Advance Topic 1

EG5085 Advanced Topics 2011-2012

AN ANALYSIS OF THE FEASIBILITY AND PRACTICALITY OF

EXTERNAL WALL INSULATION IN THE UK

I .D. Midgley1 and Dr .M. Imbabi1 1. University of Aberdeen, Fraser Noble Building, Kings College, Aberdeen, AB24 3UE

Abstract:

External Wall Insulation is a rapidly growing market. As the government releases more

schemes financing domestic and non-domestic owners to enter the low carbon society, there

become more products available for more problems and scenarios than ever before. This paper

examines how feasible it is for homeowners in the domestic sector to enter the race to cut our

carbon emissions as much and as quickly as possible. External Wall Insulation is not the only

method of cutting emissions so this paper will also look into other schemes and technologies

available to homeowners. Research found that the environmental impact of various products

was significant in reducing carbon emissions for individual dwellings.

Keywords:

External Wall Insulation, carbon emissions, thermal conductivity


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Contents

1 Introduction .................................................................................................................................. 3

2 Building fabric efficiency .......................................................................................................... 4

2.1 The role of the building fabric ........................................................................................ 4

2.2 Current and future trends................................................................................................ 4

3 Background to External Wall Insulation (EWI)................................................................. 5

3.1 External versus Internal insulation .............................................................................. 5

3.2 EWI in hard to insulate properties................................................................................ 6

4 How EWI works ............................................................................................................................ 6

5 Review of EWI products currently available...................................................................... 7

5.1 Analysis of products ........................................................................................................... 9

6 Schemes to finance EWI in the transition to low carbon..............................................10

7 Economic and Environmental impact assessment.........................................................11

7.1 Economic..............................................................................................................................11

7.2 Environmental ...................................................................................................................13

8 Conclusions..................................................................................................................................13

9 Bibliography................................................................................................................................14


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1 Introduction

Energy efficiency has become a major topic over the last 10 years with governments around the world

investing billions in lowering their countries’ carbon footprint. One way this has been done is by setting

targets and incentives for developers to build more energy efficient buildings.

One quarter of the UK’s carbon emissions come from private homes. Improving the energy

efficiency of a building generally has a direct effect on lowering the carbon footprint of the building. The

burning of fossil fuels to generate energy produces vast quantities of carbon dioxide which escapes into the

atmosphere. At least 82% of the energy heating homes in the UK is generated using fossil fuels. If more

heating energy is contained within the house, the amount of energy used on heating is reduced and less fossil

fuel is consumed.

The government is committed to a long-

term plan for cutting greenhouse gas emissions

drastically, shown above in Table 1.2. As a result

of this there are several large schemes and

incentives starting up currently, such as The Green

Deal and the Renewable Heat Incentive. To the

right is a picture, taken using a thermal imaging

camera, showing a house clad in External Wall

Insulation (EWI) amongst houses with no added

insulation. It is clear to see how much of an impact

this simple technology has on the lowering the

thermal conductivity of the building fabric.

Table 1.1 UK Government targets for Carbon dioxide emissions [16, pg. 7]

Figure 1.1 [12]


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2 Building fabric efficiency

2.1 The role of the building fabric

The fabric of a building separates ‘inside’ from ‘outside’ and refers to ceilings, windows, walls, floors

and doors. The building fabric is key to the energy equation of a building and has a large role in the

building’s energy efficiency. It is important to think carefully about the building fabric when designing a

building, as this is when the most can be done to improve the energy efficiency. That said, there are also

technologies available for existing buildings. These technologies might not be as cost effective or easy to

install but can be effectively applied during a pre-planned refurbishment. This is the best opportunity to

carry out such work.

U-Value explained

The U-value is the amount of heat that passes through one square meter of structure when the

temperature differs by one degree Celsius on either side. The units are watts per square metre per degree of

temperature difference, W/m2K [1, p. 6.0.4]. This is the value most commonly used by the government or

regulatory bodies to set energy rating targets for buildings. The lower the U-value, the more energy efficient

the building is as it loses less heat through its structure.

Carbon footprint explained

A person’s carbon footprint is the amount of Carbon Dioxide that enters the atmosphere because of the

electricity and fuel that person uses. This is measured in tonnes per year.

2.2 Current and future trends

The table below shows the government regulations for required U-Values of refurbishments on

domestic properties. Scotland consistently demands a lower or equal value owing to the temperature

difference between Scotland and the rest of the UK.

