So engineer came back after few days (I think someone more senior has interfered after I complained) and this is what they came back with. I though I'd post it here so it can serve for people to see another take on the issue.
See attached drawing.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local