Crawl space insulation?

[McCheck]

Would love your advice about how to insulate drafty period properties. We’re considering putting insulation into the (ventilated) crawl space under the floorboards. Have you got experience, would love to hear!

Also, we have two quotes. Are they reasonable? One is for 1.3K for a 13sqm room, the other for about 800.

It will make the house warmer. How easy is it to access the space? If they will have to take up and relay the whole floor then that seems like a reasonable quote to me.

thanks @Geneticsbunny one quote is for lifting floorboards (I think the cheaper one!) other one thinks it’s easy to dive under. No idea how tbh. It’s just over a foot of space on the side where I lifted a couple boards

The more expensive option use the latest ‘hybrid’ board insulation that doesn’t sag with time

Cheaper quote is a guy who doesn’t appear that expert. For example, I’ve seen online that you don’t need more than 10cm and the guy said he can put as much as we like without advising us on recommended depth.

With that amount of space, you should use boards rather than mineral wool. You need to leave room for air to circulate underneath the house so thinner, more solid insulation is the best option.
Going underneath is the best option. Lifted floorboards will never go down as well as before they were disturbed and there is not point lifting if you don't need to. Not a pleasant job but it's what you are paying for.
But if the floorboards are in poor shape, you could get rid of them and lay solid board on top of the joists after you put in the insulation. That would help as it would eliminate the gaps between the boards.
Or you could remove boards and dig out the crawl space to make it bigger but that's a big job.
Draughty houses are horrible to live in so anything you can do to eliminate them will make life better. Just be careful you are not creating damp.

thank you @redboxer321! Great advice and helping me decide on the boards option. I was just reading up on airbricks and the need for ventilation. Makes sense to not suff the space with mineral wool

I’ve just sanded off all bitumen off the floorboards so for now we want to keep them. Thanks again for your advice

It’s not going to be done properly for that price. You need to look at ventilation and a vapour control membrane.

you also need to control air movement or it just won’t work.