Rigid Foam Insulation on the outside
yojimbo2
| Posted in Construction Techniques on
There was an FHB article about installing Rigid Foam Insulation to the outside of a house. It was very vague as to how to install wood siding over this material.
Is this possible to do and not have any problems down the road, or are you obligated to use vinyl siding which is very light? If so how is this done?
I imagine you have to mark all the studs onto the insulation, and then hand nail with 4 or 5 inch nails. Predrilling required, even on 4×8 sheets of sheathing.
Replies
If I remember correctly, I think you can nail furring strips over the foam, and the siding is nailed to those strips, just as if they were studs. A typicaly rainscreen wall setup.
Justin Fink - FHB Editorial
Edited 8/7/2008 4:35 pm ET by JFink
The furring strips would strictly be for a moisture screed, no? This does not really address the issue that you are hanging a massive amount of siding which is floating on top of the foam.
I was kinda surprised that the article glossed over this issue.
It is called a rain screen, and that is part of the reason.
How thick of foam were you thinking of?
"This does not really address the issue that you are hanging a massive amount of siding which is floating on top of the foam."No, it is not floating. It is securely nailed to the studs through the shims and foam.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
<< The furring strips would strictly be for a moisture screed, no? This does not really address the issue that you are hanging a massive amount of siding which is floating on top of the foam. >>
Yes, the strips create an air/drainage space, but they are nailed through the foam and into the sheathing/studs. So the siding is nailed to the strips, which are nailed to the framing. It's the same concept as strapping a ceiling for drywall.
Justin Fink - FHB Editorial
Edited 8/8/2008 9:16 am ET by JFink
Easy Justin your NE roots are showing. In most parts of the country they go huh, furring strips on the ceiling for drywall? Whats that for?
Haven't seen you for a while. How are the sales coming? I see your advertising all the time.<G>
Sales have been a little slow on the patio Homes but we're seeing more activity now. We've been asked to be part of a study sponsored by NYSERDA to look at ways to improve the performance of building envelope design. They will underwrite costs to switch wall systems to sips and ICF walls on our upcoming sales, and monitor energy costs, along with help in fine tuning the mechanical systems. The buyers will receive those benefits at no additional cost. We just met with some prospective buyers yesterday. We are also offering to reimburse the buyers their first 12 months of natural gas usage for heat/hot water.
Our reputation for building super efficient homes is starting to really set us apart. Our phone has been ringing a lot recently for offsite custom homes.
I am glad for you, I was afraid you might have lost it in the slowdown.
Sounds real good!!
but don't they know that's the best way for the electrician to run wires in a haphazard manner without drilling holes? ;)Justin Fink - FHB Editorial
It is probably not within the codes to run the electric wires in this manner.
Its funny that everywhere but NE doesn't have a problem with this.
"It is probably not within the codes to run the electric wires in this manner."Yes, it is. The 2005 NEC make it specific about furing strips.
"300.4 Protection Against Physical Damage"...(D) Cables and Raceways Parallel to Framing Members and Furring Strips In both
exposed and concealed locations, where a cable- or raceway-type wiring method is
installed parallel to framing members, such as joists, rafters, or studs, or is installed
parallel to furring strips, the cable or raceway shall be installed and supported so that the
nearest outside surface of the cable or raceway is not less than 32 mm (1 1/ 4 in.) from the
nearest edge of the framing member or furring strips where nails or screws are likely to
penetrate. Where this distance cannot be maintained, the cable or raceway shall be
protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at
least 1.6 mm ( 1/16 in.) thick."The picture is from the Handbook. That is not code, but addition guidance and background info..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Learn sumtin new every day!!!!
I just finished an addition where I installed 2" XPS on the exterior walls. I did it just the way the article pointed out, except I used 5" Timberlocks to install the 3/4" furring strips on top of the foam. It wasn't a big problem, and it was a huge energy benefit, but I think next time I'll just use spray foam and skip the hassle and cost of the rigid.
After the cost of air-sealing, $25 per sheet of the rigid, $.75 each for about 400 Timberlocks, time to rip the furring strips and additional trim out, I could have paid for Icynene and gotten about the same performance and had it done in a day. Live and learn. The addition is super quiet and very tight though. We had one doorway open to the existing house to our 525 sq. ft. addition for a month and a half before we ran ductwork to the new space, and it stayed within 5 degrees of the conditioned space, so they'll hardly notice the new addition when the power bill comes.
