Which of these don't need skimming?

[MrsRenovator]

Filled the gap with expanding foam (as I do with every little gap I ever see anywhere round the house!) before the foil tape.

I also used a sealant on all the floor joints.

 

[cjcharles]

Thanks, in that case I might also need to fill the bottom 10mm that my labourer who was helping me seemed to insist I had - but I would have agreed with you that it just means the air gets a layer closer to the room and hence more chance of condensation....
Thanks for sharing!

 

[MrsRenovator]

His gap is probably to stop wicking from the floor level (mopping, flood) and for expansion.

I've found its easier to fill a 10mm gap successfully than it is to fill a 5mm one. So with the thinner marmox/aerogel i cut it a tight fit. With the thicker kingspan etc I leave 10mm round the perimeter and fill after.

Whatever you do, as long as you understand the effects of warm air, condensation and cold surfaces etc and work out your own system accordingly, I don't think you can go wrong. There speaks the diyer!

There's remarkably little information for renovation insulation in awkward spaces. It's mostly people like us having a go and sharing ideas. And if you ask a builder they'll say "you can't do it like that." But hey ho. You've got to try. Something is better than nothing!

Hope it all works out.