Royal Mail Cardiff Sorting Office

Cardiff Sorting Office is having its roof done! I met one of the contractors who is working on it at a local hardware store recently. (I was there with my faulty extendible rivet gun, and two of the guys at the shop had disappeared off out of sight for a good half, clearly growing increasingly immersed in the issue of the none-​releasing claws!!!) Meanwhile I was getting bored! I overhead one of the guys at the counter next to me mention that he was working on the roof of the Cardiff Sorting Office, and so I thought I’d ask him a little bit more about it.
It transpires that the entire roof is being replaced using German technology. A complex layered system of materials is being deployed, with each separate layer needing to be signed off by the manufacturer before work can begin on the next. Bauder, the roofing company provide a long term guarantee, but will only do so if they are sure that the contractors have applied each layer in accordance with their specifications.
Apparently it’s an expensive do! The contractor estimates that it costs about £150 per square meter!
I’ve tried checking on the Royal Mail website for the exact postal address of the sorting office, but they don’t list it on the site. I guess they don’t divulge the exact location for security reasons… but then why do they tell us to collect undelivered mail from their if it’s such a sensitive security risk???