I am building a house this Spring and we are contemplating which option is best. The one thing I like with the XPS is it is a vapor retarder itself (saves housewrap) you must use the rain screen (better for everything), and more importantly you remove the thermal bridge effect of the studs. Plus you seal ALL around the framed wall. Unless great care is taken when using the spray foam, (i.e sealing under bottom plates and top plates) you really only seal the stud bay itself-not the bottom or top plate with the spray foam. Even if you get R-30 in the stud bay, but have air leaks on top and bottom, you haven't gained much.
I am not sure what you are trying to say as you ran two sentences togethr."The one thing I like with the XPS is it is a vapor retarder itself (saves housewrap) you must use the rain screen (better for everything),"But housewrap is NOT VAPOR RETARDER, thank God..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Sorry for the error:) I was trying to say, that if you use rigid foam, I wouldn't use need house wrap. The foam serves as an air barrier ( with taped seams) and it also serves as a vapor retarder (replaces house wrap). House wrap itself is classified as a Class 3 vapor retarder. I have understood Class 3 as "vapor permeable" to greater than 10 perms- same as #15 tar paper. And XPS, over 1" thick, is vapor semi-impermeable- same as oil based paint or vinyl wall paper.Do you not like vapor retarders???
"Do you not like vapor retarders???"I am concerned about controling the movement of vapor (moisture) and where it might or might not condense and if it does how the liquid water can move out of the assembly.I don't know of any building products that are not a class 1, 2, or 3 vapor retarder. So any wall assembly will have and most several of those.But is important is the characteristics of THE ASSEMBLY and what climate it has to live in.Saying that any product should or should not be used is meaningless with describing the whole assembly and where that product is in the assembly and what the climate is.http://www.buildingscienceconsulting.com/resources/articles/Understanding_Vapor_Barriers_ASHRAE_2004_08.pdf
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"Saying that any product should or should not be used is meaningless with describing the whole assembly and where that product is in the assembly and what the climate is."I guess I got off track- would you use house wrap over 2" XPS or not?
Depends on how good I think the seal tape is doing and how long it will last.Don't see any technical reason that would prohibit the use of house wrap..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
>> I guess I got off track- would you use house wrap over 2" XPS or not?I assume you're going to have furring/strapping/battens over the foam, to provide nailers for your siding. In that case, why would you add house wrap over the strapping and pass up the opportunity to create a rain screen wall, instead of just taping down the foam? Especially if you add a second layer of foam, you stagger the joints and tape the seams, then the house wrap does not seem to serve any purpose. It adds expense, and reduces the ventilation against the back of the siding. Now, if you sealed it well all around, house wrap would create a dead air space with a little insulation value. It would add some redundancy in case the tape fails. However, I would think the value of a ventilated rain screen outweighs that. The furring will tend to hold tape against the foam. If the tape still fails in a few places, what is the risk of water-damage to a well ventilated wall system that is mostly foam?Edited 8/11/2008 7:44 am ET by tom21769
Edited 8/11/2008 7:47 am ET by tom21769
I agree...the foam is all the drainage plane you need as long as seams are taped and with a rain screen becomes bomb-proof!
Relying on taped foam as a drainage plain for your rainscreen is asking for trouble. The window, door and other wall perforation flashing details all rely on carefully lapped housewrap or paper.
It might work in areas not subject to frequent heavy rains, but then if that's the case, why build a rainscreen at all?
>> Relying on taped foam as a drainage plain for your rainscreen is asking for trouble. Yes, I confess to worrying about the same issue.
In fact I'm noticing that my tape already is failing in some spots during the construction process.
I think your comments on having the building paper on top of the strapping were spot on. It just interferes with the airspace and slows the drying of the siding.
In some climates where the rainscreen is provided primarily to allow the wall to breath better to the exterior, then house wrap probably isn't that important. Here one of the rainscreen's main functions is to divert water that makes it's way through the siding. The papered or wrapped wall surface, even though it is separated from the back of the siding, can get quite wet and needs a properly lapped and flashed drainage plane to be effective.
Surely he is suggesting the housewrap be put on before the strapping, which in no way interferes with the rainscreen.
