insulation, condensation, and non-wood walls

I posted specifically about rice hulls and specifically about metal walls to get no responses so I figured i'd widen things...

If you had some corrugated metal walls or roofing on an A-frame house, how would YOU personally insulate it?  Does the tendency of metal to get condensation make you change what you'd use over a wooden wall?

Or if it wasnt metal, maybe its rock or even concrete... as far as I know concrete also tends to have moisture issues or wick or something, based on how basements tend to get damp and moldy...  are there any special practices used to insulate things which tend to have condensation inside the wall and outside your insulation?

I'd originally mentioned wanting to stick up styrofoam panels inside aluminum walls of a semi truck or sealand container and some other people thought that was a bad idea...  well i'm open to good ideas.    What would YOU do?



I'd mentioned rice hulls cuz i've heard of it being used in earthbags as moisture resistant and wondered if it would be resistant enough to handle condensation...  i'm not fixated on it, it's just one option.  I'd prefer to stick to lighter insulation - i'm sure perlite would be permanently water resistant but also be a pretty heavy wall infill I mean...

Hey Brian. Don't panic. I have also noticed that just about everybody has disappeared from the forum. Either they have been abducted by aliens, or they are out in the fields planting their brains out. I'm betting on the latter.

Hi Brian, from my understanding there are several down sides to metal in general. One is the condensation issue. If the metal is a different temp than the outdoor/indoor air, condensation can form and that in contact with foam insulation can cause mold if not dried out properly. I have heard that this is an issue with Barndominiums. The second issue is with EMF (electro-magnetic) issues. Some people who are sensitive to electrical would prefer not to be in a metal building where it could somehow have current flowing through it if not properly grounded. However, some people who are electrically sensitive actually do really well in metal buildings (because it can block certain waves). So the primary issue is the condensation issue.

Have you ever considered Nexcem or Faswall bricks. I am actually designing my house right now with an architect named George Swanson, who has a book called "Breathing Walls". He has been discussed in other posts on this forum. These blocks are a type of concrete form that are essentially blocks made up of fossilized wood and concrete and then in the middle you have Rockwool insulation and then you fill it with concrete and reinforce with rebar. This can be a DIY friendly material and has the added benefit of a high-R Value along with being "Breathable". This tends to help greatly with mold issues especially. Also for interior walls you may consider magnesium oxide board instead of traditional drywall, also for mold prevention and a better material.

Happy to discuss more if any of this is of interest to you.

Yup, springtime!

There are a couple ways I would consider doing it, depending on climate and budget/availability

I am building in Tennessee, so mild winters but humid summers. I plan to use low-e or reflected.  A roll out insulation and vapor barrier between the framing and metal. It is enough to stop most condensation and thermal bridging. Then I will use rock wool because it is more mold resistant than fiberglass. There will be venting between the metal and low e.

If I were in a colder climate, I would use spray foam. It’s the cheapest way to get HIGH R values when built planning for it. It is a little gicky but all commercial insulation is and spray foam is probably the lowest embodied energy. There is a ton of diesel wasted moving around bulky insulation.

While its not specifically for dealing with condensation, building a "rain screen"  prevents moisture from reaching  the insulation and offer a way for it to dry out if it somehow reaches it anyway.
It decouple the siding from the moisture barrier via furring strips.

I think there are two approaches and I did them both on my greenhouse.  

Condensation is less likely to occur if humid interior air can't reach the underside of the metal.  So having good insulation PLUS continuous air sealing helps  to prevent humid air from weeping into the insulation to contact the metal.  A less permie way would be to apply a thick and continuous layer of spray foam against the metal.

Having a space between the metal and the insulation along with a water proof layer against the insulation to let any condensation drip out of the system instead of into the wall.  Like what William said.

Hi Brian,
Even more so, as someone with a mold sensitivity, I will never again remodel or build something that does not breath. If you allow the moisture to come and go and move around, with materials that will not be affected, then condensation is not an issue.

Ryan Mahoney wrote:Hi Brian, from my understanding there are several down sides to metal in general. One is the condensation issue. If the metal is a different temp than the outdoor/indoor air, condensation can form and that in contact with foam insulation can cause mold if not dried out properly.

Well two examples of possible mitigation...  one, say I wanted to use the styrofoam, if i 'glued' the surface of the styrofoam to the metal so that there was no gap so assumedly no condensation to form on the inside of the metal (but outside the styrofoam, because there is no 'outside' just a seamless contact).  I mean how could it condense inside?  Just like spray on foam it shouldn't condense between the two layers.  As to why not spray foam the full thickness, the sheet styrofoam used is so much cheaper...

A second was... what I posted in the original, was ricehulls.  Or for purpose of discussion lets say something like lava rock, vermiculite, or perlite.  My understanding of the problem with normal fiberglass touching metal/wood there's no 'gap' but the fiberglass itself being permeable to air, would have a temperature differential across the thickness, and if it crosses the dew point of the trapped air there will be condensation there.  (this is assumedly why people can see matted up black molded fiberglass batts at times in the walls)  But ricehulls and those aereated rock types are either resistant to mold or wont be damaged by mold, meaning if sealed up inside an envelope and internal mold developed - it doesn't damage the insulation (like it would fiberglass and some other types).

