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Advice on modelling irregular bulkhead in DesignBuilder

asked 2019-11-29 06:47:49 -0500

jadinandrews gravatar image

updated 2019-11-29 11:12:41 -0500

Hi All,

this is my first time posting here, but I have run into an issue with a new project I am involved in. We were asked to assess a library in terms of South African energy efficiency regulations, and the design has a fairly odd lightweight bulkhead design which tappers upwards towards the wall plate level in order to accommodate high level windows.

Please see image here for clarity

At first I modeled it as a separate zone, but then DesignBuilder detects the tapered edges as internal walls. I figure it should be ok to just manually set those surfaces to the required construction, (Rhinoboard), but I don't know if this will skew results in any other way.

My other thought is to model the bulkhead as a single component instead of a zone, but surely this must be a bad idea?

Kind regards, Jadin

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answered 2019-12-01 16:15:31 -0500

Chun gravatar image

Hi Jadin, If DesignBuidler detects a surface as internal then it means both sides of that wall are adjoining zones. It could be a geometry imperfection of your model. Model the bulkhead as a component block is a very bad idea as "Component blocks do not absorb or conduct heat in any way - their only effect on building surfaces in simulations is related to the shading and reflection of short-wave solar radiation and light." (

Do you have your Visualise->Model Data view of your DesignBuilder to clarify the issue of being detected as internal walls? Best regards, Chun

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Hi Chun, thank you for your reply.

I am using DB v4.7 since that is the highest approved version in SA. I don't think this matters though.

Please see the following images to give you an idea of how I modeled it:

I hope this makes my issue clear. Please let me know. I have had similar issues before where a horizontal ceiling was detected as an internal partition, but this was resolved by using the 'Rebuild' tool, but this isn't working in this regard.

Kind regards, Jadin

jadinandrews gravatar imagejadinandrews ( 2019-12-02 04:22:54 -0500 )edit

Hi Jadin, Thanks for the images, that clarify a lot of things. DesignBuilder detects those ceilings as walls since they are not flat. What you have done (set the wall as ceiling construction) is the best you can do from what I know.

I have done a similar model before:

The only main difference is that I set the roof block as "2-Semi-exterior unconditioned" under activity. So the corresponding construction type that applies to that raked ceiling is "Semi-exposed walls" and I set it as plasterboard ceiling:

Best regards, Chun

Chun gravatar imageChun ( 2019-12-03 17:12:24 -0500 )edit

Thanks Chun, that helps me a lot! I just need to remember ro manually set these constructions whenever I make changes. It would be nice if DB had the option to reclassify a surface so that it inherits properties as we would normally expect.

Kind regards, Jadin

jadinandrews gravatar imagejadinandrews ( 2019-12-04 05:14:33 -0500 )edit

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Asked: 2019-11-29 06:47:49 -0500

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Last updated: Nov 29 '19