The first set of national building standards for England and Wales, The Building Regulations, were published in 1965 (Scotland 1963). The regulations were amended in 1972, to add a first mention of “conservation of fuel and power”.
Over the following (nearly) 50 years, the insulation levels required by the Building Regulations have changed beyond recognition. This makes a home’s build date very useful when trying to assess a house’s space heating demands or sizing a radiator, boiler or woodburning stove. This article gives some background on how insulation levels have changed and what difference it has made to energy use. The historic data is taken from regulations for new dwellings in England; Wales & Scotland operate similar but not identical regulations.
It explains how building fabric heat losses in a typical 3-bedroomed house, built to the Building Regulations prevailing in each decade, have dropped from around 9,100 Watts for a 1970’s built house to 1,410 Watts for a house built in 2016. That means that a 5kWh output woodburning stove may be perfect for a 1970’s home but would be highly unsuitable in a 2016 built house (if it existed you would need a 0.8kWh output woodburning stove or a single bar on an electric fire!). The consequences for radiator and boiler sizing are similar if you want to avoid an overheated house.
U-values And Air Leakage Levels Determine Space Heating Demand
There are three main factors which determine the energy needed to keep a house warm:
- U-values: how much heat is lost through the fabric of the building – surface heat loss through walls, ceilings, floors, windows and doors
- Air leakage: how much heat is lost through ventilation heat loss – gaps in floors, windows, doors, open chimneys and loft hatches which allow cold air in and warm air out
- Thermal bridging: Which will not be considered here, is when a highly conductive component effectively allows insulation elements to be bypassed, increasing heat loss.
Heat loss through the building fabric is calculated by taking the u-value of each material used in the house. The u-value, measured in W/m², or Watts per square metre, tells you how much energy is lost for every 1°C difference between the two sides of the material. It’s relatively easy to find out the u-value of common materials and calculate this loss for a house or for a room. If you have a material with a poor u-value then you can generally improve it with insulation. The more insulation you put in the lower the u-value.
Air leakage or ventilation heat loss in a house is harder to measure and control. We need a certain level of fresh air to replenish the air that we breathe so there is guidance for how many air changes an hour each room in a house should have. The problem is that if there is too much air leakage we lose our expensively heated air much faster than we need to, resulting in bigger heating bills and colder rooms. We are not going to consider air leakage in any detail here, although as houses get better insulated to reduce heat loss through the fabric then the heat lost through air leakage starts to become more significant.
How u-values have dropped over the years
Table 1 below shows the maximum u-values permitted by Building Regulations for each component each decade, during construction of a new dwelling. In the 1970s compliance could also be demonstrated by using recognised construction details which approximated to the maximum U-value. The figures for 2019 use the Concurrent Notional Dwelling Specification to demonstrate compliance, as the regulations do allow a slightly worse performance of one component if it is compensated by better performance of another. Building Regulations actually change more frequently than every decade, usually about every 5 years or so and each part of the regulations may be updated at a different time, but it gives a good guide to what has happened over the last 50 years. Highlighted in violet is the first time the u-value requirement for a component was strengthened.
Table 1: U-values By Building Component For New Homes
| Component | 1970 * | 1980 * | 1990 | 2000 | 2010 | 2019 |
| Wall | 1.6 | 1.0 | 0.6 | 0.45 | 0.3 | 0.18 |
| Ceiling | 1.5 | 0.68 | 0.4 | 0.35 | 0.2 | 0.13 |
| Floor | 1.2 | 1.2 | 1.2 | 0.51 | 0.22 | 0.13 |
| Window/door | 4.8 | 4.8 | 4.8 | 3.1 | 2.0 | 1.4 |
* Figures for 1970 and 1980 are based on SAP2005 assumptions for homes built 1967-1975 and 1976-1982 using specifications provided by Building Regulations. Assumes uninsulated cavity wall.
Note: The figures above indicate the direction of travel on U-values at the start of each decade, rather than the date on which they changed. For more detail on specific changes see Great Home: History of maximum U-values in Building Regulations.