Ryan Mahoney wrote:
George Swanson, who has a book called "Breathing Walls"

I will look into that book...

My biggest challenge is trying to do things on a low budget.  I mean i'm assuming the two ways to try build a wall are either breathing letting it dry out, or totally encapsulated with insulation which doesn't degrade due to internal humidity trapped inside.  And some walls (like metal) will never breathe...  Is there a third way?

William Bronson wrote: While its not specifically for dealing with condensation, building a "rain screen"  prevents moisture from reaching  the insulation and offer a way for it to dry out if it somehow reaches it anyway.
It decouple the siding from the moisture barrier via furring strips.

My ears are perked.  How does this work exactly, like a vapor barrier between the metal and insulation (even if metal is already a vapor barrier of sorts), and you'd dry out the backside how exactly?

Could this work somehow with my proposed metal and styrofoam I mean without having it degrade to mold behind there.. maybe it's like how a frost free freezer keeps things from frosting up...  but here I just have to pump heated air behind the wall to dry things out periodically or somethin..

Mike Haasl wrote:
Having a space between the metal and the insulation along with a water proof layer against the insulation to let any condensation drip out of the system instead of into the wall.  Like what William said.

Yes this is the part I dont fully understand how it would work, how much space would it need, is it something freestanding like an air space on either side so the condensation stays on the vapor barrier instead of what either side touches then?

A rainscreen is exactly what I would use.. but this does complicate the assembly. And it implies that the metal is not the whole of the wall..

Starting from the outside, in my climate, you might have, for example:

Steel siding
Rainscreen (just battens to create an air gap. Vented to the outside top and bottom.
(Air barrier to prevent windwashing ext insul?)
(Optional external insulation?)
Air barrier
Sheathing
Insulation/studs
Air barrier/Vapour retarder/Interior wall



In practice, for farm buildings, that is not happening.

For a shed roof, steel over underlayment over plywood is fine for me. Occasionally a drip or two inside if there is snow on the roof and things suddenly get warm.. but night and day vs steel on purlins..



Sprayfoam directly onto steel is popular inside seacans.. gross but it works.

*IF* your foam is closed cell and you seal all the gaps well, it should work ok. No air on the steel, no condensation..

Yes, I'll say it a different way but D is spot on.

The metal is a sheathing or siding, not the structure of the wall (typically).  You build a stud wall, insulate it, put a moisture barrier on the inside to keep humid air out of it and put a vapor barrier on the outside to keep air from washing (removing) the heat from the insulation.  Over top of that you add 1/2-1" battens and attach the metal to them.  That air gap is vented at the top and bottom so it should be full of exterior air that's a bit warmer than ambient due to the warmth of the building.  When condensation forms, it can run down the metal.  If it gets on the housewrap, no biggie since it's waterproof.  Just need to make sure it can get out at the bottom without weeping in under the bottom of the wall.

I hope that clears it up, if not, keep the questions coming!

I live in a van. That flocked (‘92 GMC conversion) or felted (‘94 Ford conversion) material that lines the interior absorbs all condensation. I think the volume and surface area helps, too but that material is a godsend.

google perfect wall construction.  The wall is vented top and bottom with an air gap then some combination of insulation and air blocking layer to control vapor permeability.

Firstly, do not use metal if at all possible. Secondly,  do not use spray foam if at all possible. A better design from the outset will mean more natural materials.

However, if metal is your choice then what you want is what we call a cold roof or a cold wall. It is simply a void of some kind that allows air to pass between the metal and the structure behind it.

Max Stadnyk wrote:Firstly, do not use metal if at all possible. Secondly,  do not use spray foam if at all possible. A better design from the outset will mean more natural materials.

However, if metal is your choice then what you want is what we call a cold roof or a cold wall. It is simply a void of some kind that allows air to pass between the metal and the structure behind it.

Why not spray foam?  Does something already insulated by spray foam like a reefer sealand container or trailer have the same negatives? (since to me it seemed a faster way to the goal)

I'm still seeing benefits to use metal for cost, durability, and faraday cage effects. (no i dont plan wifi inside reflected back in, i want to keep things like neighboring cell tower radiation out)  It's not meant to be a 'forever' house, it's meant to be something to get by like most manufactured and mobile home type housing, except it's not a mobile home built by someone else.  It's just like i'd really like to do screw piles - but I may not to on the first house.  Such is what it is.

The idea of using air gaps to allow things to dry out makes sense though when I glance at excerpts from that book - it will probably make me have to rethink some things.  If I were just adding corrugated iron sheathing ie africa style roofing I could make standoffs and such and i'd probably do so. (if I build things as an A-frame)  But if metal was the outside wall like on a sealand container though I still was unsure if an inner moisture barrier inside that cold condensing metal wall wouldn't just create a pool at the bottom that gets wet first if the metal is seamless though.  If I HAD to upinsulate an existing metal box, i'm still trying to figure out the best practice for that situation...  because that may end up being my best 'temporary' house solution for a few years.