Wiring a house on the inside of VB,with no penetrations?...

[jake pogg]

Wonder if anyone here has ever done that,as in furring out the completed thermal envelope on the inside with 2x2's,and wiring within that using shallow boxes? 

I've a moderate-sized house to do that way and am puzzled about the exact manner in which the wiring attaches to walls. Any info would be greatly appreciated,thanks in advance. 

[Don P]

I think you're going to run into "box fill" problems, too many conductors for the volume of the box. I think in those shallow boxes there is enough volume to feed the device in that box, its a dead end, there is not enough volume for another set of conductors to continue a loop.

It was February in the black mining hills of Dakota, I had taken another house and we had moved camp south for the deep winter but the animals were still well below us, it was quiet. I had notched in the electrical boxes on the horses as a try to do. i meet with the electrician and ask them to bring samples of all the boxes and we walk and mark the floor with the homeowner. So I had done all that, met with the "electrician" who was a friend and we were off to the races.

There was another house going up down the road and the electrical inspector popped in one day. Reads me the riot act for my temporary, justifiably, and then looks at my box holes, and then the boxes, and it is getting really warm in there for February  :D. He actually was really informative and explained what I needed and how to figure it out. Anyway, I spent about a week of evenings on my knees chopping out electrical boxes.

[jake pogg]

Thanks,Don,yes,i noticed that as i looked over what's available for these shallow jobs in town.

(this is a job in Fairbanks that i've helped build 15+years ago,long story but call it a sabbatical from log-work,and i'm actually close to the hardware and even some specialized stores).

So far i only briefly checked out some box-stores, and there is a funky type they sell that has a compartment over on it's side,looked enough volume to stuff a few wire-nuts and so to christmas-light some outlets and so on.
If i must i'll just gang these silly things up in however numerous series that i'll need.

This system calls for 2x2 furring 2' o.c. with 1" styrofoam panels fitted in between. That remnant 1/2" i presume is to run the wires behind the foam,stapled to the studs?

One of the problems that i anticipate is that the furring itself would be a poor choice for securing the wire to as they're the nailers for all finish materials,and their shallow positioning will of course expose them to the danger of fastener jabbing right into the wire...

[beenthere]

Am thinking there are shallow electrical boxes that will fit in that 1½" space and provide room for more connectors and wires. Might take some searching. Maybe this is but one source...
https://www.homedepot.com/p/Carlon-1-Gang-18-cu-in-Shallow-New-Work-Electrical-Box-SNO18-6R/202664424

Believe there are metal plates to cover the "stud" so a nail cannot get to the routed buried romex wires.

[jake pogg]

Thank you for that link,yes,those are exactly what i've been looking at so far, and i think they'll accept one set of connectors (may end up having to use them fancy see-through ones to save space ).

Plates,unfortunately,won't work in this application: The studs (2x6) are already insulated and VB'd; the wires will run over the face of the wall in what would amount to be an 1 1/2" chase (the 2x2 furring running horizontally).

The idea in this type of system is to break to energy transfer through the studs (or most of it) by adding an extra 1" of rigid foam to the inside of the wall,while also not compromising the VB by all the electrical penetrations.

Heat-transfer through solid mat's is an issue here in this climate. We built this place a while back,and my friends never have finished the interior as was intended. Many a time visiting here in the winter i could see the transfer on the outside as on a frosty morning the outline of each stud would be clearly visible (on the horizontal rough-cut spruce shiplap siding this place is sheathed with).  
     

[beenthere]

So no wiring going through holes bored in the 2x2's to run the wires between boxes.

A pic or two would help understand better. 

Any wall covering over the 2x2's? wood paneling or drywall?

[jake pogg]

So no wiring going through holes bored in the 2x2's to run the wires between boxes. 

Well, some of that i suppose: Outlets will generally be on the same level,but some of the wires will have to change "levels" i.e. go up or down across the 2x2's.
So thank you for reminding me about the plates,a few will definitely be in order.

The way i'm envisioning it now is that the wires will be stapled to the studs,that'll put them 1 5/8" below the finished surface (1" foam + 5/8" Type X rock), all i can do is Hope that it's enough... (is "hope" a viable concept where electrical safety is concerned?...).

And yes,i'll add a photo as soon as i begin running that wiring. I've another day or two finishing the VB and i should be starting on the 2x2's.   

