Continous foam insulation on the inside or the outside of the wall?

Rio · Jan 30, 2017

Here in Cali we're in the world of the new Title 24 part 6, with high performance wall assemblies and roof attics being the default from which the energy calcs that are required in order to get a permit have to pass.

Part of the default requirement now for wall assemblies is continuous foam insulation, either 1" or 2" depending on the climate zone and other variables, being the norm.

We have the option of calling out the foam on either the inside or the outside (it complies better with it going on the outside). This brings up the question on what location is preferable? For this particular project 1" will work.

Regarding putting it on the outside we don't want to do an EIFS system with synthetic stucco, worry about leaks having heard some bad results from using the system and also don't like the idea of being able to dent the wall so easily, also there might (probably) be some issues using that system in a wildfire area. If we do a traditional 3 coat stucco system it's going to stick out 2" now and we have some concerns about hanging the lath over the foam (this is especially true when 2" will be required). We could use some sort of cement board but once again are concerned about the nails having 1 or 2 inches of foam to have to go through.

As a result for this one we are leaning towards calling it out on the inside. This will mean the rough in boxes will have to be deeper so they can extend another 1" and still be able to be attached to the studs, the nails for the trim will have to be longer, the jambs wider, etc.. I was discussing this with another GC to get his opinion and he said he has done it before and used adhesive for the foam and for the drywall itself. Of course if that's the case the adhesive will have to comply with all sorts of rules here regarding VOC's and toxicity.

Any suggestions or opinions on this vexing and ongoing issue?

griz · Jan 30, 2017

In the 80's I was involved in building several super insulated solar homes.

Thick, and sometimes double walls for high r-value fiberglass insulation.

Continuous rigid foam then wrapped the exterior under the siding and over shear.

The custom conventional style homes often had rigid foam under the siding.

I have never seen nor heard of foam being on the inside.

There is something ticking in my brain where I was once told not to put rigid foam over vapor barrier like FG batts would have on an inside foam install.

Philament · Jan 30, 2017

Lots of questions there....
I'm in a completely different climate, so the vapour drive concerns are probably opposite (we have VB on the interior "warm side"), but we have similar complications with new energy efficiency regulations addressing clear wall r-values and using continuous insulation.

Here are a few pieces of information/problems I have run into trying to deal with rigid insulation
Vapour drive and vapour permeability: I don't know the regulation you're talking about specifically, but I suspect they used terms like "continuous insulation meeting an r-value of x" and people just extrapolate that to "foam board". Not all "foam board" is created equal, they have different permeability and different r-value per in and some inflate the number by including the r-value gained from having a foil facer. The permeability of the product can help you determine if it is suitable as a vapour retarder, foil faced polyiso for example is a vapour barrier, but there are other facings they use on polyiso that are more permeable. Similarly XPS at sufficient thickness can be considered a vapour retarder (thickness required depends on your perm requirement). EPS is more vapour permeable, so you can go quite thick on it before it is considered a vapour retarder. Knowing these properties lets you better understand if it is more suitable for interior or exterior. There's also products like roxul board that are fire retardant.

Interior continuous insulation problems: It's can be very labour/detail intensive to meet the "continuous" requirement on the interior like at the rim joist. Further to that it can make finishing quite problematic like trim/cabinets, electrical outlet mounting, partition walls...etc. What isn’t mentioned often is that each of these rigid insulation products have different compression strengths, so something as trivial as hanging drywall can be difficult to keep flat or that balance between dimpling the drywall and it blowing through a screw. Sourcing the long drywall screws can be difficult too, at 2” foam, 1/2” drywall and 1” embedment, you’re looking at 3-1/2” drywall screws.

Exterior problems: Flashing details can be really tricky depending on what you're using as your WRB/drainage plane, and/or air barrier in combination with exterior cladding. The EIFS system failures you've heard about are most likely from a failure of properly understanding where that drainage plane is and not tying back things like head flashing all the way back behind the foam. If you're using something like James Hardie, the thickness of the rigid insulation determines which installation procedure you use (http://www.jameshardie.com/d2w/tech...2w/technical-bulletins/19-jh-over-advanced-framing-or-continuous-insulation.pdf). The types and quantities of fasteners have to be considered if you're greater than 1" and have to use furring strips to hold the weight of the siding.

Window installation: Windows can be a real pain, innie, centre, or outie window placement all have different flashing details and it can get really confusing. Same goes for trimming them either exterior or interior.