We have started the table with 1970. Why? Well it was the oil crisis of the 70’s which made the government first seriously think about reducing energy usage. The crisis drove changes in the 1976 Building Regulations which set minimum insulation levels for the first time. Before 1976 the standard cavity wall had not changed much since the end of the 19th Century. The violet highlight shows that walls and ceilings were the first areas that got a focus from the Building Regulations, with floors and windows following on later. Until 1994 you could still put a single glazed window in a house (u-value 4.8). When double glazing became a requirement the standard was set at 3.1 (what the double glazing industry could achieve at the time). In 2002 stricter regulations were introduced for windows for both new houses and also for replacement windows in existing houses.
So what do these improvements mean for a typical house?
Example: A 3-bedroom House
To illustrate the impact of the changes in u-values over the years let’s take an example house built in each decade. Our simplified 3-bedroom two storey example house is a rectangular box 10 metres long x 5 metres wide x 5 metres high (we don’t count the pitched roof as part of the house as we will insulate the floor of the loft). We assume that the occupants try to keep all the rooms at 20°C for 15 hours per day whilst the outside temperature is at zero (0°C); that the floor is a suspended timber floor with clay underneath. We will take a house with a cavity wall construction insulated to the standard prevailing at the time of build; we will also assume that air leakage is equivalent to 1.5 air changes per hour (we briefly use this figure to compare ventilation heat loss with fabric heat loss).
Using the dimensions above gives us the following for our simplified 3-bedroomed house:
- Ground Floor Area: 50m²
- Upstairs Ceiling Area:50m²
- External wall area: 125m² (excluding windows/doors)
- Windows/doors area: 25m²
- House volume: 250m³
Our simplified house is not that different to a house built today; today’s average house has shrunk a little over the years in length to be 8.6m with a 5.2m width.
So what is the impact of improving u-values on the heat loss from this house?
Table 2: Building Fabric Heat Loss By Decade For House Built To Building Regulations
| Year | 1970 | 1980 | 1990 | 2000 | 2010 | 2019 |
| Heat Loss (W) | 9,100 | 6,780 | 5,500 | 3,535 | 2,170 | 1,410 |
| Daily Demand kWh | 136.5 | 101.7 | 82.5 | 53.0 | 32.6 | 21.2 |
| Cost for day | £5.46 | £4.07 | £3.30 | £2.12 | £1.30 | £0.85 |
Assuming your gas cost 4p per kWh then if you lived in our 3-bedroomed house built to today’s Building Regulations you would be spending around 16% of what someone living in an unmodified 1970’s built house would spend to heat it when the outside temperature was a constant 0°C.
That figure ignores the cost of heat loss due to air leakage which is worth briefly mentioning. The ventilation heat loss (air leakage) of a 1970’s house would be about 2,475 Watts when the temperature outside was 0°C. That would add about 37kWh and £1.49 to the day’s demand, taking the total heating cost from £5.46 to £6.95.
A 2016 built house is better on air leakage but it is not dramatically better. It was only in the Building Regulations issued in October 2010 (see updated 2013 edition, Approved Document L1A: conservation of fuel and power in new dwellings) that airtightness was a specific and not very demanding requirement. Airtightness is checked by an air leakage test. A new build house is pressurised by 50Pa above atmospheric pressure using fans mounted in an outside door and the amount of air required to maintain this pressure is measured. On this test the Building Regulations target is 5m³/(hours per m²) and the maximum allowable is 10m³/(hours per m²). If you compare this with a PassivHaus designed house, air leakage is an order of magnitude lower at below 0.6m³/(hr per m²). In a 2016 built house it is likely that air leakage is a bigger cost than heat loss through the fabric. That’s the opportunity for future improvements in energy efficiency in Building Regulations.However once you go much below 3.5m³/(hr per m²) then other features need to be added to the house design such as Mechanical Ventilation Heat Recovery Systems (MVHR systems).
