Exposed area calculation

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We are converting two barns. One holiday let and one residential. The holiday let is stone and the residential is timber cladding.

We have built a new build in between which is a timber clad holiday let. The Building Control department have asked for an exposed area calculation. We are finding this difficult to do. The regs are hard to understand as our buildings are not at 90 degrees to each other. If we can't get distances of 1m are there ways around this? Class 0 openable doors and windows for example? Build an external fire wall? We are really panicking as the new build is almost complete.
 
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Is it B4 - Spread of flame and Unprotected Areas - they are on about?

The Approved Document gives two methods for checking this, assuming a 'notional boundary' between the dwellings, but IIRC they both look for at least 1m from the boundary.

There is a little known report done by the Building Research Establishment (BRE 187) which can give better results, and allows for the building(s) being at an angle to the boundary, but needs patience and time to work through the concepts and figures. If your houses are compartmented, eg by 30 min FR floors and internal fire doors etc, that reduces the size of the compartments, and helps.
(But having timber cladding does not help when calculating the sizes of unprotected areas; did your architect not bring this to your attention?).
 
Seems like a business venture, so I'd say instruct a suitable person to do this for you.
 
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If you have an architect on the project they should do this for you. I doubt whether you will be able to do it yourself or it can be explained on here to the satisfaction of Building Control. This should be all part of your submission for Bldg Regs approval. Has a Full Plans Submission been made to Bldg Control :?:
 

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