> Surely he is suggesting the housewrap be put on before the strapping, which in no way interferes with the rainscreen.According to the plan for my own current project, house wrap (labelled "optional") would go OVER the strapping to create an enclosed air space.
The order of assembly (inside to out) is: timber frame, 6 mil plastic VB, perimeter 2x blocking surrounding 2"foam, 1" foam (staggered over preceding layer), 1x4 strapping, optional house wrap, siding. No siding vents are specified.
I have a disclaimer here, I have done rain screen over typar (no foam) with flashing as you described, I have done rigid foam to the int (just finishing a great job now and presently my method of choice after Piffin's post) but I have NOT done an ext foam job w/ a rainscreen, I have only read about it.That said, I see your point. The penetrations would be a challenge. In a great book I am reading by Joe Stiburek, "Building in Cold Climates" (awesome book!!) he shows several examples of foam to the ext. w/o housewrap. And since foam is a better retarder than house wrap (once sealed), but still breathes, I figure you could save on the house wrap cost/labor-there is no weatherizing purpose, in my opinion.But, you bring up a great point on flashing. If I had to come up with a solution, I like the one in his book. It goes something like this: sheath the frame w/ 1/2" OSB, use T&G foam and tape seams, hang window to furring strips secured to frame ( maybe you could attached through foam directly?), stick sheathing tape to foam over flanges on sides and lap over framed sill on bottom and up sides (like an ext door), add sheathing tape to top flange, cover top edge of tape w/ adhesive membrane and then caulk bottom edge of siding. He also mentions a reglet cap that is "L" shaped flashing that notches into foam above window and then covers top edge of membrane.That is a long post! Please let me know what you think!!
My disclaimer is much like yours: I don't know much about foam, so I am relying on my rainscreen experience.
What you suggest sounds like it would work. My misgivings would be that it appears to rely on the long term adhesion of the tape and membrane for it's success over the house's lifespan.
Rainscreen was mandated in our code because of widespread failures of exterior walls where water penetrated the siding and caused structural damage, not only to the sheathing but studs and floor systems too. It is common to see condo buildings here with their walls and the first ten feet of the floor removed because of rot. One building I looked at recently has estimated repairs of $200,000 a unit! House wrap and carefully applied conventional flashing techniques seem like cheap insurance.
I have to agree with you on the adhesion of a product being my only warranty against leaks. With a rain screen I do feel a little better however and I would use a product that was meant to be used in such applications (once closed in it gets pretty hard to inspect). In the past year I spent so much time on the phone with product manufacturers that I am going to have start adding it into the bid!
To add one more thing....that is one of the reasons I like the idea of int foam better in cold climates (xps). It has less repercussions if we don't install this stuff perfect each and every time.
Yeah. I know Building Science has wall assemblies that they advocate using with exterior foam, and systems like the Advanctech with its taped joints and completely sealed exterior are popular, but I just don't feel comfortable not allowing the wall somewhere to dry to if it does get wet. Interior foam would seem like a safer bet to me too.
I was planning on asking this in a year or two when I got to the project, but since this thread is still going...
I am in central Ohio. The back half of my two story home has 2x4 framing with kraft-faced fiberglass covered with drywall on the inside. There is some 1x diagonal bracing let in to the inside of the 2x4s (I'm not sure how much bracing is present). On the outside are ~2 ft wide sheets of 1/2 or 3/4 inch foam (EPS) fastened horizontally directly to the framing. Very wide (and ugly) vinyl siding is installed over the foam (no tar paper or house wrap - addition built in 60s or 70s?).
The house shakes a bit when the back door is shut hard, and I am always interested in reducing utility bills.
How would you all rework this wall? OSB or plywood over the EPS with tar paper and then new siding? We plan to replace the siding, and at least half the windows.
Thanks!-Nate
"And since foam is a better retarder than house wrap (once sealed), but still breathes,"Just a warning note. I have not followed the details of what foan sheets have beenn discussed, but some have a surface covering that a vapor barrier.Most poliso is like that. But some might be punctures to allow vapor to pass.And some extruded stryfaom has a thin plastic film on the surface. Don't know what it's properties are.So verify for a specific brand and model and not just use what is in the generic tables..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Excellent point...I was referring to extruded foam with no facing to be used in a zone 6 heating climate.
