Affixing insulation board without thermal bridges?

[tinco]

Hi, I'm renovating a 1927 brick semidetached house in Amsterdam, The Netherlands. I'll be using 80-100mm thick PIR boards on the roof, the walls and the floor to get an Rc of 3.5+ everywhere.

I've been watching a lot of installation videos for these boards lately, and most of them attach the boards using long screws. Some use just one or 2 screws per board, some a lot.

There are also a few videos that use construction adhesive to attach the boards to the wall, but I fear I can't get my brick wall clean and straight enough for that to be a good option.

My question is: do the screws form a significant thermal bridge? Should I contemplate other solutions? I saw for example there are Z shapes you can buy that slide into the board to hold it down, that will reduce the depth of the thermal barrier I guess.

If I'd had to guess the screws would be about 2cm^2 of metal thermal bridge per m^2. On a 15m^2 wall, that's 30cm^2 of metal thermal bridge. Maybe not terrible but would be nice to avoid perhaps?