I've been reading about insulation, specifically radiant barrier vs. foam insulation and I now know less than I did before.  I have a building project that is a bit different:  I am building an apartment within and existing metal building.  I have a 40' x 60' shop/barn, tin in place, slab in place, and now need to build the apartment.  The structure I am building will occupy one side of the barn, and will be 15' x 60'.  The 60' side is facing the west and I'm concerned about insulation.

My original plan was to use spray on foam (closed cell) insulation, 1" thick, on the metal, then install regular fiberglass insulation within the wood frame walls of the apartment.  I've been distracted, however, by the radiant barrier option.  With no shade on the West side, it's HOT, and I believe I do need two forms of insulation to maintain electricity affordability.

All I've found regarding the foam vs foil however, pertains to attic space.  So can anyone (independent of those selling either product) tell me the best course of action?  The radiant barrier I'm looking at is by Reflectix and so is more than just foil.  I'm considering the double sided version.  Since the steel is already up on the shop, it will be "retro fit" without the benefit of the .75" thermal barrier recommended, thereby reducing my R factor to about half or a bit better, or about 4.7.  The foam is claiming an R factor of 6 to 7 per inch of foam.  It would seem obvious but I keep reading about the different ways heat is conducted so I'm not convinced the foam is a better choice.

My primary concern is keeping the space cool in summer; heat loss in winter is less of a concern in my locale.  Plus the foam I'm reading about talks about a "sealed" attic (which doesn't apply but raises questions about moisture accumulation in the walls).  Finally, the cost for the radiant barrier is about half the cost of the foam.

While I don't want to pay later for a savings of $600 now, cost is definitely a factor in my project.  Any opinions?

Radiant barrier (of any type) is not a substitute for R value, even if it reduces peak cooling loads. If it's either/or, go with the foam. But there's more...

What's the exterior finish of the steel? If it's bare-galvanized, painting it with almost ANYTHING would reduce the heat gain through that wall, but going with a highly reflective white is better. There will be some advantage to using a CRRC-rated "cool roof" paint, but it won't be worth paying much extra for over a standard white/off-white in a vertical wall installation (in a roof you might go for stuff with a higher solar reflective index though.)

If the interior of the steel is bare-galvanized, don't paint it, as almost any paint will have a higher emissivity, which would increase the radiated heat transfer into the building. Give yourself at least 3/8" space between the steel and the sheathing of the interior structure- steel siding needs to have a "rainscreen" gap between it and interior materials to properly vent & dry. If you have to, build it up a layer at a time from the steel using furring/purlins to maintain the gap.

If you put 1/2 or 1" of foil-faced rigid iso board (polyisocyanurate- comes in 4x9, sometimes 4x9 sheets) on the sheathing of the apartment that faces the steel it adds R3-R6 to the whole stackup, and a radiant barrier to boot. An inch of iso is typically cheaper than an inch of spray foam installed when talking flat surfaces. In some places foil-faced EPS (beadboard- the stuff cheap coolers & disposable coffee cups are made of), and are cheaper than iso per unit-R.

The performance of the lowly fiberglass batt is pretty poor unless you pay a lot of attention to air-sealing, and ensuring that there are absolutely no gaps or compressions. Any sprayed or blown material will usually perform to spec, but batts typically underperform by 15% or more.

Heat transfer happens in three ways:

Radiation- which requires a large temperature difference, and some air/vacuum space to be relevant

Conduction- which requires surface to surface contact to occur

Convection & infiltration - where air heated by contact with a surface become lighter and tends to rise, being displaced by cooler air, and pressure differences/wind causes air to pass through leaky surfaces.

All are important, but not of equal importance. Most of the radiated heat from outside the building, and controlling it at the outer surface is more effective than a radiant barrier placed between the siding and the room you're trying to keep cool. Lowering the emissivity (the ability of a material to radiate heat) on the interior of the steel can help but it's critical. Heat that enters the sheathing of the interior wall structure can only be controlled by insulation- materials with an R-value (a measure of resistance to conducted, and only conducted heat.) Most insulation is opaque to radiated heat- they may absorb some, and re-radiate some, but don't pass it on through.

