Knowledge Bank

Electric Car
10th February 2020

Electricity? Really? The possible impact of the move to electricity for heating and cars

The latest attempt by the government to meet its near-zero carbon target by bringing forward the move to electric vehicles and all-electric heating is well-intentioned, but I believe it is considerably flawed.

One of the biggest problems is infrastructure, or to be precise, lack of it. Let’s take electric cars as a starting point. 25 million roadside car chargers would be required by 2035, meaning 4,000 charging point installs per day until 2035, starting last week. The cost aside in terms of install, the disruption alone would cost the economy with roads and pavements being affected on a greater scale than that of TV cable laying – what cost in terms of emissions from those works?
Heat Pump
Looking at the fact that 33% of the UK use cars to commute, what happens when they all arrive home and plug in? The head of Oxford University’s Energy and Power group, Malcolm McCulloch, has warned that the National Grid would require an extra 20 gigawatts of generating capacity – putting that into context, Hinkley point generates around a gigawatt per day. Furthermore, substations would need to be installed to cope with the power needed.

Michael Gove speaking on Radio 5 live, was asked by Rachel Burden, what happens if you live in a flat with no access to a charging point. The answer showed a complete lack of understanding of the issues. “Well, you go to a petrol station to fill up, so would go to a charging station to do the same” was the answer. Ah ok, so what if there is a queue with everyone taking 20-40 minutes to charge? Oh, and what do we all do while we are waiting? And this, unlike petrol is not once a week, it is every day!

Furthermore, what happens if we are stuck in a traffic jam, where the road has been closed for an accident and it is the middle of winter on a cold night. We need the heating on, but that will deplete the battery so we could have miles of stranded cars! Throw in the mix that the batteries do not perform as well in the winter and you have a recipe for disaster. Let’s not even get into the fact that there is a limited supply of Lithium for the batteries and to cap it all, Neodymium is only mined in China…. So we get rid of petrol, only to become beholden to another foreign power … could not make it up.

Ofgem has now got involved. Their ‘Decarbonisation Action’ involves households changing the way they use energy, meaning gas boilers to be removed and switched to a lower carbon source. ‘To meet net-zero, Britain will see changes to the way homes and businesses are heated,’ says Jonathan Brearley, chief executive at Ofgem. ‘This might include using hydrogen boilers or electricity to power heat pumps and may see more customers connected to heat networks.’ Aspirational, yes but in reality, it is not possible without a huge uplift in infrastructure. This has even bigger implications than the switch to electric cars.

New build sites would require a number of substations and potentially 3 phase electric supplies. But, in the same way, that commuters come home and plug in their electric car, heating time clocks will put the electric heating on at the same time meaning yet another huge shortfall in the energy supply needed. Large parts of the country could face the kind of blackouts we saw in the ’70s. The change from gas would mean higher bills for the 80% of existing dwellings that are not energy efficient homes, in fact up to 4 times higher bills.

What about hydrogen, you say? It has been suggested that we could pump hydrogen down the existing gas network, as a solution. Supplying hydrogen to industrial users is now a major business around the world. Demand for hydrogen, which has grown more than threefold since 1975, continues to rise – almost entirely supplied from fossil fuels, with 6% of global natural gas and 2% of global coal going to hydrogen production. As a consequence, production of hydrogen is responsible for CO2 emissions of around 830 million tonnes of carbon dioxide per year, equivalent to the CO2 emissions of the United Kingdom and Indonesia combined. So not that clean then? A 20% mix of hydrogen and natural gas is also being proposed, but that does not get around how Hydrogen is produced.

At the moment, hydrogen is mainly produced industrially from natural gas, which generates significant carbon emissions, a type is known as “grey” hydrogen. A cleaner version is “blue” hydrogen, where the carbon emissions are captured and stored, or reused. The cleanest one of all is “green” hydrogen generated by renewable energy sources with no carbon emissions produced. Currently, 3% of hydrogen is produced this way. The reality is that hydrogen on the kind of scale needed for domestic heating is 5 if not 10 years away and how much testing would be required to start pumping it down the existing gas network anyway? Where the hydrogen comes from is an important factor that cannot be ignored.

Hydrogen“Correct me if I am wrong but aren’t boiler manufacturers claiming they have hydrogen boilers?“ No, they claim they have “hydrogen ready” boilers which is not the same thing at all. The claim is that by ‘installing one you would not require a whole new central heating system when hydrogen becomes available.’ Given that there are 3 boiler elements that need changing when hydrogen becomes available, elements that are in fact already in natural gas boilers, it would be highly unlikely that you would require a “whole new central heating system”. Marketing hype and smoke and mirrors as usual.

What, therefore is the answer? Reduce the energy requirements of the home by taking a stringent fabric first approach. When the heating requirement is reduced, the prime energy use is domestic hot water and there are devices out there that reduce the energy required to produce hot water, no matter what the heating system is and I predict technology in this field will start to ramp up. In Sweden, some homes are heated by body heat alone because the fabric of the building is so efficient, that is all that is required.

