Inspecting floor boarded attic insulation

What about an endoscope:

I have one of the Depstech ones. You can get them in wifi versions (that need an app), screen versions (with a fairly small screen), or camera-only versions that present as a USB webcam. I have the webcam version - turns out USB webcam support on Android is poor but the official app just about works. Using it on a laptop is much better, and with a bigger screen.

The main thing is they have a focal depth of a few cm, and often the bump into things closer than that (eg in a pipe) which you can't see clearly. But still very handy for exploring under the floorboards and down pipes.

For a cheapskate approach, you could just cut a hole in the ceiling to insert a phone camera. Would need filling afterwards, but perhaps not such a big deal? Cut-and-fill is commonly done for fishing wires through ceiling voids.

Theo

Just circular along the joints either side of a board, lift it and look. Then screw (nailing might crack ceiling plaster below) the board back down. It'll be fine without the tongue and grooved joints - just as many houses have unjointed floor boards where wiring or piping has been added later.

That should have been "circular saw along"

No, it can really hurt.

Bill

I've got a hole saw. SWMBO would not be well pleased. A laser cutter which would allow the disc to be seamlessly replaced could work.

Why can't you drill a small hole somewhere and put a cheap borescope probe in the hole ?

And plug the hole afterwards if you want to.

You don't need holesaw or borescope. Drill some 3mm holes & poke a wire in. Hold it with insulating gloves. A smear of filler repairs the holes. New insulation can be laid on top.