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Insulating parapets

Feb 27 '14 17 Last Comment
Saint in the City
Feb 27, 14 5:51 pm

I promise to stop talking about continuous insulation at some point.  Really.  

Seriously.

But not quite yet.  This friggin' IECC has me re-thinking all the crappy details my employers seem to enjoy so much.  It's like once you begin thinking in terms of continuous insulation, you can't stop.  Every gap then becomes a highly offensive thermal bridge forecasting the inevitable doom of the entire structure.

Anyone ever run rigid insulation over the studs on the exterior, and then essentially continue right up and over the parapet, and then run back down the inside face of the parapet to meet the roof insulation to create a continuous layer of insulation?

In poking around Building Science and elsewhere, I'm seeing versions of this detail.

Any thoughts?

 

TedTedTed
Feb 27, 14 6:44 pm

I have not done it on the TOP of the parapet but I have done it on the exterior and backside of the parapet wall.  Not really sure how the fastening of the parapet cap (depending on what it is) would handle fastening to the rigid and/or nailer.

I agree with you about the continuous insulation everywhere though.  I also rack my brain about how to improve details we use commonly in the office and try to convince others to rethink their approach.

citizen
Feb 27, 14 7:30 pm

I thought the title was "Insulting parapets."  I've been offended by a rude overhang or two, but all the parapets have been very nice.

b3tadine[sutures]
Feb 27, 14 11:23 pm

I have SINT, and I do it on CMU parapets. Sometimes we even spray foam, in place, insulation in stud cavities.

Miles JaffeMiles Jaffe
Feb 27, 14 11:39 pm

You'll be way ahead if you just stick to some of the crappy details.

I admire your desire, though.

Saint in the City
Feb 28, 14 7:04 am

Beta -- have you ever found it to cause any problems -- moisture, etc?

Non Sequitur
Feb 28, 14 8:22 am

Saint, in my area we continue a layer of insulation on the exterior of the studs/sheathing and pack the entire height of the parapet with mineral wool. The roofing insulation does not always run up the back side of the parapet but it is not an uncommon detail. Leaking parapets is a hot topic in our office and we are currently revising all our typical parapet details to minimize any possible condensation.

Saint in the City
Feb 28, 14 9:58 am

Thanks Non Seq -- good to know -- I'm also considering doing what you're suggesting.   Maybe I'll skip the top of wall rigid insulation that I was proposing in favor of batts all the way up (or spray foam?). That way there would still be solid blocking available at the top for parapet connection.  I may still run rigid up the backside of the parapet.

Non Sequitur
Feb 28, 14 10:25 am

Saint, I would not be too concerned about thermal bridging at the blocking/support for the parapet cap. My usual concern when detailing parapets is minimizing the amount of air that could become trapped/leak inside the cavity and therefore condense into the finish space. We've had issues last winter on a project where we spray-foamed ~600mm high on the back side of our parapets but due to bad workmanship and trade coordination... and some oversight on our part... warm air from within the floor below found its way into the parapet cavity, condensed, and rained (or dripped, depends entirely on who you ask) back into the building. Workmanship aside, had the parapet's cavity been filled properly and the roof membrane continued as it was designed, we would not have this problem.

Saint in the City
Feb 28, 14 10:58 am

^Great point on care not to create an unvented air trap in the parapet wall...  mini-rain storms are not so pleasant.

The continuous insulation thing is becoming unavoidable -- I like the energy saving potential, but the way the dew point move around along with condensation potential make a person worry.  It's a bit of a can of worms.

gruen
Feb 28, 14 11:18 am

Good discussion-post details that work?

I've tried to get this, but the contractors won't build it. Probably you can get the parapet packed or sprayed w insulation, top isn't as critical.

Non Sequitur
Feb 28, 14 11:21 am

^Correct, it's not a simple black/white type of problem but the best you can do is try to minimize water. At least for me, we also have to make sure the trades do as they are told... too often they just scoff at our request to fill the cavities and seal things up thinking "Xmm is enough, that's what I've always done, I'm not paying for more because this licensed idiot says so".

Saint in the City
Feb 28, 14 11:48 am

Good point.  One thing my office does do pretty well -- we typically have pretty extensive pre-bid and pre-con meetings -- any of these somewhat unusual details will get brought up in both of those meetings.  If they're in our drawings / specs, they will get built.

BTW, I just got some  interesting Dewpoint Analysis graphs from Dow Chemical.  I was on the phone with them earlier and described the expected wall section.  Doesn't include any parapet info as I had yet to pursue that problem.  But very interesting.  The graphs plot if / where you're likely to condense for summer and winter conditions.  Would like to get the software to create these myself -- right now we have no in-house energy modeling software.

Saint in the City
Feb 28, 14 12:22 pm

Miles, are you not building projects, or are you in a jurisdiction where the energy code isn't enforced?

Miles JaffeMiles Jaffe
Feb 28, 14 12:35 pm

There is more than one way to skin a cat.

FYI The energy code here is a fucking joke. The requirements are sometimes counterproductive, certified by the installers and otherwise unchecked by anyone with the ability to understand them.

For example, the HERS rating system pretty much mandates a geothermal heating system once a house gets to be a certain size. Geothermal is so inefficient and expensive to run that houses are piped for installation of conventional boilers after the CO is issued. Commercial structures are largely exempt.

We had a law that limits "superstores" to 15,000 sq.ft. but developers broke that in court. Houses are limited to 20,000. At least for the moment.

I could go on, but I think you get the point.

Saint in the City
Feb 28, 14 2:30 pm

^ Things have been nearly that squirrelly where I live as well, and still are at a city level.  The Energy Code is all but unenforced at a local level here.  So, most architects have sort of ignored the whole thing completely.

Where things have changed, however, and the reason for all my insulation posts, is that the State has now  fully adopted the IECC 2012, and is also fully enforcing it on all state-funded buildings.  My current project is owned by a very large corporation that is building a factory in-state and received enough state funding / incentives (you know the drill) that it falls under the State Building Code.

So the ways to skin this cat don't vary much.

There is a tiny bit of wiggle room as to how you can legally prove compliance -- Comcheck, ashrae forms, energy modeling software, etc, etc, -- but I've hit the point where I think it probably makes the most sense just to follow the code prescriptively.     

t a z
Feb 28, 14 7:23 pm

For dewpoint analysis of customized build-ups you can look into WUFI or THERM...

gruen
Feb 28, 14 8:02 pm

WUFI is awesome. And free

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