I don’t claim to have all the answers, just giving my feedback from having tried both approaches as I am still struggling with it too. I really feel that we have been let down by the governing bodies who have put in these regulations, but haven’t provided implementation details to deal with these very disruptive building methods. It’s a hell of a learning curve. 1” seems to be the magical threshold for how complicated implementation will be, < 1”, most normal building practices apply, >1” things get complicated.

Rio · Jan 31, 2017

Thanks Griz and Philament for the information. Thanks in particular Philament for going into so much detail regarding the choices. That's a really good point on going with interior continuous foam board the problem of the interstitial space where the plates and rim joist are, don't think there's any way to really do that and now I wonder how particular the inspector(s) would be on it.

As we get the screws turned by the CEC (California Energy Commission) more and more it seems the building departments we work with are getting more particular in their demands and if one gets a HERS rater involved (not sure it that's required for continuous insulation) who knows how picky they're going to be. I've heard horror stories about builders going with QII (Quality Insulation Installation) which requires a HERS rater and then failing and not being able to proceed until passage racking up the costs tremendously.

After doing some research on it and reading all of your excellent points it looks like the most affordable one is EPS applied to the outside. Like you said if it's 1" or less it should be manageable, it's perm rating is 2.5 to 5.0 perms and I think that will be okay (will have to do some research on that). If that's the case it can go over the 2 layers of housewrap or felt, just have to make sure its compressive strength is enough to pick up the loading from whatever we end up using as the finish sheathing. As you pointed out there's the other details, such as weep screed, windows, doors, etc. but it shouldn't be too bad (he said optimistically).

That's all well and good for 1" but for a lot of our climate zones down here in hot southern California the prescriptive is calling for 2" if a 2x4 wall assembly is used and that is really going to be problematic. I couldn't agree more about the lack of help from these governmental agencies that call out for the insulation but don't provide any technical support AT ALL. I called our local utility company because at one of the seminars on the subject a rep from the company had said when queried 'Just contact me, I'm in the CAHP (California Advanced Home Program) and can set you up'. I got ahold of him and he had nothing.

I just got off the phone with a HERS registry we use and during the conversation got a lead on some possible building details. Will see what I can find and if anything looks good will post.

Thanks again for all the great info!

P.S. Included the Roxul Comfortboard 80, looks like it has some really good properties but don't like the size and am guessing it's pricy, need to look into it more.

Philament · Jan 31, 2017

Rio said:
That's all well and good for 1" but for a lot of our climate zones down here in hot southern California the prescriptive is calling for 2" if a 2x4 wall assembly is used and that is really going to be problematic.

I would double check that prescriptive path to see what the r-value is as I'm fairly certain they wouldn't put it in terms of inches. The reason I'm suggesting that is that the one "foam board" material you didn't include at the bottom of your message was Polyisocyanurate. In the northern climate that I live in I do not like using foil faced polyiso on the exterior because it's r-value decreases in lower temperature, it absorbs water and for the 0 perm on the outside (can be dealt with, but generally it makes me uncomfortable). For your climate however, it may be ideal.

Polyiso has the highest r-value per in and if you use the foil face with an an air gap (rain screen) it can increase the effective r-value through radiant barrier (check with your HERS rater or AHJ because everyone treats radiant barriers differently). All that to say that you might be able to use 1-1/2" polyiso, which can make some parts of installation easier because it mates up with your standard 2x material (Window bucks, blocking, door trim backer....).

Philament · Jan 31, 2017

I forgot to mention that Huber also came out with a insulated sheathing panel that could be really helpful. It's essentially a SIP panel without the facer on one side. If it was my first time doing outboard insulation and it was available here in Canada, I would definitely be looking into this product. It solves a lot of the installation problems of determining your air barrier and wrb, which can get really complicated with outboard insulation.

http://zipsystem.com/zipsystem/products/zip-system-rsheathing

Rio · Jan 31, 2017

Thanks for the good info Philament! You're correct, the CEC calls it out as '2x6@16"o.c. framing- R19 cavity +R5 continuous' or '2x4@16"o.c. framing- R15 cavity +R8 continuous.

I did read up a little on the poly iso, it really has some impressive R-values for the thickness doesn't it? I like the idea of the Roxul as a lot of our stuff is in the Wildfire zone and from what I've heard about Roxul it's great in that respect, plan on reading the info you attached regarding attaching hardiboard and am tracking down some details from the feds, will post some and the link if they look good.

