Which floor insulation, if any?

[ottosump]

Hello group
I've recently moved into an Edwardian town house, the previous tenant has stripped all the floorboards back and waxed them up, they look stunning, but the drafts that emanate between them is gruesome. I would like to insulate the flooring by means of inserting polystyrene between the joists. The ground floors are all suspended and have a space of about 20 inches which can be crawled into between the ground and the joists. There are air bricks situated on the outside of the house which circulate the air under the floors, What I need to know is will insulating the floor cause any issues with rot, I don't want to cause condensation or damp.
Regards
Otto

 

[ottosump]

No replies as yet, does anyone have any suggestions?

 

[geraldthehamster]

No replies as yet, does anyone have any suggestions?

You shouldn't have issues with rot if you put insulation between your joists, as circulating air will still reach the lower part of the joists, in the ventilated space under the floor, and any damp entering from above, from spillages and so on, can evaporate into the room.

People have used Kingspan-type boards, or roll insulation supported by netting or chicken wire. If it was me, and I was crawling around under the floor, I'd fit Kingspan/Celotex, etc - not the cheapest route but look for seconds. With no calculations at all to back this up, I'd guess that 50mm would be sufficient.

If only I had a viable crawl space under my own ground floor...

Cheers
Richard

 

[mointainwalker]

Since I reckon your joists are likely to be at least 100 mm deep, I would fit 100 mm fibre-wool.

This will give you 25% better insulation than 50 mm Celotex etc, requires much less precision in cutting ( although you need the chicken-wire or similar) and will likely be 50% cheaper.

Will also be easier to fit than trying to manoeuvre boards in a crawl-space..

If it is an issue with you the scratchy yellow fibre-wool has generally been replaced with a different material that is pleasant to handle. The Knauff stuff is called Evose and is brown.

@ Gerald

If only I had a viable crawl space under my own ground floor...

I would have thought hamsters would not need any more space than a mouse

 

[ottosump]

Thanks guys, on your advice I'll be nipping down to the DIY centre tomorrow for some rockwool & chicken wire, I'll let you know how I get on.
Regards
Otto

 

[mointainwalker]

Rockwool is a brandname. All types of fibre-wool are very similar in insulation value. Buy on price,

Check the packaging if you want. You should be looking for something in the technical label thats says " R= 2,5" This is the R value for 100 mm.

The higher the number the better when comparing same thickness of product.

If you see any rolls of plastic mesh/netting, that will do as a support too.