[LeeB]

Please explain what VB is. ???

[jake pogg]

Please explain what VB is.

Sorry about that-VB= Vapor Barrier.

It's particularly important for us here in cold climate as far as fiber insulation is concerned.

Without vapor barrier the moisture in vapor form travels from the warm/moist inside towards the outside of thermal envelope.
Somewhere inside of that though it meets the freezing T,or dew point,and condenses as ice crystals, ruining the insulation and eventually the structure itself.

[jake pogg]

 




 

That's what your basic  AK structure looks like under the finish panelling. The VB (6 mil polyethylene in this instance,the poor man's choice) is stretched over the frame.
The black stuff along each frame member is Tremco acoustic sealant (aka The Black Death), it's applied to wood under the plastic and seals the holes as you staple the plastic film through it.
The red tape seals the joints in sheets of plastic.

In a conventional building the electric would already be done by this time,located within the frame.
But doing it that way makes it difficult to achieve a good vapor-proof seal. It also messes up the fiberglass insulation some,as well as  making it hard to add that extra layer of rigid foam that prevents heat transfer through solid materials.

So in doing it the way i'm about to now the electrical will go on the outside of what you see in that photo. 

[Old Greenhorn]

I am no construction guru by any means and I am not understanding some of your explanations about the 2x2's, so you can just discount this reply if it adds nothing. Have you considered doing it all on the surface, leaving the VB intact, and only having penetrations from room to room? There is a company called Wiremold that makes a complete line of surface mount stuff including junction boxes, etc. You probably already saw some of their stuff through HD or the other stores, but for a build like this I would go right to the company and get the full catalog and see if you can't find just what you need. It has the benefit of the UL tag besides.
 But maybe (probably) I missed something and am not understanding the true issue you face.

Good Luck

[twar]

Cool to see that you're doing this. My Swedish-built house (here in Norway) follows this principle. Here are examples of recepticles on outside and inside walls.

 

 

[Hilltop366]

Besides the reduction of thermal bridging the insulation on both sides of the VB will greatly reduce vapour condensing on the VB by reducing the difference in temperature from the inside to out side of the VB.

Would a square box with a plaster ring get you the required space for multi connections were needed?

[jake pogg]

Have you considered doing it all on the surface, leaving the VB intact, and only having penetrations from room to room? There is a company called Wiremold that makes a complete line of surface mount stuff including junction boxes, etc. You probably already saw some of their stuff through HD or the other stores, but for a build like this I would go right to the company and get the full catalog and see if you can't find just what you need. It has the benefit of the UL tag besides.  But maybe (probably) I missed something and am not understanding the true issue you face.

Thank you,i looked up their site,many Very useful things there for sure (and yes,now i remember seeing their products around).
No need to go surface-mounted all the way,but some great components there for sure,really appreciate that!

Thanks to everyone else as well, it's neat just how far-flung the membership here is,we get to compare notes with builders from All kinds of climates and different building practices!:) 

[Joe Hillmann]

I was fixing an outlet at work last week.  It was on a brick exterior wall with  2"furring strips, insulation and Sheetrock on the inside.  So similar to what you are working with.  The face plate of the outlet was normal sized but the box in back was about 6x6 behind the Sheetrock with reducing cover through the Sheetrock to allow a normal size outlet a and face plate to mount in it.  By being bigger behind the Sheetrock there was a lot of extra room to stuff the wires even though the cavity was only 2 inches deep.

I don't know what that style of box is called but it does exist, maybe if you can find them it could be the answer to part of your problem.

[Joe Hillmann]

Is your plan to put the foam insulation up first, then the 2x furring strips so there is a total thermal barrier(except for the nails/screws holding the furring strips up)?

Or is the plan to put up the furring strips than put the foam between the strips?

If you are putting the foam up first that gives you an extra inch to play with and you can hollow out spots in the foam for deeper boxes and for wires to run between cavities.

Also, are you running the furring strips vertically or horizontally?

Being able to see the studs on the outside(through dew or frost condensation patterns) isn't necessarily caused by heat transfer.  It can often be seen on super insulated building and CAN be caused by the studs taking longer to heat and cool compared to the insulated cavity beside it as the outside temperature rises and falls.  If the studs and insulation and outside air temp is above the dew point and the dew point falls the insulated area will cool faster than the studs, dew will collect there, by the time the studs cool to below the dew point the dew point has also dropped so there will be less/no dew where the studs are.  The same goes for frost. 

