anyone tried insulating under their floors?

Did it in our old place, and honestly, the difference was pretty noticeable - floors felt warmer, fewer drafts, and heating bills dropped a bit. Just make sure you're sealing gaps too; insulation alone won't fix everything.

I’m not sure I agree that sealing gaps is always necessary. If the main issue is heat loss through an otherwise intact floor, properly fitted insulation could address much of the cold feeling without adding another major task.

That said, I’d probably inspect first rather than assume. If there are obvious cracks around pipes, skirting, or between boards, air can bypass the insulation, so sealing those specific areas seems worthwhile. But for minor gaps, I’d prioritize continuous, correctly supported insulation and good moisture/ventilation control underneath the floor before trying to make every joint airtight.

Your “inspect first” point is especially important in an older house. Before fitting insulation, could you check for damp timber, leaks, or musty areas and make sure the underfloor vents aren’t blocked? Insulation that restricts airflow or traps moisture can lead to rot in joists and floorboards, even if the floor feels warmer at first. I’d want the crawlspace dry and adequately ventilated, then install insulation with proper support while keeping vents and access points clear.