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Best practice for adding insulation to exterior of home?

Best practice for adding insulation to exterior of home?

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  #1  
Old 06-17-16, 08:51 AM
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Best practice for adding insulation to exterior of home?

I have an small addition (9' x 20') in my home that's ~50 years old that I'm in the process of rehabbing. 2x4 framing with T&G sheathing is the only thing that's staying. I ordered new windows with integral nailing flange and J channel built in, so I can install siding right into the J channel and not have to worry about capping.

I can install the siding/windows/exterior the traditional way. House wrap over sheathing, build sill pan/flash windows properly, the install siding into the J channel. However, I wanted some sort of foam insulation on the exterior. I was thinking the following:

1. House wrap over the sheathing.
2. Foam insulation over the house wrap (1/2" or 3/4").
3. Fill strip the same thickness as the foam to allow for nailing of window flanges
4. Siding into the J channel.

I have pre-formed inside corners and a roll of stick flashing to build sill pan/flash the window properly, but how can I do this if I install the rigid foam?? Can I stick my flashing right onto the fill strip/foam insulation??

THanks for any insight. Please see my attached photo sketch for clarity.

PS - I could always get the siding with foam built into the siding plane, but those are unnecessarily way expensive, and would have too many spaces due to the expansion/contraction gap, etc.

EDIT - in this sketch, PINK was intended to be the housewrap.

Name:  EXTERIOR SECTION.jpg
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Size:  27.0 KB
 

Last edited by mookie3333; 06-17-16 at 09:02 AM. Reason: add photo
  #2  
Old 06-17-16, 11:48 AM
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You can do it 2 ways... you can either forget the housewrap (since if done in the manner below it would be optional / redundant)... and tape all the seams on the foam so that the foam itself is your wrb (and your windows and flashing tape would then go on top of the foam) -or- even better... you would put your wrb (your housewrap) on top of the foam, and the windows on top of that. (The flashing tape would then be sticking to the housewrap on the sides of the window, but it would be tucked behind the housewrap on top).

But you don't want to do housewrap, then foam, then windows... because that would make it more likely that if there was a leak, and water got behind the top nail fin, that water would leak on top of the window and drip right off the top of the window and into the home.

Doing it in the proper order removes the potential for a leak. You will find arguments both ways on where the housewrap should go, but I am saying on top of the foam purely because it's the best way for window installation.

Windows are often installed on top of foam with no wrb... or even tge way you depict it in your illustration, but you are resting all your confidence on the tape that you put over the nail fin of never letting go... ever. And if the seams in the foam are not taped, you are also hoping there is not a butt joint in the foam right above a window... that would be a potential path for water to get behind the nail fin. This potential is even greater with vinyl siding... especially when you have a 2 story house with windows above letting water behind the siding which can then run down the wall behind the siding and leak in on the windows below on the 1st story.

At least when you have the housewrap on top of the foam, you can cut a flap above the window, tape the sides to the housewrap, tape the top to the foam, then fold that flap of housewrap back down to "flash" either the drip cap that would go over the trim -or- in your case, to protect the flashing tape on top from ever getting wet.

The idea is that no water should ever get behind the housewrap under normal condtions. Behind the housewrap = dry... in front of the housewrap = wet. If water gets behind the foam or the housewrap (such as if there is an ice dam on the roof), it's probably going to leak in at a window no matter how you do it.

Nice illustration, btw... but you forgot some space around the window. (the rough opening is usually 3/8" to 1/2" per side for shims and insulation.)
 
  #3  
Old 06-19-16, 07:54 PM
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Thanks for the input. Your suggestions make sense. I'm sure I could find the answers on Google regarding the physical attaching, but what's the best way to attach the foam board to the sheathing? Then, what's the best way to attach the house wrap to the foam? Hammer tacker is out, I'm sure.
 
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Old 06-19-16, 08:33 PM
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HD galv roofing nails or round plastic cap roof nails. Some don't like the cap nails because they protrude ever so slightly. I'm not that picky. I also prefer that the house wrap doesn't blow off.
 
  #5  
Old 06-20-16, 06:08 AM
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Did see that about using cap nails on Tyvek's site last night. Too bad- I was definitely excited to give my new hammer tacker a run. Thanks for all your help, XSleeper!
 
  #6  
Old 06-24-16, 12:15 PM
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Sleeper,
I have one more issue I was hoping you can help with. I was concerned with water getting between the extension, and the main brick structure. (where the J channel meets the brick). Are my thoughts correct? Should I caulk the joint between the J channel and the brick wall? Am I missing some sort of flashing?

This situation may be worse on the other side of the house, where the extension is flush with the brick wall - i.e. after adding the 3/4 insulation and siding, the "extension" will stick out ~1-1.5" past the main structure.

Please see attached sketch. Thank you in advance.Name:  EXTERIOR CORNER.jpg
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Size:  15.4 KB
 
 

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