Thermal Resistance
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Thermal Resistance
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The BP Wall Systems, including Excel II and Enermax, offer a natural architectural strategy that maximizes energy efficiency without compromising the building envelope long term structural integrity.
Reducing energy consumption to condition inside air?heat inside air in the winter and cool it in summer- is best achieved by the combination of:
1. reducing heat flux transfer (higher thermal resistance of the assembly) and,
2. increasing the air tightness of the building envelope (minimizing the exchange of air between the conditioned interior and the exterior).
EXCEL II
Adds to the thermal resistance of the assembly at an effective rate of R3 per inch. Excel II is available in a thickness of ½? with a thermal resistance of R1.5.
Incorporates a rigid air barrier that is 40 times more effective than the 1995 NBC requirement in terms of air leakage. Test results show 0.005 l/(s.m²) for Excel II where the maximum accepted in the code is 0.02 l/(s.m²).
ENERMAX
Adds another R4.7 to the total insulation value including the reflectivity performance of the aluminum facer.
Combines a second line of defence against air ingress with its integrated rigid aluminum air barrier membrane.
Excel II and Enermax, individually or in combination, can be used to build walls that yield up to R30 nominal thermal insulation values AND meet any air tightness requirements, nominative or prescriptive.
WALL SYSTEMS EVALUATION AND SELECTION
The following links will bring you to our wall systems evaluation and selection guide:
*As buildings minimal thermal resistance is not legislated on a national basis, you should verify with local authorities for applicable minimal requirements.
** Based on average retail price in Montreal, Canada in January 2001.
SYSTEM PERFORMANCE
In the process of developing new standards*** to regulate minimal thermal resistance values (generally according to climatic zones), building science has recognized the fact that this wall property cannot be dealt with as a totally independent factor. The efficiency of a greater R-value is significantly reduced when a large volume of air is exchanged with the exterior due to poor assembly design or bad construction practices. Similarly, the relation between thermal insulation and water vapour permeance properties of the building materials should be thoroughly understood to avoid premature structural damage and possible interior air contamination.
***Some building codes and related legislative documents
NBC A-9.25.1.2.
Location of Low Permeance Materials.
"...If the material (low permeance) is located where the temperature is below the dew point of the interior air, the water vapour will condense and accumulate as water or ice. This reduces the humidity level and encourages the movement of more water vapour into the assembly. If this temperature remains below the dew point for any length of time, significant moisture could accumulate. When warmer weather returns, the presence of a material with low water vapour permeance can retard drying of the accumulated moisture. Moisture, which remains into warmer weather, can support the growth of decay organisms."
The concept supporting the BP Wall System has over 60 years of existence and time has proven it right. The designer can dramatically improve the building energy efficiency without compromising the other properties of the envelope.
The National Building Code (NBC) pertains to all aspects of the construction having consequences on security, fire safety and health. This document does not include minimal values for thermal resistance but addresses related subjects such as air permeance-min. of 0.02 l/(s.m²) and water vapour permeance.
The Model National Energy Code for homes/buildings (MNEC) determines what should be the effective minimal thermal resistance values for all regions across the country.
The R2000 Program sets a number of guidelines to improve energy efficiency through minimal thermal resistance value (R20 nominal for walls above grade) but also incorporates a measure for air leakage for the envelope that needs to be tested to receive certification at a maximum of 1.5 air change rate per hour (ACH). The toxicity of the building materials is also taken into account.