no more than 0.6 air changes per hour @ 50 Pa. (UK Building Regulation Standard is 10m³/m²/hr @ 50Pa).

Then to control / manage the air, by a mechanical ventilation heat recovery system (MVHR) that exchanges inside air with outside air, BUT heat exchanges the outgoing air with incoming air, so you don’t loose the warmth.

The idea worries people, “I want to sleep with the window open ….”. But reading more and more about this, even sceptics rapidly find the air quality is better in these buildings than those with open windows. And, you can just open the window if you want to ! (eg in summer).

Notes from  the Ecobuild expo talks:

I’ve read elsewhere, that the builders being on-side re the thermal, sealed objectives is key.



Rainwater harvesting

If there is going to be rainwater harvesting:

  • “Green / grass” roofs may mean little roof water run-off.
  • It seems that people tend to either go for a Grey Water recycling or a Rain Water harvesting system, not both. Have to cost these both up.

Anyway, if there is going to be a rainwater harvesting system, it would seem that putting the storage tanks for this on the west side of the house could be ideal.

  • This side of the house should have little if any people traffic.
  • The roofs could all be sloped to drain to the west so that the drain pipes could flow down to a single rain water harvesting tank.

Eco Building Products: Spring health check for green roofs

Spring health check for green roofs

An extensive green roof has the potential to bring many benefits – such as saving money on air conditioning, supporting wildlife, increasing the value of a building and improving its appearance – but none of these benefits apply to a green roof that is poorly maintained.

Most green roofs are low-maintenance, but ‘low-maintenance’ is not the same as ‘no maintenance’. A little bit of TLC carried out this spring need not be time-consuming or expensive and will pay dividends.

Enviromat offers a competitively priced green roof maintenance service, but if you prefer to care for your green roof yourself, here are some reminders of what needs doing this spring:

1. Do a quick check to make sure that any waterproofing you can see is in good order, that fall restraint systems are in place and in good condition, and that walkways, etc are as they should be.

2. Remove any rubbish or fallen leaves from the roof.

3. Ensure all drainage outlets are clear and that rain can run off freely.

4. If you have pebble edgings on your green roof, pull out any vegetation that may be growing through them.

5. Check that you do not have any unwanted vegetation on the living part of the roof. Be on the lookout for tree seedlings and pull them out – their roots could damage the waterproofing.

6. If you have any bald patches on the roof, now is a good time of year to replant these areas. On a sedum roof, simply break pieces off healthy, well-established plants and push them into the growing medium. Keep them well watered and they will soon take root.

7. Apply fertiliser. Enviromat recommends using Nutrifusion Spring/Summer feed. Follow the manufacturer’s instructions carefully.

8. If no rain is forecasted, give your green roof a nice long drink of water. This will activate the fertiliser and help new cuttings to establish.

Appliance Energy Saving Tips

Siemens have recently brought out a miracle A+++ fridge; the KG36EAW40. It has the best energy rating on the market right now. Annually it costs you £18 a year to run, compared to a more modest A rated model, which costs you approximately £51. That’s a saving of £33.

Get a frost free freezer

Don’t leave cooking appliances such as your microwave on standby. It wastes approximately 7kW of energy per day – annually that’s a huge £84 per appliance.

An induction hob is the most efficient hob you can get: it’s 90% more efficient than gas or electric, mainly because the hob only heats up when it recognises the pan so no energy is wasted when the pan isn’t present.

Another good tip is to use halogen lighting in your oven as they’re 20% more efficient and 36% brighter than standard light.

The Bosch Logixx WAS32461GB washing machine, which has a function that measures the exact amount of water needed depending on the weight of your wash. It means you won’t waste any extra water or energy to get the load washed. It’ll only cost you £22.68 a year to run, which is minuscule compared to other machines.

EcoBuild: Toilets (waterless urinal & sensor on water tap)

Two toilets and a commercial tap sensor stood out at the Ecobuild expo:

One of the efficiency and eco objectives is a house that is water efficient.

Two slides, from different sources on domestic water use / water consumption:

My initial straw polling, is getting a strong reaction to the idea of a urinal, let alone a waterless urinal, from  at least 50% of the girls reacting!

Waterless Urinal

This has the potential to drastically reduce the amount of water used in the house.

They are marketed as “clean, green, odour free and waterless”.

I had it all explained to me on the Odourwise and Twyford stands. The module that fits into the bottom of the urinal converts all uric acid to a form that prevents lime scale, clogging up the system, takes away the smell etc. It seems that urine and water are a big source of limescale and other loo waste pipe problems, hence trying to dilute this away with (usually) lots of water.

All you need to do, is a few times a year (depending on use levels) replace the cartridge. In this photo the plastic bit on the top is the device to extract the Odourwise bit so that it can be replaced with a new cartridge.

A google search reveals there are a few alternatives, so more research needed.

My current thought is a urinal in the bathroom  off the main living area and also one in the bathroom off the study.

Also on show at Ecobuild 2012 will be the Odourwise™ Waterless urinals. Twyford Bathrooms offers the revolutionary Odourwise™ Waterless system for two of its urinal ranges, Centaurus and Galerie Plan. Centaurus is the first hybrid urinal that is truly waterless, combining maximum water savings with enhanced hygiene. The cutting-edge Odourwise™ Waterless technology requires neither chemicals nor electricity, keeping it eco-friendly as well as economical. The urinal is also entirely rimless, making it easy to clean (both within and outside the bowl). Installed with the Odourwise™ Waterless system, Galerie Plan offers the same cost-effective and eco-friendly benefits as Centaurus.

Toilet Sink Taps to be Sensor Driven?

Why use your hands to touch the tap to get the water flowing, before you’ve washed your hands ?

Why have the water running when hands aren’t beneath the taps ?

I need to check out the cost and any other implications. I assume they use a tiny amount of electricity, but best to check.

Combine the Sink and Loo ?

This great combined unit captures (there is an optional bypass if you don’t want it to, eg if you’ve cut your hand) the water you use to wash your hand and then stores this to flush the loo. Integrated 1 unit grey water system.

BUT, £2,500 !!!!!

I’m pretty sure I can have an entire house grey water system for a similar amount.


EcoBuild: Air Source Heat Pumps

Air Source Heat Pumps

The installers / advisors to projects that were speaking at the lectures for self builders were all very positive about air source heat pumps in terms of how they work and how they stack up from an environmental / energy / sustainable point of view.

There are now automated systems for (for example) an air source heat pump to kick in when Photo Voltaic (PV) panels are producing more electricity than the house is using, and so at those times top up the water thermal store in the building. This can then be used for hot water or heating (under floor works at lower temps) at other times (if needed).