Acronyms, Abbreviations & Glossary Of Common Terms

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This thread was originally posted in the other place, and is a team effort to collect together as many acronyms and abbreviations used in the building trade as we could.

If you know of any abbreviations missing, or think there should be a correction to the list, then post them as a reply to this topic and one of the moderators can edit the original list to keep it all up together.


AAV = Air Admittance Valve. (Sometimes referred to as a Durgo Valve.)
AAV (alternative) = Automatic Air Vent.

ACH = Air Change [per] Hour

AONB = Area [of] Outstanding Natural Beauty

Article 4 Direction = Removes Permitted Development (PD) rights. (See: http://www.brighton-...cle-4-direction )

ASHP = Air Source Heat Pump (And see also: http://www.planningp...ects/heatpumps/ )

BC / BCO / BI = Building Control / Building Control Officer / Building Inspector (Often prefixed with LA = Local Authority, as in LABCO.)

BR = Building Regulations (Regs)

CIL = Community Infrastructure Levy (= a charge levied by a LA based on the sq.m of a property. Note: self-builds are exempt.)

CO = Conservation Officer. (Now often designated: Heritage Officers. Specialized - although often not particularly qualified - planning officers working in a local authority Conservation/Heritage department. Have the power to over-rule BC where the Regs are concerned if a proposal is considered likely to impact on the "historic character" of a building, whether Listed or not, or in a Conservation Area.)

{Listed Building, see: http://www.planningp...ing_consent.pdf }

{Conservation Area, see: http://www.planningp...ns/conservation }

CU = Consumer Unit

CCU = Cooker Connection Unit

CWS = Cold Water Storage [tank]. (Large plastic tank often in attic.)

CYL Stat = hot water cylinder thermostat for control of DHW temperature.

DeltaT = ΔT (Greek symbol Δ =delta in Greek alphabet) Temperature difference. (In the building context usually referring to the difference in temperature across a wall when discussing the effectiveness of insulation.)

DG = Double Glazing (Sometimes referred to in shorthand as 2g = double glazed; 3g = triple glazed. Also expressed as 'd/g')


DCW = Domestic Cold Water

DHW = Domestic Hot Water


DNO = Distribution Network Operator (electricity supply)

DPC = Damp Proof Course

DPM = Damp Proof Membrane

EA = Environment Agency

EDPM = Roofing membrane. (EPDM rubber (ethylene propylene diene monomer (M-class) rubber), a type of synthetic rubber,)

EPC = Energy Performance Certificate (See: )

EPS = Expanded Polystyrene Insulation


EV - Expansion Vessel

EWI = External Wall Insulation

F&E = Feed and Expansion tank. (Small plastic tank often found in attic alongside CWS.)

FCU = Fused Connection Unit

FWIW = "for what its worth". (As in: "That's my opinion FWIW.")

FYI = For Your Information. (Now often seen in formal letters since they took the form of emails, and especially in the header of an email forwarded to keep someone "in the loop".)

GCN = Great Crested Newt

GSHP - Ground Source Heat Pump

HC or VHC = heat capacity/volumetric heat capacity

ICF= Insulated Concrete Formwork

IGU = Insulated Glazed Unit (industry term for double or triple glazing)

IMHO = "in my honest opinion." (Alternative: "in my humble opinion.")

IIRC = "If I remember correctly."

IWI = Internal Wall Insulation

KISS = Keep It Simple Stupid. (Usually expressed as: "Stick to the KISS principle.")

LA = Local Authority

LBC = Listed Building Consent. (Needed to carry out work on any Listed building, whether domestic or commercial, privately or publicly owned, which is protected by law because of its historic significance, whether by age or architectural importance attested to by English Heritage.) (See also: Listed Building, above.)

LPA = Local Planning Authority

LPG = Liquefied Petroleum Gas


M&E = Mechanical and Electrical

MCB = Miniature Circuit Breaker

MDPE = Medium-density polyethylene also referred to as Alkathene. Pipe used to carry mains water and gas, usually buried underground.

MI = Manufacturers Instructions

MVHR = Mechanical Ventilation [with] Heat Recovery.

NPPF = National Planning Policy Framework

OEM = Original Equipment Manufacturer

OLIVE = Compressible copper ring accompanying threaded plumbing fittings that compresses around the pipe when the fitting is tightened to form a watertight seal. Often reinforced with PTFE tape [see below].

OSB = Orientated strand board

Party wall = An internal wall common to two properties. (Not always a contentious issue, but see: http://www.planningp...on/partywallact )

PDR = Permitted Development Rights. (Sometimes just 'PD'. See: http://www.planningp...ssion/permitted )

PGM room stat = Programmable room thermostat: selects both operating times and temperatures.

PI = Professional Indemnity (Insurance)

PINS = Planning Inspectorate

PME = Protective multiple earthing

PIR = Rigid Polyisocyanurate Insulation

PoE (or POE) = Power over Ethernet. Enables power to be provided to the device (phone or a network camera) using the same cable as that used for network connection.