People see that and automatically assume it is because the studs are loosing more heat than the insulated area.  In typical construction that is usually the case,  But with what you are doing and having a total thermal break between the inside and outside there is a good chance that you will still be able to see where the studs are when the dew/frost sets and it is due to the studs resisting temperature change rather than the studs loosing more heat.

[jake pogg]

 Joe,thanks for all that.

I'm putting the furring 2"x's first,with foam in between them. Not as thermally bullet-proof as the other,but much better joint mechanically,wood on wood.

And yes,those are the boxes i'm using,large area in back/face-plate reducing the opening to a single-outlet size. They're around 18" cu.,which is supposedly enough for most connections.

Thanks for the theory on thermal transfer,a bit tough to wrap my pea-brain around but i'm trying,and i'm sure you're correct about the physics.

A bit late starting on all that actually beginning today,and will take some photos once some area is done.   

[jake pogg]

Also, are you running the furring strips vertically or horizontally?

Sorry,missed that. It's a conventional (2x6) frame,so the furring strips go on horizontally.

I've ran into some technical difficulties with wiring,having to do with where i run the circuits TO (working inside a lived-in house that has no electrical system or breaker panel yet).

But this entire deal is new to me so i'm moving along slowly,having to feel and guess my way along.

One concern i had was just how tight can i fit the foam,in theory (how tight does it Need to be to make sense?) and practice, as the layout on top of plastic and bulging insulation is not the most precise process.
Ended up doing it as i go-foam cut on a table-saw goes on an installed strake,than the next run strake gets nailed to the studs while exerting some pressure against the foam. I like it so far,it makes the friction fit very doable/controllable, and without tons of time or fuss.

[jake pogg]

Something like this:





 



 

[Don P]

Just from a cogitating point cause I know nothing here. You are "loose" at the foam layer, lots of air leaks. There is a VB behind that insulating layer. Will that foam insulation create a below dew point plastic surface. Warm moist gets through the foam layer, condenses and runs down the plastic? Purely wondering.

[jake pogg]

Don,it's a valid concern. I think the trick here,why it Shouldn't happen,is that the foam layer is pretty thin (1"),and is equal to only a small amount of resistance to heat transfer (i believe 5 or 6 R even nominally,but measured overall would average even less?).

So with any amount of heat inside the house the dew point would be further towards the cold side of envelope,much further in than the VB.

This job is an addition to a friends' house,and when i resumed the work on it in September it ws a bare frame. After some weeks siding it and sticking in windows and doors i finally enclosed it and got inside and insulated the whole thing.
At that point the weather was well below freezing,so i opened it to the main house to hang the VB as it's hard to hang visqueen in the cold,and it became in effect a part of the heated lived-in space.

It took me a couple-three days to hang plastic all over,and at some point by feeling behind the insulation i found a layer of frost building on it's outside surface,against the Tyvek membrane.

So at That T the dew point was clear on the opposite side of insulation;as it gets colder i'm sure it moves further in towards the warm side,but just how far in is the question...

So again-hopefully not as far as that space between VB and foam...


At this juncture i must say the following: This idea to do it this way is not mine, but has come from the folks at this organisation: Cold Climate Housing Research Center – Healthy & Sustainable Housing for Alaska (cchrc.org)

To be completely honest i personally don't have much use for this outfit,having watched them over a number of years. I believe they tend to a bit too much theory and nowhere near enough testing and practice of much of what they proselytize. 
There's a great number of other sins that i'd charge them with as well,elitism and so on,but pushing untested and over-complicated theory is the gravest in my book.

However for whatever reason this project was designed with this feature and i could not change that at this late stage.
My hope was that this system was not originated by the CCHRC,and that i could find some info on here from others with related experience, (as very little of the "research" that they do is in fact original to any degree),but possibly i may've been wrong as neither here, nor in a few other places that i looked can i find any trace of a similar technique..... 

[Sod saw]

.

Jake,  Don is correct that the room inside of each "outlet box" is important in deciding how many wires and the size (gauge) of those wires.  If you look in the newest edition of the electrical code book (available from your local electrical supply house) you will find charts showing how many conductors of a given gauge that can fit into a given size box.  If the box has no device (switch or outlet, etc) then you can fit more conductors.

