Unusual technique for foam insulation???
I know I’ve passed the weirdo test with this one….but
I prefere to use foam insulation on the outside. Piffin has explained it depends on the climate. Down south they normally put foam on the outside. I live in Chicago. I also know from previous threads the wall has to breathe. Foam on the outside with a vapor barrier on the inside will result in disaster.
Now am I nuts……… If I plan to use a 10′ 4.5″ wall with a drop ceiling , lowering the ceiling to 9′. If I use 10′ wall board with a 1/2 inch space between the floor and wall board, then I will have a gap of 1″ on the top, and have exposed fiberglass insulation (unfaced) . Would the wall then breathe????? I have a hunch it would be a fire code issue
What do ya think???
Replies
"I also know from previous threads the wall has to breathe."
How does a wall "breathe".
A wall does not have to take in oxogen and give of CO2.
So what does a wall have to do that you call "breathing".
http://www.buildingscience.com
"Foam on the outside with a vapor barrier on the inside will result in disaster."
Not nessecarily.
Check the messages for PERSIST system.
Edited 9/17/2005 8:50 pm ET by BillHartmann
Edited 9/17/2005 8:53 pm ET by BillHartmann
I was refering to breathing as the ability of condensation to evaporate.
openning a wall to breathe that way is more likely to let more moisture get into the stud space than to get out of it again resulting in a net gain of moisture within the wall during winter.Walls do not neeedd to breathe. Only on aan old house buolt with green lumber and no insulation do they need to breathe. On new one, build it right the first time so no moisture gets into it and you won't have to worry about any getting out of it.To demonstarate how yours will gain moisture, let's talk this thru - You know that heaat energy is needed to hold water as vapour. Inside the house, there is going to be plenty of vapour generated, and a lot of heat to keep it in the air.now - introduce that air with the moisture it contains into a stud space that is cooler than the interior of the house, more so closer to the outside portion of it, even with Foam on the outside. The air moving through is going to cool down and then is no longer capable of carrying as much moisture, so it dumps a little in the form of condensation on the inside of the sheathing and within the glas fibres.Then that air exits the stud space cooler than it came in having lost some heat energy along the way - to the outside of the house - defeating the reason for having insulated spaces. It has to get warmed back up again, at which time, it is picking up more moisture from inside the house.So the end result is that you lost more energy than you should, while adding moisture to the stud spaces.
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Like I was jsut explaining previously, it takes heat energy for it to evaporate again. in your wall, that heat would have to come from the outside of the wall, throguh the foam panel, in a climate where there are more days of heat flowing out than in. That temp differrential is the main reason why a souther cooling climate is the right place to use foam on the outside.
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Well, even in Minneapolis, it's what Joe recommends.http://www.buildingscience.com/housesthatwork/cold/minneapolis.htmThe assumption is that the condensate will evaporate out.
heh
and we're back to 2" space roofventing.
be a one and a half to 0
sleeps till noon but before it's dark...
Edited 9/18/2005 7:21 pm ET by rez
I hope you studied that close enough to see that except for the exterior foam, none of those details are tha same as what we are discussing here. It is imperative that a whole system be designed so all parts work together
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Piffin,
You said "a souther cooling climate is the right place to use foam on the outside."
And all I'm saying is that Building Science recommends using foam on the outside in heating climates.
And yes, all the parts must work together.
What I am pointing out is that they do not recommend using foam on the outside in all circumstances in that northern climate. What they recommend is that when done according to ALL the design particulars in the drawing, it can work in northern climates.but when someone just puts foam on the exterior side of a wall, without payiong attention to the way all the other components MUST be installed to work together, the occupants WILL have troubles.
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Agreed.
Back to Curley's original query, then, the answer is IF you detail the wall as suggested by Building Science, you can definitely use foam on the outside. Note that the wall cavity is sealed up very well against infiltration, on the inside surface and outside surface. (Curley's proposed wall was not, and you rightly talked him out of it.) There is not, however, a vapor barrier on the inside, so small amounts of condensate dry to the inside via permeation. Note that this is their preferred configuration in several cold climates.
done.
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What do you think about using this product on exterior walls above grade (even though it is designed for the inside of basement walls).http://www.owenscorning.com/around/insulation/products/insulpink.aspI have used it on basement wall interiors, but wonder if it could be installed vertically with 2x6 framing 24" oc. I install it with 1x3 rips of 3/4" plywood to hold it in place. This system would provide plywood nailing strips for siding and trim without dimpling the foam and causing wavy siding.