That article is awesome!!!!!Thanks!!!!
It does mention that a Class II is needed in zone 6-7 (home sweet home)but only if the perm of the ext. sheathing is .01 perm or less....that is class I!!!! What the hell does that mean! I am looking at section 9 on page 10.
First of all zone 6 & 7 are way too cold for any human. And my brain freezes up even thinking about it so I am not responsible for anything that I say <G>.#7 and #8 says that in zone 5, 6, & 7 if you have an insulated wall with an internal vapor retarder of class II or less AND the external sheathing has a perm of 1.0 (#7) or between 0.1 and 1 (#8) then any moisture that moves into the wall can move out through the wall without condensing.#9 says that in zones 5, 6, & 7 for an insulated wall and the internal VR is class 2 or less and the sheathing has a perm of 0.1 or less then the moisture can't move out fast enough and you can get condensation on the sheathing.Thus you need to keep the warm side of the sheathing warm enough to keep it above the dew point. That dewpoint is given in table 1.And the calculation is for average OAT at the location.Then look at the section at the end "What does this mean from a practical perspective".Specifically the last 3 paragraphs.In Chicago 1/2 coated poliso will keep the inside warm enough. But in cold Minneapolis 1" is needed.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
It can be cold, and wet....but Maine is my home and I have learned to love it.I have read little about this but I am learning more all the time. That article is great. And now we can see if a vapor barrier is needed for the house in question, but first we have to see where it is!! If it were in Maine, no VR over the foam-as long, as you already mentioned, the tape job is sufficient. Why is it a only see and read about rigid foam to the ext and not on the int?
"no VR over the foam-as long"No, that is why I don't like the term VR and HATE the term vapor barrier.What might go over the foam is a weather barrair such as Tyveck.And as you said that class III VR.Well, a class III VR means that is minimal slow down the movement of vapor, if it slow it down at all.Using the term VR when talking about the exterior, in cold climate, is only confusiong unless it is part of a complete discussion such as in that paper..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"Why is it a only see and read about rigid foam to the ext and not on the int?"Perhaps because you have not read enough of my posts?;)I am on Islesboro - Midcoast region of Maine. Not too far from you.You and I are late comers peripheral to this thread so your situation is not entirely clear here.There is a general rule of thumb for whether to use foam on the inside or outside of the wall studs. That is that if the heating degree days are in excess of 6000, the foam should be designed on the interior. There are a lot of variables to this, but the reasoning is that when placed to the exterior, then moisture that migrates into a wall cavity from the interior can become trapped behind the foam acting as a vapor retarder and cause mold in the cavity. So it is essential to keep an intact VB on the inside esp at penetrations, to keep moisture out of that cavity in the first place.
But when placed on the inside face of the studs, the foam does the job of providing the thermal break and acting as VB/ retarder.What I have often done is to put the foam ( 1/2" to 1" Thermax) on the inside, with the cavity having been filled with cellulose or chopped fibreglass. Then use strapping over the foam to provide good nailing surface for the sheetrock and a raceway for wiring.I am on borderline of 6000 heating degree days. I believe you would be over that line.I have done the foam on inside and on outside. I like the idea of inside best for our area, but have no clear cut objective evidence of long term comparison of pros and cons myself. Other design considerations always play their part in the decision.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I wrote a nice long thank you and I erased it! Damn!It went something like this:Glad to meet you!!! You dried out yet!!!I climb in the Camden area often and know how pretty it is your way. Do you work in Belfast mostly?Thanks for answering my question as it is one I have been thinking about lately. I am installing 1" XPS on the int of a home (weatherizing project) and I think it is the way to go. I am taping the seams and caulking the foam around windows/doors. 1st question....do you use air tight outlet boxes? Also, i think we are both zone 6 @ 5400 heating days a year, Houlton is in zone 7. 2nd question, when blowing the cellulose you mentioned, did you do it from the ext or int? I am building my own house next summer in Farmington and I am considering blowing in cellulose after the foam-any thoughts?I have alreay learned lots from this forum and wanted to say thanks!!Oh, and I will read your posts as soon as I find out how!!
All my work is right here on-Island. There are close to a hundred workers come out here on the ferry every day doing construction. No need to go off!