Some facts to leave this post with. IVL Swedish Environmental Research Institute was commissioned by the Swedish Transport Administration and the Swedish Energy Agency to look into car battery production. The report says that each car battery produced releases as much Co2 as 8 years’ worth of driving a petrol vehicle. The manufacturing processes involved in building a car is more than 17 tonnes. Putting that in context, that is equivalent to 3 years’ worth of gas and electricity emissions for the existing UK home and more like 15 years’ worth for a typical new build home. However, there is an elephant in the room that the building industry needs to address. On average there are 50 tonnes of carbon emissions from the construction of one new dwelling. Off-site construction would not help much as each 2 storey home needs to be delivered by 2 lorries and with 100,000 homes a year predicted to be built this way that is 200,000 lorries on the already crumbling national road network. Maybe that is for another post!

About the author

Gary Nicholls the MD at Briary Energy.

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Heat-loss Building
3rd January 2020

Differences between new build EPCs and EPCs for previously constructed buildings

The letters’ SAP EPC’ reference Energy Performance Certification issued in accordance with SAP methodology and employing SAP software. Such certification is issued by an ‘On-Construction Domestic Energy Assessor.’


SAP calculations are how the energy performance of new UK homes is determined. SAP calculations are a requirement for all new homes, converted dwellings or dwellings subject to a change of use. Specialist assessors use SAP calculations to create an EPC outlining the energy efficiency of each tested building.

Assessors derive part of their results from architectural drawings, together with construction, ventilation, and heating information.

EPC’s for Existing Dwellings

The majority of EPC’s relate to existing homes for sale or let. At one time, this sort of EPC formed part of the potential home purchaser’s or tenant’s Home Information Pack. At present, Home Information Packs are no longer used, and a new process for delivery of EPCs has been put in place.

First, a Domestic Energy Assessor visits the dwelling and carries out a survey. To produce the EPC, the assessor carries out a simplified energy assessment called an RDSAP (Reduced Data SAP). In cases where the inspection fails to yield precise details of how a home has been assembled, the RDSAP methodology may incorporate age-based values and assumptions to help assessors reach meaningful conclusions.

Essentially both types of EPC are identical. Both provide snapshots of the dwelling’s energy efficiency and costs. It’s just that one is constructed from highly detailed construction and service specs and architectural drawings (SAP EPC). The other type relies on on-site surveys. In general, EPCs for existing homes tend to be cheaper to purchase than those derived from SAP Calculations.

SAP Calculations and Extensions

Who doesn’t want plenty of light?

Part L1b of the current Building Regulations determines that new glazing must tot exceed twenty-five percent of the new floor area. Extension designs often propose higher percentages, and so render themselves non-complaint. This is where we can help. SAP Calculations are generated by energy assessors holding industry derived accreditations. These calculations can help demonstrate how your specific proposal may remain building reg compliant and still incorporate substantial amounts of glazing.

How do SAP Calculations for Extensions Work?

More heat escapes through glazing than is lost through roofs and walls. This explains why Building Regulations set limits. It is possible to reduce the negative effects of large-scale grazing by upgrading or over-compensating when constructing other areas. Or by demonstrating other solar gains conferred by additional glazing.

These are not the only options that take account of upgrades to an existing dwelling. ‘Change-of-use’ schemes may also fall under SAP regulations, with examples including flat conversions and commercial-to-residential conversions.

What’s Needed?

To carry out a full SAP L1b assessment, your assessor requires:

  • A set of plans for the existing property
  • A further set of plans for the proposed property (scaled)
  • A detailed summary schedule of all intended construction and services proposals

This is enough to allow the assessor to carry out a desktop assessment. No site visits or surveys will be required.

We specialise in SAP Calculations For Extensions

Every day, nationwide, we help 100s of contractors, architects, and homeowners make large numbers of SAP Calculations for extensions. We are therefore best placed to offer guidance and advice in such matters. If necessary, we can deal directly with your Building Control Officer, taking care of everything on your behalf.

EPC’s, SAP & BRUKL: A Planning Guide

It is the responsibility of an energy assessor to produce SAP, BRUKL, and EPC documentation for new buildings. Such documents offer evidence about how a new build is compliant with the regulations for lower carbon designs.

The EPC is the sole document audited by the accreditation body that governs Energy Assessors’ professional conduct. This renders the EPC the most comprehensive verification of the accuracy of the SAP or BRUKL document for third parties.

This short guide has been designed to help third parties understand the documentation and to make sense of what precisely the document says about a building’s energy performance. We’ll explain differences between SAP, BRUKL, and EPC reports, as well as what is meant by the terms’ design’ and ‘as built.’

What kind of information will I find in EPC, SAP, or BRUKL Documentation?