Existing Buildings – Scotland (England & Wales)

Domestic altered/refurbished

Lofts 0.15 (0.16)

All other roofs 0.18 (0.18)

Walls 0.22 (0.28)

Floors 0.18 (0.22)

Table 2.1 Government Regulation U-Values (W/m2K) for refurbishments [14]


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As energy prices rise yearly, this year seeing rises of 9.4% within some of the largest suppliers, it is

expected that the government will lower the required U-Value. There are no predictions of what these values

might look like but as insulation technology progresses it could soon be possible to achieve a U-Value of 0

W/m2K. Already it is possible to achieve 0.10 W/m2K, so it is only a matter of time before the regulations

reduce required value to something similar.

3 Background to External Wall Insulation (EWI)

Solid walled properties

With new building methods and materials it is looking likely that the government’s targets for new

super high-energy efficiency ratings will be met. This doesn’t address the problem of existing houses

however. Houses built before 1920 do not have cavity walls, instead their walls are solid brick or stone.

These types of houses make up 36% of all the houses in the UK, which is currently 24.5 million homes [2].

3.1 External versus Internal insulation

Insulating the walls of existing buildings dramatically improves a building’s energy efficiency. For

buildings without cavity walls this means external or internal insulation where added insulation material is

fixed to the exterior or interior of a wall. There are advantages to both and deciding which is most suitable

depends on several aspects. Below is a table comparing External and Internal Wall Insulation:

Pros of Insulation EWI IWI

Doesn’t require good external access Renews outside appearance

Improves weather and sound proofing

Fills gaps and cracks in the wall

Increases life of the wall

Doesn’t need planning permission Doesn’t reduce internal floor space of the

room

Can be installed room by room Not disruptive to household

Doesn’t affect fittings to the internal wall Damp problems can be dealt with after

installation

Table 3.1 Comparison of pros for EWI and IWI


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Why EWI?

As shown in the table above, EWI provides more benefits than IWI for insulating homes without

cavity walls. Although IWI is cheaper, if the wall is old there is an increased likelihood of other problems

such as poor structural integrity and damp. EWI can also alleviate or help these problems as well as

dramatically reducing the building’s CO2 footprint by increasing thermal efficiency.

3.2 EWI in hard to insulate properties

There are scenarios where EWI is difficult to implement and IWI is not an option. IWI may have to be

ruled out if there are features inside the property that cannot be replaced, such as detailed architrave or wall

coverings. A property could be hard to insulate for several reasons such as: the current wall is an extremely

poor insulator; the wall cannot support any extra imposed loading; or, particularly in old stone properties, the

walls are not straight or flat. EWI offers the simplest option as with such a large market in the UK there are

wide ranges of EWI products for many scenarios. In section 5 ‘Review of EWI products currently available’,

I will look at the most competitive products available for EWI today and the specialist scenarios they are

designed for.

4 How EWI works

External Wall Insulation works like a tea cozy, by wrapping the building in a material with a low U-

value. Insulating the walls externally can lower the U-value for a solid brick wall from 2.0, to as low as 0.15

W/m2K. Insulating material is attached to the external walls of the building, sometimes in layers depending

on the original U-value, and then they are covered in a weatherproof breathable membrane and then

rendered.

Figure 4.1 [12]


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5 Review of EWI products currently available

Kingspan

Kingspan Insulation is part of Kingspan group, one of Europe’s fastest growing building materials

manufacturers. Kingspan produces one product suitable for externally insulating existing solid walled

properties, the Kooltherm K5 External Wall Board for masonry walls.

As shown in figure 5.2 below, the K5 External Wall Boards come in various thicknesses, 50-125mm,

and has a thermal conductivity of 0.02W/mK to accommodate a wide variety of needs. The consumer has the

option to lower the U-value of their property to 0.15 W/m2K using the thickest board, 125mm. The K5 is

also structurally stable enough to support a variety of cladding systems; slate, timber or a regular render.

This flexibility gives consumers a wide scope for meeting buildings regulations whilst still having a lot of

stylizing options.

PermaRock

PermaRock is one of the UK’s leading Insulation manufacturers and is based in Loughborough,

Leicestershire. Unlike Kingspan, PermaRock have five different systems specifically designed for external

wall insulation. These systems are; Mineral Fibre, Expanded Polystyrene (EPS), Phenolic Foam, Lamella

and track EPS.

