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Old 02-02-2019, 06:33 PM   #1
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Exterior Insulation & Windows Joint


Hi All. For the addition I am planning I want to go with an exterior insulation 100% (i.e. no framing cavity insulation at all) using rigid foam board. To meet the code of zone 5 where I am at I would need to install 4" of insulation.


My question is to how go around the windows and doors with such a setup? What would be a preferred and a more aesthetically pleasing look? Should I bump out windows 4" and butt the rigid foam against the reveal, or should windows be mounted traditionally onto the sheathing? The latter method will give just over a 4" window recessed look when all said and done. Planning to use a cement board siding as a final finish. But am also considering stucco.


Would much appreciate any feedback from anyone who came across or who has actually done something like this.
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Old 02-02-2019, 08:21 PM   #2
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Re: Exterior Insulation & Windows Joint


Windows can be installed as innies or outies, putting the recess on either side. This link may help.

As for doors, an in swing door prefers to be installed to the inside. That complicates installing a storm door on the outside but may be discussed in that link, been awhile since I read it.

From what you have described "SIPs" come to mind structural insulated panels. I've never used them and no idea where they would fit cost wise but they would do a better job and probably easier than what you are planning.

Curious, what is going on the inside, empty stud cavities?

Bud
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Old 02-02-2019, 09:43 PM   #3
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Re: Exterior Insulation & Windows Joint


There are pluses and minuses to both. Really depends on what the trim schedule is and the look you are going for.



As an "innie" the windows tend to perform a bit better because they are inside the warm wall. That being said, they loose some of the trim options and the look can be a bit weird.
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Old 02-02-2019, 11:40 PM   #4
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Re: Exterior Insulation & Windows Joint


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Originally Posted by Bud9051 View Post
Windows can be installed as innies or outies, putting the recess on either side. This link may help.

As for doors, an in swing door prefers to be installed to the inside. That complicates installing a storm door on the outside but may be discussed in that link, been awhile since I read it.

From what you have described "SIPs" come to mind structural insulated panels. I've never used them and no idea where they would fit cost wise but they would do a better job and probably easier than what you are planning.

Curious, what is going on the inside, empty stud cavities?

Bud

Thank you for a link to a super informative article. Looks like innies/outies is a debate and the one that has been going on for some time now.


SIPs I am kind of not a big fan of simply because there is a complication in terms of running electrical and possibly plumbing. Unless I am completely thinking about it in a wrong way.


Empty stud cavities is indeed what I am thinking of. With 4" XPS insulation (2 layers of 2" with seam overlap) would give R-20, - exactly like code requires. While ISO panels of same total thickness will give R-26.


I've been trying to learn as much as possible about different wall assemblies and it looks like exterior insulation is a great way to go because dew point inside the wall system falls into the insulation layer as opposed to a sheathing. Since XPS and ISO are vapor barriers and not "afraid" (don't rot) of water on top of that, the wall system assembly is very healthy. When dew point falls onto a sheathing that's when rot can occur unless polyethylene vapor barrier is installed on the interior between studs and drywall. But with exterior XPS or ISO one saves on cavity insulation and vapor barrier installations. Not to mention that studs no longer represent thermal bridging.
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Old 02-03-2019, 06:34 AM   #5
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Re: Exterior Insulation & Windows Joint


So you don't have to reinvent this process search "exterior rigid insulation GBA". GBA stands for Green Building Advisors a great source of information and that search should bring up many related articles.

John Krigger is a co author of Residential Energy a book used to teach classes on energy efficiency. He also undertook a major project of covering the exterior of an older home with very thick insulation. Here is an article on his project. You will see a lot of the retail work that is involved with this approach.

Bud
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Old 02-03-2019, 07:12 AM   #6
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Re: Exterior Insulation & Windows Joint


Not sure about your experience but you may be reversing parts of the building and upgrading. Cavities can be filled with blown in and if must, you can work around it for electrics and plumbing. You must be cold there.


Adding 4" of insulation outside is about the same as building a new house. You will more or less have to bump the walls out, rehang all windows, doors and it extends to roof, roof overhangs, electrical roughs, any plumbing and vents, just few basic things. Then all has to be sheathed and sided. Why do something like this? Extra unnecessary cost can be put into heating fuels now and wait for better times. Do the electric and plumb first. You can even install them in place and not use them for now.



That's my take. It is your house and money but I still can't see the justification for what you want to do.
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Old 02-03-2019, 08:21 AM   #7
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Re: Exterior Insulation & Windows Joint


Just an added note:
Code minimum insulation is (in my experience) based upon the cost of energy. House in NJ back in early 70's required 3.5" in walls and 6" in the ceiling. 6 months later they said 12" in the ceiling so I asked "why the change"? Answer was, the cost of energy went up. Energy costs are the basis for calculating how much you can spend on insulation and still get a reasonable payback.

