Retrofit Glossary

Retrofit Condensed Glossary

"The Retrofit Academy CIC is at the heart of delivering leading-edge training and professional development to a new generation of retrofit professionals in the UK.

Our vision is a world where every home is warm, healthy and low carbon. To deliver 27 million retrofits over the next 30 years in the United Kingdom, we need an army of retrofitters in both white and blue collar roles. Our mission is to enable this.

The Retrofit Academy is central to driving PAS 2035 compliance by shaping retrofit best practice, sharing our technical expertise with industry peers, and advancing the sector through our Centre of Excellence."


The Retrofit Glossary - reproduced here by very kind permission of the Retrofit Academy

A-value – Water absorption coefficient of a material  in kg/m2s0.5.

Absolute Humidity – The measure of water vapor (moisture) in the air, regardless  of temperature. It is expressed as grams of moisture per cubic meter of air (g/m3).

ACH - Air changes per hour – The number  of times per hour that the air inside a building is changed.

Air permeability – Defined in BS EN 13829. Units m3 /m2hr at 50 Pascals or m/h @ 50 Pa.

AECB – Association for Environment Conscious Building, a network for promoting sustainable  building and creator of the Carbonlite Retrofit Course.

Airtightness – The fundamental building property that impacts infiltration* (the uncontrolled inward  leakage of outdoor air through cracks, interstices or other unintentional openings  of a building, caused by pressure effects of the wind and/or stack effect). (*

BBA Certification – British  Board of Agreement - the UKs leading construction certification body.

BEIS – Government Department for Business, Energy & Industrial Strategy.

Biomass boiler – Biomass boilers  take solid fuel such as logs, wood chip, or pellets and burn them to provide  central heating and hot water. Their main advantage is in their use of renewable  fuel, which results in lower CO2 emissions. They are best suited to “off-gas” properties. They are eligible  for the renewable  heat incentive..

BRE – A multi-disciplinary, UK based, building science centre with a mission  to improve buildings and infrastructure, through research and knowledge generation.

BREDEM – BRE Domestic Energy Model. Used to underpin SAP.

Cavity wall insulation – From around  1920, houses in the UK were typically built with a cavity in between two layers of brick wall. Heat loss through this type of wall can therefore be reduced using cavity wall insulation, which is installed by blowing insulating material  into the gap. Where applicable,  it is often one of most cost- effective energy saving measures.

CDM – Condensation, Damp & Mould.

CFL – Compact Florescent Lighting.

CHP – Combined  Heat and Power engine.

CIGA – Cavity Insulation Guarantee Agency.

Combi boiler – A combi boiler  is both a water heater and a central heating boiler,  combined (hence the name) within one compact unit. Therefore, no separate hot water cylinder is required.

Condensing boiler – Condensing  boilers  use heat from exhaust gases that would  normally be released into the atmosphere through the flue. As a result, they tend to be more efficient  than non-condensing boilers.

COP – Coefficient  of Performance  – the degree to which the heating system used converts  energy in the fuel to heat in a dwelling. For example, a GSHP which converts  1 unit of energy in to 3.5 units of heat has a COP of 3.5.

CWI – Cavity wall insulation.

DCV – Demand Controlled ventilation.

DEA – Domestic Energy Assessor.

Delivered energy – The amount  of energy which is supplied  to final users, e.g., households, office buildings, schools, factories  and cars.

DSER – Doorset Energy Rating.

DSM – Dynamic Simulation Modelling. The most complex  modelling technique  for energy in buildings.

DPC – Damp Proof Course.

ECO – The Energy Company Obligation (ECO) is a Government subsidy scheme paid for through a levy on UK households’ energy bills. It provides  grants towards  in the installation of energy efficiency  measures, such as solid wall, loft and cavity insulation, with a focus on fuel poor and “hard to treat” homes. (https://w w /energy-company-obligation)

EER – Energy Efficiency rating from SAP.

EnerPHit – The Passivhaus retrofit energy and comfort standard.

EPC – Energy Performance  Certificate.

EPS – Expanded Polystyrene.  An open cell rigid insulation.

ErP – Energy Related Products Directive.

EWI – External wall insulation – External wall insulation (EWI) is another  solution for solid walls or hard to treat cavities. Although room sizes aren’t affected, the outside appearance of the building will be affected and roof eaves may need to be extended. The insulation is applied to the walls and then covered in a suitable material  – usually render but brick slips, pebbledash  or cladding  is also available. EWI can be expensive, but can often attract a grant/ subsidy.

FGHRS – Flue gas heat recovery  systems.

FMB – Federation  of Master Builders, a trade association  in the construction industry.