If you look at those charts you will also see that the ground conductors are considered differently than the current carrying conductors.

I have a full case of boxes that are too shallow because they were legal to use a few decades ago, but the code changed and I can not use them any longer for outlets etc.  Oh well, so much for stocking up so I didn't need to run to the supply house at the last min.

The suggestion to use a shallow metal 4 x 4 inch box with a 1/2 inch deep mud ring is a very good idea although somewhat more costly for materials and more labor time intensive.  These metal boxes and mud rings are available for more devices so you can mount 2 or 3 or 4, or what ever, outlets/switches in the same box.  That Home Depot link is  also a good suggestion for single devices.

3 way switches and wires will probably not fit into the plastic boxes with the switch unless it is a dead end.  Check those code sizing charts, gauge .

Be very careful with your wires and do protect them from nail or screw points as they across studs or go thru the 2x2 furring strips.  Can the romex be "pushed" behind the horizontal strips to reach the ceiling and /or floor without damaging the vapor barrier?

Can you use "normal" switch boxes in the interior partitions where 2x4 or 2x6 studs are used?

If you try to fit Ground fault outlets or Arc fault outlets into those smaller shallow boxes, you may find that they will not fit (depth).  Use GFI, AFCI breakers instead.

As for penetrating the vapor barrier, , ,  remember that the code requires outdoor outlets. One on the front of the house as well as one in the rear.  Each  outside door must have a light near by too.  Door bell button? etc.  How will the service entrance wires enter the structure?  There are foams and tapes available to solve those few penetrations.

When ever I have a new job where I am uncertain about some details the first thing I do is to call the electrical inspector.  Those folks love to show how much they know.  They will also be much more forgiving when they do find some detail that should be changed, they will usually explain why as well as how to comply with the codes.  It sounds like you will benefit from a pre-work call to the inspector who will actually be visiting your job site.

As for the condensation on the vapor barrier. I assume that he walls are at least 6 inches thick?  The amount of "outside" insulation will keep the condensation location far enough outside of that vapor barrier so as to not happen with only 1 inch of foam..

have fun with the challenge


.

[jake pogg]

.

Jake,  Don is correct that the room inside of each "outlet box" is important in deciding how many wires and the size (gauge) of those wires.  If you look in the newest edition of the electrical code book (available from your local electrical supply house) you will find charts showing how many conductors of a given gauge that can fit into a given size box.  If the box has no device (switch or outlet, etc) then you can fit more conductors.

If you look at those charts you will also see that the ground conductors are considered differently than the current carrying conductors.

I have a full case of boxes that are too shallow because they were legal to use a few decades ago, but the code changed and I can not use them any longer for outlets etc.  Oh well, so much for stocking up so I didn't need to run to the supply house at the last min.

The suggestion to use a shallow metal 4 x 4 inch box with a 1/2 inch deep mud ring is a very good idea although somewhat more costly for materials and more labor time intensive.  These metal boxes and mud rings are available for more devices so you can mount 2 or 3 or 4, or what ever, outlets/switches in the same box.  That Home Depot link is  also a good suggestion for single devices.

3 way switches and wires will probably not fit into the plastic boxes with the switch unless it is a dead end.  Check those code sizing charts, gauge .

Be very careful with your wires and do protect them from nail or screw points as they across studs or go thru the 2x2 furring strips.  Can the romex be "pushed" behind the horizontal strips to reach the ceiling and /or floor without damaging the vapor barrier?

Can you use "normal" switch boxes in the interior partitions where 2x4 or 2x6 studs are used?

If you try to fit Ground fault outlets or Arc fault outlets into those smaller shallow boxes, you may find that they will not fit (depth).  Use GFI, AFCI breakers instead.

As for penetrating the vapor barrier, , ,  remember that the code requires outdoor outlets. One on the front of the house as well as one in the rear.  Each  outside door must have a light near by too.  Door bell button? etc.  How will the service entrance wires enter the structure?  There are foams and tapes available to solve those few penetrations.