Low density fiberglass is an exception- it's slightly translucent to radiated heat, but that's not usually a big deal in a wall cavity, since it's fully in contact with the sheathing- and the vast majority of the heat transfer across a fiberglass batt will be a combination of conducted and convected heat. As the hot side of the wall cavity heats up the air in the batt, the air next to the hot side becomes lower density and begins to rise, allowing cooler air on the cool side of the cavity to fall, forming a slow air-flow loop. If there are air leaks from the interior conditions space into the cavity, even the room air participates in the convection loop. The bigger the temperature difference, the faster the loop, and the more poorly the insulation performs. Foam insulation doesn't have this issue, since every cell of the foam is it's own mini-air barrier- no convection loops occur, and it's insulative value is fairly stable over temperature. (It does change though for other reasons, but not nearly as much as low-density fiberglass.)

Bang for buck, wet-sprayed cellulose is usually cost-competitive with batt-jobs and tends to perform better in the real world. As a fiber insulation it still allows some convection currents, but at standard density it's on the order of 10% of that of low density fiberglass. Sprayed in place, it has no gaps/compressions/voids, and can fill even 1/4" wide mini-cavites that would be a PITA to do with stuffed fiberglass (but foam might be easier/better still.) Cellulose also adds thermal mass to the structure, enough to measurably slow the rate of heat-up. In a 2x4" cavity sprayed cellulose is like adding another 1/4" of thickness to the wall board- not huge, but will have a measurable performance edge over low-thermal mass goods of similar steady-state R value in a predominantly cooling or mixed climate.

But if this is a DIY job and it's batts or nuthin', frame it out with the studs 24" on center and use high density (typically ~ R15 for 2x4 framing) "cathedral ceiling" batts. Take care to split the batts to drape behind & in front of roughed-in wiring, etc, and pay attention to buckling at the tops/bottoms- if the batt needs to be trimmed a bit to keep the front face flat, do so, but not so much that you have a gap at the top or bottom, trim & set snugly around & behind electrical outlets, etc. Every square inch of un-insulated gap pass a HUGE amount of heat compared to the insulated areas- gap areas must be minimized.

If you're reasonably handy, dry-blowing cellulose isn't rocket science, and can be done as a DIY job with a box-store rental blower. Use "borate only" or "sulfate free" goods though, since those that use aluminum sulfate as fire retardent can corrode metal should it ever get wet from a rain or plumbing leak. (All wet-spray material meets the spec, and can be dry blown. It's often called "stabilized cellulose", since the water-activated adhesives keep it from ever settling even in low-density applications.)

Whatever the stud-cavity insulation, if you use foil-faced goods on the exterior you should take care not to use anything more vapor-retardent than kraft facers on the interior. In hot-humid areas you're better off using unfaced goods when using batts, and put lower vapor permeance materials on the exterior side, whether foil-faced foam or radiant barrier (which can be VERY low permeance), or even 3/8" semi-permeable fan-fold XPS foam.

Got a zip code?

Wow...first off let me say that you are the first source of any useful information about insulation! Nobody else I've consulted nor anyplace I've looked on the net has explained insulation quite as well. The only problem I have is that you're talking about three feet above my head and I'm pretty sure I only understood about half or less of what you said.

There are a couple of points I'd like to clarify and get your advice on.

First, the metal building is already constructed, uninsulated, made of 26 gauge steel U-panels, painted white (both sides, not the cool roof type). The posts are 4" steel square tubing with 2" steel square tubing perlins (sp?). Our plan was to spray closed cell foam, 1" thick, directly onto the metal. The apartment structure will have wood framing and will be constructed up against the perlins, thereby leaving an approximate gap of 1" between the framing and the foam coating on the steel. We then planned to use batt insulation in the wood framing.

We hadn't planned to install sheathing between the framing and the metal. That being the plan, do you advise that we install a vapor barrier on the outside of the framing? Something along the lines of Tyvek? I was thinking that moisture forming on the metal would be eliminated by the foam insulation, but after reading your advice I'm not sure about that.

