white panel +++ instead of sprayfoam

[Dave Maxwell]

If I put 1/2 white foamboard between studs on wall in pole building and fill any gaps with great stuff. Then fill with r19 bats and vapor barrier will it be OK. I can't swing all spray foam. The white is r3. Thanks

 

[ksj9393]

Poor man's "Flash-n-Fill"... thought of it myself more than once. I know of it's succesful use, the only issue is making sure you don't sandwich the R-19 "fill" between two impermeable layers.

Any moisture that gets into the wall, has to dry to the inside or outside. Exapnded polystyrene 1" thick (~R4) is 3 perms, or vapor semi-permeable. However, assuming your pole shed has steel exterior, the steel is not. Thus, your fill would need to dry inward and so you need to be careful about installing a vapor barrier on the inside wall. Of course, many regions require it as "code", thus creating a conflict..

 

[Dave Maxwell]

I've taken expansion foam and sprayed the bottom channel where the wall sits. Filling the voids. If that helps with moisture

 

[lowell66dart]

Any moisture that gets into the wall, has to dry to the inside or outside. Exapnded polystyrene 1" thick (~R4) is 3 perms, or vapor semi-permeable. However, assuming your pole shed has steel exterior, the steel is not. Thus, your fill would need to dry inward and so you need to be careful about installing a vapor barrier on the inside wall.

Not trying to steal the thread but I have a question about the statement above. Would Roxul wool insulation, which has no vapor barrier be a good choice? I have a new pole barn that needs something in the wall before I close things up.

 

[ksj9393]

Any moisture that gets into the wall, has to dry to the inside or outside. Exapnded polystyrene 1" thick (~R4) is 3 perms, or vapor semi-permeable. However, assuming your pole shed has steel exterior, the steel is not. Thus, your fill would need to dry inward and so you need to be careful about installing a vapor barrier on the inside wall.

Not trying to steal the thread but I have a question about the statement above. Would Roxul wool insulation, which has no vapor barrier be a good choice? I have a new pole barn that needs something in the wall before I close things up.

It is not the choice of insulation that matters. Rather, it is the presence (or absence) of the vapor barrier. Unfaced fiberglass, Roxul, cellulose... all are worthy for consideration.

 

[danski0224]

If I put 1/2 white foamboard between studs on wall in pole building and fill any gaps with great stuff. Then fill with r19 bats and vapor barrier will it be OK. I can't swing all spray foam. The white is r3. Thanks

Not enough R value there to prevent condensation on the foam surface.

That white foamboard isn't air tight until it is about 4" thick.

Those steel sheets aren't smooth, so you have air channels between the steel and foam.

Do what you plan, and you will regret it.

 

[Dave Maxwell]

Nope. Won't be doing that then. Thanks. Will just wait a couple years to heat and insulate

 

[pfarber]

Who is having this condensation issue on a steel sides pole barn/garage? I'm reading a lot and whenever there is a question about insulation someone posts about condensation like its the great boogy man of, well, insulation.

Maybe if propane is your heat source (it better not be if you garage is as sealed as you say it is). But electric/wood/pellet doesn't generate significant moisture from combustion/use.

My house was build in 1876 and never had a vapor barrier... nothing is rotting/rusting because of no vapor barrier.

My 1000sq/ft+ garage was heated all last year with a propane torpedo.... not a drop of water anywhere.

 

[Highbeam]

While a continuous sheet of steel is water tight, the steel barn siding is not continuous.

I see little to no benefit of adding this layer of foam before putting the batts in. What are you trying to accomplish other than an additional R-3 for the wall? If it is just an extra R3 then you don't need to fuss with sealing the edges. If it is for vapors then you don't want a VB on the outside in a heating climate.

It would be cheaper and easier to just putt up the batts like everybody else.

 

[Dave Maxwell]

Was trying to seal it. Didn't think about the ridges. Can't swing spray foam. Need it as quiet as possible

 

[lowell66dart]

When you say cheaper and easier to just put up batts would they be faced?

I always thought that you should try and keep the warm inside air from comntacting the cool outside steel with some sort of barrier on the INSIDE. There are a few replies here that suggest otherwise. Can anyone provide more detail.

 

[danski0224]

Who is having this condensation issue on a steel sides pole barn/garage? I'm reading a lot and whenever there is a question about insulation someone posts about condensation like its the great boogy man of, well, insulation.

If the flash and batt is done improperly, you get condensation on the inside of the building, in the wall cavity, on the foam, next to the fiberglass.

The foam must have enough R value to prevent this condensation.

 

[ksj9393]

If the flash and batt is done improperly, you get condensation on the inside of the building, in the wall cavity, on the foam, next to the fiberglass.

