Exposed Steel and Condensation 2

[JAE]

This isn't directly a structural question but it involves the use of exposed structural elements in cold climates.

I have a book by Charles Thorton called "Exposed Structure in Building Design" that discusses many buildings in which the structural elements were exposed to view, and to the outdoors.

Very interesting topics with lots of examples - and most of the discussion revoled around the thermal issues of taller buildings...i.e. the exposed beams or columns would create thermal stresses and structural deflections if not carefully considered.

All well and good.

However, I've been working on a number of projects over the last several years where structure was extended from inside the building to the outside.

This concerns me due to the colder climate that they are in - where the elements would begin to cool and the big fear is that the interior warmer, moister air might condense on them and cause water problems inside.

Is this a real concern? How do you detail or handle the concern? I've got some architects wanting to do this more often and I'd appreciate any knowledge on this as well as any links to resources.

 

[Lion06]

JAE-
We do this quite often. We detail a thermal break at the curtain wall. It is basically an end plate moment connection with a korolath pad between the two end plates. This will serve as the "thermal break" to keep that cold air from outside the building from causing condensation on the inside.
The amount of condensation can be significant.

 

[JAE]

How thick is the pad? It's not the air movement I'm worried about - it is the thermal tie between inside and
outside.

I would think that even with a pad of some kind, there would be heat transfer between them.

I see this done all the time so I think the condensation only can occur if the inside air is very moist.

 

[Lion06]

I designed a few of these for the last building I did. I will check the detail when I get in the office, but I believe it was 1/8" - just enough to break the steel-to-steel connection. The pad may not block 100% of the heat transfer, but it does the job well enough to stop the condensation.
I don't think the air needs to be overly moist for condensation to occur. Even moderate humidity will cause the condensation. With no thermal break, and an outside structure subjected to 15-30 degree weather will cause significant cooling of the warmer air around the beam inside the building and cause condensation.
I am not sure what the coresponding relative humidity would be, but I would think that a dew point even of 50 degrees inside the building would easily cause condensation if exposed to 30 degree steel for an extended time.

 

[Lion06]

Yes, it was a 1/8" korolath plate between the end plates.

 

[lkjh345]

StructuralEIT: Quite a clever solution. Have come to this problem before, but didn't have a good solution for it. Your solution makes a lot of sense.

 

[drscottuk]

Does anyone know if there is any recognised insulation method for insulating steel against condensation which extends out of a structure and cannot be split with a korolath plate, for example:

a steel frame swimming pool where humidity is high inside and the overhead roof beams extend out past the side walls to form part of a large architectural overhang?

 

[Lion06]

Is there a reason you could not use the korolath plate? The end plates are a moment connection. Size the connection for your required moment.

 

[csd72]

This is also an issue for structures over interior swimming pools, you may want to direct your research in that direction.

Do you have any upturned lips on purlins, channels e.t.c. that may also catch the condensation?

csd