When you climb Mt Battie, you are looking out over Islesboro in the bay. it is the long one. Used to be called Long Island.I spray foam around boxes and at base of the foam panel to subfloor or top at ceiling which also gets the foam.While geographically we are same zone, the water surronding us does moderate the local climate some. fewer extremes.When blowing insulation in, the insulator staples insulmesh to the studs first to contain it,, and then cuts a hole near top of the bay and sticks the nozzle in there. When blowing ins in air has to be able to come out to be able to get even consistency and be sure there are no gaps. Insulmesh lets them see what they are doing and air comes right out. Then a roller tightens it in place and they clean up and go.
It is after the loose insulation is in that the foam goes on. It does not5 get penetrated that way, except for the plasticap nails holding it, and other fasteners running thru it.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
"I just finished an addition where I installed 2" XPS on the exterior walls. I did it just the way the article pointed out, except I used 5" Timberlocks to install the 3/4" furring strips on top of the foam."If I understand correctly those timberlocks are going through 3/4" + 2" + 1/2" (sheating).That leave 1 3/4" to go into the studs.It was just probabality that you did not hit an wiring unless you specifically ran all wiring up and down the stud and not through holes..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I didn't hit any wiring. I take photos before I insulate for reference and I have a good electrician who is neat and runs all of his wires at the same height.I did seal the bottom plate and all other seams and penetrations. Obviously you can't do that if it's already built, but I always do it when I build anything new.
if this was done before wiring, it would not hit any wires either
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
What about vertical siding ?
Everthing FHB has done on rainscreen walls has been for horizontal siding. I have put up two building with vertical siding using horizontal furring strips over rigid foam and I don't think I am having any problems, but have no reason to take anything down to look for problems. I just kind of figured things out as I went along and I still have some nagging moments of doubt that I may not have gotten it all right.
I have the JLC book on moisture control and the vertical siding subject isn't in it either.
I realize you guys try to cover the most commonly used materials and techniques, but you also give ink to some high end custom stuff that is not the norm. How about looking at vertical siding/furring/rainscreen combinations.
I am in complete agreement with you Dave. Tell you what, send me an email privately: jfink@taunton.com - I think this would make an excellent topic for our Q&A section. Justin Fink - FHB Editorial
I did one with vertical.It was studs, the 1/2" Advantec, 1" Thermax tped at seams, then shims for screen were horizontal, but each was 28-40" long, random staggered at 16" oc with an inch between butting ends to allow drainage. rough pine B&B over it all.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
If you must use foam, I prefer to install it on the inside instead of the outside. It seems to cause so many problems for trim, siding, etc when installed on the outside of a house.
I have done it both ways many times.
I have done it both ways many times.
OK then, how about applying XPS to the outside of the poured concrete first floor walls of a super-insulated, three story house?
I'd like to use the thermal mass of the 8" concrete wall to best effect, by insulating the outside of that floor to very high R-value.
Setting aside the problem of the horizontal joint between floors for a moment, how would you fasten 4" of XPS and what system would you use to apply a stucco finish?
Sorry, You're asking the wrong guy that question! I wouldn't put myself through all of that fuss for any reason.
You are probably going to have so much wood on the outside of that structure by the time you are done detailing the windows, doors, corners, soffits, etc. etc. that you may as well build it out of wood in the first place.
I must be getting old, but I just can't wrap myself around the concrete house idea.
My only experience with that was helping my Dad build a new block house in Florida. I think it took my brothers and I two weeks to finish. At least nothing has eaten it yet!
We use Dryvit on some commercial buildings, but usually over 1 1/2" or 2" foam. In that case the windows are set back to the wood sheeting and the stucco is returned in to the window or door. I suppose that would work on 4" thick foam too.
That whole concept causes me some sleepless nights wondering if it means troubles down the road.
You're asking the wrong guy that question!
How so? You said you had experience with that type of material applied to that surface.
So...you're not able to answer a simple question, as presented, without imagining a lot problems which don't exist.
I should know better by now, I suppose. Why ask a product related question here that can be answered by a sales rep on the phone or on the manufacturer's web site?
In hopes of getting more objective advice, from someone who has worked with the material? Ah, yes, that's it.