The foam must have enough R value to prevent this condensation.

Agree with Danski... vapor diffusing through a wall will condense as soon as the dew point temperature is reached (there is a temperature gradient through a wall, dropping from the warm interior wall surface to the cold exterior wall surface in winter). There is a great article on this subject at Building Sciences: http://www.buildingscience.com/docu...ng-cold-weather-condensation-using-insulation

Depending upon what climate zone you are in, you may need enough foam for as much as an R-15 foam insulation layer, or as little as R-2.5. To get a crude estimation of the appropriate foam thickness needed to minimize condensation risk, see this Green Building Advisor article on the subject: http://www.greenbuildingadvisor.com...lating-minimum-thickness-rigid-foam-sheathing

And we all though insulation was simply a matter how much itching did we wish to endure!

 

[lowell66dart]

Very good info in those links but it does make my head hurt

One thing I learned from the second link is the 3" of foam that all the contractors are trying to sell me to spary on the underside of my polebarn roof is not really needed for what I am trying to do. 2 inches would do. I am just trying to seal the building and keep moisture out.

A little background info:

I am in Louisiana, Zone 2A. 40X80 polebarn, 13 foot ceilings. 26 guage metal exterioor skin. The garage doors (three 12x12's) will be insulated and have an R value of around 10. The walls have bookshelf girts every two feet so this gives me a nice place to staple fiberglass insulation. This building will have a metal ceiling but I don't want insulation on top of it. This structure will never be conditioned. It's going to be fans in the summer and maybe some sort of heat in the winter. This is a workshop for me to play in.

My tenative plan:

2 to 3 inches of open cell foam sprayed on the underside of the roof and also on the end gables.
3 1/2 faced fiberglass in the walls. This will leave an 1 1/2 air gap between the exterior metal and the figerglass.
The interior walls will be OSB for the top 8 feet and some sort of metal at the bottom.

Again, my goal is to keep the inside dry and somewhat more comfortable than the ouside temps. I would appreciate any feedback that you guys could provide.

 

[danski0224]

3 1/2 faced fiberglass in the walls. This will leave an 1 1/2 air gap between the exterior metal and the figerglass.

Bad idea.

You will have convective air currents set up in that airspace. Air movement through fiberglass negates any insulating value of it. You will have a 3.5" air filter.

Fiberglass MUST be enclosed on all 6 sides to hope to achieve the R-value established in a controlled laboratory environment.

 

[bglad]

I live in the Northeast where the winters will drop into single digits. My pole barn is built with 6 x 6's and 2 x 4 purlins to hang the metal siding giving me a gap of about 7". I was thinking of putting an 1 1/2" of spray foam and then batts due to price. Would this cause a problem with condensation? How thick would the spray foam have to be to prevent condensation?

 

[walrus]

I live in the Northeast where the winters will drop into single digits. My pole barn is built with 6 x 6's and 2 x 4 purlins to hang the metal siding giving me a gap of about 7". I was thinking of putting an 1 1/2" of spray foam and then batts due to price. Would this cause a problem with condensation? How thick would the spray foam have to be to prevent condensation?

R-10 is the magic number to prevent condensation according to www.buildingscience.com. Which would be about 1.5 inches of closed cell foam

 

[pfarber]

Read this:


"The interior conditions within a building during cold weather are critical variables in understanding the risk of condensation, and must be known if predictions and calculations are to be made. Interior temperatures are often in the 70 °F / 21 °C range, but relative humidity levels, and thus air moisture content, can vary significantly. In most office, school, and retail occupancies, ventilation rates are high enough that the RH during winter months is in the range of 25 to 35%. In some residential occupancy, the interior moisture generation is higher and exterior air ventilation rate lower than commercial occupancies, and hence the RH will often be higher. In special occupancies, such as swimming pools, both the interior temperature and relative humidity levels will be higher (78°F/25 °C and 60%RH), resulting in very high absolute humidity levels."


Bold is mine.

I stopped reading after this paragraph as these are in no way indicative of the typical garage. The entire article related to the WARM MOIST INSIDE AIR moving OUTWARD towards the cold air, and at some point in the wall condensating.

Who's garage is seeing 70F and RH of 80+% and running the heat in winter?

Who's seeing any significant RH in the garage that would even be close to condensating if the dew point it reached?????

The article in itself is sound... I just have to question the starting assumptions as they relate to a garage's ambient starting conditions pre-heat turn up.

Show me the math where you get condensation with outside and inside temps are roughly equal with less than 20-30% RH.

 

[lowell66dart]

Bad idea.

You will have convective air currents set up in that airspace. Air movement through fiberglass negates any insulating value of it. You will have a 3.5" air filter.

