Insulating crawl spaces makes a lot of sense, but there are a whole range of different ways of tackling the problem – and not a lot of information to help you in your research. This page links out to some of the few useful sites and provides you with a good primer to the topic – so you can read for yourself what works and what doesn’t!

Crawl space ceiling insulation

Otherwise known as insulating the floor joists. Every winter, people complain about cold floors – which is down to poor crawl space insulation between the joists. Historically, this always been installed in a particularly way, as defined in the building regulations. These specify R-19 fibreglass wool insulation with a (kraft) paper backing. If properly installed, the paper backing should be nearest the conditioned side of the floor (ie facing up towards the room). However, if the insulation has ever been replaced, it’s pretty likely that it has been installed upside down with the paper below the fibreglass wool in the mistaken belief that this stops the wool falling down.

Installed properly, fibreglass wool will help insulate between the crawl space and the warm inside of your home. However, it’s not perfect since the crawl space will always be cold unless you seal and insulate between the ground and the crawl space as well as between the joists.

One good way of doing this is to use rigid foam insulation panels rather than fibreglass – unlike a spray foam insulation, the foam panels can be removed for inspection but don’t sag or lose their thermal insulating ability when wet (which is a problem with fibreglass wool).

The government provides excellent reference material to help you tackle this tricky topic.

Read this account of the pitfalls if you insulate crawl space wrongly.