FiT or Feed-in Tariff – The Feed-in Tariff (FiT) is a Government subsidy scheme that is designed to incentivise the installation of measures that generate renewable  electricity, such as solar panels. Under this scheme, households are paid for the each unit of electricity that they generate, as well as being able to sell excess electricity to the grid. This significantly increases the payback of renewable  heating measures. (https://w w /feed-in-tariffs)

GDAO – Green Deal Advice Organisation.

GDA – Green Deal Assessor.

GFI – Ground  floor insulation.

GHG – Greenhouse  gas emissions.

Glaser method – A simplified modelling tool for analysing  moisture in building constructions. Suitable for moisture closed designs.

GSHP - Ground source heat pump – Similar to their air source cousins, ground source heat pumps (GSHPs) takes heat from the ground and uses this to provide  central heating and hot water. As, below a certain level, the ground stays at a fairly  constant  temperature all year round,  these can achieve a higher  Coefficient  of Performance  (COP) than air source heat pumps (which work better in milder  temperatures). They are eligible  for the renewable  heat incentive  (RHI, see above).

GWP - Global Warming Potential – A measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative  scale which compares the gas in question  to that of the same mass of carbon dioxide (whose GWP is by definition 1). For example, methane, nitrous oxide and sulphur  hexafluoride have GWPs many times that of CO2, although CO2 is being emitted  into the atmosphere in much larger quantities.

HAM – Heat, Air and Moisture simulation, or Hygrothermal simulation. A dynamic  simulation method  used to evaluate moisture in building constructions (see WUFI).

Heat Loss Parameter (HLP) – A building’s specific heat loss (in units of W/K) divided  by the building’s floor area

(measured internally i.e. within the thermal  envelope). Units W/K.m2.

HHRSH – High Heat Retention Storage Heaters IAQ – Indoor  Air Quality.

IES – The producer of a complex  dynamic  simulation tool for modelling energy use (and overheating) in buildings.

IEV – Intermittent extract ventilation.

INCA – Insulated Render and Cladding Association.

Infiltration – Non-deliberate ventilation leading to unwanted air-leakage.

IWI - Internal wall insulation – Older walls, especially solid walls, have relatively low insulation values. As there is no cavity to fill, one option  is to apply internal wall insulation (IWI), which is then covered by plasterboard. A variety of materials  can be used and therefore the thicknesses required  to reach Building Regulations  varies, but will usually be between 40mm and 100mm. Although internal wall insulation will reduce the room size it is worth  remembering that it is only applied to external  walls. IWI can be expensive, but can often attract a grant/subsidy.

LZC – Low and Zero Carbon Technologies.

MCS – Microgeneration certification scheme, required  in order to claim the Renewable Heat Incentive and Feed In Tariff.

MEV – Mechanical  Extract Ventilation.

MHCLG – Ministry of Housing, Communities & Local Government MMSP – Metering and Monitoring Service Package.

MVHR – Mechanical  Ventilation with Heat Recovery -a system of ventilating buildings, in which heat is recovered  from the exhaust air stream to preheat the fresh air intake. Normally there are two sets of ductwork, both connected to an air-to-air heat exchanger,  with the air flows in the supply and exhaust branches carefully  balanced.

N50 – The air tightness  at 50 Pascals pressure, measured in air changes per hour (ach) NIA – National Insulation Association.

OSB – Oriented  Strand Board. A type of construction board made from wood and glue.

PAS 2035 – Retrofitting Dwellings to Improve  Energy Efficiency: Specification and Guidance.

Payback Period – The period of time required  for an investment to recover its initial  outlay in terms of income and/or savings generated.

PIR/PUR – Polyisocyanurate – high performance insulation. PIV – Positive Input Ventilation.

POE – Post Occupancy Evaluation.

Primary energy – The amount  of energy mined or extracted  at source; e.g., from coal, oil, natural  gas, uranium or wood. Includes losses within processes such as electricity generation and transmission.

PSV – Passive Stack Ventilation.

PU foam – Polyurethane foam. Closed cell insulation that can be sprayed.

PV – Solar Photovoltaic panels.

PV-T – Solar Photovoltic panels combined with solar thermal  into one panel.

Q50 – Air permeability at 50 Pascals pressure in m3 /m2hr.

R-value – The R-value is a measure of thermal  resistance]  for materials.  It gives an indication of how quickly they will lose heat (their thermal  resistance). The higher  the value of R, the better the thermal  performance and heat retention of the material  or assembly, and the slower any heat loss. Units are m2W/K (m2  x Watts / Kelvin).