You must be smoking something?? I told the OP I had built a lot of houses with foam on the inside and foam on the outside... and that I preferred to install it on the inside, for a number of reasons. Actually, I prefer not to install foam at all. I think there are better alternatives for insulating & isolating walls.
Then you ask some question about installing 4" of foam on the outside of a concrete house and I tell you I'm not the one to ask about that.
What exactly don't you understand??
I think you should read the post by RedfordHenry, maybe you could begin to learn something about some of the problems encountered when installing foam on the outside of a house.
If you think it's so easy, why don't you just dive in and go for it?
BTW, maybe you should call one of the sales reps...you might learn something!
Hey, I found this:
Rigid Foam Sheathing<!----><!----><!---->
Table 5. Nail Sizes for Bevel Siding-Foam Sheathing Systems <!----><!---->
<!----> <!---->
Recommended Nail Length (inches) <!----><!---->
Siding and Sheathing Thicknesses <!----><!---->
Smooth Shank <!----><!---->
Ring Shank <!----><!---->
1/2" siding and 1/2" foam sheathing <!----><!---->
2-3/4 (9d) <!----><!---->
2-1/4 (7d) <!----><!---->
1/2" siding and 3/4" foam sheathing <!----><!---->
3 (10d) <!----><!---->
2-1/2 (8d) <!----><!---->
1/2" siding and 1" foam sheathing <!----><!---->
3-1/4 (12d) <!----><!---->
3 (10d) <!----><!---->
5/8" or 3/4" siding and 1/2" foam sheathing <!----><!---->
3 (10d) <!----><!---->
2-1/2 (8d) <!----><!---->
5/8" or 3/4" siding and 1" foam sheathing <!----><!---->
3-1/2 (16d) <!----><!---->
3 (10d) <!----><!---->
<!----><!---->To avoid hand nailing looks like 1" is the max thickness you want to use.
I am planning on doing the same. Adding 4" rigid foam (I dont know whether to use foil face or not). I am also planning on adding to outside. I added 2" on inside of retrofit- I think inside is worse with details- still have windows to deal with but also outlets, switches and so on. In addiiton, outside would make it more continuous.My plan was to add 4" rigid foam and attach to studs with 1" firring strips, using 6" screws. To the firing strips I plan to attach my siding- wood clapboard. The firing strips also act as a rainscreen which needs some detailing at bottom with mesh screen.I will end up with walls with nearly R40, and R20-28 even where wood studs are located.For me the reason to do this is reduced heating bill. I live in New England.
There is a recent FHB 194, pp. 51-57, which shows how to trim out windows.Do you not think this will work. More details on firring strip application would be nice.
>> My plan was to add 4" rigid foam and attach to studs with 1" firring strips, using 6" screws. To the firing strips I plan to attach my siding- wood clapboard. The firing strips also act as a rainscreen which needs some detailing at bottom with mesh screen.This is similar to the method I'm using. I'm farther south (mid-Atlantic), and use 3" of foil-faced Dow "Tuff-R" polyisocyanurate on the walls (4" on the roof). This goes over a vapor barrier (6 mil plastic), which goes over T&G, which goes over a timber frame. The 1x4 furring strips (a.k.a. strapping or battens) are screwed through the foam into the frame using 6" torx headlok screws (driven with an impact driver NOT a drill or you'll go nuts with stripped screw heads). At the sills, corners and top plates, and around windows, the foam is edged with 2x blocking to provide nailers for the furring. You may need to find or make up some true 2x blocking to match the foam thickness. Clear, vertical grain WRC siding (primed 4 sides) is nailed to the furring.At the top and bottom of the walls, I plan to terminate the furring with Cor-a-Vent siding vent strips. The Cor-A-Vent web site has some good diagrams (look for "SV-3 and SV-5 Detail Drawings"). If you cannot find the product in your area, call them to order direct.The furring serves several functions. If used under house wrap, it provides for an enclosed air space to increase the effectiveness of the foil-faced insulation. It provides a drainage plane and ventillation channels. It provides nailers for the siding. However, this is a rather labor intensive building method. If your structure is large, or your budget is not too tight, I'd recommend SIPs instead. I'm using it on an addition, where the walls are not perfectly plumb and square. This method is a little more forgiving than SIPS in these conditions. Not to mention, you can buy the materials locally, and assemble the whole shebang by yourself, without a crane.