SAP & BRUKL reports verify compliance with Part L of the Building Regulations for energy conservation. Planning authorities occasionally reference these documents to check compliance against low-carbon targets. But perhaps the clearest distinction between Standard Assessment Procedure documents & Building Regulations UK, Part L documentation is that the former relates to dwellings. At the same time, the latter is concerned with non-domestic dwellings.

BRUKL documents may also be referred to as Simplified Building Energy Model reports. Both documents record a Dwelling Emission Rate (known as a DER) or a Building Emission Rate (known as a BER). Both figures predict the amount of carbon generated by the building in kilograms per square metre per annum and for new buildings must not exceed the TER (Target Emission Rate). Target Emission Rates are bespoke for each dwelling. They are the key deliverable of Part L of the Building Regulations.

Part L contains other rules which rely on SAP and BRUKL documentation, including a domestic Target Fabric Energy Efficiency and minimum scores for fabric and equipment performance.

EPC certification contains information targeted at consumers, which facilitates easy comparison between properties regarding running costs, amongst other things.

EPC, SAP, and BRUKL reports may be issued only by an accredited energy assessor working from government-sanctioned computer applications. These documents may vary in look from provider to provider; however, the information they contain is derived from identical data and methods. In some cases, specific assessors add bespoke summaries of their results and assumptions to the standard output.

What do the terms’ design stage and as built mean?

SAP & BRUKL reports are produced at the design stage of a project and are intended to be predictive, based as they are on a design team’s spec or an assessor’s recommendation. They do not confirm the final performance. Instead, they predict outcomes based on accurate dimensions and specs which remain unaltered throughout construction.

The term ‘As built’ refers to reports generated post-construction and intended to reflect the finished building accurately.

EPCs are generated along with ‘as built’ documents after verification — typically emerging from a mixture of on-site tests, certification from third parties, and self-declarations.

Energy Performance Certificates from Briary Energy

We issue EPCs just before the project comes to an end where residential new builds, conversions, and extensions are concerned. Our STROMA-accredited engineers will issue a residential EPC.

These following actions are carried to dot the I’s and cross the T’s:

  • We check that the Dwelling Emissions Rate (DER) meets the Target Emissions Rate (TER) determined by your SAP calculations.
  • We determine any changes or updates to the building’s fabric, cooling, heating, or ventilation systems.
  • We allocate an EPC rating between A–G, where A indicates the most energy-efficient and G, the least.
  • We Log the property in the government’s landmark register to officially complete the EPC certification process.

In general, dwellings are required to have an updated EPC once a decade. However, one may be necessary sooner where a major change has occurred — the introduction of a new heating system, for example.

Why Choose Us?

  • Discounts for SAP/SBEM Calculations
  • Full UK Coverage
  • Experienced and Accredited Team
  • Practical Advice
  • Same Day Certificates

Related SAP Calculation Services

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Passivhaus OSB Vapour Tight
17th December 2019

Air-tight OSB for timber-frame buildings

Passivhaus is a low-energy performance standard that can be applied to many types of buildings, from homes, care homes, schools, hotels, and supermarkets. This aims to reduce room heating and cooling energy demand while providing excellent indoor comfort levels. This is accomplished mainly by following a “fabric first” approach to construction, with very high airtightness, improved insulation rates and decreased thermal bridging, and the use of mechanical ventilation with heat recovery.
Airtightness is an integral part of building energy-efficient and a Building Regulations necessity. According to NHBC, home energy usage accounts for nearly 27% of UK carbon dioxide emissions. A 2002 BRE report found that air leakage can account for up to 40% of building heat loss. Buildings designed to meet the Passivhaus specification achieve a 75% reduction in space heating requirements compared to standard practise for new buildings in the UK. Therefore, the Passivhaus model provides a reliable approach to help the construction industry achieve the government’s goal of reducing carbon emissions by 80% by 2050.

Airtightness with Passivhaus

The key principle for achieving airtightness is to create a single, continuous, durable airtight layer covering the building’s heated area. It is typically located on the insulation’s warm side, thus also fulfilling the vapour control layer requirements.
To obtain Passivhaus certification, under test conditions, a building must achieve airtightness of less or equal to 0.6 air changes per hour. This is expressed as n50≤0.6h-1 @50 Pa, where n50 is defined as the number of air changes per hour at a 50 Pa reference pressure difference. The result is measured using the building’s internal air volume (m3) instead of its surface area (m2), thus the units are expressed as m3/m3.h, simplified to h-1. This must be the average pressure and depressurization conducted using a blower door sample. Meeting this level of airtightness is difficult but achievable with a clear design plan, with the final result being sensitive to on-site workmanship quality
Current Building Regulations require air permeability at 50Pa to be 7-10m3/h/m2, depending on whether a project is in England, Wales, Scotland or Northern Ireland, so the Passivhaus limit is about five times lower than the maximum allowed. A uniform comparison between air-permeability values and n50 air-change rate values is not feasible because there is no direct relationship and each uses different test and measurement protocols. But to put this in context, the airtightness rate of n50 ≤0.6 h-1 @ 50 Pa is roughly equivalent to a crack in the building’s envelope that is less than a 5p piece per 5m2. For contrast, a building that meets the restricting airtightness requirement for Part L (2013) of the Building Regulations (Section 6 of Building Standards, Scotland and Building Regulations Part F, Northern Ireland) would have a 20p piece gap per 1m2 of envelope.

