topic Re: gbXML - understanding building elements in Revit MEP Forum

gbXML - understanding building elements

Anonymous — Fri, 02 Oct 2015 08:33:04 GMT

Hi,

I drawn my own model to make sure everything is perfectly allined and connected. However when I export I can see that all spaces have ceiling as floor but 2 spaces have ceiling which is called ceiling. I have rooms below and above as this is middle level.

1. I am trying to understand where is explanation to each surface type?

2. what is difference between floor and ceiling?

3. can I somehow change this ceiling to floor?

Re: gbXML - understanding building elements

Zsolt.Varga — Mon, 23 Nov 2015 13:00:51 GMT

Hi Mdengusiak,

I understand you have ceilings drawn both as ceiling elements and floor elements in your Revit project.

To your questions 1. and 2.:

1. I am trying to understand where is explanation to each surface type?

2. what is difference between floor and ceiling?

Differences in reality and in the architectural model:

Floor elements in Revit were meant to represent the construction dividing building levels, ceilings are rather constructions of the interior design, such as compound ceilings for example hanging from a load-bearing floor above them. Floors tend to have load-bearing functions while ceilings are more often constructed in order to hide unaesthetic building elements such as mechanical equipments above head. Mostly they cannot bear any other weight but their own and probably some integrated leightweight fixtures such as lighting fixtures etc.

Revit has different properties and parameters for these 2 kind of building objects - so it handles them in different categories and system families.

You can read more about them in the Revit Help menu here:

About Ceilings
http://help.autodesk.com/cloudhelp/2015/ENU/Revit-Model/files/GUID-15615B41-B1B2-4B72-86CA-3ECF8729A730.htm

Floors
http://help.autodesk.com/cloudhelp/2015/ENU/Revit-Model/files/GUID-8099AC26-F02D-4C9A-9209-AAD95A10D119.htm

Differences in the gbXML analytical model:

The gbXML analytical model is based around the definition of rooms which are superimposed on the underlying Revit architectural model. Any gbXML subsequently generated is based on the analytical model only and not on the underlying Revit architectural model.

Rooms are identified based on bounding elements such as walls, floors, roofs, and ceilings. The gbXML data exported from Revit is based mainly on rooms and their bounding elements. The DesignBuilder gbXML import mechanism identifies and converts these rooms into blocks and zones. Other building components like doors, windows and shading surfaces are created automatically as well.

In the case, you describe, you probably have set some ceilings as room bounding so the analytical model doesn´t recognize the "real" room bounding floor above those ceilings. Make sure to uncheck the parameter "Room bounding" for the ceilings.

You find detailed information about the gbXML model and it´s surfaces here:

file:///E:/01_Downloads/Training/db_revit_tutorial_v1_185.pdf

To your question no. 3. - can I somehow change this ceiling to floor?

You cannot change a ceiling to a floor by one click, but you can use it´s geometry to recreate the floor from the ceiling in case the floor is actually missing. You probably won´t need it once you have corrected the ceilings in the architectural model setting them as non-room-bounding, but in case you happen to need to use ceiling geometry to create floor:

Go to Ribbon > Architecture > Build > Floor
Specify properties of your floor as you wish
Define floor geometry by using "Pick Lines" of the existing ceiling´s boundary
Finish Edit mode
Delete ceiling

I hope you´ve found this information helpful. Please, mark it as a solution if it answers your questions.

Thanks.

Regards,

Re: gbXML - understanding building elements

Anonymous — Mon, 23 Nov 2015 13:30:03 GMT

@Zsolt Varga

Hi Thanks for your message. I think my problem is a bit more complicated so aswer does not deal with core issue.I draw model myself as architect model was not acceptable quality.

2. I did not use any ceiling element all rooms I drawn the same way so using only floor element in Revit. My issue is that in few rooms I have ceiling rather

than floor. This part I do not underatand.... revit generate ceiling insead of floor based on what? gaps, allignment?

1. question is just help to undersanf gbXML difference between floor and ceiling. I am aware about revit differences but as I wrote above I did not use ceiling and Revit gbXML transoform my floor into ceiling and trying to find out what is difference in gbXML between ceiling and floor

This link does not work, can you please uplad again:

db_revit_tutorial_v1_185.pdf

Re: gbXML - understanding building elements

Zsolt.Varga — Mon, 23 Nov 2015 13:45:49 GMT

Hi,

Thanks for your feedback.

Sorry, i have copied the wrong link, but here you find the document attached.

I understand your issue is different from what I understood the first time.

In order to understand and investigate your case better, I would suggest to continue working on it together in a support case.

I am sending out an email to you in a couple of minutes and we can continue the conversation within this case and post results here once we have resolved your issue.

Regards,

Re: gbXML - understanding building elements

Anonymous — Wed, 25 Nov 2015 21:07:24 GMT

Thanks for guide,

I chose this opportunity and add one more guide with more examples,

gbXML_Guide.pdf

Re: gbXML - understanding building elements

Zsolt.Varga — Tue, 01 Dec 2015 08:49:02 GMT

Hi,

I´ve done some more research and I found the following information:

This links to the help topic: Surface Element has information on why a surface would be defined as a ceiling/floor.

However, since I understand that there are no celling elements within the model, this wouldn’t explain floors getting converted to ceiling surfaces. Such behavior has been reported in previous buildes of Revit and it was fixed in Revit 2015 Update Release 2 (and later versions).

If you are using Revit 2015, please, make sure, that you update your product to the latest version available.

I have attached a guide about the upgrade path to the current version of Revit 2015 Update Release 10.

I hope you find this information helpful.

Re: gbXML - understanding building elements

alancvct — Tue, 08 Jul 2025 15:47:39 GMT

Olá.

Onde encontrar a definição de cada superfície analítica: o Revit segue o padrão gbXML, e as “Analytical Surfaces” são agrupadas em categorias como Exterior Walls, Interior Walls, Floors, Ceilings e Air Gaps. A nomenclatura e regras de classificação estão descritas no esquema gbXML (ver seção “SurfaceType” no XSD v7.03 em gbxml.org) e na documentação Autodesk (Help → gbXML Export).

Diferença entre “Floor” e “Ceiling”:
- Floor é a superfície inferior de um espaço (o limite que separa aquele espaço do espaço abaixo ou do solo).
- Ceiling é a superfície superior de um espaço (o limite que separa aquele espaço do espaço acima).
Na exportação gbXML, o Revit usa seus “Room/Space Limits” (offset inferior e superior) e a orientação das faces para classificar cada face como piso ou teto.

Transformar um “Ceiling” em “Floor”:
Você não altera o tipo de face diretamente no gbXML, mas sim ajusta os Room/Space Limits no Revit. Para que a face superior do espaço de baixo seja exportada como um Floor (em vez de Ceiling), defina o Upper Limit Offset desse espaço exatamente ao nível do piso do espaço acima. Isso fará com que a face em comum seja considerada piso de um espaço e não teto de outro.