Thanks so much for the good info, it's really a help!

fjn · Feb 1, 2017

Over 25 yrs. ago,I built several block homes with 4 " of foam on exterior ! The wire mesh was screwed 1' o.c. both vert. and horizontal. There are large plastic washers for this system. The foam went down continuous and rested on top of footing. The stucco we used was Parex with their elastomeric coating. The homes look as good as they did when job was completed.

Golden view · Feb 1, 2017

In Fairbanks Alaska (-50 degree winter weeks) where I began my building career an outfit did a bunch of research and hundreds of buildings have been built with little to no stud insulation and 4-6" of exterior insulation. They performed extremely well. Vapor barrier was outside of the sheathing (in other words on the warm in winter side of the insulation).

The framing moisture levels were superior, the air infiltration readings were spectactular, and certain details were easier, like almost no penetrations (outlets and switches) in the vapor barrier. Plumbing and HVAC could be run in exterior walls.

I personally built structures with foam outside and others with it inside and was not able to decide which I liked better.

There really are lots of considerations with high performance buildings.

Youngin' · Feb 1, 2017

Golden view said:
In Fairbanks Alaska (-50 degree winter weeks) where I began my building career an outfit did a bunch of research and hundreds of buildings have been built with little to no stud insulation and 4-6" of exterior insulation. They performed extremely well. Vapor barrier was outside of the sheathing (in other words on the warm in winter side of the insulation).

The framing moisture levels were superior, the air infiltration readings were spectactular, and certain details were easier, like almost no penetrations (outlets and switches) in the vapor barrier. Plumbing and HVAC could be run in exterior walls.

I personally built structures with foam outside and others with it inside and was not able to decide which I liked better.

There really are lots of considerations with high performance buildings.

I'm also in a cold climate. Haven't had -50 in a while but it does crop up every once in a blue moon. Seems so odd not putting insulation in the stud bays (our code is all about the VB and r-value) but I'd sure like to see one of those buildings go up.

I suppose the closest to that I've seen around here is a few full ICF homes.

Golden view · Feb 1, 2017

Youngin' said:
I'm also in a cold climate. Haven't had -50 in a while but it does crop up every once in a blue moon. Seems so odd not putting insulation in the stud bays (our code is all about the VB and r-value) but I'd sure like to see one of those buildings go up.

I suppose the closest to that I've seen around here is a few full ICF homes.

Generally they did do fiberglass but the energy calculations showed it didn't help a whole lot. So exterior walls could be 2x4, and they could use dirt cheap R-11 instead of 13 or 15. In fact I believe it was preferred to do R11 because of dew point considerations. Too much insulation inside of the vapor barrier and condensation could happen.

I haven't looked at their site in years, but the group that does the research is http://www.cchrc.org/

Philament · Feb 1, 2017

Youngin' said:
I'm also in a cold climate. Haven't had -50 in a while but it does crop up every once in a blue moon. Seems so odd not putting insulation in the stud bays (our code is all about the VB and r-value) but I'd sure like to see one of those buildings go up.

I suppose the closest to that I've seen around here is a few full ICF homes.

The system goldenview is talking about is fantastic.
The system was originally developed at the National Research Council of Canada termed the PERSIST wall (Pressure Equalized Rain Screen Insulated Structure Technique) in the 1960's

Then the Alaska Cold Climate Research Center created a variant of it and refined the process. Excellent reading material by the way, very comprehensive.
http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf

The fellows over at buildingscience.com use a lot of the principles of those for their "Perfect wall" concept.

https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall.

Matt Risnger did a series on a house he built using the "perfect wall" system. Really neat if you want to see the how it goes together. The beauty of the the system, be it PERSIT, REMOTE, or Perfect Wall is that it works in all climates, so don't be put off by the fact that it's down south
https://www.youtube.com/playlist?list=PLDYh81z-RhxgCk1qJD6AJktVHZH7-BLSR

Youngin' · Feb 1, 2017

Philament said:
The system goldenview is talking about is fantastic.
The system was originally developed at the National Research Council of Canada termed the PERSIST wall (Pressure Equalized Rain Screen Insulated Structure Technique) in the 1960's

Then the Alaska Cold Climate Research Center created a variant of it and refined the process. Excellent reading material by the way, very comprehensive.
http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf

The fellows over at buildingscience.com use a lot of the principles of those for their "Perfect wall" concept.

https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall.