Passivhaus Internal


Traditionally, air and vapour control layer (AVCL) membranes have been used to achieve airtightness, although there is surprisingly no industry standard or test process. The degree of vapour diffusion depends on the composition of the material and the quality of such systems depends on site design, installation and workmanship.
An alternative is to use certified air and vapour-tight oriented strandboard (OSB). Standard OSB (and other wood panel types such as plywood, particleboard and MDF) are not ideal as an air and vapour tight layer as their air and vapour permeability is variable and can vary greatly between production cycles and production sites. Air and vapour-tight OSB is a new technology: a structural OSB panel that has built-in vapour control and air-barrier properties for the timber frame industry.
The main British and European specifications regulating specification and use of OSB panels are BS EN 300 and BS EN 13986.
BS EN 300 provides a classification system specifying four OSB levels in terms of mechanical quality and relative moisture resistance.
These are:
• OSB1: general purpose boards and boards for interior fittings (including furniture) for use in dry conditions
• OSB2: Load-bearing boards for use in dry conditions
• OSB3: Load-bearing boards for use in humid conditions
• OSB4: heavy-duty load-bearing boards for use in humid conditions.
OSB3 is suitable for a variety of internal and protected external uses including roofing, sarking, flooring, site hoarding and sheathing for external walls, partition walls, internal walls and partitions, spandrel (gable) panels, warm walls, reverse walls and insulated structural panels.
Air and vapour tight OSB panels (classified as OSB3) offer an alternative to air and vapour control layer membranes. The panels are air-and vapour-tight, ensuring airtightness and preventing interstitial condensation within the timber frame structure without a separate membrane.
OSB is made of softwood wood strands such as spruce and pine, wrapped in three layers with a moisture-resistant, formaldehyde-free synthetic resin (bottom, core and top surface) and pressed under high temperature and pressure to form a rigid and dimensional stable wood board. The wood strands are alternately bent by 90 ° to the right angles to the outer layers. This distributes the strength, stiffness and spanning capacity of the finished OSB panels, which are approximately twice as strong in length (major axis) as in width (minor axis).
To address the unpredictable air permeability in conventional OSB, care is taken during production to minimise differences in density and air gaps. Most air and vapour tight OSB panels are accredited by the Passive House Institute (PHI) to achieve maximum air permeability of 0.01m3/(m2h) (PHI Class A).
To overcome inconsistent vapour permeability in OSB, a water vapour-resistant polymer coating coats the inside of the panels. It provides consistently high-water vapour resistance across the panel layer, and its smoothness also guarantees good airtight tape adhesion at panel joints.


In timber-frame buildings in cool temperate climates, the hot side (inside) of thermal insulation requires a vapour control layer to prevent excess water vapour from spreading into the building fabric. Warm air contains more water vapour than cold air and has higher vapour pressure. Vapor diffusion transfer occurs when the hot, humid air inside a building migrates (diffuses) through the building fabric to the low vapour pressure cold air (outside). If this vapour transfer is uncontrolled, condensation within the building fabric (interstitial condensation) can occur as moist air cools and vapour condenses on the assembly’s cold side. Therefore, the vapour control layer’s function is to limit the amount of water vapour entering the building fabric.

Air and vapour-tight OSB panels can also help prevent summer condensation by serving as a buffer. Materials made from cellulose fibres are hygroscopic and therefore can absorb and release small amounts of water vapour from the surrounding environment. In the limited number of cases of reverse vapour diffusion, OSB panels can help to prevent condensation within a structure. This is where moisture from a building envelope’s outer leaf is warmed by summer sun and permeates to the cooler inner layers, creating a possible condensation hazard unless managed or planned.
Research into the suitability of OSB panels as the air and vapour barrier in timber-frame structures found that installation reliability was as important as the panels ‘ intrinsic vapour resistance. This was quantified by the Fraunhofer Institute of Building Physics in 1989, when investigating the effect of a 1 mm tear in the plastic vapour control layer. The difference was found to increase vapour transmission from 0.5g/m2 to 800g/m2 (nearly two pints in 24 hours) as vapour was transported by convection and not by diffusion–convection was found to bring 1600 times more moisture into the system. Therefore, it is important for well-insulated buildings ‘ long-term quality that both airtightness and vapour tightness are considered in conjunction at the design stage and that appropriate, fit-for-purpose and approved products are chosen.

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Air Source Heat Pump Noise Issue
16th December 2019

Are heat pumps a noise nuisance in our garden?

Increasing the use of heat pumps following the release of the Future Homes Standard consultation may create acoustic problems that need to be planned.