When ever I have a new job where I am uncertain about some details the first thing I do is to call the electrical inspector.  Those folks love to show how much they know.  They will also be much more forgiving when they do find some detail that should be changed, they will usually explain why as well as how to comply with the codes.  It sounds like you will benefit from a pre-work call to the inspector who will actually be visiting your job site.

As for the condensation on the vapor barrier. I assume that he walls are at least 6 inches thick?  The amount of "outside" insulation will keep the condensation location far enough outside of that vapor barrier so as to not happen with only 1 inch of foam..

have fun with the challenge


.

Sod saw i thank you Most kindly,that's a great bunch of very sound info,much of it i was not aware of before.
Regarding inspection/inspectors/local codes:I'll have to look around and ask some people (actually i've a Zoom (!:)) appointment coming up tomorrow with a home insurance agent so will start there.
I'm in a somewhat odd are of the US,there's no mandatory residential code but all different optional/voluntary ones dictated by assorted financial institutions and some by the State.
Many residences here were built without ever consulting authorities of any kind;but the times are also changing and i'll try to puzzle out what's really going on nowadays.
But yes,excellent idea to consult the code book for specs and an inspector for info.
Types of outlets,yes,check on that also. I actually switched from the previous sort with a hinged half (18 cu.in.) to the plain shallow 4"sq. ones,+a 5/8" mud-ring,and these are 20 cu.in.
The number of conductors is very helpfully printed on the inside of each of the boxes,by gauge,i.e. 3 pair of 12 ga. and so on,making it a bit easier. 
The runs of Romex can very easily be slid up behind 2x2's on vertical runs,and run along the studs and are stapled on the horizontal ones.
Places where i must drill through the 2x2's for wire i make Sure to use the steel plates over.
The outdoor outlets with GFCI's are most commonly wired using that grey plastic conduit and externally-mounted boxes of same material,i noticed that it's done that way even on some commercial buildings (it's common for Alaska to have plug-ins for vehicles outside an office- or a commercial building to plug in the vehicle's engine heater on cold days).
So check that too.
My friends that i'm helping with all this are anything but cheap,and would never dream of trying to save money on small details Especially something like the electrical system or any other where the safety is at stake.
I can ask for any and all proper hardware that is needed,bless them,no need to cut corners on the supplies and materials...
(Alaska is some goofy place where many choose to live without running water or many other conveniences considered necessities in other places,an outhouse and packing water in 5-gal jugs is a lifestyle that many here are not only used to but prefer,and are actually sentimentally attached to!:)).
BTW,while trying to gather data for this style thermal envelope i've come across even a weirder version:
The external wall framing is filled with fiber insulation and covered with the VB.
Then the 2" thick blue or pink polystyrene is nailed over the entire wall area on the inside.
Then on top of that foam 1x3" stringers are run horizontally 2' o.c.,(attached through the foam with 3" screws)and then-Another layer of 1x3" vertically on top of that,making that furring run vertical once again.
2" foam plus 3/4"x2=3 1/2",so the openings get edged with a 2x4" on edge.
This also leaves only 1 1/2" clear depth for boxes but the boxes can also be countersunk into foam some,allowing for the use of standard-depth electrical boxes...
Now how you like them apples? ALL that work in order to preserve the pristine virginity of the VB,is that over-thinking or what?! 

[Don P]

Critter condo  :D

It just popped to mind when you said the boxes were marked with the allowable conductors... I'm stale but make sure that is after the device is in the box or figure out how many conductors the device is dinging you.

[jake pogg]

Critter condo  :D

It just popped to mind when you said the boxes were marked with the allowable conductors... I'm stale but make sure that is after the device is in the box or figure out how many conductors the device is dinging you.

10-4 on that,Don,thank you.
Speaking of critters...One of my chores here is to figure out how to exterminate a colony of Flying squirrels in one part of the roof. One slat of soffit was left out under the main roof and that's all it took.
They're cool little beasties,many people even here don't know that they're around,as they're strictly nocturnal and well camouflaged,a dark-grey color.
The trees around the house are very tall,and these funny little critters can glide just about forever by jumping from that high up. Sometimes you see them slam down onto the wall next to a bird-feeder,they velcro onto mill-sawn siding Real well,big old nocturnal eyeballs on 'em,like lemurs or space aliens!:)
Kinda hate to kill them but they're a major liability as far as insulation in the roof...Seen a video recently about this traditional hats they make in Transylvania out of doormouse...takes about 16 for an average hat...Really soft fur 
I bet these are even softer,something about airdynamics....

