Insulating under a floor from beneath

[Adam Funk]

The hole into the crawl space is 65 X 60 cm, so I can't fit whole boards into there anyway.

The space under the kitchen has two air bricks to the outside & a square hole (a bit smaller than the main one) to the space under the dining room. That space has one air brick & the 65 X 60 cm hole to the front cellar, which has some air bricks. The cellar is musty (especially near the cellar floor) but all the joists are OK.

I'm inclined to think that putting the insulation between rather than under the joists is better for ventilating the joists themselves.

[Adam Funk]

(Sorry for the delay in replying to this thread --- my leafnode server went down & has just been fixed.)

The builders who are doing some work elsewhere in our house now are insulation enthusiasts so I've seen a lot of Celotex in the past few days. They've been using an ordinary crosscut saw to cut it --- but possibly (probably?) not the same one they use on timber.

[Adam Funk]

All the Celotex I've seen (in the past few days) is like that too.

[Tim Watts]

Not so relevant - the key factor is whether the air bricks are *lower* than the bottom of the joists. You need to ventilate below the insulation, not in the space you insulated.

[Adam Funk]

Thanks (& to others) for the advice. (I've got some other irons in the fire around the house right now, so I'm not sure when I'll get round to this.)