Are you really saying that you would build a habital structure in Denver or someplace in MN just by slapping up gypboard directly on the inside stud surface? That nice pink insulation will stay dry and do it's job? Ever seen some crap construction in a bathroom where drywall was put up as the substrate for tile in the bath? I've ripped out alot of it and water was everywhere. Insulation mouldy. I owned a storm window company back when tax credits fueled that business. The vapor from inside would leak through the prime windows (junk) and freeze on the inside of my storms. Even people with lots of indoor plants didn't realize that watering those plants, plus heat raised the relative humidity so much the vapor would pass through their primes. I finally went to inside storm windows.
Windows don't have any where near the R value of a wall but it's going to take a little more convincing for me to dump vapor barriers (6 mil) before the gypboard goes on.
This is kind of like the 1.6 gallon toilets when they first came out. Junk. Now traps are fully glazed and pressure systems make things flush.......how far something goes in a 4" pipe (minimum 100') is another story. Problems then solutions. I'll keep reading and watching. Tyr
Check out some of Ray Moore's posts. If you add enough insulation to the outside of the building (for your climate), the temp in the stud space (uninsulated) remains above the dew point. No condensing surface inside the wall means no vapor barrier needed. I'm new to this approach and have not tried it myself. Here is a quote from Ray Moore: 58518.4 in reply to 58518.3 "Winter vapor drive is from inside to outside. The first condensing surface is the inside of the exsterior sheathing. From the standpoint of condensation inside the wall, the act of adding foam insulation to the exterior side of the assembly will raise the temperature of the first condensing surface and lower the risk of condensation.In the summer, the Kraft paper will allow some drying to the interior due to it's elevated perm rating in a high RH environment. The question then becomes an issue of rates. At what rate is moisture introduced from the outside. What is the material to the exterior of the plywood sheathing? Can you count on it or the foam to act as an effective drainage plane? If not then you may end up with bulk moisture trapped within the wall.A good system is to add a rubberized membrane to the exterior of plywood and use the foam on the exterior in an amount sufficient to entirely insulate the building with no insulation in the stud cavity. The first condensing surface then is held to room temperature and no VB of any kind is used on the interior. All drying is to the interior. This is a very durable and forgiving system as well as one that exhibits superior air tightness."
Thanks for the info. I'm a little confused by the quote which says moisture moves from inside to outside in one sentence and in another refers to moisture from outside to inside. I know you didn't write it but am I missing something? Tyr
It depends on the climate and time of the year.During the winter, in the colder climates. You the moisture level in the house, even when "dry", is such that if it leaks through the walls and contacts an cold outside, then it can condense.In the summer you often have very high, warm moisture levels on the outside and cooler, dry inside with AC.And if the moisture moves from the outside to a cooler inside wall it can condense.
Maybe this and maybe that. Where are you located? I'm in the Denver area. It is pretty arid here. Moisture from vapor condensing and FLOWING doesn't happen here regards of theoretical cold surfaces. The real deal is that no one is going to kiss off insulating the area between studs here. Common old 2X4 construction is relegated for the shed to store your lawn mower (if the grass ever gets water to grow).
2X6 construction is the norm. Poly Iso gives me around R40. A 1/2 Poly Iso sheathing is around 4.2. Which would you take? These are not foamed in place which would be tighter but the price vs gain makes that a hard sell.
I have watched an unfaced R-19 batt covered with 6 mill plastic every season of the year for more years than I care to admit. It's on my addition to my house. I hear about it from my wife all the time. There is no condensing. Granted it isn't a bathroom or kitchen but I just pulled the board from the adjacent bath while replacing an exhaust fan. Nothing. And my wife does not run the fan while showering because "It makes me feel cold".
So where do you experience this. I'm giving you practical field experience over 30 years. Sure I have a degree too but Criminal Justice doesn't apply here. Tyr
Most parts of the country starting in KS and going east have large amounts of summer time moisture.Now in the very northern parts the the amount of AC used and the relatively short time does not cause that much moisture built up from condenstaion during the summer.In the far south it is all "summertime" as far as moisture drive goes.And in the middle you have significant peroid where it can condense on either surface.http://www.buildingscience.com/housesthatwork/default.htmhttp://www.buildingscience.com/topten/south.htm
http://www.buildingscience.com/topten/north.htm
The real deal is that no one is going to kiss off insulating the area between studs here
Ah, but there's the Building Science point. R40 with a 2x thermal bridge is not a true R40. Every stud represents a radiation source (in my neck of the woods, where I've found studs by their temp), or a heatsink (in colder climes).