Our zip code is 76270, addressed out of Sunset, Texas, although we are actually located in a very rural setting (5 miles from paved road...way out there...lol). The geographical location is roughly 65 miles NW of Fort Worth, Texas. We are less humid than the metroplex, more humid than West Texas; humidity and moisture are not a real problem for us.

Our motivation for the addition of the foam was the length of Western exposure (60'....the apartment will measure 60' x 15'), with no shade at all. Right now I suppose we're super sensitive to the idea of heat generated by this situation as we're about 3 weeks into 100+ degree temperatures. The west side of our home has some shade and is still difficult to cool in the late afternoon. We therefore decided that adding the foam in addition to the batt insulation was a smart idea. I was distracted by the idea of radiant barrier but after reading your post I'm thinking it won't help as much as I'd thought.

I really appreciate your feedback on this. Again your post was remarkably informative. As a retired firefighter, my husband is pretty handy but this was an area we just weren't certain about. I'm willing to spend now to save utilities later but wanted to be a bit more informed that I wasn't wasting my money.

roxxy,
You have not mentioned why you have to build the apt. on the west wall of the building. If you are so worried about the heat transfer, I would look at maybe putting the apt. on the east side of the building. Also, have you considered building your apt as a completely free standing unit, with its walls a foot or so off the building wall? This would allow for substantial air movement that would moderate the heat transfer. Finally, I would look at using SIPS panels to build the apt. No need for exterior wall or roofing finish makes SIPS ideal for a building within a building concept.

Would love to put it on the East side but foundation is already in place complete with plumbing. Can't come in from the West wall because am limited on how far East I can go, and I'm unwilling to go narrower than 15' which is all the space I have. The building is a working shop with a center drive through, hence the East wall limitation.

The apartment was planned from the time we built the shop 13 years ago...just now being forced to build it. I am a tax accountant and my office lease just tripled so need to use the space for a while as an office. We know having an independent apartment (i.e. income producing property) on our place will make it more marketable when we decide to sell so that's why the ultimate plan is an apartment.

I didn't know what SIPS panels were so just googled them and looks like a good idea. If I can just get some pricing I can compare. It's a pain to be on such a shoestring budget but finances are tight and this wasn't an anticipated expense. We're doing the lion's share of the work ourselves so we'll see how it turns out...lol.

I appreciate your input, it's given me another direction to look for energy efficiency.

Roxxy

The performance difference between any standard white enamel/paint and "cool roof" materials won't be significant on a vertical wall- don't spend any money here. Most white paints will radiant heat back much faster than they absorb it, whereas most bare metal finishes, while they reflect heat well, can't radiate it away, and their temperatures will be much higher than the same panel painted white, which only reflects 1/2-3/4 as much as bare metal or aluminum paint does.

Unless you're going to foam the entire barn (reducing the overall heat transfer into/out of the barn) or make the interface between the sheathing and the foam air-tight spot-foaming the steel siding isn't going to buy you much performance. Spray-painting the inside of the steel with a "radiant barrier paint" may lower the peak radiated heat transfer into the building by lowering it's ability to radiate heat to the siding to the sheathing of the inner building nearly as much (but even that might not be worthwhile.) Putting the foam on the other side of the air gap- onto the sheathing of the studwall would provide measurably higher performance, but it's hard to install, and more expensive than foil-faced rigid-board insulation which would outperform it due to the foil. With foil-faced sheathing most of the heat radiating off the interior of the steel siding will be reflected back to the siding. The foil would be convection cooled to a degree or two above the temperature inside the barn despite it's inability to radiate the small fraction of heat that it absorbs.

The foil facer on inch of foil-faced iso is basically half a radiant barrier, since the other side is in contact with the foam inside the panel, but it's delivering at least 3/4 the benefit of a radiant barrier, and delivers the full R-value of an inch of closed cell foam. If you sprayed the interior of the steel siding with radiant-barrier paint AND put an inch of foil-faced iso on the studwall side of the gap you'd have a full benefit radiant barrier AND the R value of an inch of spray foam for less money than the spray foam and the foam would be insulating that side of the apartment from the ambient barn temperature.

