nailscrew

No, nothng supports these boards other than friction and some foam on the edges, hence my worry. That offcut just happen to be there, I believe it was removed later. Last photo is to show depth of the panel relative to the joists.

Thanks. What if it was EPS?

We are in the process for installing underfloor PIR insulation boards and I have a question regarding electric cables. On a photo cable rests on a beam and insulation board will be installed on top, squishing it. Is it acceptable? Shouldn't cable be moved under the beam? Do I need to ask builders to make a cut in a PIR board to leave air gap around cable at least?

Added photos showing finished underfloor with PIR boards installed.

When board depth matches joists, so that they can sit flush with the top and bottom this method would give me peace of mind. Unfortunately our boards go deeper than joists, so it is very hard to make support for them :( Nothing at the bottom? Is friction + foam + tape enough to keep them in place for years? Wont tape lose stickyness over time allowing boards to "migrate" down? What's wrong with properly installed PIR boards?

Hi All, we hired a crew to install floors and put insulation into underfloor on the ground floor in our house. We ordered 120mm PIR insulation boards , even if underfloor joists are 100mm, contractors didn't warn us that it will be pretty inconvenient to install 120mm boards, we just wanted extra warmth So now they are doing a lot of extra cutting into those PIR boards so that they fit on top of beams joists are resting on. One thing I noticed is that these boards are not secured at all. They are kept in place with friction + some expandable foam in gaps applied with the gun. Contractors say that it is secure enough, but I'd like to hear other opinions. My worry is that as timber contracts and expands with temperature and moisture fluctuations, PIR boards will sag and eventually drop on the ground, leaving portions of the floor completely uninsulated. I asked to put a tape across boards to prevent PIR boards from moving down over time, well as long as it remains sticky. My request was received with the look that I don't know what I am talking about, which is true, hence my message here Do I worry over nothing? How PIR boards should be secured in this situation? With a PIR boards thinner than joists I'd ask to instal battens so that panels can rest on them, but what to do when panel goes deeper than joists? That is if friction is not enough of course. Many thanks in advance.