To show a little more detail about how the heat loss figures are calculated, below are the fabric heat loss workings for the 1970’s house.
Table 3: U-value and Fabric Heat Loss for a 1970’s Built House
| Surface | Area m² | U-value | Temp Diff °C | Heat Loss Watts |
| Wall | 125 | 1.6 | 20 | 4,000 |
| Ceiling | 50 | 1.5 | 20 | 1,500 |
| Floor | 50 | 1.2 | 20 | 1,200 |
| Window/door | 50 | 4.8 | 20 | 2,400 |
| Total thermal loss | 9,100 |
This tells us that ignoring air leakage, on a cold day we will require power of 9,100 Watts or 9.1kW to maintain a 20°C temperature. For a 15 hour period we multiply this figure by 15 and we get 136,500 Watt hours which is best expressed as 136.5kWh or kiloWatt hours. If you are paying 4p per kWh for your gas
then this would equate to about £5.46 on your gas bill for this day.
The heat loss as a result of air leakage (ventilation heat loss) is calculated by multiplying the volume of the house (250 m³) by the air changes per hour (1.5) by the temperature difference (20°C) by 0.33 (energy required to heat 1m³ of air). This gives 2,475 Watts of heat loss which converts to an extra 37.12kWh of energy and £1.49 per day. Air leakage probably reduced as construction standards have generally improved between 1970 and 2016 but it is hard to quantify without air leakage testing on individual houses
I hope you have enjoyed this brief look at the impact of Building Regulations u-value changes over the last 50 years. Please feel free to comment on my simplified approach to explaining it and correcting any errors I have made.
Building Regulations Publishing Dates (England)
These include:
- The Building Regulations 1965
- The Building Regulations 1972
- The Building Regulations 1976
- The Buildings (Second Amendment) Regulations 1981
- The Building Act 1984
- The Buildings Regulations 1991
- Approval Document L1 1995 edition
- 2002
- Approved Document L1: Conservation of fuel and power in dwellings (2002 edition)
- Approved Document L2: Conservation of fuel and power in buildings other than dwellings (2002 edition)
- 2005
- Approved Document L1A: Conservation of fuel and power in dwellings (2005 Interim Edition)
- Approved Document L1B: Conservation of fuel and power in existing dwellings (2005 Interim Edition)
- Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings (2005 Interim Edition)
- Approved Document L2B: Work in existing buildings other than dwellings (2005 Interim Edition)
- 2006
- Approved Document L1A: Conservation of fuel and power in new dwellings (2006 edition)
- Approved Document L1B: Conservation of fuel and power in existing dwellings (2006 edition)
- Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings (2006 edition)
- Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings (2006 edition)
- 2010
- Approved Document L1A: Conservation of fuel and power in new dwellings (2010 edition)
- Approved Document L1B: Conservation of fuel and power in existing dwellings (2010 edition)
- Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings (2010 edition)
- Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings (2010 edition)
- 2013
- Approved Document L1B: Conservation of fuel and power in existing dwellings, 2010 edition (incorporating 2010, 2011 and 2013 amendments)
- Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings, 2010 edition (incorporating 2010, 2011 and 2013 amendments)
- Approved Document L1A: Conservation of fuel and power in new dwellings (2013 edition)
- Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings (2013 edition)
- 2016
- Approved Document L1A: Conservation of fuel and power in new dwellings (2013 edition with 2016 amendments)
- Approved Document L1B: Conservation of fuel and power in existing dwellings (2010 edition incorporating 2010, 2011, 2013 and 2016 amendments)
- Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings (2013 Edition with 2016 amendments)
- Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings, 2010 edition (incorporating 2010, 2011, 2013 and 2016 amendments)
- 2018
- Approved Document L1B: conservation of fuel and power in existing dwellings, 2010 edition (incorporating 2010, 2011, 2013, 2016 and 2018 amendments)
In which year did cavity wall insulation become compulsory in new builds? I have read that it became compulsory during the 1990’s but have not been able to establish the exact year. Please can you advise?
