Insulating bathroom floor - Just solid board or rockwool

JP_

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OK, so building the bathroom. Have 10cm joists, I was going to put in 5cm kingspan and 5cmrockwool on top. But having thoroughly swept up dust and removed rubble to reduce opportunity for moisture to accumulate, is rockwoll a sensible idea? All pipes and drainage will be below it, and plans is to have vinyl sheet, so only risk of water is from shower tray, toilet, basin - but, is it worth the risk? Have treated all the timber. But could just put 10cm kingspan in instead....

I have enought kingspan and rockwool for either option sitting in the loft, I think ...
 
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SFK

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What is below your bathroom?

If another room, in theory not needed (as heat from room below will heat your bathroom floor).
If garage then use Kingspan and rockwool as you want a warm floor.

I put in only rockwool as I wanted to slightly improve the sound proofing so hear less bathroom noises in room below.
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JP_

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Concrete subfloor then Earth. Bungalow. Had damp issues, well, rot issues - caused by covering of air bricks and creating a concrete path that goes up to damp course. Have removed concrete, opened air bricks, still need to replace with plastic one and dig some soil out to get it 2-3 courses below damp - there's always a line of moisture on the floor along the outside wall and the floor has been up for a month now.

The reason I am thinking about not using rockwool is because if there was a leak it could soak up water then pass into joists, if just kingspan more likely to drip down to subfloor and evaporate away.
 
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If you get the ventilation right then you won't have problems with damp coming up (do put a membrane under whatever subfloor you decide on).
If you get the plumbing right then you won't get leaks from above.
It is lots easier getting a draught free job with rockwool, but you'll need about 150mm to get the required U value for renovations so you'll need more digging to get the minimum 150mm air gap to subfloor and you'll need to net or something 50mm below the joists to support the rockwool.
Board (being closed cell) won't hold any moisture and won't be damaged by a bit of wet but it is more expensive and tedious to get a draughtfree install.
Choices choices
 
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JP_

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I've already done 3 bedroom floors, one with 25mm kingspan + 50mm rockwool, one with just 50mm kingspan and one with 50mm kingspan and 50mm rockwool!

I think 50mm kingspan + 50mm rockwool would be equiavent of 150mm rockwool? I am happier putting kingspan in -system now involves srewing trellis poles across on the underside of the joists for the kingspan to sit on, then foaming the edges, then dropping rockwool on top. Also tape up edges with extra kingspan and insulation tape.

I think I'll chuck it in - as you say, it shouldn't be leaking anyway. Besides, I have some in the loft already, gotta use it for something (other than insulating the loft!)
 
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From memory rockwool is 2/3rds as efficient as pir for any given thickness, so your 50/50 plan equates to about 80mm pir or 115 mm rockwool- wee bit skinny (though floor covering might get you over the u value line).
I've been shabbier with support- polyprop rope stapled under the joists. Strawberry net would work for rockwool :)
 

JP_

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oh yeah, my maths went a bit mad there didn't it?

I guess if I wanted to go really crazy I could screw the pir under the joists (perpenicular) then fill the the whole gap with rockwool .... not sure I need that much. Floor will be 20mm+vinyl.
 
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Unless you've got a very deep subfloor that'd be a nighmare job. Tho you could use polyprop and battens to hold the stuff up (poke string thru kingspan and a bit of 2 x 1 then back through 2 x 1 & kingspan, staple string to joist sides).
Never bothered working out R value for chipboard but it'll be better than nowt...
 
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