Mineral Fibre is made by spinning filaments of molten rock to form a board with low thermal

conductivity of 0.035–0.036 W/mK, and is available in thicknesses 30-200mm. Mineral Fibre systems are

highly versatile and can be used where more advanced specifications are needed, such as high fire resistance,

acoustic noise reduction and water vapour permeability [9].

EPS is a low cost lightweight option for EWI with thermal conductivity as low as 0.038 W/mK for 20-

350mm thicknesses. This system is ideal for situations where imposed loads need to be kept to a minimum

Figure 5.1 [7]


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on buildings with a lower level of structural integrity. The EPS system can also be more easily profiled to fit

unusual contours and features [10].

Phenolic Foam, like Mineral Fibre, is highly versatile as it also has the highest level of fire rating (0).

The thermal conductivity is exceptionally low at 0.021–0.024 W/mK and therefore thin, only available in 20-

100mm thicknesses [11]. This is a lightweight and low maintenance system but is more expensive than the

previous two.

The Lamella system is deigned for a feature not easily

accommodated by the previous three systems, curved walls. Lamella is

made from Mineral Fibre, however the fibres are orientated

perpendicular to the wall’s surface enabling the boards to fit curved

surfaces. Lamella is also fitted using high bond strength Lamella

Adhesive so no mechanical fittings are required. These boards are

available 30-300mm thicknesses and have a thermal conductivity of

0.04W/mK.

The PermaRock Track-EPS system varies again with the insulating

EPS (0.04 W/mK) boards being fastened to a track leaving a gap between

the boards and wall. This is most beneficial for uneven surfaces where it is

necessary to create a flat even finish.

Knauf Insulation

Knauf Insulation is the UK’s leading insulation manufacturer and operates in 35 countries around the

world. Knauf Insulation has one product specifically for EWI, the EWI Slab.

This system is made from mineral wool, like the mineral fibre system produced

by PermaRock. Knauf boast their KrimpactTM technology gives them an

advantage, with a consistent density and lightweight slab compared to other

similar products on the market. The EWI Slab has Thermal Conductivity of

0.038 W/mK in thicknesses from 40-150mm. This system can be fixed

mechanically or using adhesive. The slab is water repellent preventing water

damage to the underlying wall [13].

Xella

Xella is an International German company and is one of the world’s largest aerated concrete

specialists. Aerated concrete provides structural strength whilst still being lightweight and easy to handle; the

small air bubbles in the concrete also make it a superb insulator. From their Ytong range, the Ytong Multipor

Figure 5.4 [13]

Figure 5.2 [8]

Figure 5.3 [8]


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is a mineral panel made from aerated concrete with a thermal conductivity of 0.045 W/mK. This system is

available in thicknesses of 50-200mm providing a solution for a wide range of insulating needs. The

Multipor is ideal for scenarios where structural strength is an issue as these boards will also give a wall more

strength rather than take away from it. This product has also been awarded a certificate for its ‘exemplary

ecological compatibility’ by the German Institute for Construction and the Environment [15].

5.1 Analysis of products

The External Wall Insulation market is competitive and successful in the UK. As a result of the

competitiveness of the market there are many different solutions available for many scenarios. PermaRock

have the largest number of EWI specific solutions including bespoke solutions for some very specific

scenarios such as the Lamella system that is able to curve to fit the contours of buildings. It may be an

expensive solution, yet if your house has curved walls this is the only product available for EWI that would

be able to match the contours exactly. It does have one of the highest thermal conductivities at 0.04W/mK

however is available up to 300mm thick so is able to insulate a wall to a U-Value of 0.15W/m2K.

PermaRock’s other alternative solution, Track-EPS, gives the consumer the ability to totally redesign

the look of their home. Most solutions fit directly onto the wall and therefore show up anomalous contouring

and uneven surfaces. This system uses EPS boards attached to a track that is pre-fitted to the wall, giving a

crisp even finish. Some insurers require that there is a drained cavity space between insulated render and

existing wall when used on metal or timber framed buildings. This solution has been designed with this in

mind and meets insurers’ requirements.

