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Modelling of Exposed Slab Edge in OpenStudio

asked 2018-09-13 14:32:31 -0500

jfine gravatar image

updated 2018-09-13 18:45:22 -0500


I am trying to model a building that has exposed concrete slab edges for each floor in the building. There are also balconies, which are a continuation of the concrete floor slab and act as fins for heat loss/gain.

When creating the construction of the interior floors of the building, I include the 6" concerete material layer, but it appears that the exterior walls fully encompass these floors and the slab does not penetrate through the wall. I have also tried to create a separte space, which represents the 6" slab and penetrates through the wall, but Im not certain this is the best pratice.

If you have any recommendations, they would be greatly appreciated!


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answered 2018-09-14 06:42:47 -0500

The Building Envelope Thermal Bridging Guide from BC Hydro provides a method for dealing with exposed slab edges and balconies, among other things like roof parapets, etc. The guide itself explains the approach and appendices A and B are where the detailed information is provided for the different architectural components.

Basically, you end up accounting for the thermal bridges (exposed slab edges, etc.) by derating the thickness of the insulation layer of the exterior wall construction to create the effective assembly U-value.

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Thanks for the tip!

I forgot to mention that using a modified wall resistance, calculated outside of openstudio, was another method I had considered. I wasn't sure if this method was appropriate for this software because I thought that the modified floor temperature near the edge could potentially be accounted for.

jfine gravatar imagejfine ( 2018-09-14 06:59:17 -0500 )edit

That's true. The approach I suggested won't account for the modified floor temperature near the edge. Did you try to model more than one wall for each exterior exposure with a 6" tall wall and then the remaining wall height and assign the appropriate constructions to them? This could be done in SketchUp to make the slab wall type align with the floor.

Are you hoping to account for the thermal comfort impacts of the modified floor temperature? Otherwise, the approach I mentioned seems easier and should be roughly equivalent from a thermodynamic point of view.

anchapin gravatar imageanchapin ( 2018-09-14 07:34:14 -0500 )edit

When I did try the separate geometries, I created a space to represent the thickness of the slab underneath the unit. However, I didn't finish the entire model, and at first glance it didn't appear to look quite right in the settings.

It would have been preferable to be able to model the comfort, but with the whole-building model, I dont think its necessary. I think im going to stick with the modified wall resistance method from that report, which seems to be the norm for openstudio based on my research.

Thanks again for your help!

jfine gravatar imagejfine ( 2018-09-15 08:02:25 -0500 )edit

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Asked: 2018-09-13 14:32:31 -0500

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Last updated: Sep 14