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Old 03-11-2019, 11:03 AM   #1
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Insulation


I have a spray foam contractor telling me that r 13 is more than enough for my 2x4 exterior walls in New York City does that seem right

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Old 03-11-2019, 11:16 AM   #2
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Re: Insulation


This is what they are proposing

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Old 03-11-2019, 12:21 PM   #3
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Re: Insulation


If you're just shooting for r13, you could just do dense pack cellulose.

Going to higher R value in a 3.5" wall cavity by using closed cell would probably get you moisture issues.

I've put 2X4 whalers on to get 5" cavities so the R value can be increased.
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Old 03-11-2019, 12:39 PM   #4
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Re: Insulation


So there proposal makes sense?

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Old 03-11-2019, 01:29 PM   #5
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Re: Insulation


What does code call for in your area?

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Old 03-11-2019, 01:29 PM   #6
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Re: Insulation


Are there energy code requirements there? Out here everything is called out per the energy code.
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Old 03-11-2019, 01:52 PM   #7
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Re: Insulation


What code are you on & is this NYC proper - climate zone 4a? If so no as you either need R13 interior + R5 exterior or R19 interior only
For a quick chart & more info - http://thehtrc.com/2018/state-wide-c...ly-locally-faq (click the thumbnail picture for a chart based on 2006 - 2018 code levels)
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Old 03-11-2019, 02:15 PM   #8
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Re: Insulation


Quote:
Originally Posted by nickelec View Post
So there proposal makes sense?

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I don't think so. Check code for you area. If there is no code, the rule of thumb is roof is double the wall R value. To get the most benefit from an R38 roof, you'd need to try for walls closer to R19.
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Old 03-11-2019, 02:18 PM   #9
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Re: Insulation


I read r19 mysef

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Old 03-11-2019, 02:53 PM   #10
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Re: Insulation


SLSTech is the pro on all this. As a practical matter, it's tough to get better than R13 in a 2X4 stud wall short of putting in faced polyisowhateveritis board. I've done it, it isn't perfect. Lots of edge to stud sealing, and over time, you can't really count on that seal.
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Old 03-11-2019, 03:03 PM   #11
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Re: Insulation


Plus, when you use faced board, it's a moisture barrier, so you're now going to have to deal with moisture issues and how to prevent them.

IMO, if you're stuck with R13 walls, dens pack cellulose is a cost effective approach, and it will help even out moisture levels.

BTW, some jurisdictions use a remodel code which is more lax.
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Old 03-11-2019, 06:09 PM   #12
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Re: Insulation


Quote:
Originally Posted by hdavis View Post
BTW, some jurisdictions use a remodel code which is more lax.
Good call, that actually requires filling the bay only per the code (unless amended locally)

Personally I wouldn't waste my money on R13 open, I would go dense pack or even an R15 batt making sure airsealing is done right (yes you still have to even with open cell) from not only a cost but performance basis
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Old 03-25-2019, 10:40 AM   #13
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Re: Insulation


NO!

Start with the energy code.

That small amount of insulation will not keep your sheathing cold and you will have condensation issues.

Further more, by not filling the stud bays, you will have bridging into the cavities reducing perfirmance: one of the failing points of closed cell spray foam, cavities are seldomly filled as the foam can not be shaved flush to framing components. Thus, open cell foam, which can be shaved and fill cavities, often performs better than its higher r-value, more expensive counter part.

The suggestions for dense pack are good, as are mineral wool batts and buiding-out the studs so that you can accomodate r23.

Air seal, air seal, air seal!!!

Be sure to use a smart vapor retarder such as Certainteed Membrane, which will allow your walls to dry to the inside.

Last edited by chrisinnh; 03-25-2019 at 10:43 AM. Reason: typos
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Old 03-25-2019, 10:53 AM   #14
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Re: Insulation


Edit:

Just looked at your quote and would like to add:

Bottom line with closed cell: sheathing cannot dry to the inside as the foam is not vapor permeable. You must use enough insulation to keep the sheathing cold and avoid a condensation point on the inside of the wall cavity. Roofs too!

If you're stuck with the 3.5" cavity, I'd go all open cell, wet spray mineral wool, or carefully installed mineral wool batts. Be particular about air sealing and installation of your vapor retarder.

If you can, fur out the stud bays.
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Old 03-26-2019, 07:38 AM   #15
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Re: Insulation


Chris - it looks like you are starting to get a good grasp of Building Science but you are off on a few items

First the object is not to keep the sheathing cold but rather above the dew point so thus warmer. If the sheathing is cold the vapor will condense there thus creating issues and that is one reason why exterior foam / insulation is required in colder climates --- http://thehtrc.com/2011/what-is-a-hot-roof

Bridging into the cavities - never heard of that, as thermal bridging is based on conduction - the flow of heat through an object or in his case the studs, sheathing, exterior siding... --- http://thehtrc.com/2012/building-sci...fer-mechanisms

Smart vapor retarders - depends on your climate, for most of the country it is a complete waste of money & can still make issues worse. In NH, you should be good

Don't buy the hype on open cell being superior, most have been written by salesmen - both can act as a vapor barrier though closed cell is a true barrier. Open cell will block it after a certain amount but just like a sponge it will hold said moisture & rerelease it back into the structure as many down south & even way up north have found out the hard way. No you don't need to completely fill the bay with closed cell which actually is a nice thing as you don't have to shave off material you paid for & eliminating the hard outer shell --- http://thehtrc.com/2012/myth-misconc...e-code-garages

I have no issues with creating moisture sandwiches - closed cell inside, closed cell on the exterior sheathing because if water doesn't get there, it's all good. Now for many that can be a recipe for disaster because you have got to get your details bang on which leads me to a quick kudos to you...

Yes - air seal, air seal, air seal that is the biggest issue besides making sure you don't allow moisture in, in the first place

Hope this helps

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