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Decking wall plate and potential bridging of DPC

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Hi Everyone, 


This is my first time posting so I hope I have gone through the correct channels, 


I have a timber frame extension that I'm designing and I have concerns about the wall plate of the decking bridging the DPC. Please see attached drawing with red circle highlighting area of contention. I have found some useful information from the timber decking association link below but I woudl love a sense check if anyone would be kind enough to help. 


I'm hoping this detail will be acceptable with building control as the decking has a roof so only driving rain on the odd occasion will reach the back wall however the project is situated in Cornwall facing the prevailing wind direction. I was thinking about raising the DPC above the deck and adding a 100x100mm concrete block to create better baring for the wall pate but this has knock on effects with the sole pate being below DPC. 


I not sure how building control will react to this detail and as its a timber frame my concern for water tracking into the structure is heightened. 


Any comments or suggestions woudl be greatly appreciated. 


 https://www.tdca.org.uk/faqs/timber-decking-questions/dpc-where-should-i-install-the-ledger-board-when-the-deck-is-attached-to-a-house/#:~:text=The damp proof course (dpc,level with patio%2FFrench doors.

AN-G - RVB - DT_SEC - Proposed - Detail Sections.pdf

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Personally I wouldn’t have the decking above the sliding door sill.  The sill will have weep holes for rainfall running down the glazing, but the decking at that height height would deflect and channel more rain (and gunk) into the door channel and likely to block and overwhelm it.  Especially with driving rain.  Then the door  channels will pool up and water will seep inside the house.


just my opinion based upon common sense and some experience with sill weep hole issues, others may have expertise to counter my opinion, but I think you’re asking for trouble with that design.   I can only assume you're looking at having the decking being flush with the interior flooring for aesthetics, but you’re doing the right thing to consider the practicalities of doing so.   I do see house designs with exterior being flush with interior so I assume there are ways to do so successfully.  Maybes some sort of decking grates.

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