The PERSIST system, which, IIRC, uses 2" of polyiso rigid completely outside the stud bay plane, was developed and tested in Alaska. Occupational hazard of my occupation not being around (sorry Bubba)
I suppose I'll have to see if I can find archives or other info on the PERSIST system. Sure I have found studs (more often truss locations) because on a frosty morning I can see where heat has been transferred from inside (warm) to the outside and melted the area where the truss is located. Poly Iso 2" thick is about R 16.5. There may be other factors but if I had a choice of picking between heat transfer through a 1 1/2 strips of wood 16" OC (obviously not a good conductor because it's a selling point for Anderson, Pella, others) and R40 over a 14.5 inch stud cavity I know which way I would go.
It reminds me of the sales pitch my competitors used to sell their wood or vinyl framed windows versus my aluminum framed windows. Where is the surface area? The glass. Regardless of the frame material. Give me an aluminum framed window with a thermal break any day over ANYTHING else.
The older houses with wood framed windows were scrape and paint (repeatedly) or repair the rot. Vinyl was unproven and very color limited. Why do you think the wood window people HAD to come out with clad windows? Maintenance added to the cost of the high replacement cost (to add a wood window) was killing them.
I tried a wood Marvin sliding patio door. It looks like hell and the plastic track that guides the upper end of the screen broke in a million places but the IG hasn't lost it's seal....which I can't say for Norandex--the window with a thermal break.
So the R16.5 to insulate the wood studs was it huh? How about R16.5 to slow the thermal bridge (in a twenty foot wall that would be about 22.5" of thermal bridge) and then have R40 in the rest of the wall (18'). I guess that would put about R62 for the wall because the sheathing would be cover the bays too. Hmmmm. Of course I build with the studs sheathed completely with 3/8" plywood, then the Poly Iso, then the siding (usually cedar). Add the R40 for the bays, sealed electrical outlets, and I can heat the place with a match. Stays cool in the summer too. But I'll check out the PERSIST data. With a Dad who spent his life as a research engineer and two engineer brothers, it should be interesting. I guess that's why I was a white collar crime detective way ahead of the current buzz words. Tyr
It's my impression that PERSIST is relying on whole-house ventilation to reduce moisture build-up from exhalations and such....
PERSIST is relying on whole-house ventilation to reduce moisture build-up from exhalations and such....
Hmm, that's a question that Ray Moore could likely better answer. I do know that the concept is 'driven' by moisture control as much as a dedicated insulation plane. I want to remember, though, that internal moisture control was a key factor--I just can't remember the "hows & ways" of it. (I'm not sure I wouldn't want some sort of heat exchanger system for my bath & kitchen venting north of up around 50ºN, in any event.)
I'm not used to ciphering for moisture control in a majority heating climate at all, so I'm not "armed" with working examples--I have to go from calculations & formulas and recomendations. My climate down here is such that the driest season is spring, only running about 25-30% humidities.Occupational hazard of my occupation not being around (sorry Bubba)
If the battens (in your picture) were vertical, then a drainage plane would be created which would allow the water to run to the outside. This can work in the noth.All I ever Needed to Know I learned in Kindergarten- Robt. Fulghum
I think the reason for the foamboard on the outside, even in northern climates is not because it is best on the outside theoretically, but because there are too many penetrations on the inside of the walls for use on the inside. Continuous, high R-value insulation and vapor barriers on the inside of the building envelope are notoriously difficult to implement...insides of exterior walls are like Swiss cheese.
Continuous, high R-value insulation and vapor barriers on the inside of the building envelope are notoriously difficult to implement...insides of exterior walls are like Swiss cheese
Which is where the PERSIST system works better, as RayMoore has championed here before.Occupational hazard of my occupation not being around (sorry Bubba)
I see your point, thanks alot.
Edited 9/18/2005 11:32 pm ET by curley
I'm not sure about those gaps at top and bottom, but tal;k you your local Dow Corning rep; they have a whole presentation devoted to the advantages of foam on the outside and the condensation question.