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Question about how wall, roof, and floor thickness affects internal zone dimensions in DesignBuilder

asked 2025-05-23 16:37:46 -0500

James2183's avatar

updated 2025-05-23 17:05:59 -0500

Hi everyone,

I'm working on a model in DesignBuilder and I've defined a block with dimensions 8 m × 6 m × 3 m. I'm trying to understand how material thicknesses for walls, roofs, and floors affect the actual internal zone dimensions used for thermal simulation.

I noticed that when I assign a wall thickness (e.g., 30 cm), it seems to be applied inward, reducing the usable interior space. I would like to confirm the following:

Does this same behavior apply to roof and floor thicknesses? For example, if I assign a 30 cm thick floor or roof, does that also reduce the 3 m internal height?

Is there any way to define wall/roof/floor thicknesses so they apply outward, preserving the internal zone dimensions?

Are there any official manuals, documentation, or forum discussions that explain this behavior in detail?

My goal is to make sure that the simulated thermal zone represents the actual conditioned internal volume (e.g., exactly 3 m of usable interior height).

Thanks in advance for any clarification or references!

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answered 2025-05-26 21:50:15 -0500

Rebecca Powles's avatar

DesignBuilder is flexible in how this is handled: see here: https://support.designbuilder.co.uk/s...

which links to further information on these options in the help file: https://designbuilder.co.uk/helpv7.3/...

The DesignBuilder online help is very comprehensive, but sometimes you have to know what you are looking for... I can highly recommend skimming through it to get a sense of what information is available and how it is structured as it is a really good resource.

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answered 2025-05-27 08:42:28 -0500

Luís Filipe Sousa's avatar

DesignBuilder applies surface thicknesses (walls, roofs, floors) inward from the external block dimensions. This means that the zone's inner volume is reduced by the thickness of each surface.

This behaviour can be overridden, where the zone volume boundary can be set to the block external dimension by using a zero fixed thickness set at Construction tab > Geometry, Areas and Volumes > Fixed Surface Thickness.

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Asked: 2025-05-23 16:37:46 -0500

Seen: 210 times

Last updated: May 27