Excellent web site and range and breakdown and costs clearly explained.
(Might add – costed at present day rates) Wonder how it relates to typical incomes but that might be going too far
A further development would be to expand to a year based on ext temp/heating days
Figure relates to gas but could other fuels be factored in especilaly with expected reduction of gas use for boilers
Links to other items also very good – any figures on MVHR installation?
This is great Jon, many thanks. Do you by any chance have a table of all the historic minimum u-values by element? If not are the historic regs all online somewhere to extract this from?
Hi Dominic,
Sorry, I don’t have a table of each element, although most could be extracted from the various Acts of Parliament and then Approved Documents if you can trace them on the web. The information in the article was more to show the direction of travel than to capture the timing of every change. It does to some extent depend on what use you will put information to – whether it is to work out typical values in an era or the maximum u-value permissible.
Just as background the original Building Acts were for all buildings, new and old. Over the years we have seen approved documents developed for both new and existing dwellings and new and existing buildings other than dwellings. So there are now four different standards, all with some common history. In historic regulations there were also different ways of achieving this, of which U-value was one. The original mentions of insulation were often based on construction detail – as long as you used that construction method/materials then you met the standard rather than having to calculate a U-value. Also the U-value only applied for some elements i.e. suspended floors but not solid concrete floors as they to an extent considered fabric loss and ventilation losses together.
Kind regards
Jon
Update: 11 Nov 2020. Having gone back through my files, you may find found this document helpful https://great-home.co.uk/pdf/Great-Home-Tracking-changes-to-building-regulations.pdf
Very useful. Cheeky question … might this be updated to reflect the UK’s Future Homes Standard?
Hi Richard,
I do revisit this article from time to time to check on new standards. At the moment we are still awaiting the government response to the the Future Homes Standard consultation (which closed in February 2020) so details may change depending on what uplift in energy efficiency standards are agreed upon compared to current regulations (20% and 31% are the two options offered in the consultation). Once we have the response to the consultation (which may have even bigger changes such as the option of a hydrogen ready boiler rather than just a heat pump) I would look to update this.
Kind regards
Jon
Thanks Jon. Will keep an eye out. At 20% and 31% reduction from consultation, your figure of 21.2kWh/day (assuming 0°C externally and internal reqt. of 20°C in your model house) would be reduced to 17kWh and 14.6kWh respectively. Impressive when compared to the 1970 figure of 136.5 kWh. But of course, we have the issue that 80% of the homes in 2050 have already been built; but at least the standards will stop us piling further problems onto that retrofit legacy.
I was playing a bit with your numbers. I assume, to estimate the heat lost in your model house as a function of external temperature, one could simply use a linear interpolation between, say, 21.2kWh (0°C) and 0kWh (20°C), to give a trivial equation ‘Fabric Heat Loss at Temp. T’ = ((20-T)/20) * 21.2 kWh (at least in the range 0-20 °C).
Hi Richard,
Your assumption is a good rule of thumb, although for heating purposes one normally assumes that space heating is not required above 15.5C outside air temperature so it would be better to use this as a zero base. This is because other factors potentially come into play; solar gain, appliances giving off heat, even the number of people in the house.
The other factor to bear in mind is that these are fabric heat losses only. At low levels of fabric heat losses then ventilation heat loss starts to become much more significant so Building Regs also needs to address a tightening of this to achieve the overall energy efficiency improvement. At 2019 levels these ventilation losses are higher than the fabric losses. That’s why Passivhaus is so obsessive about air tightness, allowing around 10% of the ventilation losses of current Building Regs.
Hi….
Help…. ( LOL ) …
Could someone please assist me in calculating BTUs for my Hall stairs & landing… ? Every website I’m looking on has their own BTU calculator, each giving completely different calculations. It’s very confusing. Ideally I’m looking to buy a 2 column traditional vertical radiator. 1800mm H, no wider than 390mm W..
Room size…..
Length = 5.805mm ,
Width. = 2.990mm
Height. = 5.235mm
It’s only a small space as you walk through front door ( composite ) north facing..