[Don P]

I guess its been a couple of years ago now. My partner had never seen a flying squirrel and we were removing a 30 year old onduline roof and putting down metal. It was log, cathedral and heavy timber and they had flying squirrels.

The roof was 12/12 but not much scaffold needed on the strip, just stomp into the onduline corrugations and clean above and alongside. I fully expected major roof repairs from what we were seeing. They had been trying to find someone for 3 years and had gotten full value out of the old roof but thankfully it had held.

For the uninitiated... we really don't want to go digging the yuk and joy out of your house  :D. This one turned out to be quick and easy for everyone.

Anyway, we were taking a break sitting on the roof deck, DB was above me closer to the ridge. Motion caught my eye. A flying squirrel popped out of the now open ridge, takes a short bound to DB's shoulder from the back, and launches. On that end we are 40-50' up and actually, we are above the river there, that guy could have gone forever, but lit in a tree a hundred feet or so away. Don never knew what hit him till he saw it gliding.

[Sod saw]

.


The National Electrical  Code is the guiding "bible" that is used in most places in the USA.  Most insurance companies as well as building inspectors require any electrical installation to comply with that code to be sure that the electrical work is safe, and safety is the number one goal when it come to electricity.  Many insurance companies will not pay for a loss if the electrical installation was never "inspected" and the loss is caused by said faulty electrical installation.  The result is often that the person who did the installation will pay for the loss.  To my knowledge, there has been no loss payments being refused  by an insurance company with a valid final electrical inspection by a qualified electrical inspector here in America.  

Good call Don, , , ,   As for boxes and number of conductors in those boxes. . . . The code book is made up of sections; sort of like chapters.  Those sections are numbered by subject.  Your box fill section is 370.  Within this section the code requires that two conductors be subtracted from the allowed fill for each switch or outlet.   Those conductors that are subtracted must be two of the largest conductors.  I suspect that most of your boxes will have only one wire gauge size so the math will be easy.  

Onward to the box fill. . . .  Using the example of 18 cubic inch steel box, the code allows 8 #12 gauge conductors.  With romex wire you will have 3 conductors per each run of 12/2 romex (2 carrying current and one ground).  Therefore 2 romex cables can enter (or leave) a box and still have room for the subtraction of those two conductors for the outlet (or switch).  Needless to say, 14 gauge wires will allow more conductors in a given size box.   10 gauge fewer.  3 wire romex is a bit more challenging as I find it hard to count all the way up to 4.

Using GFI breakers instead of outlets might save you from future repairs as the outdoor humidity sometimes attacks the GFI outlet circuitry.  Yes, even with in-use covers.  Will they want extra switched outdoor outlets for Christmas lights to plug into?

With all that cold and insulation do you all use triple pain glass windows?  My daughter will be building a new home soon with R-60  double walls etc. with the vapor barrier in the middle between outside and inside somewhat as you described.  The indoor side of the walls will be 2x4 studs so the mechanical systems will be "normal" but with no penetrations as your project requires.

We live near the shore of Lake Ontario but are in the woods.  Our friendly flying squirrels had taken up residence in our ceiling (roof). My daughters cat has been known to proudly present them to her at nite when she is in bed.   After removing the bird feeders we hung a large piece of metal window screen over the hole in the outside wall.  The screen had a weight on it so the hole was blocked by the screen preventing the critters from getting in. The ones within the house could push the screen aside to get out but we're unable to return as the screen fell back over the hole.  The operative word is LARGE piece of screen.

Sometimes a .22 rimfire will help but its hard to see them (the squirrels not the cat) at nite.

However, you are correct.  They are fun to watch gliding from tree to tree (or your house).


.

[jake pogg]

.


The National Electrical  Code is the guiding "bible" that is used in most places in the USA.  Most insurance companies as well as building inspectors require any electrical installation to comply with that code to be sure that the electrical work is safe, and safety is the number one goal when it come to electricity.  Many insurance companies will not pay for a loss if the electrical installation was never "inspected" and the loss is caused by said faulty electrical installation.  The result is often that the person who did the installation will pay for the loss.  To my knowledge, there has been no loss payments being refused  by an insurance company with a valid final electrical inspection by a qualified electrical inspector here in America.  

