Suspended Floor Insulation Choice Wood Fibre and Rockwool

[TriMattRdg]

I'm getting around 30 SqM of suspended floor insulated in two weeks time.

I'm torn between Steico Wood Fibre Flex 100mm or Rockwool 100mm - I can't find much on wood fibre being used but I really like what I have read about the material.

Also we currently have traditional floor boards - the installer has suggested to replace this with T&G Moisture Resistant board - is this a good move ?.

My suspended floor is clay and the surface does get damp but the ventilation is good under there and we are hoping to improve this further when taking the floor up, the installer has suggested that Wood Fibre may fill with water but my understanding if anything it could help with moisture control under the floor. I ordered a sample and stuck it under the floor to see what happens!

The insulation will be laid on a breathable membrane in a Hammock.

Would welcome any advice on the above. Thanks

 

[JohnD]

Heat loss through a floor is mostly by draughts. There is no convection, very little radiation, and not much through conduction.

Most of it comes up round the edges of the walls, where there is a gap between void, floor, skirting and wall. Square edged boards, with no carpet, also have gaps.

Mineral wool, stuffed tightly between the joists, will block the draughts.

It does not absorb water or rot, and has little weight. IMO it is superior to a wood fibre product.

If you have original timber floorboards, and they are well screwed down, they are a better floor than chipboard. Mark on the floor the position of pipes and cables below.

Your installer has in mind that chipboard is cheap, quick and easy to lay. He expects to be long gone before you discover it cracks and squeaks.

While working, clean out the void, remove any organic matter, lag any pipes, lay or renew any cables or pipes you might want in the next 50 years, and clean out the airbricks. If you want to add an access trap, put it in a corner of the room away from the doorway and foot traffic.

 

[Mr Chibs]

Looks like you have a bit of wet wood/rot on the joist ends, slide in a strip DPC (as the bitumen might have failed) and repair/replace the joist end.

I used rockwool insulation in my floor, then covered the whole floor in building paper (bitumen layered) before nailing down solid wood floor.

Insulate all your pipework, there's gaps.

 

[cdbe]

Doing mine at the moment, using Rockwool (it's some kind of acoustic slab that I picked up cheap but it still has very good thermal performance). I have 60mm continuous under the joists sat on hanging hammocks made from the old t&g boards (they're scrap when they come up), then two more layers of 60mm between the joists. New 22mm chipboard flooring with joists at 450mm centres screwed down with 90mm screws at 100mm spacing - there's no creaking.

 

[TriMattRdg]

Thanks, going to take all the above into account . I am opting to have all the boards taken up to do this as I want to try and get everything sorted under there as really want it do be the last time I go under the floor!. When we moved in we noticed salts on the dot & dab walls and on prising off some skirting recent there was some mould underneath so I am looking at replacing this dot & dab with something else after we have got the floor done. . I believe a lot of the damp problems were caused by very poor sub floor ventilation after we moved in 3 years ago , I have since at least doubled the airflow underneath ( last year) by unblocking air-bricks, and replacing with plastic air bricks.

 

[TriMattRdg]

Out of interest how have you dealt with the detail where the joists go through the wall , and the join with the wall ? -Should I look to fill the gaps where the joists enter the wall with a lime mortar mix ?. Have you used vapour barrier on top and sealed at the ends or simply butt the insulation tight to the wall ?. My intention is to later use wood fibre boards for IWI to the external walls.