Gable end ( west facing ) extends up to roof space. Part of which is pitched, part insulated but pitch is not.. Cavity wall insulated.
Also there is one small double glazed window, 1mtr square. None opening with slide vent.
Ground floor in hallway is soil under solid floor.
I only have one area in which to place the radiator which is at the bottom of the stairs.
Kind regards
Sue.
Hi Sue,
I think your challenge is to get reasonable estimates for each of the fabric elements and to form a view on how draughty the hall is. This will allow you to best size radiators so that they are sufficient for the job but not over specified which could overheat the hall, especially upstairs.
Whilst you may feel its only a small space, from the dimensions it has a volume of circa 91m3 which is significant. It would be helpful to know the age of the house as cavity wall insulation standards have changed over the decade and that is a key factor. Using one radiator may create unwanted air circulation effects so in this volume or room it may be better to look at two radiator locations rather than one.
From your description I have interpreted the following, using the Great Home BTU calculator assumptions
Wall 1: 5.805m external cavity wall built prior to 1990 u-value 0.6
Wall 2: 2.990m external cavity wall built prior to 1990 u-value 0.6
Wall 3: 5.805m internal wall
Wall 4: 2.990 external cavity wall built prior to 1990 u-value 0.6
Window in wall 2: 1m2 area double glazed installed after 2002 u-value 2.0
Door in Wall 2: 2m2 area composite door installed after 2002 u-value 2.0
Floor: Concrete floor. You do not say whether it is insulated or not so assume uninsulated with u-value 1.2. If you know it to be insulated then you could use a lower u-value.
Roof: You do not indicate how well insulated the insulated area is. The pitched area will have some insulation level, depending on its construction. If we assume 100mm insulation on average over the roof then this is a u-value of 0.4
Assume a 21°C hall temperature with 1.5 air changes per hour (same as a standard lounge) and that the hall is not especially draughty.
Based on these assumptions then the heat losses, allowing for 15% overcapacity, are likely to be around 3.2kW or 10,800 BTU at -1°C. Your radiators would need to cover this. If you can get more precise details on the wall and roof insulation and the door u-value then you can use the Great Home BTU calculator to calculate a figure that more accurately reflects your home. See Great Home BTU calculator. Do bear in mind that if you can improve the insulation in the roof it would be smart to do this first, so you can use a lower output radiator.
Hope this helps. Good luck with your project.
Kind regards
Jon
HAVE LOOKED AT VARIOUS WEB SITES AND THE U VALUES GIVEN DIFFER WHICH IS THE CORRECT SITE
Hi Paul, Thanks for your query. You could well see different figures quoted for England, Wales & Scotland who all operate slightly different systems. Also different manufacturers will probably recommend using slightly better than minimum Building Regulation standards for the components they produce.
The u values for England are set by the Building Regulations, which for insulation are covered under part L and are split into:
L1A – covering conservation of fuel and power in new dwellings
L1B – which covers refurbishment of existing dwellings.
The Building Regulations (England) require a builder to demonstrate compliance with a notional dwelling specification which in 2019 means, for a new dwelling:
External walls: 0.18W/(m2K)
Floor: 0.13W/(m2K)
Roof 0.13W/(m2K)
Windows: 1.4W/(m2K)
These figures are the notional dwelling specification to demonstrate overall compliance. The regulations do allow a slightly worse performance of one component if it is compensated by better performance of another.
For refurbishment of an existing dwelling then other figures can potentially be used, depending on the extent of the refurbishment and whether new thermal elements (walls etc) are being built. Refer to guidance in L1B on these as it it depends on the level of refurbishment.
You can find the full details of the current Building Regulation Part L in force in England at planningportal.co.uk/info/200135/approved_documents/74/part_l_-_conservation_of_fuel_and_power
There are similar documents for Wales (also called part L) and for Scotland (Section 6 of the Building standard technical handbook).
Hope this help
Kind regards, Jon