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Exposed structure transferring heat/cold

Nov 1 '12 5 Last Comment
Thecyclist
Nov 1, 12 1:01 pm

I've been told when designing a building, to not allow structural elements (floor slabs, columns, etc.) to be exposed to outside temperatures because there is the potential for the transfer of heat.  

Is this truly an issue?  The concept sounds correct, however, can enough heat/cold transfer to cause the interior to become uncomfortably cold or warm?  It seems a bit of a stretch.

I know the Boston City Hall has massive rectangular concrete columns coming down to meet the public space below, and countless other buildings have the same situation.

 

jla-x
Nov 1, 12 1:25 pm

first off there is nothing such cold transfer.  Cold is just the absense of heat.  It all depends on the local climate, the type of materials, the type of heat  it is being exposed to (direct radiant heat from sun).  there are alot of factors, but anytime a material is a bridge between 2 different temps, heat transfer will occur.  The rates and degree of transfer depend on the materials emmisivity, thermal mass, the temp difference, the surface area exposed, the volume of the interior space...  There are alot of factors

gwharton
Nov 1, 12 1:30 pm

Many jurisdictions won't allow you to expose steel or concrete structure unless you put a thermal break behind it (which is great for controlling heat loss, but not so great for structural continuity). I know the Washington State Energy Code requires this in most cases. You can get around it by doing a performance-based analysis of the entire envelope, but it's a pain in the butt.

jla-x
Nov 1, 12 1:30 pm

to add... in a  space with a huge interior volume and a high mass low emmisivity material like concrete it will probably not be such a big factor.  A small space with steel collumns that bridge between inside and out in a hot arid climate will probably be an issue.

accesskb
Nov 2, 12 1:14 am

depends where you build.. In cold climates, there is always insulation.  Even when using concrete, rigid insulation is sandwiched between concrete slabs.  For metals, you need to create thermal breaks.

IamGray
Nov 2, 12 8:34 am

As others have said, it of course depends on the region, but yes in northern North America and Europe (and similar wintery climates), any thermal bridges, which allow heat to escape (or as many people colloquially say, "letting the cold in"), are to be avoided. If you look at the detail sections, you'll see various ways of getting around this. Usually it's pretty straight-forward stuff, ie.  simply cutting a "break" and stuffing in a layer of poly or similar. Where it gets interesting is when the illusion is to have a monolithic piece of concrete extending from interior to exterior, like the Educatorium:

Even if it isn't as "true" as it appears to the eye, I still have to wonder if  such a construction would be do-able in a climate like Canada's, for example. I certainly have my doubts.

As for the Boston city hall example, I speculate that either:

a) there are some strategic thermal breaks or insulation

b) it was (like many of it's Modernist and Brutalist contemporaries) built in the 60's and nobody gave a ****. Obviously attitudes, practices, and legislation have changed since then.

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