The remaining EWI products are fundamentally the same: a board type insulator to be attached using

adhesive or mechanical fixtures. The difference is what the boards are made of, both PermaRock and Knauf

have a Mineral Fibre product made from filaments of molten rock. Both products also have thermal

conductivity of 0.038W/mK. The PermaRock solution is very heavy, however it is available in thicknesses

up to 200mm providing a U-Value of 0.19W/m2K. Using KrimpactTM technology, Knauf Insulation’s

mineral fibre boards are lightweight and easy to handle, making them more suitable for structurally less

stable walls. These boards are only available up to 150mm thick, which can only give a U-Value of

0.25W/m2K. Although is up to the standard of today it isn’t planning for the future where energy prices are

higher and new houses are being built with a U-Value of 0.

Expanded Polystyrene is the budget option for EWI; it is lightweight and easy to fit. Due to its weight

it is available up to 350mm thick giving a U-Value of 0.10W/m2K. EPS is ideal for walls that cannot take too

much extra imposed loading or where the wall material is fragile, so fixtures can’t hold much weight. The

problem with EPS is that it is bulky and can make windows and doors look very sunken into the wall, as

large thicknesses are needed to achieve suitable U-Values.

Then are there products that reach into the ‘premium’ ranges of EWI: the Kingspan Kooltherm K5

External Wall Board, PermaRock’s Phenolic Foam Board and the Xella Ytong Multipor. Each has developed


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a more advanced and engineered material providing excellent results in the areas of fire protection, strength

and longevity. Both the K5 and Phenolic Foam have exceptionally low thermal conductivity of 0.02 W/mK.

This means thinner boards can be used making the insulation look like it has always been there. The Ytong

Multipor doesn’t have the same exceptional standards of thermal conductivity; however, being made from

aerated concrete, it does provide the best structural support for walls which otherwise wouldn’t be able to

support any EWI at all.

6 Schemes to finance EWI in the transition to low carbon

CERT (Carbon Emissions Reduction Target)

The government’s Carbon Emissions Reduction Target (CERT) requires all domestic energy suppliers

with more than 50,000 domestic customers to actively lower the quantity of CO2 emitted by households in

the UK between 2008 and 2012 [3;4]. Ofgem regulate the energy suppliers and provide quarterly reports to

the government. Suppliers meet their targets by promoting the uptake of low carbon energy solutions. The

aim of CERT is to make a contribution to the UK’s target under the Kyoto Agreement to cut greenhouse gas

emissions to 12.5% below 1990 levels by 2008-2012 [3].

CESP (Community Energy Saving Programme)

The Community Energy Saving Programme (CESP) is another government initiative aimed at helping

families improve their energy efficiency and reduce energy bills with an emphasis towards low-income

areas. 4,500 areas are eligible in the UK, selected using the Income Domain of the Indices of Multiple

Deprivation England, Scotland and Wales. In England the lowest 10% and in Scotland and Wales the lowest

15% qualify [5].

The Green Deal

The Green Deal, to be released in Autumn 2012, is the government’s flagship carbon cutting initiative

and part of the Energy Bill, introduced in Parliament on 8 December 2010. The Green Deal gives consumers

the opportunity to improve the energy efficiency of their home without having to pay anything up front. The

‘Golden Rule’ [16, pg. 5] is that the expected financial savings from the new insulation must be greater or

equal to the cost of the work done. Energy suppliers and private firms will provide the capital for the work.

Repayments will be made through the customer’s energy bills but the amount repaid won’t exceed the usual

energy bill once the new energy efficiency measures are in place. To be eligible for the Green Deal, as with

most government schemes, there are numerous hoops to jump through first.

The first step is to have an accredited assessment to determine what energy efficiency measures are

suitable for the property in question. The assessor will also give a total cost for the work, the amount saved


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in energy bills and the length of the repayment depending on the type of repayment chosen. The Green Deal

repayment scheme, meaning repayment is made through the energy bill, can also be passed on to future

occupiers.

Once finance has been approved an accredited installer must be chosen from a list accredited by the

Department of Energy and Climate Change. Accredited installers will all hold specific certification ensuring

a standard of product and material certification, and that codes of practices are adequately met; they will also

ensure warranties covering materials and work are all equal.

7 Economic and Environmental Impact Assessment

This Economic and Environmental Impact Assessment looks not only at External Wall Insulation but

other carbon cutting technologies too.

