Prescriptive vs Performance

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Prescriptive vs Performance, which Path should I choose?

Since the 2014 the Alberta Building Code has Included Section 9.36 which is specifically  referring to Energy Efficiency of Houses and Small Buildings. The application of this is meant to reduce the Carbon Footprint related to Residential Housing.

There are essentially 4 ways of complying with Section 9.36 of the Building Code:

  • Prescriptive Path
  • Prescriptive with Trade-off
  • Performance Path
  • ENERGY STAR / LEED etc

Since Prescriptive with Trade-Off is based on Prescriptive we will not go into further detail at this time. If you are considering the ENERGY STAR / LEED path you likely already know enough that you don’t need to read on. Feel free to discuss this option with us, but we will not go into further explanation here. So that leaves us with Prescriptive Path vs Performance Path.

 

What’s the Difference?

Prescriptive Path compliance basically means that you need to meet the minimum requirements as set out in the building code for every element of the building envelope and heating/cooling system. Think of it as meeting the Prescribed minimums of the code.

Performance Path compliance does not require every element to meet prescribed Building Code minimums, as long as the finished house Performs as well or better than the Building Code requires. This is calculated using software modelling to compare the proposed house specifications to a similar one that uses Building Code minimums.

The end result is that the regulation requires us to show that the house is built to either (1) a minimum standard, or (2) that if the minimum standard is not met on all elements it will not adversely affect the efficiency of the house (*see more below).

(To Illustrate: When shopping for a vehicle, some might look for a particular engine configuration (eg V8 or Diesel) to meet their needs, whereas others may not care what the engine configuration is as long as it is rated to tow a particular amount.)

 

Which is Better?

This is where things get tricky. While you may hear different arguments as to which path is the better one to use, the fact is they both have their pro’s and con’s.

Prescriptive:

Pro’s:

  • Building a solid envelope is key. Prescriptive compliance requires each element of the envelope (many of which are difficult to upgrade later) meet code minimums.
  • If you want to upgrade your efficiency at a later date, this is relatively simple to do by upgrading mechanical equipment to higher efficiency models.
  • Streamlined Planning workflow. There are less steps required in the planning stage, which means that blueprints can be completed in a more timely fashion.
  • Prescriptive compliance does not have to be recalculated each time you build the house (should you build it more than once).

Con’s:

  • In order to meet minimum targets, it is often advisable to include a HRV (Heat Recovery Ventilator). This means adding a piece of mechanical equipment to the heating system that otherwise may not be required.
  • It is often the more expensive way of meeting the Code Requirements.

Performance:
Pro’s:

  • Ability to ascertain the real world value of increasing efficiency/insulation in various areas of the structure. (eg would there be greater benefit to increasing the efficiency of the furnace versus adding more insulation?)
  • Often the more economical way of meeting the Code Requirements.

Con’s:

  • Typically adds more steps (and therefore time) to the planning stage.
  • It is difficult to upgrade efficiency at a later date, as initial performance compliance often relies on upgrading mechanical equipment to higher efficiency in order to meet compliance.
  • Performance compliance must be recalculated each time you build the house (should you build it more than once).
  • Is not necessarily as energy efficient as a Prescriptive Path compliance (*see more below)

 

Theory vs Application?

In theory, both performance paths should yield a similar result to the overall efficiency of the house. However this is not exactly true in application. In theory, Performance Path is often recommended as a superior method as it allows you to ‘target’ key areas of energy efficiency. In application however, we have found that many builders prefer to use Performance Path compliance not because it produces a superior result, but because it is typically the cheaper way of meeting Code requirements.

Why would Performance compliance save money over Prescriptive if they both provide the same result in the end, you may ask? The fact is: they don’t provide the same result. Which is why you should understand the difference before selecting a compliance path. While Performance Path does allow you to ‘target’ cost effective methods of increasing efficiency (eg using a higher efficiency furnace rather than more insulation), Performance Path also allows for certain concessions that Prescriptive doesn’t. By taking advantage of these concessions, Performance Path compliance can still meet code while in fact achieving a less efficient house than if you were to build the exact same house meeting Prescriptive compliance.

So the theory of Performance Path compliance is that you are making best use of your funds by upgrading the building elements that will have the largest effect on efficiency. In practice however, Performance path compliance is often used to take full advantage of concessions to lower the efficiency of the home and save money in construction.

(Please note: We are not saying that Performance Path will always produce a less efficient house, just that in practice it often does.)

 

Which should I choose?

We recommend the following considerations:

You should choose Prescriptive Path if:

  • You prioritize a higher quality building envelope (insulation) over reducing construction costs on the envelope.
  • You realize that Prescriptive Code requirements are only a minimum, that you may choose to improve on those.
  • You are on a tight time frame for planning.

You should choose Performance Path if:

  • You are only looking to meet code minimums and want to reduce your construction cost.
  • You want to build a higher quality home, but want to choose where to put the extra investment into energy efficiency
  • You realize that Performance requirements are only a minimum, that you may choose to improve on those.

 

Conclusion

While many drafting offices may promote one compliance path over another, we feel that as the owner and/or builder that it should be up to you to make an informed decision. We are happy to provide Code compliance via Prescriptive Path, Prescriptive with Trade-off, or Performance Path. If you are still unsure which path to choose, come talk to us!

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About the Author:

Andrew has a Diploma in Applied Science (Architectural Technology). He refined his skill as a designer working for several award winning architects, and established Global Design Studio in 1999.
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