Compressor and heat pump fans cause the main noise and vibration concerns.

As air source heat pumps (whether for individual homes or part of a heat network) are typically externally located, there is the potential to create noise nuisance in and around the building, disrupting residents. Careful attention will be given to the position of the plant in relation to noise-sensitive receptors and equipment attenuation means.

A BS4142:2014′ Methods for rating and assessing industrial and commercial sound ‘ assessments should be performed to ensure the plant does not impact the external background noise levels. Heat pumps can generate 60dB. Attenuation measures could include installing silencers and enclosing the ventilation heat pump with sound-absorbing panels and acoustic louvres. These add costs and require additional space, either in plan area or vertical height.

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Changing Specification
19th November 2019

The Dangers of Changing the Specification

Calamity, the merchant can’t get the Aircrete blocks specified for your build, but can offer you medium dense instead. A block is a block, right? Wrong for a variety of reasons that will determine whether your dwelling fails or passes Part L of the building regulations.

An Aircrete Block can have a lambda value as low as 0.11 W/m2K – which is the heat conductivity of a material. This value applies to thermal calculations on buildings and their thermal components. The lower the value the lower the heat loss. By comparison a medium dense block can be anything between a lambda value of 0.28 and 0.60 W/m2K meaning a greater heat loss an in turn higher heating bills.

You can thus see changing the blocks would have a serious impact on the SAP result due to that heat loss being greater. This is one example of where it is possible to fail, by making one decision at the merchants counter or from that call that says “sorry we can’t get those blocks for a week”.

Before making any changes at all, run the potential change past the SAP assessor to see the implications because it is likely that the changes will cost you more than you thought, but there may be an alternative solution that means the build is not held up.

Communication with your SAP assessor, across all aspects of the design and construction process, is vital to ensure the SAP calculation represents the design and construction of the dwelling. In both cases satisfies compliance. Commercial pressures can sometimes impact the quality and accuracy of assessments and information provided, so involving an assessor throughout the process can have significant benefits.

During the build process, communication back to the assessor, when making any changes that could affect the energy efficiency of the dwelling, is paramount. Check that the revised assessment will pass, before implementing any changes. Do not inform the assessor of requirements to get the As-built assessment and EPC produced. This will create issues with the audit process, carried out by the assessor’s accreditation body. The accuracy of the EPC will also be at question.

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U-Value Insulation
19th November 2019

What is a U-value?

U-values measure how effective an insulator is. When it comes to thermal performance, we look in detail at terminology and core concepts.

Although the main focus of the environmental performance of buildings is now on the use of carbon, the thermal performance of the building fabric still needs to be considered as a contributing factor. Thermal performance is measured heat loss and is expressed as U-value or R-value in the construction industry. U-value calculations will be required when designing construction strategies. Many terms have similar meanings, and conflicting interpretations can be found on the Internet. Various terminology and how they relate to each other are explained in this article.

U-value or thermal transmittance (reciprocal R-value)

Thermal transmittance, also known as U-value, is the frequency of heat transfer through a structure (which may be a single material or a composite material) divided by the difference in temperature across that structure. The measurement units are W/m2K. The better-insulated design, the lower the U-value. Workmanship and construction quality may have a significant impact on thermal transmission. If the insulation is designed with holes and cold bridges, the thermal transmittance can be higher than expected. Thermal transmittance takes into account the loss of energy due to conduction, convection and radiation.

Calculating U-value

The basic calculation of the U-value is simple. The U-value can be determined by finding the reciprocal amount of each material’s thermal resistance that makes up the building component concerned. Remember that the internal and external faces, as well as the surface resistances, also have resistances to incorporate. These are fixed values.
A variety of requirements cover thermal transmittance measurement methods.
Simple U-value calculations can be made by considering layer-by-layer construction of the building component. Though, this does not compensate for cold bridging (e.g. by wall ties), air gaps around insulation, or the various thermal properties of e.g. mortar joints.

Measuring U-value

Although design calculations are hypothetical, post-construction measurements are also possible. These have the advantage that they can compensate for workmanship. Heat flux metre can be used to measure thermal transmittance for roofs or walls. It consists of a thermopile sensor attached to the test area to control heat flow from inside to outside. Thermal transmission is derived from dividing average heat flux (flow) by average temperature difference (between inside and outside) over a continuous span of about 2 weeks (or over a year in the case of a ground floor slab due to heat storage in the soil).

U-value calculators

Because calculating U-values can be time-consuming and complex (especially where cold bridging needs to be accounted for, for example), many online U-value calculators were published. Many of these, though, are only available on subscription, and those free appear to be too simplistic. Another alternative is to request a u-value calculation estimate from Briary Energy.
Building Regulations Approved Documents L1A, L2A, L1B and L2B in England and Wales all apply to the publication BR 443 U-value calculation conventions for approved calculation methodologies, while the companion document U-value conventions in operation.

