IES-VE User Forum

Hi All, a completely newbie question here - sorry!

It's regarding assigning roof constructions for Part L, EPC through SBEM.

Do I assign the relevant u value and km value to the upper most ceiling of the property or to the actual pitched roof itself. In IES you seem to be able to do both.

I only ask because in Design Builder (which I have used for 6 years) the uppermost ceiling is deemed the semi-external element - and the u values for the ceiling, any insulation, roof void air gap, and pitched roof construction - would be assigned to this ceiling element.

I'm thrown by the fact that in IES you can assign both the upper ceiling element and the roof construction.

Hi Sentobe

The short answer is, you assign both as they actually are. The pitched surface is seen as a "roof", the layer between the occupied zone and the roof void is seen as a "ceiling".

The question basically boils down to whether the roof space is a "warm void" or an unheated buffer zone of some description. If you are planning on running the insulation on the pitch itself then you apply an insulated roof construction to it and leave the ceiling as some sort of plasterboard construction (for example). If the insulation is running below the roof void, ie in the ceiling, then you apply an insulating layer to the ceiling construction and set the roof construction as representative of what is there, say roofing tiles and some sort of underlayer.

If you have insulation on both ceiling and roof then you can assign the space as either warm void or unheated depending on what you feel is most appropriate I think.

The reason it is important to assign the correct conditioning to the space is so that the notional building runs its thermal boundary along the same surfaces as your actual building.

CP