Putting the foam on the outside of a 2x4 studwall increases it's thermal performance by more than you might think. The 1.5" strips of stud edge allow heat to pass into the wood, which has a conductive R value of only R1 per inch (~ R3-R4 for standard density 2x4s). If the cavity fill is R13, the amount of heat conducted through the 1.5" of R3.5 studs is a large fraction of what is being conducted through the 14.5" of R13 fiber insulation. By putting R6 of foam over that stud, you've raised the R-value in those sections to R10 cutting the heat transfer by 2/3, even though it only reduces the heat transfer over the center-cavity by 1/3.

In your roughly equal mixed heating/cooling climate no vapor barrier is required. But note, Tyvek is NOT a vapor barrier, but rather an air-barrier. Vapor barriers block both air and water-vapor, whereas air-barriers block only air, and are more-or-less permeable to water vapor. (Water vapor molecules are roughly half the size of the more common diatomic gases in air such as N2 and O2, making it a bit harder to block. Air barriers can still be fairly waterproof to liquid water though, since the surface tension of the liquid forms droplets orders of magnitude larger than N2 or O2 gases.) Air barriers are a GOOD thing- a well insulated leaky sieve of a wind-tunnel house is still pretty expensive to heat or cool. But air-tightness can be achieved by other means- gluing/caulking the strucutral sheathing to the framing, and taping any seams that don't coincide with framing timber with sheathing-tape (you have to paint the seams with a decent latex or latex-acrylic primer to get the tape to stick though.) Foil facers on rigid-board insulation ARE a vapor barrier, but as long as you only have one vapor barrier in the assembly you're good to go. In your climate it can be on the exterior, interior or in the middle-doesn't matter as long as there are no more than one. That means only unfaced batts (if you go with batts) and no vapor-barrier type interior finishes foil/vinyl wallpapers, etc. Stick with standard latex or acrylic paints on the interior, and it'll be permeable enough to water vapor to dry out.

An inch of spray foam is semi-permeable (a vapor retarder rather than a vapor barrier) but it's air-tight. Kraft facers on batts are semi-IMpermeable and still allow the wall assembly to dry (if slowly.) Water gets into a wall by any number of ways, but gets out primarily by vapor diffusion. Since your wintertime temperature averages are above the dew-point of normal conditioned-space air, you don't need anything more vapor-retardent than standard latex or acrylics to keep from ever experiencing condensation on the structural wood. If you have an inch of rigid foam on the exterior of the studs and an air gap to the steel siding that's even more the case- you can literally get away with an unpainted interior if you wanted to in your climate- the wood would always be above the dew point.

I'd still recommend going with blown cellulose insulation rather than batts. Even low-density dry blown goods that settle 5% in 20 years in a wall cavity will perform better in it's aged state than "typical" batt installations did on day-1. A guy named Karg has 1001 online tips on how to install blown cellulose, maybe 20% of which would be relevant to your setup, but it's not hard, and will result in higher performance & higher comfort. (And lower fire risk- every ~15" of vertical cellulose in a studwall is the rough-equivalent of installing 2x4 firestop blocking.) Between the higher thermal mass and lack of gaps/compressions it's a better value and higher performance than batts. You'd have to go to high density R15 batts and pay close attention to installation detailing to do better with batts.

How were you planning on insulating the ceilings?

Ok, now I want to know if you're married...LOL...as this is the best response yet and you sound like a great catch for anyone who is a homeowner...lol. We were ready to bite the bullet on using spray foam on the metal walls but your first paragraph convinced us that we wouldn't be getting the best bang for the buck by doing so. We plan to follow your advice and use foil backed iso on the outside of the framing then using blow in insulation within the walls.

We had planned all along to use blow in insulation in the ceiling so it all works out. We're using 2x10 studs along the top...there will be little to no weight on top as we don't need the storage space. The building center is preparing a quote for enough ceiling blow in insulation to give us an r30 factor. Do you suggest we use the foil backed iso as our top decking as well? There will be a 4' - 9' space between the "attic" decking and the shop roof. Again, while we might store some lightweight stuff up there (i.e. a few spare vinyl siding sheets from our home, stuff like that) it's not really designated as storage space for us. Most of the "stuff" in the shop is iron and too heavy to store that high anyway.