RdSAP – RdSAP is the method  used to produce  Energy Performance  Certificates (EPCs). Rd stands for Reduced Data, and the method  is designed to allow surveys to be completed more quickly and therefore more cheaply than a full SAP survey at some cost of accuracy. RdSAP underpins both Green Deal assessments and the minimum standards regulations. We can offer EPC assessments if required.

Retrofit Assessor – Carries out all assessments of a retrofit, see PAS 2035Trustmark | PAS 2035/2030:2019 | Warm Home Discount Scheme for full definition.

Retrofit Coordinator – Oversees all retrofit design, construction, handover  and monitoring, see PAS 2035 for full definition.

Retrofit Designer – Prepares a retrofit design, see PAS 2035 for full definition.

RHI - Renewable Heat Incentive (RHI) – The Renewable Heat Incentive is a Government subsidy scheme that is designed to incentivise the installation of renewable heating measures, such as biomass boilers  and ground source heat pumps. Under this scheme, households are paid for the each unit of renewable  heat that they generate. This significantly increases the payback of renewable  heating measures.

SAP – SAP (Standard  Assessment Process) is a method  for assessing the energy performance of houses using a standard  methodology specified by the UK government. The current  version  of SAP is SAP 2012, and it calculates a ‘SAP rating’ as well as an estimate  of energy bills and CO2 emissions  associated with the estimated energy use. The SAP calculations are based on building dimensions, construction (and therefore energy performance) of building elements such as walls and windows, details of the heating and hot water systems and controls, and any installed renewable technologies including solar PV panels.

Sd value – The Sd value is a measure of a materials  resistance to water vapour,  but is dependent  on the thickness of the material.  It has units of metres of air layer thickness (m).

SPF – Seasonal Performance Factor. A metric usually used for heat pumps, boilers  and other space heat generating technologies.

SRHRV – Single Room Heat Recovery Ventilators .

Stack effect – In winter,  the warm air inside a building is less dense than the cold external  air. Consequently, cold air tends to be drawn in through cracks and gaps at the base of the building, with warm air exfiltrating through openings in and near the top of the building.

STBA – Sustainable Traditional Buildings Alliance is a forum  for sustaining and improving traditional buildings.

SWH – Solar water heating.

SWI – Solid wall insulation.

SWIGA – Solid Wall Insulation Guarantee Agency.

TFA – Treated Floor Area. The useful, heated floor areas within a building.

Thermal Bridge – A thermal  bridge,  also called a cold bridge  or heat bridge,  is an area of an object (frequently a building) which has a significantly higher  heat transfer  than the surrounding materials resulting in an overall  reduction in thermal insulation of the object or building.

Thermostat – A thermostat is a component of a heating control system which ensures the temperature is maintained at a set level. Your bills will typically fall – all other things being equal – for each degree C you drop your thermostat’s temperature setting.

TRV - Thermostatic radiator valves – A thermostatic radiator valve (TRV) is a self-regulating valve fitted to hot water heating system radiator, to control the temperature of a room by changing  the flow of hot water to the radiator.

Non-Repeating Thermal Bridge – Junctions between thermal  elements (doors and walls, floors and ceilings etc) Thermal capacity - the ability  of the constituent materials  in a building to store heat, for a given rise in temperature, measured in units of kWh/K for a whole building or in Wh/K.m2 to indicate the building’s thermal  capacity per unit floor area.

Thermal envelope – The insulated external  fabric of the building. Useful space heating energy the amount  of heat actually put into the heated space.

U-values – U-values measure how effective a material  is an insulator. The lower the U-value is, the better the material is as a heat insulator. U Values are expressed in Units of W/m2K (W(atts) / m2 per K(elvin)).

UKCMB – UK Centre for Moisture in Buildings, a network  and knowledge base for moisture in buildings.

WLCA – Whole Life Cycle Analysis – the total cost of a measure including the capital cost, the reduction in fuel bills and the associated maintenance costs over the lifetime of the measure or building.

WUFI – A complex  modelling software  for modelling moisture movement in building construction. Suitable for moisture open or moisture closed designs.

WWHRS – Waste Water Heat Recovery System.

XPS – Extruded polystyrene. A closed cell rigid  insulation.

Zoning – When the heating system of a house is set up or changed such that different areas are heating at different times and to different temperatures it is called zoning. The saving benefits can be large as you are essentially  reducing the house volume  every time you aren’t heating a room.

ψ (psi) value – The heat loss per unit length of thermal  bridge.  Units W/mK.

λ (lambda) value – The thermal  conductivity of a material.  Units W/mK.

Χ (chi) value – Point thermal  bridge  heat loss coefficient. Units W/K.

μ-value – The Mu value is the resistance of a material  to water vapour  relative  to air, it has no units and is independent of the thickness of the material.

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