Fiberglass MUST be enclosed on all 6 sides to hope to achieve the R-value established in a controlled laboratory environment.

Ok, R-19 on the way. This is turning into a very interesting thread.

 

[pfarber]

Bad idea.

You will have convective air currents set up in that airspace. Air movement through fiberglass negates any insulating value of it. You will have a 3.5" air filter.

Fiberglass MUST be enclosed on all 6 sides to hope to achieve the R-value established in a controlled laboratory environment.

Theoretically yes, but we all know of walls that have insulation and are exposed to air movement that still provide an acceptable level of heat control.

How much air do you think is going to move and at what rate that it would effect (significantly) the R value of a 3.5 inch fiberglass bat? Maybe a 20MPH wind. But the convective current of the space in a rolled steel wall? Really?

Your statement, while technically correct, is pretty much out of the realm of possibility with respect to a normal steel garage. Convective air currents in the nooks of a rolled steel garage panel.... put up the batts and enjoy the warm garage.

 

[danski0224]

One way to find out would be to do a section of wall with the air space and one with the space filled with fiberglass, and then view the wall with a thermal imager.

With the sun beating down on the exterior, the wall temperatures could easily get into 3 digits, depending on the color. There could be condensation issues on either the steel or the inner surface of the insulation, and wet fiberglass doesn't work so good.

I'm not a steel building expert, but the ones I have seen are held together with thousands of screws and air stops along the bottom and top are pretty much non-existant. Setting the panel into a c-channel or butting it to an angle doesn't really count. Corrugated walls are not easy to seal up. Wouldn't take much of a breeze to get into the building.

I would just do the job right and fill the space with insulation, on all 6 sides like it is supposed to be.

If the person doesn't want to spend the money for the extra 1.5" of insulation, then I'd **** the insulation up to the exterior wall and put the airspace inside.

I see many indoor comfort issues that are rooted to the improper installation of fiberglass insulation and poor definition of the conditioned space. Often, these issues are difficult and expensive to fix later, and doing the job right in the first place would have been much less expensive. To each their own.

 

[pfarber]

One way to find out would be to do a section of wall with the air space and one with the space filled with fiberglass, and then view the wall with a thermal imager.

With the sun beating down on the exterior, the wall temperatures could easily get into 3 digits, depending on the color. There could be condensation issues on either the steel or the inner surface of the insulation, and wet fiberglass doesn't work so good.

I'm not a steel building expert, but the ones I have seen are held together with thousands of screws and air stops along the bottom and top are pretty much non-existant. Setting the panel into a c-channel or butting it to an angle doesn't really count. Corrugated walls are not easy to seal up. Wouldn't take much of a breeze to get into the building.

I would just do the job right and fill the space with insulation, on all 6 sides like it is supposed to be.

If the person doesn't want to spend the money for the extra 1.5" of insulation, then I'd **** the insulation up to the exterior wall and put the airspace inside.

I see many indoor comfort issues that are rooted to the improper installation of fiberglass insulation and poor definition of the conditioned space. Often, these issues are difficult and expensive to fix later, and doing the job right in the first place would have been much less expensive. To each their own.

Thermal Imagety? Test Panel? What???

I don't know of ANYONE with water in the wall issues.... I live in PA and there are homes like mine (built in the mid 1800's) and new construction and there is no hot debate about water in walls.

The temp differential in a small part of the equation. The biggest factor is how much moisture is in the air to begin with (aka Relative Humidity). I think you need to reread whatever literature you are using an pay special attention to the RH numbers. Few states have cold, humid winters. In PA the average winter dew point is 0 to -20 (that's right ZERO to MINUS 20!)

Now you could discuss that the the dew points in fall/spring would incur much more moisture as the dew point is higher and the RH is also... but that can be controlled by simply ventilating the garage (aka open a window). If there is no temp difference across the insulation, then the dew point is moot.

If you did add heat, then you might have an issue.... but unless your heat up cycle takes hours the temp rise up to the dew point and past it would be quick and the amount of condensation would still depend on 1. the starting RH, the temp differential inside to outside and the time it takes to cross the dew point.

Put up the batts as planned. Spending $3-4k to spray foam 1.5 inches to seal the steel garage is money not well spent.

 

[Highbeam]

Bad idea.

You will have convective air currents set up in that airspace. Air movement through fiberglass negates any insulating value of it. You will have a 3.5" air filter.

Fiberglass MUST be enclosed on all 6 sides to hope to achieve the R-value established in a controlled laboratory environment.

This does not pass the sniff test.

It is ridiculous to think that all 6 sides must be enclosed. Ever heard of attic insulation? Blown in or batt FG has been used for decades, not enclosed on 6 sides, and it works.