Just want to thank you again for sharing your expertise...I know we're overthinking much of this project but have found from experience re-doing because we screwed something up is such a time waster...measure twice cut once so to speak.

R30 between the joists will pretty much fill up a 2x10 cavity. Simply blowing another 3" over the joist-tops would give it an ~R10 thermal break (doubling the R-value of those thermal-shorts) would be enough thermal break- no iso necessary. That'll give you a center-joist R of ~R40 (better than code-min), but that also means you get no storage capacity out of it. If you really need that storage loft, blowing cellulose full between the joists, laying down a deck of 3/8" of OSB and putting 2-3" of EPS (bead board) on top.with another thin layer of OSB to protect it should work, but it's a lot more money than an extra 3" of cellulose. (EPS is usually quite a bit cheaper per R than iso, but takes ~50% more thickness to achieve the same R value.) At your anticipated loading even the cheapest "Type-I" low density EPS used in commercial roofing applications would be fine. Getting a decent thermal break over the framing timber is key to getting the full performance out of the cellulose. The 10" joists are only ~ R9, and doubling that or more with the thermal break is huge even if it's only a 25% improvement on the center-cavity heat gain/loss.

Hopefully you've avoided punching that ceiling full of holes with recessed lighting, etc, which tends to make it harder to air-seal, and makes for thin-spots in the insulation layer.

In that part of TX the subsoil temps are in a reasonable range for utilizing "earth coupling", where you extend the insulation of the walls down to at least a foot below the frost line, or 18, whichever is deeper. See: http://mb-soft.com/solar/soilmap.gif This may be difficult/impossible to do depending on what the barn slab/footings look like. If you're in a termite prone area ~4" of borate loaded "termite resistant" EPS would be about right. If you do this you should add a 10mil poly ground vapor retarder to keep ground moisture/radon etc under control, and mastic seal it to the walls. (Any overlaps of sheets need 12" and a mastic-seal. Duct mastic used for AC/heating ducts is suitable.) If this is a new slab, this should go under the slab, otherwise, between slab and finish-floor or crawlspace would be right. (If a crawl, it needs to be ventilated to the conditioned space air, not the barn.

With a fully insulated reasonably air tight box coupled to a high thermal mass 65-70F chunk of dirt, that thermal mass will moderate both heating and cooling loads substantially. (Slab-on grade homes with insulated slab edges or insulated stem-walls below work well in most of mid & northern TX.) If you're pouring footings for the inner building, look into using insulated concrete form (ICF) systems, which would pretty-much be all that's necessary. Then be sure that the iso sheeting on the frame building above extends down to (or even overlaps) the outer foam on the footing to be sure that there are no gaps in the insulation.

Also be sure to use sill-gaskets between any concrete/wood interface to keep the capillary draw of ground moisture well-bounded. In termite country using copper flashing in combination with a poly-foam sill gasket or copper-faced polyethylene sill gasket is recommended.

If the barn roof is low-pitched (under 2:12) or has an E-W ridge with a large span angled toward the sun, at some point a CRRC rated cool-roof coating may be in order. Try to find the aged Solar Reflective Index (SRI) of anything you put up there- over 75 is good, but over 85 is GREAT. (Many will have an inital SRI of over 100, but the solar reflectivity tends to drop with time.) The CRRC rates the reflectivity an emissivity measurement seperately, but they can be plugged into a downloadable spreadsheet calculator (courtesy of the Berkeley National Laboratories) which will cough up the standardized SRI based on those numbers.

See :

http://www.coolroofs.org/index.html

and

http://www.coolmetalroofing.org/elements/downloads/SRIcalc9.xls


I'm already taken- (year-13 anniversary coming up in about a month...)

> If it's bare-galvanized, painting it with almost ANYTHING would reduce the heat gain

Bare galvanized beats dark colors in testing and in cooler climates like Chicago, it's overall better than white.

Posted By jonr on 07 Sep 2010 11:21 PM
> If it's bare-galvanized, painting it with almost ANYTHING would reduce the heat gain

Bare galvanized beats dark colors in testing and in cooler climates like Chicago, it's overall better than white.