Matt Risnger did a series on a house he built using the "perfect wall" system. Really neat if you want to see the how it goes together. The beauty of the the system, be it PERSIT, REMOTE, or Perfect Wall is that it works in all climates, so don't be put off by the fact that it's down south
https://www.youtube.com/playlist?list=PLDYh81z-RhxgCk1qJD6AJktVHZH7-BLSR

I downloaded the pdf and I'll give it a closer look when I have a chance but just glancing over the first cross section it doesn't actually look that bad to do. I'll pass it along to the boss too. Most of our homes now get exterior foam and ICF but not to that extent.

RedAdobe · Feb 1, 2017

I say exterior foam all the way for most of the usa, less penetrations the better. easier , faster, cheaper and better (has to be flashed right)

I get why a few might think keeping hvac inside would be easier with foam inside but the amount of holes inside and the way things are framed and trades do things just make it too hard to be =

I see poorly cut rock around boxes all the time, no insulation behind or around top of box, and 1" holes thru the top plate for romex. Plumbers and hvac guys butcher things as well. then you get some new guy or stoner not putting in tape of even a piece of insulation in and you have air loss in lots of little places and it adds up fast.

I know if i build someone an addition I do take the steps to air seal and usually the comment later its more comfy there then existing is.

Philament · Feb 1, 2017

Youngin' said:
I downloaded the pdf and I'll give it a closer look when I have a chance but just glancing over the first cross section it doesn't actually look that bad to do. I'll pass it along to the boss too. Most of our homes now get exterior foam and ICF but not to that extent.

You guys in the west adopt the NBC pretty much verbatim I think, so you'll be dealing with a lot of this stuff with the latest revision depending on when you adopt (might have already). In Ontario we have a real basterdised version of the NBC, they make a lot of changes for the special interest groups here, all the energy stuff is in a supplimental. So stupid

Youngin' · Feb 1, 2017

Philament said:
You guys in the west adopt the NBC pretty much verbatim I think, so you'll be dealing with a lot of this stuff with the latest revision depending on when you adopt (might have already). In Ontario we have a real basterdised version of the NBC, they make a lot of changes for the special interest groups here, all the energy stuff is in a supplimental. So stupid

Our new code came through last November but we as a company haven't built under it yet. Boss knows all the new code but I only know bits and pieces until we (hopefully) start our next project. New insulation requirements for certain though. Much of what we do exceeds it anyway but the high volume builders probably don't like it.

Youngin' · Feb 1, 2017

RedAdobe said:
I say exterior foam all the way for most of the usa, less penetrations the better. easier , faster, cheaper and better (has to be flashed right)

I get why a few might think keeping hvac inside would be easier with foam inside but the amount of holes inside and the way things are framed and trades do things just make it too hard to be =

I see poorly cut rock around boxes all the time, no insulation behind or around top of box, and 1" holes thru the top plate for romex. Plumbers and hvac guys butcher things as well. then you get some new guy or stoner not putting in tape of even a piece of insulation in and you have air loss in lots of little places and it adds up fast.

I know if i build someone an addition I do take the steps to air seal and usually the comment later its more comfy there then existing is.

That's good of you, you actually take pride in the work. After framing and initial rough in Iike to do a walkthrough and spray foam holes, patch others and make note of weaknesses in the vapour barrier.

It's the little things that add up.

Inner10 · Feb 1, 2017

Youngin' said:
I'm also in a cold climate. Haven't had -50 in a while but it does crop up every once in a blue moon. Seems so odd not putting insulation in the stud bays (our code is all about the VB and r-value) but I'd sure like to see one of those buildings go up.

I suppose the closest to that I've seen around here is a few full ICF homes.

I worked in a building like that in Ottawa, thought for a sec they forgot to insulate and the drywaller had lost his mind. Then I went to run a wire outside and realized there was 9 inches of foam on the exterior.

Youngin' · Feb 2, 2017

Showed the boss the first cross section and he looked at it for a few minutes. Asked me to send it to him so it's piqued his interest.

Philament · Feb 2, 2017

Youngin' said:
Showed the boss the first cross section and he looked at it for a few minutes. Asked me to send it to him so it's piqued his interest.

If you get more interested in it, look for some of the work and writing by Thorsten Chlupp. I like reading the theory from buildingscience.com team, but I find it really lacking in the implementation part. Thorsten was (is?) a builder, so his writing speaks to me a bit better.

Here's one where he goes into some further details on the REMOTE system.
http://www.jlconline.com/how-to/insulation/installing-exterior-insulation-in-cold-climates_o

Glad to hear he was at least receptive. :thumbsup:

Continous foam insulation on the inside or the outside of the wall?

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