State of Practice for Thermal Bridges

asked 2021-12-28 14:14:28 -0600

Hello all

I'm not a modeler myself but do a lot of design review of project architecture plans and I am also heavily involved in advancing building codes. I have four questions for you experienced modelers out there that would help me tremendously -

How common (and how thorough) are thermal bridges accounted for in building models?
Would you say that modelers are commonly (or rarely) using the "presolved" thermal bridge solutions from references like BC's Building Envelope Thermal Bridge Guide avail here link text
Do you see modelers using BC-type thermal bridge accounting more in future? Are modelers going in that direction, or would you say you are already there?
Finally - to what extent is there a feedback loop between the architectural design team and the modeler to ensure that any thermal bridge mitigation which may have been needed to meet code, satisfy LEED, etc gets "into" the project drawings and built? (Or, the corollary - that poorer performance is accurately represented for buildings which are not thermal bridge mitigated.)

Thank you!

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answered 2021-12-29 05:53:23 -0600

Denis Bourgeois
2896 ●107 ●8 http://www.rd2.ca

updated 2022-01-01 09:00:09 -0600

Hi Paul, great questions! About a year ago, we released the Thermal Bridging & Derating (or TBD) OpenStudio Measure, which does most of the heavy lifting to account for major thermal bridging. Allow me to refer you to its online guide to start with, as it does provide some context and partial answers to your questions - and it's written for newcomers to energy modelling! I'm also referencing Canadian documents, code requirements, etc. - many European modellers are likely to be quite familiar with this already, given EPBD requirements.

In my experience with energy modelling and training, awareness seems to depend on (a) where you are (state/province) and (b) who's on the design/analysis team. With the advent of the RP-1365, BETBG, and thermalenvelope.ca, building professionals and energy modellers in BC (and more recently in Quebec) are likely to be very familiar (and somewhat thorough) with this, given provincial code requirements. Yet I still come across modellers who are quite unfamiliar (they stop at clear-field RSi requirements), or who will simply not invest the extra time ($) it takes to do the heavy lifting - something we hope TBD remediates.
In jurisdictions where this is now code (or for initiatives like PWGSC projects), I would say pretty frequently (unless they have access to new manufacturer data e.g., the latest thermally-broken cladding clip). I would much prefer seeing professionals rely on these presolved sets, than wing it. BTW, TBD integrates a handful of psi sets from BETBG ("poor", "regular", "efficient", and curtain wall variants), but we recommend switching over to custom sets as designs evolve.
I can't see energy modellers voluntarily taking on more work if they don't have to. But if it's required by code or set in performance targets by e.g. PWGSC ("28% better than NECB 2017"), then it's more a question of organizational inertia vs compliance.
In most cases (75%?), communication between client, architect, structural vs HVAC engineer/modeller is poor in this regard (despite claims on IDP). I have witnessed better brass tacks discussions when clients and design teams have their backs up against the wall e.g., not achieving targets, or more frequently not having the (planned) budget to address prescriptive major thermal bridging requirements. I suspect this will evolve/improve over time ...