With bare galvanized you get low-emissivity on the interior side which helps, but I'd be surprised if it actually beats cool-roof rated whites with SRI's >70 (as opposed to a generic whites) for raw cooling load reduction in the upper midwest.

The low-E interior face of galvanized steel or bare aluminimum probably helps heating season performance measurably on buildings with low levels of insulation too, which may make it a better choice in places with significant heating loads.

You talk about there being a gap between the foam and the interior structure. Personally I don't see the point of that and it would degrade the other insulation. I have not hear a lot of talk about air tightness and air sealing of the living space. If you are going to use cellulose or fiberglass then they will perform better in a sealed system. Foam i done right will create it own sealed system.

If you are using cellulose or foam at the proper levels then you will get a radiant barrier just not a reflective barrier. When it comes to radiant heat the thing to remember is that it travels through air. Fiberglass has lost of larger air pockets than cellulose or foam and the radiant heat will travel through the air pockets. That is why fiberglass is less effective at stopping radiant heat flow.

It is hard to find good info and when it is cost effective to use a radiant barrier. The benefit of a radiant barrier decreases as the quantity if insulation increases. Spend more money on cellulose and foam and you don't need a reflective barrier in most cases.

I am not sold on you using foam on the steel and leaving an air gap. I didn't see any talk of air sealing and making an air tight living space. You are going to have a living space inside a steel building but what else will be inside the steel building. Will there be chemicals, plants, equipment with gas tanks etc. My thought is there will be things stored in the metal building that will degrade indoor air quality. I would plan the living space accordingly.

First off I would start with a very tight shell for the living space. This could be accomplished in a number of ways. For starters I would not insulate the steel structure. Instead I would leave an air space between the steel and the structure. Since there is a gap you don't have to worry about water or vapor drive on an exterior cladding. I think I would build a OSB sheated wall inside the steel wall. Then I would use 1 in of foam as an air sealer. Then I would wet spray the walls with cellulose. For the so called roof I would make sure that there is a continuous air barrier across the ceiling. Make sure the wall to ceiling barrier is continuous. Again 1 inch of spray foam. On top of that I would pile up a ton of cellulose.

Since the living space is being made air tight I would have an ERV and have everything set up so that the living space has a slight positive air pressure. This will keep the polluted air from the steel building from entering the living space.

A couple of other things. Be sure the air ducts are within the envelope. Also be sure that there is a capillary break between the slab and ground, insulate the slab under the the living space.

The gap between the faced iso and the steel siding is to allow the siding to continue a rainscreen function. If you but the foam board up against the steel it can't, with potential to deteriorate the foam board. When using foil-faced iso the radiant-barrier aspects are something of a freebie.

The difference in heat gain between a 120F steel siding and a 100F steel siding (with or without the interior air gap) is considerable, which is why exterior finishes count. But assuming it's a reasonable SRI white paint, you'll still get some benefit from the foil facer on the iso facing the steel siding.

Making foil-faced goods air-tight is also pretty easy, and cheaper than a full overcoat inch of SPF.

Dana

What I read was that he wanted to spray 1in on the steel then have an air gap and insulate the walls with fiberglass.  From a performance stand point that is a horrible set up. Fiber glass is crappy to begin with and then you don't have it enclosed- even worse.

Since the steel frame is up I see some challenges in building a structure inside a building. If you have a stud wall how do you access the side that faces the steel. I know you could tip the walls up but you have to mind your air sealing details.

Since the steel is a the weather barrier the wall could perform much like a rain screen but better with a larger gap. I would pay attnetion to  details making sure  to drain any water from between in the steel and the inside structure. 

I think it is very important is to keep the living space air tight for energy efficiency and air quality. Has the OP stated what will be stored outside the living space?

I think you could skip the spray foam and add more insulation to the wall. Plant some trees to shade the building, like you should do anyway, and you will cut down most of the radiant  heat from the steel.

Option 1 - build a wall with foil face foam and insulate the cavity with cellulose. Seal everything up and pile the cellulose high and deep on top.

Option 2 - build a wall with OSB sheating, spray foam the inside and then fill with cellulose

Option 3 - Spray foam the steel  and fill with cellulose right up against the foam.  No benefit of a rain screen, metal building tend to leak more at the slab level.