7.1 Economic

EWI cost benefit analysis

Type of solid wall

insulation

Saving per

year

Total

cost including installation

Carbon dioxide saved per

year

Internal Around £445 £5,500 to £8,500 1.8 tonnes

External Around £475 £9,400 - £13,000 1.9 tonnes

Table 7.1 [6]

Renewable Heat Incentive

The Renewable Heat Incentive (RHI) scheme

aims to make renewable heat financially attractive to

businesses and house owners. By offering financial

incentives for installing renewable heating, the

government hopes to cut down on the amount of fossil

fuel the UK uses and help work towards the

greenhouse gas reduction target. The influx of money

into the renewable energy industry will create jobs

from researchers to installation experts. This review

will focus on the RHI for domestic homes. Figure 7.1 Figure 7.1 [17, pg. 9]


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above shows the need for the RHI in the UK with only 1.5% of heating energy in 2008 coming from

renewable sources.

The RHI will be implemented in phases; Phase One has been in operation since August 2011. This

first phase has brought in the Renewable Heat Premium Payments that focuses on houses without a gas

mains supply. The government has set aside £15 million specifically for the premium payments that provide

grants for solar thermal, biomass boilers, air source heat pumps and ground or water source heat pumps. The

solar thermal is the only renewable heating measure open to all UK houses as the others are only open to

homes not connected to mains gas. Below is a table showing the grants available for each renewable heating

measure and the amount each measure costs to install.

All Houses Houses not heated by gas from the mains

Technology Grant Installation Cost Technology Grant Installation Cost

Solar

thermal £300 £4,800 [19] Biomass boiler £950 £11,500 [20]

Air source heat pump £850 £6,000-£10,000 [21]

Ground or water source heat pump £1250 £9,000- £17,000

[22]

Table 7.2 grants available and cost of installation for renewable heating measures [18]

To be eligible for these grants the house must have basic loft and cavity wall insulation. The measures

to be installed must be listed under the ‘Microgeneration Certification Scheme’ found at

www.microgenerationcertification.org. The homeowner must also complete two surveys once the system is

up and running to give the government feedback on the RHI scheme and the measures installed.

Phase Two of the RHI will come into effect sometime in 2012 to coincide with the Green Deal. Phase

Two for domestic homes will see the government bringing in tariffs to pay home owners for their renewable

heat. This will be open to anyone with renewable heating measures installed since 2009, not just those

installed through the Renewable Heat Premium Payments scheme. These tariffs provide the longterm

financial incentive needed to make domestic renewable heat technology feasible to homeowners.

Feed in Tariff Scheme (FITs)

The Feed in Tariff Scheme is similar to the RHI but for electricity production. The government has

tariffs for various renewable electricity generation methods based on the amount of electricity you generate


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per year and how much is exported to the grid. For a typical domestic solar energy scheme the homeowner

per year could earn £1,060 from the generation tariff, £40 from the export tariff and save £90 in energy bills.

7.2 Environmental

To put carbon cutting into context, the average UK home produces 10 tonnes of CO2 per year. Below

is a table showing the number of tonnes of CO2 saved by various carbon-cutting technologies. The amount

saved depends on what energy source is being replaced; for example, coal produces large quantities of CO2

whereas gas produces relatively little.

Technology CO2 saved per year

(Tonnes)

IWI & EWI 1.8 - 1.9

Solar thermal 0.25-0.5

Solar electricity 1

Biomass boiler 3 - 7.5

Air source heat pump 0.8 - 5.4

Ground or water source

heat pump 0.8 - 5.4

Wind turbines 5.2

Table 7.3 Tonnes of CO2 saved using renewable technology

8 Conclusions

External Wall Insulation is definitely feasible and practical in the UK. EWI is not the only carbon

cutting technology showing promising results, however. As shown in section 7.2 Environmental, some

measures available such as Biomass boilers can cut CO2 emissions by 75%. When one quarter of the

UK energy use comes from domestic these types of technology could have a major impact on the

national carbon footprint. EWI alone can cut 20% off the carbon emissions from a home and with

government grants this has become very feasible.

Despite the difficulties in insulating solid walled houses, due to the high demand EWI has

become a competitive market with numerous bespoke solutions for many scenarios and house types.

Even for houses with listed facades where EWI is not possible there is IWI. While it may not be as

favorable, it still has a huge impact on reducing the energy consumption.

It is beneficial financially to spend money on upgrading insulation now while the government is

funding lots of schemes. Once a house has achieved basic up to date insulation the homeowner can

apply for grants to fit renewable heat and electricity technology and actually start to earn money. At the

same time the home will be helping to contribute to the UK’s targets for carbon reduction.