Good call Don, , , ,   As for boxes and number of conductors in those boxes. . . . The code book is made up of sections; sort of like chapters.  Those sections are numbered by subject.  Your box fill section is 370.  Within this section the code requires that two conductors be subtracted from the allowed fill for each switch or outlet.   Those conductors that are subtracted must be two of the largest conductors.  I suspect that most of your boxes will have only one wire gauge size so the math will be easy.  

Onward to the box fill. . . .  Using the example of 18 cubic inch steel box, the code allows 8 #12 gauge conductors.  With romex wire you will have 3 conductors per each run of 12/2 romex (2 carrying current and one ground).  Therefore 2 romex cables can enter (or leave) a box and still have room for the subtraction of those two conductors for the outlet (or switch).  Needless to say, 14 gauge wires will allow more conductors in a given size box.   10 gauge fewer.  3 wire romex is a bit more challenging as I find it hard to count all the way up to 4.

Using GFI breakers instead of outlets might save you from future repairs as the outdoor humidity sometimes attacks the GFI outlet circuitry.  Yes, even with in-use covers.  Will they want extra switched outdoor outlets for Christmas lights to plug into?

With all that cold and insulation do you all use triple pain glass windows?  My daughter will be building a new home soon with R-60  double walls etc. with the vapor barrier in the middle between outside and inside somewhat as you described.  The indoor side of the walls will be 2x4 studs so the mechanical systems will be "normal" but with no penetrations as your project requires.

We live near the shore of Lake Ontario but are in the woods.  Our friendly flying squirrels had taken up residence in our ceiling (roof). My daughters cat has been known to proudly present them to her at nite when she is in bed.   After removing the bird feeders we hung a large piece of metal window screen over the hole in the outside wall.  The screen had a weight on it so the hole was blocked by the screen preventing the critters from getting in. The ones within the house could push the screen aside to get out but we're unable to return as the screen fell back over the hole.  The operative word is LARGE piece of screen.

Sometimes a .22 rimfire will help but its hard to see them (the squirrels not the cat) at nite.

However, you are correct.  They are fun to watch gliding from tree to tree (or your house).


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Thank you yet again,that explanation of conductors and their math Really helps,as well as all other advice.
Super cool way of dealing with the squirrel problem,an inverse of a fish-trap funnel,that's very clever!:)
And yes,most often the windows around here are inert gas filled triple-pane. In spite of that they're inevitably quite a breach in the thermal envelope,you can feel how cold their surface is on cold days...
On a serious project such as your daughter's house sounds to be sometimes people install those neat insulated "shutter" drapes,the kind that slide in a channel on each side,to conserve heat in the night.
At times i thought of experimenting with the real rigid shutters just like they had in the past but with some type of foam lining to bear against the glass.
The truoble designing something like that would be the hardware to open and close these,as the old-style,simple forged kind went through the wall,and being a moving part would be difficult to seal.
Never did come up with solution to that,maybe nowadays there's some tricky electronic/cordless device that could be used!:)

[Joe Hillmann]

Is this on a home they live in and keep heated all the time or a cabin that cools off?

I ask because if it is heated all the time I would have no concern with having the vapor barrier behind some insulation.  But if it is allowed to cool to near freezing then warmed up , then  cool and warmed up again and again(such as at a weekend cabin) at the beginning and end of each cool-warm-cool cycle conditions will be perfect for large amounts of condensation to form between the vapor barrier and the insulation.  If that happens once or twice a year, it isn't a problem, if it is happening every day and what ever is behind the vapor barrier stays cold it could be a major problem.

[jake pogg]

Yes,thank you,got that though it took me some mental grunting to understand what you mean.

You're absolutely right;if allowed to freeze from the Inside it could form ice between the plastic VB and the (vapor) impermeable foam.And keep forming each cycle.

The place i'm working on now is a permanent residence,constantly heated. But Very good point,thanks.

  

[Joe Hillmann]

I discovered first hand how bad it can be.  We built a greenhouse this fall and as of now it is unheated, every day it goes from below freezing, up to the high 60's+, then back below freezing.  Every time the tempature of surfaces warms or cools to the dew point huge amounts of condensation  forms on the windows, ceiling and insulated walls.  If that condensation were to happen against the vapor barrier it would be a problem.