Anyone know of a 50mm thick solid wood fibre board?

[Alan Ambrose]

This is for filling the bits of our 50mm service cavity that don't have services in.

 

I can find plenty of 40mm & 60mm offerings...

 

 

[MPH243]

Have you tried Mike Wye, I don't know how much delivery would be as they are in Devon. 

[Redbeard]

I don't know whether you mean rigid or flexi. I have used a lot of rigid and never seen 50mm. Up to now I had also never seen 50mm flexi, but this link suggests it exists:

https://buildgreener.co.uk/products/naturheld-flex?currency=GBP&variant=49966431469915&gad_source=1&gad_campaignid=23967636703&gbraid=0AAAAA9vqH-jF7IOSs__UWCmfJE33AFZU-&gclid=CjwKCAjwpefSBhBvEiwAzyEtZ3XCW0_Kjt0zQszRO681RUVvIHowW4VmcRKpm3xXx6ZsqvIe0zhr9hoCkOQQAvD_BwE

 

As @MPH243 says, Mike Wye also seem to do 50 flexi.

[Alan Ambrose]

Thanks, but by ‘solid wood’, I mean more stiff sheathing / rendering board than soft flexi fill.

[ProDave]

25 minutes ago, Alan Ambrose said:

Thanks, but by ‘solid wood’, I mean more stiff sheathing / rendering board than soft flexi fill.

Why does it need to be more solid?  I understood it was just fill of a void and would be covered with plasterboard?

[-rick-]

Doesn't someone here work for a wood fibre company? Maybe @sgt_woulds?

[SteveG40]

From the few rigid wood fibre boards I've seen the base material is actually only made 20mm thick. Then they bond multiples together to give you the thicker boards.  Hence always usually 20, 40, 60, 80mm etc.  I'm guessing it's to do with manufacturing processes?  Maybe its too difficult to make 10mm thick and 30mm is too unstable?

[Alan Ambrose]

Yeah, reporting back, I can see just one 50mm offering:

 

Savolit Plus - Wood Wool Boards  https://bio-space.co.uk/products/savolit-plus

 

@ProDave - internal it's 12mm ply / 50 mm service cavity / 12mm ply / 15mm plasterboard

 

If we use flex, we'll have to batten everything. If we use 'wood wool board' we won't as it'll hold its thickness OK.

 

This is my list for anyone going down the same path:

 

 

We could use much cheaper XPS, but it's flammable as f..k.

 

We may well do 60mm service cavity on the next barn to avoid this problem.

[ADLIan]

Do not confuse wood wool and wood fibre boards - they are very different materials.

[-rick-]

Does it have to be wood fibre? Can you get some mineral wool/rockwool boards at the right thickness just for this area?

Edited Saturday at 12:54 by -rick-

[SimonD]

1 hour ago, Alan Ambrose said:

If we use flex, we'll have to batten everything. If we use 'wood wool board' we won't as it'll hold its thickness OK.

 

If you haven't battened, what is it that is forcing you to stick with a 50mm service void and not adapt it? 

[ProDave]

1 hour ago, SimonD said:

 

If you haven't battened, what is it that is forcing you to stick with a 50mm service void and not adapt it? 

Have you measured your "50mm" battens?  I bet they are closer to 45mm?

[Nickfromwales]

9 minutes ago, ProDave said:

Have you measured your "50mm" battens?  I bet they are closer to 45mm?

Indeed. Anything regularised will be between 38mm and 44mm, with only “sawn” timber being 50mm (2”).

[SimonD]

22 hours ago, ProDave said:

Have you measured your "50mm" battens?  I bet they are closer to 45mm?

True on most normal  2 x 2 unless you're picky and double up 25 x 50 roof battens. But that's really why I asked the question of the OP and what's forcing the 50mm.

[Alan Ambrose]

The 50mm service cavity was the design number and is based on the gap between the inside of the walls right now and the oak frame, so not much to play with. Could be reduced, say to 40mn, but at the expense of losing service cavity room.

 

My oversight of course. I can’t remember what I was thinking re insulation in the part of the service cavity that doesn’t have services in. Will have to look at old docs.

 

Seems there’s one 50mm option though. That will save us from battening I believe - will buy some 25mm boards locally to check.

Edited 13 hours ago by Alan Ambrose

[JohnMo]

On 18/07/2026 at 16:10, ProDave said:

Have you measured your "50mm" battens?  I bet they are closer to 45mm?

Ours were 45x47.

 

Just batten it out and don't bother with the insulation. If your already well insulated the additional insulation compared to an unventilated cavity isn't with the effort.