Just thought I'd tell everyone we found no fix as such, but someone else on the team has the pro version of SketchUp and that has the export options we needed. I don't understand the incompatibility between all these programmes but at least I have my problem sorted.

Anyone interested, on another forum someone's explained to me that in the first image what I've labelled #2, the white squares, is a dormer. That makes sense to me with what Dave said earlier about #3. I've actually e-mailed the UK National Trust to see what they could tell me about that round yoke. I'll post back with their answer in case anyone's interested.

I had this sorted almost immediately after posting the initial topic but I was having the same problem as yourself, Box. It must have to do with being a new member. After posting I edited the post as I'd forgotten something and noted an error, which apparently requires awaiting moderation if you're a new member. Well, then no-one put it through so I couldn't tell everyone the good news until much later. Then I edited that one (my keyboard is old so I make errors a lot) and it disappeared for a bit. So, I'd love to have my questions answered about SketchUp's faces and verts as compared with programmes like Maya and its polygons and verts, and additionally, in future, I'd like to provide the information that's apparently missing. What should I have done? just attach the file? I suppose I'd just assumed I couldn't possibly the first person to have this problem and that someone experienced would tell me it was common and how it's fixed. Thanks.