This is a question for Chris (or anyone familiar with metal SIPs) in regards to SIPs, specifically metal SIPs. An OSB SIP is somewhat vapor permeable due to the OSB. The thickness of the EPS will determine the exact rate but for this example; OSB, plus 5" of Type 1 EPS, OSB = 0.33 perms.

Joseph Lstiburek, PE stated the following in his book about SIPs: (pages 111-113) PDF

"What about all those sheet metal faced SIPs? Well, they are always somewhat of a risk as they rely on "perfect" joints and no penetrations since they can never "dry" outwards or inwards. They are pretty good for freezers if you don't preforate them with holes - so they would be a dumb idea as an exterior wall system with cladding attached with screws, but would be a pretty good idea if they were painted or had a direct applied stucco system."


What I gather from Joseph is that he is stating a metal SIP, unlike an OSB SIP, cannot dry outwards and of course inwards. Once penetrations are made in a metal SIP via screws on either the interior (drywall, furring strips, etc) or exterior (roofing, vinyl siding, etc), the SIP is somewhat compromised. At least that is what I gather from his statement.

A metal SIP cannot rot but it still can retain water and if that water/moisture can never dry, what happens to the SIP? Will it eventually delaminate or begin to rust?

I've also read that peel & stick membranes are used on metal SIP roofs. Joe was also quite apposed to that but it was due to preventing an OSB SIP from drying outwards. With a metal SIP, it's sort of a moot point, since it cannot dry outwards due to the metal skin preventing any permeability of vapor.

With wood SIPs, the vapor/water problem always will present itself because the wood will rot and the SIP will delaminate. With 26 gauge steel SIPs, it will not rot but can it still delaminate?

Posted By Lbear on 19 Jul 2013 11:29 PM
This is a question for Chris (or anyone familiar with metal SIPs) in regards to SIPs, specifically metal SIPs. An OSB SIP is somewhat vapor permeable due to the OSB. The thickness of the EPS will determine the exact rate but for this example; OSB, plus 5" of Type 1 EPS, OSB = 0.33 perms.

Joseph Lstiburek, PE stated the following in his book about SIPs: (pages 111-113) PDF

"What about all those sheet metal faced SIPs? Well, they are always somewhat of a risk as they rely on "perfect" joints and no penetrations since they can never "dry" outwards or inwards. They are pretty good for freezers if you don't preforate them with holes - so they would be a dumb idea as an exterior wall system with cladding attached with screws, but would be a pretty good idea if they were painted or had a direct applied stucco system."


What I gather from Joseph is that he is stating a metal SIP, unlike an OSB SIP, cannot dry outwards and of course inwards. Once penetrations are made in a metal SIP via screws on either the interior (drywall, furring strips, etc) or exterior (roofing, vinyl siding, etc), the SIP is somewhat compromised. At least that is what I gather from his statement.

A metal SIP cannot rot but it still can retain water and if that water/moisture can never dry, what happens to the SIP? Will it eventually delaminate or begin to rust?

I've also read that peel & stick membranes are used on metal SIP roofs. Joe was also quite apposed to that but it was due to preventing an OSB SIP from drying outwards. With a metal SIP, it's sort of a moot point, since it cannot dry outwards due to the metal skin preventing any permeability of vapor.

With wood SIPs, the vapor/water problem always will present itself because the wood will rot and the SIP will delaminate. With 26 gauge steel SIPs, it will not rot but can it still delaminate?

Lbear, I am aware of Joe's comments in the book and have personally met Joe and participated in his CED course "How to Build in Hot Humid Climates", I beleive he is referring to metal faced OSB SIPs, it would be problematic to seal in wood

soley Metal skin (both sides) do originate from the cold storage industry, this industrial application is the most harsh /obusive proving ground for the product, with many penetrations and the most extreme interior/ exterior temperature differences, if they did not perform , they simply would not be used, there is a reason why OSB is not used in cold storage applications,
the steel skin SIPs that we used have a USDA approved paint finish, approved for food processing applications, if they were rusting they simply would not be allowed.

Lbear,
the manufacturer has never done vapor perm tests , because it is pretty much understood they are impermeable, but the have done impact and wind/ water penetration tests (sent to you in private email) for the Florida Department of Education.
You will see there is no penetration even after test walls were impacted with projectiles

sorry for the poor quality, had to compress enough to post, the emailed copies are much clearer

I beleive he is referring to metal faced OSB SIPs

Sounds to me like Joe is referring to plain sheet steel and foam SIPs. But if he doesn't have more details than "dumb idea", I'd look at real experience vs what he says. His use of "would" suggests to me that he doesn't have much actual experience with exterior wall steel SIPs, so it may be an "arm chair experiment".

I do agree that steel SIPs see huge temp differences between inside and outside. I assume -20F inside and sometimes 90F outside temps are common.

So that supposed issue of steel thermal contraction rates and delamination is false. It was brought up that if the steel SIP is constantly fluctuated between temperatures, eventually due to the expansion and contraction rates of metal, the SIP would lose adhesion to the EPS over time.

So basically a steel SIP has zero vapor permeability, correct? With the exception being at the SIP connection areas, correct? Those being dependent on how well they are detailed to prevent air flow.

If a roof projection is made for a plumbing stack, how does that not create a thermal path for vapor condensation? The hole is always wider than the stack and even though it might be made "water tight" at the roof, there is always a gap and missing insulation which creates a cold spot in winter for condensation to form.

Posted By Lbear on 20 Jul 2013 07:22 PM
I do agree that steel SIPs see huge temp differences between inside and outside. I assume -20F inside and sometimes 90F outside temps are common.

So that supposed issue of steel thermal contraction rates and delamination is false. It was brought up that if the steel SIP is constantly fluctuated between temperatures, eventually due to the expansion and contraction rates of metal, the SIP would lose adhesion to the EPS over time.

the expansion is not as great as you think, steel expands and contracts about the same as concrete
interior temps are always constant, exterior temps will vary, I have never heard of loss of adhesion over time, have you?
I certainly would not have built my home with metal SIPs if I ever thought that,
short memories: on several occasions I have posted accelerated aging tests, the tests show panels going thru Fifteen- freeze minus 70 degrees for 8 hours / oven heated to 160 for 48 hours / submerged in water for 48 hours / placed in environmental chamber at 101 degrees and 100% humidity for 64 hours cycles, panels and adhesion are absolutely unaffected , the other panels unfortunately cannot make it past one cycle.
Life expectancy 300 plus years

Posted By Lbear on 20 Jul 2013 07:26 PM
So basically a steel SIP has zero vapor permeability, correct? With the exception being at the SIP connection areas, correct? Those being dependent on how well they are detailed to prevent air flow.

If a roof projection is made for a plumbing stack, how does that not create a thermal path for vapor condensation? The hole is always wider than the stack and even though it might be made "water tight" at the roof, there is always a gap and missing insulation which creates a cold spot in winter for condensation to form.

zero

we always foam around the stack and tape the joints, there is not much getting in or out