Double-Stud Wall Continuous Insulation
Hello GBA community,
We live in south-eastern Ontario, Canada in a rural township that does not see a lot of green buildings. We have designed and built a double stud wall assembly and we’ve come up against a series of questions from the building official at the time of the framing inspection
. The building code compliance package for energy efficiency that our project is designed to comply with specifies the following in the above ground walls – R22 plus R10 continuous insulation. By ours, our designers and our insulation contractor’s calculations, our wall exceeds this. But at the framing inspection, the building official has said, and I quote, ” the R22 must be inbound of the CI, it is debateable that the fibrous insulation constitutes a CI.”
Is there anyone out there in the GBA community that knows Ontario Building Code, who can help us respond to this comment? We can’t find anything in the OBC or related SB12 that specifies an inbound requirement of the CI.
Thank you all in advance!
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Replies
cmylks
Can you specify which building code compliance package for energy efficiency that your project is designed to comply with? That would be the starting point.
I would think that the person who stamped your drawings would have followed the code. If they did not, then they are the ones who will be responsible. The first step is to identify which package you are complying with.
Hello Mr. Hugh! The compliance package for our project is Table: 3.1.1.11 (IP) Electric. The walls above grade are to be R22 plus R10 CI. Our designer has calculated our wall assembly at RSI effective 33.7. The building official approved the permit for our build 6 months ago. At framing inspection, he is now raising a concern saying that the wall has to have R22 *inbound* of the R10 CI....in our case, the CI is *integral* to the wall (i.e. inside the wall) and we have R9 between the interior 2x3 stud wall, R14 as the CI in the space between walls, and R10 on the exterior 2x4 stud wall.
We have never heard this concern before about the R22 needing to be on on the interior side of the CI. In a single stud wall, we understand that the CI is normally on the exterior but in a DSW, the CI is normally integral to the wall. We think our building inspector may just not be familiar with this double wall assembly. We can't find anything in the OBC or SB12 that says the R22 must be inbound of the CI...have you ever heard this before?
Thanks again so much for your insights!
The electrical heat refers to resistance heat. If you have a heat pump with no strip heater, it doesn't count as electric and you can use less insulation. In your case, you are well above any the R values anyways.
The table has U factor based compliance, you can simply crunch the numbers for your wall and make sure it is less than the U factor in the table. A good example of this is from:
http://effectiver.ca/calculator/wall.php?id=17022
The U factor based compliance doesn't have any prescriptive levels of CI as it only cares about the performance of the whole assembly.
As for the CI issues, there is no requirement anywhere for it to be outside the wall, as long as it is continuous it can be anywhere. A good question to ask in cases like this is to point you to the section of the code that you don't comply with. Again, you only need CI if you use the prescriptive R22/R10CI path, it is not needed for U factor.
I know it was in there somewhere:
Continuous Insulation (ci)
......
Insulation may generally be installed on the interior or the exterior, or may be integral to any opaque surface of the building envelope. .....
Thank you Akos. This is all super helpful and reinforces our feeling that we are on the right track. Indeed, our designer had already provided the 'effective R' using the NRCan tables, and he also had already provided reference to that clause in the SB-12 that you quote (which specifies that the CI can be interior, exterior or integral). The building official has persisted in his request for us to remediate the wall (his suggestion: add foam insulation to the exterior, so that the R10 ci is outbound to the R22. But from everything I've learned, foam on the exterior side of a DSW is a no-no, and would actually create a condensation problem, so we are *not* going to follow that suggestion!). At this stage, we are awaiting the building official's call back, and if he won't accept our additional information then we seem to have no choice but to get an engineer's stamp on the wall to override him. It frustrates us to no end that we may have to pick up this additional $500-$750 cost for an engineer due to this official's reluctance to open his mind. But as November sets in and winter looms, we need to get our project back on track!
Never mind that your wall complies with SB12, if your wall is built according to the plans approved by the city planner, the inspector doesn't have much leg to stand on. Nowadays $500 is not much to keep the project moving, but out of principle I would push back on this.
This is not about accepting different ways to build, this is about doing their job which means making sure the building follows to submitted plans. They can use judgement for any detail that is not specifically called out for in the plans, which doesn't sound like the case here. If they have a beef with the approved wall assembly, they can take it up with the city planner.
Akos, really appreciate your input here. The principle *does* matter, and we too are not happy to have to pay our way out of this issue. And here's the thing - we live in a small rural township with a 3-person building department. The official that is questioning our wall assembly now is the same official that approved our building permit application 6 months ago! We decided to push back on this point today and a fairly sharply worded (but still diplomatic) email seems to have made a difference. He responded and conceded that our CI is 'likely fine' with him, but he's now going back to his other issue...the 'possible condensation risk' (https://www.greenbuildingadvisor.com/question/possible-condensation-risk-in-double-stud-wall-assembly?cid=238474&discussion=response#comment-238474) which we had thought was resolved, grrr! Our designer has done a 'dew point analysis' for him today and we are sitting on pins and needles now, hoping that this official will finally just get out of the way and let our project proceed.
Thanks again. We have found your comments and this GBA forum overall a very informative and supportive source during this frustrating stage of the project.
I am hoping everything worked out for you. Can you share any updates?
Here's what the inspector is thinking about: in a cold climate your walls need to dry to the outside or have enough impervious insulation to keep the temperature in the pervious insulation from getting low enough to allow condensation. If the continuous insulation you're using is impervious foam, it needs to go on the outside. He's not sure the continuous insulation can be anything other than foam, which has to go on the outside, so he's not sure the continuous insulation can be anywhere other than the outside.
Indeed, you are probably right. This official seems to be stuck in a particular mindset, not curious to learn about new green building approaches or expand his understanding of low carbon building materials. Sad and frustrating....
cmylks, not sure if you found that quoted text in the OBC. If not, here it is.
The document describing the updates to SB12 back in 2016
https://www.publications.gov.on.ca/store/20170501121/Free_Download_Files/510155.pdf
MMA Supplementary Standard SB-12
https://www.peterborough.ca/en/doing-business/resources/Documents/Building-Documents/Supplementary-Standard-SB-12-Energy-Efficiency-for-Housing---final-update.pdf
Page 55
Appendix A
Explanatory Material for SB-12
Chapter 1: General
1.3.2.1.(2) Defined Terms
"Continuous Insulation (ci)
Continuous insulation (ci) is intended to minimize the thermal bridges in an assembly. It is generally uninterrupted across all structural members. Exceptions to this include fasteners and service openings. Insulation may generally be installed on the interior or the exterior, or may be integral to any opaque surface of the building envelope. It may generally be made of various material such as board, blanket, sprayed or other types of insulation. Compressions such as blanket fasteners are permitted."
Thank you Mr. Hugh!