I was reading on another forum about issues regarding steel thermal bridging on structural materials that overhang from the exterior and transition into the interior. The issue of the steel thermal bridging was one factor but the bigger problem was that a lot of moisture problems were occurring since the cold steel sitting outside thermally bridged to the interior where it hit warm air and condensation occurred. This then will lead to rust, rot, mold, drywall issues, etc.

I know that some recommend cutting the underside of a steel SIP with a saw to thermally break it but that undermines its strength and seems less than desirable. Any other suggestions on how to address this thermal bridging issue when one uses a steel SIP roof with a soffit overhang of 24" ?

Posted By Lbear on 08 Mar 2014 12:15 PM
I was reading on another forum about issues regarding steel thermal bridging on structural materials that overhang from the exterior and transition into the interior. The issue of the steel thermal bridging was one factor but the bigger problem was that a lot of moisture problems were occurring since the cold steel sitting outside thermally bridged to the interior where it hit warm air and condensation occurred. This then will lead to rust, rot, mold, drywall issues, etc.

I know that some recommend cutting the underside of a steel SIP with a saw to thermally break it but that undermines its strength and seems less than desirable. Any other suggestions on how to address this thermal bridging issue when one uses a steel SIP roof with a soffit overhang of 24" ?

Peter,
please site a link for the issue, my guess is it is not about SIPs , but rather a steel frame building
I would maintain that the saw cut has little affect on the integrity of the overhang for downward pressure or up lift

By adding soffit framing one can compensate for saw cutting the panel as you can see in this prototype meal SIP detail. One also needs to have a thermally broken top channel.

Posted By cmkavala on 08 Mar 2014 03:43 PM

please site a link for the issue, my guess is it is not about SIPs , but rather a steel frame building
I would maintain that the saw cut has little affect on the integrity of the overhang for downward pressure or up lift

Chris,

They were discussing steel beams but wouldn't that apply to any steel structure that transitions from the outside to the inside without a thermal break?

GBA

Posted By Lbear on 08 Mar 2014 10:33 PM

Posted By cmkavala on 08 Mar 2014 03:43 PM

please site a link for the issue, my guess is it is not about SIPs , but rather a steel frame building
I would maintain that the saw cut has little affect on the integrity of the overhang for downward pressure or up lift

Chris,

They were discussing steel beams but wouldn't that apply to any steel structure that transitions from the outside to the inside without a thermal break?

GBA

Peter,
I read the thread , the original poster says nothing about SIPs, or rust, rot and damage?
albeit not the best thermal construction technique, as you say this is not about SIPs , but about steel beams
BUT..........keep in mind that there is a reason that steel SIPs are globally used commercially in cold storage warehouses, it is beacause they offer the most durable, cost efficient product available and because of the extreme interior/exterior temperature differences, manufacturers have developed effective thermal break details.
when the SIPs are used in a residential application they rarely see the extremes that are seen in commercial use and with most steel SIP residential construction in the southeast US, thermal transfer is of little concern , in that the temperature difference is usually only 20 degrees, it is not an issue.
Having been involved with steel SIP construction for the last 20 years in projects from Florida as far west as Texas as far north as North Carolina and Northwest as far as Missouri, I have never once heard of a thermal issue complaint.

Hmmmmmmmmm........My first SIP job of any type was a freestanding metal SIP office built(interior temp.72 degrees) inside the Tropicana twister distribution warehouse kept at a constant 33 degeees in Bradenton, Florida.

Posted By JeffD on 08 Mar 2014 09:25 PM

I would be curious to see some thermal readings on the interior portion on a 30F outdoor night. The exterior thermal shot on the overhang would show a 30F surface temperature on the bottom side of the SIP but what would the temperature be on interior ceiling portion of that SIP right at the wall transition point?

On a non-overhang condition, thermal bridging wouldn't be a problem.

It would be interesting to see thermal shots/readings for the above.

Posted By Lbear on 10 Mar 2014 04:07 AM

Posted By JeffD on 08 Mar 2014 09:25 PM

I would be curious to see some thermal readings on the interior portion on a 30F outdoor night. The exterior thermal shot on the overhang would show a 30F surface temperature on the bottom side of the SIP but what would the temperature be on interior ceiling portion of that SIP right at the wall transition point?

On a non-overhang condition, thermal bridging wouldn't be a problem.

It would be interesting to see thermal shots/readings for the above.

Peter,
Yes I would like to see that too on OSB, solid wood is also a thermal conductor that already has moisture content, in thermal imaging you can see every stud in a wall because of it.
Everything has thermal conductivity, but a proper thermally broken metal SIP system can be reduced to .03 conductivity.

Lbear,
Fibercement, OSB and steel

Posted By cmkavala on 10 Mar 2014 08:22 AM
Lbear,
Fibercement, OSB and steel

Chris,

What were the parameters of this test?

I assume it was a direct sunlight test using a laser thermal gun to read surface temperatures. What were the ambient temps outside and how long did the panels sit in the direct sunlight?

It is interesting to see that the OSB was the hotter surface temperature which seems counterintuitive since metal is a heat sink, especially in direct sunlight. Although the white color on the steel panel reflects a lot of the direct sunlight.

I just did a quick test of my own:

83F Outside Temperature
Sunny - Phoenix, AZ - 900 feet elevation
Noon - 3PM full sun exposure
Thermal Laser Gun showed Steel SIP surface temperature of 125F - 130F

Posted By Lbear on 10 Mar 2014 04:53 PM

Posted By cmkavala on 10 Mar 2014 08:22 AM
Lbear,
Fibercement, OSB and steel

Chris,

What were the parameters of this test?

I assume it was a direct sunlight test using a laser thermal gun to read surface temperatures. What were the ambient temps outside and how long did the panels sit in the direct sunlight?

It is interesting to see that the OSB was the hotter surface temperature which seems counterintuitive since metal is a heat sink, especially in direct sunlight. Although the white color on the steel panel reflects a lot of the direct sunlight.

,Lbear,
Not really, the white is reflecting the heat , while the OSB an fibercement are both darker and porous and absorb heat
I did this 6 years ago and don't remember all the paramaters , but I believe it was in June and probably about 85 degrees, I am guessing they were all exposed for about an hour