R-value, or thermal insulance (reciprocal of U-value)

Thermal insulance is the opposite of thermal transmittance; in other words, a material’s ability to resist heat flow. R-values are more used in some parts of the world (e.g. Australasia), as opposed to UK U-value choice. Thermal transmittance measurement units are m2K/W and, again, a higher figure suggests better performance (unlike the lower U-value figure).

k-value, or thermal conductivity (also known as lambda or λ value; reciprocal of thermal resistivity)

Thermal conductivity is a material’s ability to conduct heat. So, high thermal conductivity means a higher level of heat transfer across a material; note that this is also temperature-dependent. Thermal conductivity devices are W/m2k. Like U-values and R-values, yet, k-values don’t depend on the material’s thickness.

Y-value, or thermal admittance, or heat transfer coefficient

A material’s ability to absorb and release heat from an internal space as temperature changes in that space is called thermal admittance (or heat transfer coefficient) and is described in BS EN ISO 13786:2007 Thermal performance of building components. This also provides the basis for the Simple dynamic model in CIBSE Guide A: Environmental design, used to measure cooling loads and summer space temperatures. The higher thermal admittance, the higher the thermal mass. Thermal admittance is like thermal transmittance (using the same measuring units). Still, it tests a material’s thermal storage efficiency, i.e. a material’s ability to keep and release heat over time, usually 24 hours. Together with thermal transmittance, measuring units are W/m2K.

Note that ‘ Y-value ‘ thermal admittance should not be confused with ‘ y-value ‘ thermal bridging factor described in the Standard Assessment Procedure (SAP) Appendix K as derived from linear thermal transmission.

Psi (Ψ) value, or linear thermal transmittance

Measurement of heat loss due to a thermal bridge is called linear thermal transmittance (as opposed to’ area’ thermal transmittance otherwise called U-value), with the units of measurement again being W/m2K. Psi values are used to

Thermal mass

Hitherto ignored in the UK construction industry, thermal mass (unlike thermal admittance) is derived from the specific heat capacity (the ability of a material to keep heat relative to its mass), density and thermal conductivity (how heat can pass through a material). SAP 2012 uses thermal conductivity as the’ k’ (or kappa) factor in measuring the thermal mass parameter (TMP). The’ k’ value is the heat capacity per unit area of the building element’s’ active’ component (only the first 50 mm or so of the element’s thickness has a real impact on thermal mass, as it decreases the element’s depth by increasing; the effect is negligible beyond 100 mm). It should be noted that the’ k’ value is an estimate, as assumptions are made about the size of a material’s active volumes; yet, it ignores the effect of thermal conductivity in measuring the time during which heat is absorbed and released from the material. BS EN ISO 13786 offers a more effective thermal mass determination process. Isolation should not confuse thermal mass.

Why not try our U-Value resource.

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PSI Values
18th November 2019

What are PSI Values?

Psi values are a key component of low-energy building design, but what does PSI in building mean?

Historically, design teams have given them a cursory look, often leaving default values and’ assumed results’ in the region. But times change and an appreciation of Psi principles becomes important when an effective building project is being put together.

What are Psi Values?

Have you ever come across a u-value first of all? This is a heat loss calculation by a square metre of thermal component (e.g. a wall).

Okay, Psi values are a measure of heat loss along a metre of junction between two thermal elements, such as the line between a ground floor and an outer wall (see green line in the adjacent picture), and are calculated in W/mK. Collectively these junctions are known as thermal bridging.

Why are psi values important?

U-values compensate for heat loss by thermal components, but not the fabric’s total heat loss. There is additional heat loss at the junctions called non-repeating thermal bridges.

This is due to the geometry of the junction and also, in many cases, to the layout of the junction: the geometry since we calculate internal measurements in SAP and assign U-values to the calculated thermal elements (e.g. external wall and ground floor). Therefore, we underestimate total heat loss. Unless we calculated exterior measurements, we will overestimate total heat loss (assuming no psi-value of construction) The construction because the materials used at the junction often have a higher thermal conductivity than those used in the thermal elements (e.g. a block of concrete at the junction instead of continuous insulation around the junction).

What to do with Psi Values?

In SAP Assessments, we factor in PSI values for all junctions as well as U-values for all exposed elements in order to best model the energy efficiency of a dwelling. Psi levels must be kept to a minimum to satisfy the new building regs.

In reality, designers needed to follow existing schemes such as Accredited Construction Details and Enhanced Construction Details for a realistic shot at achieving compliance.

They have fixed junction configurations depending on the type of construction, i.e. a timber set, as well as a masonry set and a steel set. Nonetheless, these schemes are now obsolete and in the next update of SAP and Part L regs their use will be limited.

This ensures that designers are likely to either use or have their own measured approved make-ups (with related, predetermined Psi values attached) from manufacturers.

Many manufacturers of timber frames and SIPS provide their own super low Psi values that your assessor can use. Customers will need to model heat loss at junctions with custom-made Psi quality calculations on some very low energy builds, such as Passivhaus ventures.