I am coming in a little late, but thought I would throw my hat in the ring....I agree 4" foam on the ext is overkill. Anything over R25 in a heating climate wall is great. But is only as good as the amount of air infiltration. I would go with 2", make sure to seal all points of entry and spend the money on a heat exchange vent system. I have read of a couple of methods recently, but have tried none myself:>Put 2" foam on the ext. cover with 3/4 furring strips (for vertical siding you run the strips horizontal and leave a 1/4"-1/2" short on the ends for bulk water removal (!)...( all siding will let in water but, vertical siding should dry faster than overlapping horizontal siding right?) And remember vapor barrier on the int. if you are in a heating climate.>or, put the foam on the int. add furring strips and then drywall. you can use the foil faced in this app because the foil is to the int.>build a larrsen (sp) truss. Add plywood sections in the 3 places along each stud, ripped to your desired wall thickness. Attach new framing (2x3) to the edge of the ply and use aa a new wall face. Result: as thick a wall as you like that can be insulated with fiberglass ( not worth a whole lot unless installed to the letter!!!) or cellulose (high density is the way to go). Just some thoughts is all...
I just finished retrofitting 3" of Thermax to the outside of an antique house. After stripping the old siding off, I rimmed each window with 4" wide strips of KOMA (on edge). I also framed the outside edges of the walls with strips of 2x ripped to 2.5" (PT for the bottom edge). I also framed around each window with 2x.
Then installed the first layer of foam horizontally right over the old sheathing. I used an occasional 3" roofer just to tack the panels in place. Along the top edge of each horizontal course of foam I nailed another strip of 2x. Did this all the way up to the soffitt. The horizontal wood strips will provide solid nailing for the next layer.
For the second layer, I rimmed the perimeter with another layer of 2x strips, then installed 2 foot wide strips of foam vertically. In between each vertical strip of foam I nailed another strip of 2x vertically. These vertical strips become the solid nailing for the siding.
Thermal bridging is limited to where the wood strips intersect, along the perimeter of the wall, and around the windows.
Remodelman used vertical furring strips attaching them through the foam to the house. Do you think this is as good as your system? Eliminates the thermal bridging.
I'm on the fence about using long screws to fasten furring through thick foam. In my case, it was an old house with post and beam frame (i.e. not much regular framing for solid attaching of the furring) which is why I used the method I did. Always better to minimize bridging whenever possible, but I don't want to see siding drooping in a couple of years when the mechanical fasteners start to sag.
I think we'll be reading more about exterior foam retrofits in the future. Stay tuned.
First, I am assuming you are talking a retrofit not new construction. In my opinion, adding more than 1 1/2 to 2" rigid foam is overkill if you install it tightly with careful attention to sealing the wall system for air infiltration. R value is only part of the picture and I also assume the existing wall already has some insulation in it? Lets say You have an existing R-11 wall, you add 1 1/2" of poly iso foam {R-10 1/2} for a total wall value of say R-23 or so including wood sheathins etc. The advantages of the foam layer are both improving air infiltration and reducing thermal bridging. Going for much higher R values starts to become cost ineffective vs payback. You have much higher labor and material costs for the slightly better performance.
We have been using a combination of 2x6 walls with spray foam open cell foam in stud bays, coupled with 3/4" foam insulated sheathing over our structural sheathing as a wall system for a while now and find it gives us the best balance of an extremely efficient wall system with no additional labor to speak of. The foam installation takes about the same labor as a tyvek or other building wrap. There is no need for special detail work at windows and doors other than an increase in extension width. Coupled with attention to details of sealing at all possible air infiltration points {windows, doors, sills,rim joists, etc} the performance has been great.
As for installing wood clapboard over foam sheathing, in our area {Central New York State} this has not been an issue as long as wood is back primed. Rain screening shouldn't be an issue if installation is done right and everything flashed and caulked. We have installed wood over foam for over 20 years and haven't seen any problems, including where we have gone back and removed siding for additions.
"if installation is done right and everything flashed and caulked."I think it has more to do with the whole wall system than just the exterior. moisture gets to that space under siding two ways. one is from wind driven rain on exterior surface and is adressed with flashing, wrap and caulk. The other is from interior pass through. I have heaard of one house where there was no interior VB or retarder used and it appears that moisture has migrated out to condense on the back side of all the siding with bad results. I don't know too many of the details on that one, but know it is possible from other jobs.
