Forums >> Revit Building >> Technical Support >> Building external walls single skin, or double?

whatuser

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Joined: Thu, May 31, 2012
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Hey guys,

I have a question about building external walls for a multi-level apartment building, and best practice.

I know this question comes up quite often, but I still am unsure about whether there really is a best practice method for this.

Over the past few years, I have worked on a number of different multi level residential buildings, and each one has been set up differently in terms of external walls, from single wall-type per floor, two separate skins per floor (external finish + structure and internal finish), to two skins (structure and internal finish per floor) + (external finish ground to top). 

Each one has advantages and disadvantages. On one hand, having a single wall external wall means you don't have to worry about moving things twice, its easy to tag and quantify, on the other hand if you use curtain wall windows, you end up having to build your reveals into the window/panel as the walls will not wrap on both sides, or you end up with issues where you have mullions breaking the wall into two.

I generally like using a single wall, and having as few pieces as possible, however, I also believe in modeling things the way they would be built in the real world. So, if I was going to do that, I would actually build the external wall as two separate skins, the external finish as one part, and the structure and internal finish as the other. This method is great because you can define your internal spaces to the internal wall parts, and don't have to worry as much about them moving. Also if the external finish changes, or the slab edge moves, the walls and spaces aren't affected as much, but you have to remember to move both walls if something changes, your windows and doors do not automatically cut both skins unless you join them, so you see both have positives and negatives.

I know a lot of structural engineers prefer working with a separate structural buildup, but I am curious about how everyone else works??

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WWHub

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If I understand you correctly - and that is hard to do as you wrote this, I don't see any reasons for dual walls while only considering the exterior.  And that wall is full height.   But if you are using walls to quantify interior finishes that change from room to room, then I might consider thin walls for the interior.

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whatuser

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WWHub, let me try and clarify my question, as I am not quite sure what you mean by "only considering the exterior and that wall is full height".

In the real world, if you are using a framed steel system similar to metsec on a multistory residential building, the external wall would essentially be built by setting up your metal frame, then adding your internal buildup so that people can work on the units, and then eventually adding your external cladding as the building moves forward.  The detail would look something similar to this

http://www.metsec.com/images/steel-framing/external-finish-insulated-render-build-up.jpg

Drawing this up in Revit as a single wall is fine if you are using traditional windows and doors, and your wall thickness does not change. However if instead of a traditional window, you have a framed panel that is divided into opening sections, solid panels, or louvers, all surrounded by a frame of mullions, then you start running into problems. Take the example below. 

In elevation the juliette balcony, the fixed panel, and the solid panel next to them are all surrounded by a frame of mullions and transoms. In plan, this is all fine, except I do not want to see the solid panel from the inside of the apartment (plan1).  If I use a single external wall, and insert my curtain wall "bay" (for lack of a better term), then the mullion creates a break between the solid panel and the wall (plan2), if I use two walls, I can have my inner wall run all the way to the fixed panel, and avoid having the break (plan3).

I know there are a million ways to build this "bay" so that it might work a bit better, but this is just 1 issue. As I tried to explain in my previous post. Defining a room, and an area is an other issue. 

Anyone working on highrise residential projects knows how often internal and external layouts change. If using a single wall type, the slab edge moves out a couple of feet and the wall follows it, then this would result in an error of the room/area not being enclosed properly. If on the other hand you have separated the internal and external halves, then if the team working on the facade moves the external wall, it doesn't immedietly affect the teams working on the internal layouts..

Again, on one hand I prefer having less items, rather than more, and as such like having my external wall as a single wall type. But I also like having a realistic model, so by that rational, the extenal wall of a framed system is essentially built as two separate elements, an external finish, attached to a steel frame with the internal finish (and insulation etc).

I don't know if this has clarified anything, its kind of long and convoluted, but hopefully someone can make some sense out of it.

Thanks.

Attached Images

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WWHub

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Joined: Tue, May 16, 2006
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Your question is very complicated and the images do help.   But really this is several questions.

Question A:  Double or not double walls.

If you use double walls and a normal embedded curtain wall, then the CW will cut both walls and the interior wall can not be pulled past that panel on the right like you did.  I would assume that you do want to join these walls so that the heavy outside wall line goes away between the two walls. See first image.

So - What are your options? 

• I might do something like the second image.  Here you can use either two walls or one wall.  The CW is set to not automatically embed so now we need to cut the opening.   I did so with a stepped opening that is parametric with some instance and some type variables.
• Look at the 3rd image.  Here I added a small fill in wall that has the end joins turned off.  The problem here is the 'joint' at the end of that wall.

Attached Images

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Double-Skin Facade as a "Curtain System" on a "Mass".

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Master Spec and Double Skin walls

0

Complex External Wall Modeling - Urgent Help Needed

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Double Skin facade with folding shutters

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Dividing an external wall into different parts per floor

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