There are also a few schemes set up by the manufacturers of insulation which allow you to demonstrate improved performance by using a combination of their goods.

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EPC certificate
18th November 2019

What is an EPC?

So, what is an EPC Certificate? The Energy Performance Certificate (EPC Certificate) measures the energy efficiency of a property on an A-G scale.

Energy Performance Certificates, launched in England and Wales in 2007, are a legal requirement to sell, lease or build a house. An EPC is valid for 10 years once it is issued.

The most efficient homes-which are expected to have the lowest fuel bills-are in Band A. The Certificate also tells you, on an A-G scale, about the impact the home has on the environment. Better-rated homes should have less effect on CO2 emissions.

The UK average property is in bands D-E for both ratings. The certificate provides tips on ways to improve energy efficiency at home to save you money and help the environment. EPCs also refer to commercial buildings, where a commercial epc is also measured on an A-G scale only by CO2 emission ratings.

Minimum Energy Efficiency Standards (MEES) Legislation

In April 2018, adopted Minimum Energy Efficiency Standards made it a legal requirement for all private properties to have an EPC score of at least an’ E’ before being sold or let. The law extends to both residential and commercial properties, while exceptions exist, for example if a property is a listed building.
Those who fail to make the necessary changes will impose substantial fines: up to £ 5,000 for domestic homes and up to £ 150,000 for non-domestic property.

What is involved?

If you need an EPC, you need a certified energy assessor like Briary Energy to perform an energy assessment.
Energy assessors may enter this data on-site or at home to generate an Energy Performance Certificate lodged in the central registry.

How do I get a copy of an EPC?

If you have the report reference number (RRN) or address, you can easily obtain an EPC by going to the register, or EPC finder.
For properties in England and Wales Landmark EPC click here.
For properties in Scotland, Scottish EPC Register click here.
For properties in Northern Ireland click here.

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SAP Calculations
18th November 2019

What Are SAP Calculations?

They might have flummoxed and annoyed you, but SAP calculations are a critical part of the design cycle for any residential scheme.

Building Regulations require SAP calculations and are required for all newly built dwellings in the UK. After 1995, a SAP score has been required for all new homes under Part L of the Building Regulations, so most developers will recognise it.
For many, though, it will be a new and often daunting part of the planning and building control process.
SAP Calculations do three things:

  1. They assess a SAP score (dwelling’s energy-related operating costs)
  2. They show compliance with Building Regs Part L
  3. To are used to generate an Energy Performance Certificate (EPC certificate)

You may also need a conversion or extension SAP, but different rules apply.

What Does SAP stand for?

SAP means’ Standard Assessment Procedure.’ It’s the only official government-approved method for determining a new home’s energy score. SAP assessors must be accredited with a certification body. SAP is part of Building Regulations Part L.
A SAP score is a way to compare the energy output of different homes, resulting in a value between 1 and 100 + (100 reflecting zero energy costs and anything over shows you export electricity). The higher the SAP score, the lower fuel costs, and the lower carbon dioxide emissions.
The SAP calculations determine an energy cost based on the dwelling construction, heating system, internal lighting, and any renewable technologies. It doesn’t include cooking fuel or appliances.

Why is SAP important to me?

Home builders will need to obtain a “pass” on their SAP calculations in order to comply with current building regulations. Without this calculation, the development is not approved and the building cannot be let or sold.
Nonetheless, there are other reasons why SAP is used. A SAP assessor may help the developer or architect shape a new dwelling’s energy profile, reducing energy use and carbon emissions.
The effect on the ground can be accurately measured and given by different built forms, heating systems and engineering.
Another important issue is that the SAP score communicates the property’s energy efficiency, and informs both purchasers and tenants of the Energy Performance Certificate (EPC certificate).

A ‘ pass ‘ is obtained by several compliance goals around:

    • How well the dwelling fabric absorbs heat
    • Construction quality and system commissioning.
    • Solar Gain
    • Dwelling CO2 predicted emissions

Emissions are Key

The DER / TER figures are used to achieve the benchmark emission target Through comparing the Target Emission Rate (TER) with the expected Dwelling Emission Rate (DER), CO2 emissions are measured.
In the SAP calculation, this target rate is set using a set of baseline values, by comparison to a notional housing of the same size and shape.
Importantly, developers and councils are now using these numbers progressively as a means of achieving certain goals–from achieving green targets and local recycling policy to determining Section 106–type community contributions.

Fabric Energy Efficiency

Homes built in England after April 2014 are also assessed on Fabric Energy Efficiency. This is not a carbon indicator, but energy demand per m2 per year in units of kilowatt-hours. How well a home absorbs the energy it produces can impact its CO2 emissions as well as be measured separately for compliance calculation.
The performance of fabric energy is measured using estimates from DFEE / TFEE. As with emissions a range of baseline values depending on the size of the property is used to set the target under SAP.

What’s Involved?