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I agree with you, but my point was, using the wall system I did, moisture from within the building was pretty much not a factor with spray foam bay insulation and foil faced foam sheathing with taped joints. We are caulking plate connections too, so short of a plumbing or roof leak, there should be no real potential for moisture moving from the interior of the wall to backside of the siding materials. I suppose there could be potential problems if a homeowner didn't maintain a good paint finish on siding and moisture worked right thru the wood siding. I think back to the house I grew up in that was clapboard siding re-sided with cedar shingles. There were all kinds of "drainage planes" between that mess and in fly season the house buzzed so loud your head would spin. How do you manage to keep all the critters out of those areas?
sigh and say oh well.Your system sounds good. The spray foam is my favorite insulation, but some clients cannot afford it and other fear for fire safety. Probably the most of my walls have cavities full of BIBBs and an inch of thermax
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BIBBS is a good system too. We have used that also, but in our area, the biobase foam isn't that much more cost.
Corbond is the primary foam around here.Is biobase open or closed cell?
VB?I haven't heard of it before.
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Biobase is a open cell foam made from about 40% soy base. While not as high of an R value as the closed cell foams it still is close to R-4 per inch so if we fill a 2x6 with 4 1/2- 5" and add 3/4" -1" foam sheathing it gives a decent R value and a tightly sealed wall with a thermal break over framing. It is less than half the cost of closed cell spray foams here. So far we have had great results with heating costs in the homes we have used it. One customer showed me his natural gas bills for this previous January and February that were about $124 per month for both heat and hot water. He is heating close to 4000 sq.ft. in his home which is actually a combination of ICF and 2x6 walls with this detail. Our smaller ranch homes in the development were running mid $80's per month, same time period, with the complete house framed with 2x6 and this detail.
We are spending extra time on air sealing, etc. also.
Testing on these is giving us HERS ratings of between 88 and 94 depending on house plan, size, and the wall construction.
Piffin, what are BIBB's?
Blown in cellulose is called Denspak or just Cells.BIBBs is chopped fibreglass dense blown and called BlownIn Blanket System( BIBB)
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You the man Piffin!!!!What are you using for ventilation on the island? Also, I am going to be getting my Maine Home Performance cert. , do you have any experience with auditing and retrofit weatherizing with this program?Thanks again!!
ventialtion is a long complicated thing to speak of. I do mostly renovations and additions so I study and deal with each case individually. No one single solution. Some are nonvented.One of the bigger problems in that line is HO education.If the design needs as dehumidifier in the crawlspace, they turn it off and wonmder why the problems.If it calls for venting a crawl ion spring and fall only, they leave it open all summer and invite that humid air intot he cool to condense and wonder why they have problems. If it calls forkeeping things sealed, they open it up and ibid.Had a guy in CO who thought he was doing himself a favor by leaving the hatch to the attic open. I got a call about roof leak. He had icicles hanging from rafters and a half inch of ice sheathing the back side of the plywood.I have done some houses here with central AC - I get calls that the AC is not working right. I go by and find half the windows open. Now I appreciate a sea breeze as much as the next guy, but don't invite the damp humid 90°F air inside and then tell me there is something wrong with the AC system or design!So I try to make things as foolproof as possible. Problem is that the fools keep gettting more foolish.
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Thank you Piffin...if I start to ask too many questions, just let me know~I agree with the ventilation, as I mentioned, the State HomeHP program covers a lot of weatherizing but not enough of ventilation. I have just ordered a book about of ventilation by John Bower. That should point me in the right direction.I have to get to the job before my dry waller has a heart attack, but I would like to ask another question later today. To give you some notice, it is my sister's granite crawl space, bath fan is vented to crawl space, dirt is exposed and is below grade, no gutters to speak of, and hot air furnace is located right in the middle. Oddly, there is a noticeable smell of mildew in the air---hmmmmmmmmmmmm.Thanks again and will be in touch!!
all those conditions mean she is asking for water and mildew. Damp is comon in old maine cellars, but there is plenty one can do.
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I agree, HO education is a major problem in our society today. I guess we all have to do our part.
OOOhhhh...you mean H.O.. Oohh. Ooops.