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9 Bibliography

[1] The Scottish Government (SG), (15 October 2011) Technical Handbooks 2011 Domestic

Energy, http://www.scotland.gov.uk/Resource/Doc/217736/0120386.pdf

[2] National Insulation Association (NIA), (15 October 2011) Solid Wall Insulation,

http://www.nationalinsulationassociation.org.uk/householder/index.php?page=solid-wall-

insulation

[3] Department of Energy and Climate Change (DECC), (17 October 2011) Carbon Emissions

Reduction Target (CERT],

http://www.decc.gov.uk/en/content/cms/funding/funding_ops/cert/cert.aspx

[4] Ofgem, (17 October 2011) Energy Efficiency,

http://www.ofgem.gov.uk/Sustainability/Environment/EnergyEff/Pages/EnergyEff.aspx

[5] Department of Energy and Climate Change (DECC), (17 October 2011) Carbon Emission

Saving Programme (CESP), Communities: Areas of Low Income,

http://www.decc.gov.uk/assets/decc/consultations/cesp/1_20090630123736_e_@@_decccomm

unitesareasoflowincomecesp.pdf

[6] Energy Saving Trust, (17 October 2011) Solid Wall Insulation,

http://www.energysavingtrust.org.uk/In-your-home/Roofs-floors-walls-and-windows/Solid-

wall-insulation

[7] Kingspan Insulation, (March 2011) Kooltherm K5 External Wall Board,

http://www.kingspaninsulation.co.uk/getattachment/890a52c7-2425-4c29-88f2-

3cd508a8e364/Kooltherm-K5-External-Wall-Board.aspx

[8] PermaRock, (26 October 2011) Products/ External Wall Insulation,

http://www.permarock.com/products/external_wall_insulation_systems.aspx

[9] PermaRock, (29 October 2011) External Wall insulation Systems/ Mineral Fibre,

http://www.permarock.com/products/external_wall_insulation_systems/mineral_fibre.aspx

[10] PermaRock, (29 October 2011) External Wall insulation Systems/ EPS,

http://www.permarock.com/products/external_wall_insulation_systems/eps.aspx

[11] PermaRock, (29 October 2011) External Wall insulation Systems/ Phenolic,

http://www.permarock.com/products/external_wall_insulation_systems/phenolic.aspx

[12] PermaRock, (29 October 2011) PermaRock existing buildings brochure,

http://www.permarock.com/downloads/PermaRockExistingBuildingsBrochure.pdf


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[13] Knauf Insulation, (29 October 2011) EWI Slab,

http://www.knaufinsulation.co.uk/products/rock_mineral_wool_slabs/external_wall_slabs/ewi_

slab.aspx

[14] Kingspan, U-Value Health Check, 2006

[15] Xella, (31 October 2011) Ytong Multipor Brochure, http://www.mhe-

multipor.com/Ytong%20Multipor%20MHE.pdf

[16] Department of Energy and Climate Change (DECC), (1 November 2011) The Green Deal

– A summary of the Government’s proposals, 2010,

http://www.decc.gov.uk/assets/decc/legislation/energybill/1010-green-deal-summary-

proposals.pdf

[17] Department of Energy and Climate Change (DECC), (2 November 2011) Renewable Heat

Incentive, March 2011,

http://www.decc.gov.uk/assets/decc/What%20we%20do/UK%20energy%20supply/Energy%20

mix/Renewable%20energy/policy/renewableheat/1387-renewable-heat-incentive.pdf

[18] Department of Energy and Climate Change (DECC), (2 November 2011) Renewable Heat

Premium Payments- factsheet, 2011,

http://www.decc.gov.uk/en/content/cms/meeting_energy/renewable_ener/incentive/factsheet/fac

tsheet.aspx

[19] Energy Saving Trust, (2 November 2011) Solar Water Heating, 2011,

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Solar-water-heating

[20] Energy Saving Trust, (2 November 2011) Wood Fuelled Heating, 2011,

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Wood-fuelled-heating

[21] Energy Saving Trust, (2 November 2011) Air Source Heat Pumps, 2011,

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Air-source-heat-pumps

[22] Energy Saving Trust, (2 November 2011) Ground Source Heat Pumps, 2011,

http://www.energysavingtrust.org.uk/Generate-your-own-energy/Ground-source-heat-pumps

Documents

Advance Topic 1