Option 4 - a Double wall giving room for extra insulation

 There would be other options too.    Personally I think spray foam or rigid foam is expensive and should be use judiciously.

this gentleman asked about  radiant barriers and it takes a lot of digging to get real information. He should scrap that idea. Learn that foams and cellulose block radiant heat but are not a reflective type barrier. If a reflective surface is one of the properties of a material use it but don't spend extra.


My research on radiant barriers show little benefit.  Reflective barriers work best in a vacuum bottle.  Convection degrades the effect of a radiant barrier and so does dust.  Plus walls have less of a need for a radiant barrier then does a roof.  A radiant barrier does its best when a structure is not well insulated. As the insulation level goes up the need for a radiant barrier goes down. It gets to the point that a radiant barrier is not needed.   The radiant barriers seller will tout the benefits of the product but ignore other insulation and air sealing issues.  The mark up on radiant barriers is phenomenal, in bulk it can be had for $0.15/sf. If you want to make a quick buck sell it.  It you want to solve someone problem look for real solutions.

From what I read, the gentleman is actually a woman (unless TX has gone the way of MA, and he wasn't cluing us in with the husband reference. :-) )

Your recommendations are pretty much along the lines of what I'd already discussed at length, with the exception of wider use of SPF where I'd recommended rigid iso (for stated cost & peformance reasons).

I too had noted that the benefits of radiant barrier are between slim and none on an insulated vertical wall, but if it basically comes at no additional cost on an iso facer, it'll still have a measurable (albeit small) benefit. The performance benefit of the thermal breaking of the studs plus the RB aspect on the steel-siding face make the expense of an inch of rigid iso "worth it"- with far more boost in performance for less cash than any 1" SPF recommendations thrown out there in this thread.

But I''m glad we agree so vehemently! :-)

Option 1 is the best bang for buck- the clear wall R value is higher, and the solar gain lower than 2 & 3, and it costs less than 2-4 (which is why I recommended it)

Option 2 is more expensive than 1, and significantly lower performance due to both thermal bridging at the studs and a lower center-cavity R.

Option 3 is a dog from a cooling season performance POV relative to option 1 & 2 unless using a high SRI exterior paint, at which point it roughly breaks even with #1 on performance, but at higher cost.

Option 4 is ridiculously complex & expensive for the climate zone. In that part of TX you can hit PassiveHouse levels of heating/cooling loads without resorting to double studwalls or Larsen Trusses. But it can deliver the performance, at a cost.

The degradation of vertical or slanted radiant barriers is less than what you might think- even with some dust settling. (And dust won't easily collect on a vertical surface, eh? )

Convection neither hurts nor harms radiant barrier performance in most applications- the same amount of convective heat transfer is the same with or without a radiant barrier in place. In rafter applications where the RB forms the interior side of a soffit-ridge ventilation scheme the slight cooling effect of the ventilation side air movement out the ridge reduces the temp of the RB itself, thus reducing the convective heat transfer to the interior that would have occured between the roof deck and attic space, but that's a secondary benefit.

But to get anything at all of of radiant barrier requires some isolating air space, and a high delta-T. In the configuration we're discussing here the air-gap is small but rather than convecting from the hot siding to the iso-facer, the warmed air in contact with the hot siding convects up and out into the greater barn space, with fairly low convective heat transfer to the aluminum facer. (Actual convective performance depends on just how laminar that air flow is, but high-turbulence it is not.) Whether the delta-Ts are high enough for the aluminum facer to matter depends on just how hot and emissive the interior face of the siding is, but if it's a low SRI exterior paint and a high-E interior on the siding it'll count for quite a bit. The effect on this assembly could be as much as doubling the R-value under the absolute peak siding temp conditions or so inconsequential under any conditions that it's unmeasurable (which would require a high SRI paint on the exterior, with a low-E interior face, both of which are unknowns.) Since foil faced iso comes at lower cost than an SPF solution and at similar cost to going with XPS sheathing for a thermal break on the studs why not take the RB benefit, even if it proves to be next-to-nothing? The only problem with it would be if it created a moisture trap problem by being an exterior vapor barrier, but that issue is easily avoided in this climate.