The whole concept that air will flow within any insulation to any significant degree is hogwash.

 

[danski0224]

Go attend some BPI classes and get back to me.

 

[ksj9393]

This does not pass the sniff test.

It is ridiculous to think that all 6 sides must be enclosed. Ever heard of attic insulation? Blown in or batt FG has been used for decades, not enclosed on 6 sides, and it works.

The whole concept that air will flow within any insulation to any significant degree is hogwash.

I was going to make the same point as Highbeam - attics clearly are ready examples of "open-faced" insulation, be it fiberglass, cellulose, whatever.

However, air movement over such insulation WILL reduce its effectiveness as convective forces are thusly accentuated. This is clearly understood by recent revisors of the building codes, as wind washes are now spelled out to reduce air movement from soffit vents blowing over and possible damaging the insulation in vented attics.

Lowell66dart - you would do well to minimize air gaps between your wall construction layers. Many walls are designed with a gap, called a rain screen, on the exterior, but this is used to mitigate the adverse effects of water penetration through the exterior cladding. I am no expert of steel building construction, but I would be inclined to believe that water intrusion into the wall assembly through steel siding would be nominal, so long as no gaps exist.

And that's the point, I believe, that Danski is trying to make... build your wall with an air barrier. Definitely seek to make your interior surface airtight if possible, but strive for the same on the exterior surface as well. So, if possible, seal between the exterior steel and the header board and at the sill plate. Then it matters little whether your insulation is against the steel or not.

Just my 2CW...

 

[danski0224]

Fiberglass attic insulation is exposed because that is the conventional installation practice.

Yes, it would work better if the insulation was enclosed on top and along the exterior perimeter.

 

[lowell66dart]

Lowell66dart - you would do well to minimize air gaps between your wall construction layers. Many walls are designed with a gap, called a rain screen, on the exterior, but this is used to mitigate the adverse effects of water penetration through the exterior cladding. I am no expert of steel building construction, but I would be inclined to believe that water intrusion into the wall assembly through steel siding would be nominal, so long as no gaps exist.

...

I am meeting with the foam guy this week to look at my job. Where the roof meets the the top of the wall is one of the areas I want to show him. I want this covered. I am also going to try to get him to throw in doing the four wall corners from top to bottom. I don't think with the steel overlap there is much if any air leakage.but it is what it is. The only other thing I need to look at is where the bottom of the wall meets the floor. I may just have to buy a case or two of Great Stuff or caulking of some sort.

 

[pfarber]

Go attend some BPI classes and get back to me.

BPI is hogwash! ITs a commercial course that says you are an 'energy auditor'!

I hope you don't think that a payware course made up by people who most likely never installed any insulation is somehow authoritative on the subject.

"What is BPI Accreditation?

BPI Accreditation is a standards-based home performance program that helps you differentiate your business from the competition...."

SO YOU CAN SELL MORE STUFF.

Good luck on your BPI career.

 

[danski0224]

Wow, what made you so bitter?

I sense some issues

Good luck to you and your closed mind. It must be full already.

 

[pfarber]

Claiming to be the insulation guru after taking a class does really not get you very many credibility points.

'I took a class I know better' professional.... that's what I find questionable.

The OP's original installation method is good enough. I will agree that your way may be technically (as in a lab where you can measure minute air currents and their effects on fiberglass batts) but in a cost analysis, typical home owner's world:

Seal the joints on the outer wall, insulate to the R value recommended for your zone with fiberglass batts.

Easy peasy.

 

[rsa]

The whole concept that air will flow within any insulation to any significant degree is hogwash.

The abstract from a report on Thermal Performance of Fiberglass and Cellulose Attic Insulations performed by Oak Ridge National Laboratory:

A series of experiments has been completed on the thermal performance of fiberglass and cellulose attic insulations under winter conditions using an attic test module in a guarded hot box facility. Experiments with one type of loose-fill fiberglass insulation showed that the thermal resistance at large temperature differences (70 to 76°F) was about 35 to 50% less than at small temperature differences. The additional heat flow, attributed to natural convection, was effectively eliminated by applying a covering of fiberglass batts or a combination of a polyethylene film and fiberglass blankets. No significant convection was found either with fibergl;wbatts or with one type of loose-fill cellulose.

My bolding.

 

[Highbeam]

"was effectively eliminated by applying a covering of fiberglass batts"

So fiberglass prevents air movement within fiberglass. See where this is going? The thread was about walls where FG batts are used.

 

[danski0224]

I have thermal images of walls that show that the 2x4 stud, at roughly R-1 per inch, has a greater insulating value than R-13 fiberglass. Believe what you want.