A SAP Assessor will work with a complete HVAC (heating, ventilation and air conditioning) specification from the architects ‘ plans and design details. Drawings need to be scaled, accurate and show all plans for elevations, sections, floor and location.
The assessor will either digitally or manually scale off these plans to create a dwelling(s) template in SAP software
Once the site is established heating, lighting and ventilation systems are introduced–different items are chosen from the databases of the manufacturer where they are identified.
Along with all measurements for thermal junctions, all thermal elements (walls, floors, roofs and openings) are included in detail. Renewable technologies and cooling are also added.
When complete, a SAP analysis will generate a range of comprehensive reporting outputs, ranging from site type, heat losses and energy demand to seasonal variations, CO2 emissions and contributions to renewables, to name a few.

How Do I Make Sure of a Pass?

It is fair to say that designers and architects have not paid much attention to SAP in the past–but since the significant changes in 2005, SAP 2009 and again in 2014, compliance with the SAP regulations and, in effect, Part L of the Building Regulations has become much tougher. Working without a SAP model now causes more problems!
This is mainly due to the immense tightening of the CO2 emission targets–driven by European and UK climate policies. The average 5-year-old new build is significantly different to today’s regulations.
We are often asked to explain why some builds fail and some succeed, and it’s not always easy to give a straight answer. Numerous factors will play a part, from the size of the boiler to the junction in the wall, to the thickness of the insulation in the floor and in which direction the house is pointing!
Some factors may be beyond client control–for example, having no mains gas link may mean having to use an oil or LPG network. Such fuels have higher cost and CO2 emission factors within SAP, and as the target emission rate is set on the basis of the mains gas system, you are hitting.


Every day we run SAP calcs–spanning single self-constructions up to 30 storey apartment blocks, so we have a good idea of what works and what doesn’t.
If we disregard the broader issues of climate change, avoid tactics, and conclude that we are not trying to create a zero carbon home, we can tie down some good principles that will give you a good chance of success:
There are minimum u values to beat, not followed. If the building material is well insulated, no fancy renewable technologies are required to get you through.
Pay attention to the u values on the openings you specify to get them as low as possible, preferably 1.4 W / m2 K or less.
It’s not the boiler it’s the controls that will often have a more significant effect on the SAP score than the boiler itself.
Get it airtight. All new builds require the completion of the Air Permeability Test and the resulting figure goes into the SAP Calcs. Ensure that the envelope is sealed and conduct a pre-test review if possible.
Pay attention to thermal bridging. This is heat loss across outer wall junctions. Follow a scheme like Accredited Construction Details (ACD’s) that will allow us to avoid using the default information. See our Thermal Bridging section for our guide.

Start as Early as Possible

The one key point is to start early–even more important than those above. If we get a set of plans halfway through a construction, there’s not much we can do to improve the building’s energy efficiency.
This situation often leads to a lot of bad practise and generally the introduction of unnecessary, costly technology added in hindsight just to pass building regs or satisfy a planning requirement.
Prevent this by communicating as early as possible with your SAP assessor in the process–often before planning has even been submitted, and definitely well before building applications for regs.

Is SAP just for New Builds?

Not at all, most extensions, conversions and change of uses require SAP calculations under Part L1b of building regulations.

Contact our friendly team today on 020 3397 1373 or use the contact form here.

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Thermal Bridging Calculations
16th November 2019

Thermal Bridging

A thermal bridge (sometimes referred to as thermal bridging, a cold bridge or thermal bypass) describes a situation in a building where there is a direct link between inside and outside via one or more thermally conductive elements than the rest of the building envelope.

This will result in unnecessary heat transfer across this component, its internal surface temperature may vary from other, better insulated internal surfaces, and condensation that occur when hot, humid internal air comes into contact with the potentially cold surface. This condensation can cause mould growth.

Thermal bridges are common in older buildings, poorly constructed, poorly insulated, with single-skin construction and single-skin glazing.

Thermal bridging can occur in modern buildings due to poor design or poor workmanship. This is normal when building components penetrate through its isolated material, e.g. through glazing, or where the framework penetrates the building envelope, e.g. on balconies.

Nonetheless, as buildings have become better insulated, with increasingly strict regulation, so thermal bridges that may have previously been considered negligible in terms of a building’s overall thermal quality may actually cause considerable thermal inefficiency. There is potential for such inefficiency at each opening and junction (even in party walls).

For example, thermal bridges can be classified as’ repeating’ where wall links periodically bridge the cavity, or’ non-repeating’ such as wall junction or lintel.

The Approved Document Part L of the Building Regulations (Conservation of Fuel and Power) state that’ Building fabric should be built so that there are no fairly avoidable thermal bridges in the layers of insulation created by gaps in the various elements, at the joints between elements and at the edges of elements such as those around window and door openings.’

Thermal bridges in completed buildings can be exposed with thermal imaging cameras, but they can be very hard to rectify, particularly if replicated throughout a house.

Briary Energy can complete Thermal Bridging Calculations, please contact us for further information

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