Today energy costs more so codes require more. In the ceiling increasing the amount is relatively easy, but in our walls there are other costs associated with thicker walls that become part of that cost/return calculation.

My point is for the original poster in that 4" of rigid insulation may reach the minimum code but leaving empty stud cavities bypasses an easy opportunity to go beyond the minimum and there are good reasons to exceed that number.

The articles I have linked will lead to this conclusion and give the op more options to build a better than minimum addition.

Bud
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Old 02-04-2019, 09:24 AM   #8
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Re: Exterior Insulation & Windows Joint


Totally agree with bud about the insulation. In a way, more and air tighter is better. But op:


One detail why hold off: there is no 4" framing lumber. You could use 2x4 (3.5") or rip 2x6 (5.5") into 4. Also you can't glue on 4" insulation to existing sheathing and nail/screw on a siding. Longer nails will droop, most likely. You have to consider that you will have to attach new framing every 16" and sheath again with 1/2" ply or osb. This is what I mean by building a new house. This will encroach on the roof and soffit. You may have to reframe/sheath the roof gable ends, minimum. All electric cables can be installed first and left loose until you can get the electrician, example. New cables don't have to thread through the wall studs from one box to another. It takes more cables but each box can have homerun from basement and tied in one box. But check with your town electrical inspector about doing it this way. In nj and passed 20 yrs ago, but all rules have become stricter. Change the cables to 12 ga and temp connect with the cable from the main panel. You can mix 12 ga with 14 ga as long as you keep the 15 amp breaker. Again, check this kind of work with your inspector. Permit must specify this kind of wiring. Again, if allowed and homeowner wiring allowed.
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Old 02-17-2019, 09:06 AM   #9
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Re: Exterior Insulation & Windows Joint


Definitely won't have to add new framing/sheathing on top of the rigid foam. 4+ inches of rigid foam installed outside is very common in high performance home building. Concerns about sagging siding are remedied with strapping/battons installed over the foam with long screws/nails in which the siding is attached too. Green Building Advisor (the site Bud linked to) is a treasure trove of info on high performance building.

My home has between 2 and 4 inches "outsulation". I installed the windows normally and have innies (though they have nice sills inside as well). This pic is during installation of the stone but you get the idea.

https://photos.app.goo.gl/RroSK8SjxvpqeqX77
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Old 02-17-2019, 10:33 AM   #10
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Re: Exterior Insulation & Windows Joint


Hi @wewantutopia, have to ask, how is the comfort level with all of the new exterior insulation. I have about 80% covered with 3.5" of rigid and added new windows at same time. The other 20% will have to wait for life to get out of my way.

But this cold winter has been amazing even with less than full coverage. I sit next to a supply register and sometimes it goes for over an hour with -10 temps and wind. I've gone from babysitting the thermostat to rarely touching it.

Hopefully will get all finished this summer and be able to run some blower door and infrared testing.

Bud
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Old 03-03-2019, 08:06 AM   #11
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Re: Exterior Insulation & Windows Joint


Quote:
Originally Posted by Bud9051 View Post
Hi @wewantutopia, have to ask, how is the comfort level with all of the new exterior insulation. I have about 80% covered with 3.5" of rigid and added new windows at same time. The other 20% will have to wait for life to get out of my way.

But this cold winter has been amazing even with less than full coverage. I sit next to a supply register and sometimes it goes for over an hour with -10 temps and wind. I've gone from babysitting the thermostat to rarely touching it.

Hopefully will get all finished this summer and be able to run some blower door and infrared testing.

Bud
Hi Bud,

Sorry, just noticed this. With walls between R28 and R37, roof that is R50 to R90 and our Alpen 625/925 triple/quadruple pane windows the comfort level is outstanding! During the polar vortex of 2013, I was only about half way done with the retrofit and, using actual natural gas usage and HDD, I calculated using only about 12,000 btu/hr. This last vortex seemed even better! This is a 1911 craftsman bungalow so it's come a long way!

Everyone questions ROI of energy upgrades but I think its worth every penny for comfort alone.
Bud9051 and schreibdave like this.
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Old 03-03-2019, 08:18 AM   #12
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Re: Exterior Insulation & Windows Joint


One of the distinctions I have notices is the time interval between heat cycles. The size of the heating system plus the heat loss determine the time for the on cycle. But the heat loss alone determines the rest cycle. I sit right next to a supply register so know when it comes on and paid attention one night, -10F or so with wind and it was over half an hour before the next call for heat, and that is with a 1 thermostat. When the wind isn't blowing it is even better.

I love it.

Thanks for sharing
Bud
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