PRV = Pressure Relief Valve


PRedV - Pressure Reducing Valve  


PHE - Plate Heat Exchanger


PTFE (tape) = (polytetrafluoroethylene) Tape used to seal threads and joints (e.g. around olives in compressions fittings) in plumbing.  Also known as Teflon tape outside the UK

PUR = Rigid Polyurethane Insulation


PV = Photovoltaics e.g. Roof Solar panels

R-value = Thermal resistance [insulation] (the higher the better)

RCD = Residual Current Device

RCBO = Residual Current circuit Breaker with Overcurrent protection

RDF = Refuse Derived Fuel

RTFM = Read The Flipping Manual. (The polite version; the less inhibited version is usually expressed with the 'F' meaning what you think it means.)

SAP = Standard Assessment Procedure (See: ) (See also: ) ( )



SE = Structural Engineer

SEPA = Scottish Environmental Protection Agency

SFCU = Switched Fused Connection Unit

SHC = Specific Heat Capacity (heat is another word for energy, don't confuse with temperature)

SIPs = Structural Insulated Panels

SSSI = Site of Special Scientific Interest

Stat = Thermostat. (Room stat = wall mounted thermostat/central heating control.)


SWA = Steel Wire Armoured (cable)

SWMBO = She Who Must Be Obeyed (Attributed to "Rumpole of The [Old] Bailey", who used the phrase when referring to his wife, but actually from Rider Haggard's "She": )

TAF = Temporary Amphibian Fence

TBH = "to be honest" (As in: "TBH I don't know.")

TBF= "to be fair" (As in: "TBF to the builder, he hadn't a clue.)

T&E = Twin and Earth (cable)

T&G = Tongue and groove. (Often given in lower-case: t&g.)

T&PV = Temperature & Pressure [relief] Valve

TS = Thermal Store

UFH = Under Floor Heating. (Also expressed as 'Underfloor Heating' but usually still given as UFH.)

U-value = Rate of transfer of heat [insulation] (get it as low as possible, below 0.15 if you can)

UVC = Unvented Cylinder

VCL = Vapour Control Layer

WUFI = "Wärme und Feuchte instationär" - Heat and Moisture transfer analysis

XPS = Extruded Polystyrene Insulation

ZV = Zone valve, motorised or other. (Directs heating medium to wherever needed according to programmed requirements.)



L x W x H = Length times width times height. (But note that when giving dimensions for windows and doors ALWAYS follow the convention of width first, following by the height.)

J = joule (not Joule)

W = watt

h = hour

s= second

k = kilo (thousand)

kW = kilowatt

kWh = kilowatt hour

kWp = kilowatt peak (Solar installations - literally peak output.)

m = metre (not meter)

m2 = square metre (not metre squared)

t = time

T = temperature

°C = Celsius or Centigrade

K = kelvin (not °K or degrees Kelvin)

k or k often means conductivity

R = resistivity

U = 1/R

g = gram

kg = kilogram (the odd SI unit, use it)

J/(kg.K) = J/(kg.K) =

W/(m2.K) = W/m2.K = W.m-2.K-1

f(x) = function of x. (Common usage in thermal and stress calculations as well as statistics.)

e = Exponent (1+1/1!+1/2!+1/3!+1/4!...) how things heat up and cool down, how fast things grow,

π = pi ratio of a circles diameter to its circumference


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9 hours ago, ProDave said:

m2 = square metre (not metre squared)

I think this is the wrong way around (and I think I may have posted it originally too)

Square meter is shape dependant, e.g. a rectangle of 1 m length by 1 m width.

A metre square is not shape dependant, e.g. the surface area of the Cornwall (as it is a really odd shape) 3.563824e+9m²

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On 19 January 2017 at 10:51, Nickfromwales said:

Just giving this thread a bump for the benefit of our many new members. 

Enjoy! :)


The Management 


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TMV = thermostatic mixing valve:  a valve that blends hot water with cold water to ensure constant, safe shower and bath outlet temperatures, preventing scalding.

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PC (or PC sum) = a prime cost sum is an allowance for the supply of work or materials that will be nominated by the client.

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ST = solar thermal 

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Swing shovel = what they call an excavator in Devon (or at least @joe90 does)

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As requested in a thread about battery storage of renewable generation:


DoD -- depth of discharge (essentially the opposite of state of charge)

SoH -- state of health (a percentage of how much charge it can hold, compared with the as-new spec) 

Wh -- Watt-hour (a measure of energy)

BMS -- battery management system

LiFePO4 -- lithium iron phosphate (a rechargeable battery chemistry)

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EDPM → EPDM  Noticed that because I often make the same mistake. It seems quite common for some reason.


R = resistance (not resistivity).


Is it worth a note that mm² is (mm)² (not m(m²)) and that when people talk about 1, 2.5, 6 or whatever mm cable they usually mean mm² (i.e, cross-sectional area, not diameter)? There was a time when I was confused about that.

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