7 JUNE 2019 between thetwo. technically mean that R10 can be either 10 m 10 either be can R10 that mean technically It is common to fi can beexpressed ineitherinchesormillimeters, milesorkilo resistance is measured with metric units (m The United States usesUSCustomary unitswhichare iden *To convert from RSI to imperialR-Value mul *To convert fromimperialR-Value to RSI divideby5.678 (thermal resistance). across aspecifi *It isimportant to remember thatR-Value (thermalresistance) it isthemeasurement ofthermalresistance withimperialunits referredcommonly is wr WhatR-Value be as toshould reality in have bothimperialunits(IPunits)andmetric units(Interna be the Thermal resistance is the measure of a given material’s ability R-Value andRSI Resistance Understanding Thermal Toll Free: 1(877)470-9991 •Fax: (416)759-7402 Avenue501 McNicoll Toronto, ON,CA,M2H2E2 units. Construc and BULLETIN TECHNICAL hr Units are: units. resistance measured inimperial R18 (18hr Example R (Abbreviated to R-Value) Thermal Resistance IP orR-imperialisthethermal

2 F/Btu er insulator the material is. Thermal resistance is a similar a is resistance Thermal is. material the insulator er

2 on) industry generally assume that a R10 labels refer to imper referto labels R10 a that assume generallyindustry on) /t)RSI 3.17(3.17m F/Btu) c thicknessofamaterial. Somematerials might requireaddi nd products listed as R10 which indicates a thermal resistance metric units. resistance measured in R m Units are: SI 2 K/W =Thermal cal for length andarea withImperial units(except for survey 2 K/W). This is the same when measuring length and that a given m ply by5.678 2 K/W or 10 hr hr 10 or K/W 2 /)1i ncne pcn 406mmon center 16inoncenter spacing K/W) onal System ofUnits(SI)). to resist heat fl meters, etc.

2 (hr is alwaysameasurement oftheresistance ofheatfl F/Btu. Professionals in the AEC (Architecture, Engineering (Architecture,AEC the in ProfessionalsF/Btu. units. Length measured inimperial Length miles (m) yards (yd) feet ( inches (inor“) Units are: i en and verbally said as RIP or R-imperial, meaning that meaning R-imperial, or RIP as said verbally and en

measurement to length or temperature, all of which of all temperature, or length to measurement 2 F/Btu). WhenspeakingofRSI, itmeansthat thermal or ‘) ow across it. The be onal thicknessto achieve asimilarR-Value ial units while a RSI10 labels refer to metric referto labels RSI10 a while units ial of 10. The lack of units in this instance can ing) whilevolume and weight are diff BUILD TO A HIGHER STANDARD metric units. Length measured in spacing kilometers (km) meters (m) cen millimeters (mm) Units are: er/higher the resistance, meters (cm) www.amvicsystem.com easurement erent ow TECHNICAL BULLETIN UNDERSTANDING THERMAL RESISTANCE

Nominal and Eff ec ve R-Values

The thermal performance of the walls is o en discussed in terms of its thermal resistance (R-Value). When doing so, there are two primary methodologies, nominal and eff ec ve. The nominal R-Value (thermal resistance) of a wall refers to the clear wall only, without taking into account the eff ect of thermal bridging (e.g. studs) since the framing components have much lower thermal resistance than insula on.

Eff ec ve R-Value (thermal resistance) can some mes be called actual R-Value since it takes into account reduc ons from thermal bridging in the wall providing for a more accurate representa on. In some cases, the eff ec ve R-Value only takes into account the insula on and framing components while in other cases it incorporates all of the wall components making it more of a total or assembly R-Value.

Both nominal and eff ec ve approaches are measured with thermal resistance (R-Value) which can either be in imperial or metric units. In order to diff eren ate these more easily, they can be wri en as Eff ec ve R-Value and Nominal R-Value or

R-ValueEff and R-ValueNom.

Nominal Eff ective

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