by bluebirdnick » 18 Nov 2020, 16:37
Thanks both. Malcolm- I suspect if I go that route it will end up with doing a few rounds of scrubbing, vacuuming and drying!
I'd never even considered a chipboard floor - it seemed an unnecessary task/cost to install one as I thought I'd have a good flat clean concrete floor. I don't really care what my finished floor is made of, as long as it is flat, level, clean, dry and durable.
The slab should be dry - the builder put in a DPM under the concrete. But obviously this is not built to building regs standards and despite my little trench around the outside which should reduce moisture getting in to the side of the slab, it is surely inevitable that some moisture will find its way through. So I cannot bring myself to just put chipboard (or OSB or whatever) directly onto the concrete. I do however have a lot of DPM left so could easily put that down underneath. Not sure there would be any downside to this, so for now let's assume I'd do that.
As regards insulating under a chipboard floor: Height-wise, I am struggling a bit. Inside, it is just about head height at the side walls, and about 2.1m under the ties. It feels fine at the moment because I've not lined the roof - it is going to be a bit tighter when I do. But One more importantly, my doors open inwards so clearance is an issue. I think there is about 50mm potentially - the new brick plinth is maybe 20mm higher than the last one, and there was a timber strip under the doorway in the previous location so adding those things together, I get to a potential 50mm clearance before I need to adjust the doors (I would install door stops anyway to avoid excess drafts.) So there might just be about space for 25mm of PIR insulation under a chipboard floor, which I think would still leave acceptable headroom. I am assuming that the thermal benefit would be negligible. (I am discounting poystyrene - just don't like it).
To be honest the main function of the insulation for me would be to flatten out the rough bits so the chipboard has a smooth flat surface to rest on! The cheaper alternative would be to use a normal flooring underlay under the chipboard, like you might with a floating engineered wood floor.
So my options are:
1) clean floor and put down SLC wear layer and paint (hard; time consuming; surprisingly expensive; but doesn't reduce headroom)
2) 22mm chipboard (or OSB, ply) layed directly over concrete with DPM underneath (cheap, quick, clean, more comfortable, no material reduction in headroom; but as concrete floor isn't great I'm not sure how good this would feel)
3) 22mm chipboard (or OSB, ply) layed over 25mm PIR insulation with DPM underneath, either on bearers or as a complete "sheet" covering the floor (more expensive than option 2 but still considerably cheaper and considerably easier than 1; expect it to feel nicer under foot; loss of headroom / door clearance should be manageable. Thermal benefit expected to be negligible)
4) 22mm chipboard (Or OSB, ply) floated over laminate underlay like Timbermate Excel, with built-in DPM. (cheap and quick, minimal impact on headroom; no concerns on door clearance)
The more I think about it, the more I am tempted by options 3 and 4. I would still give the concrete a decent brush and vacuum, but if nothing else it will save me about £250 on the Ardex SLC (and let's be honest - I could easily make a mess of doing the SLC on an area that large, it is twice as large as any I've done before). I'd paint the chipboard with floor paint to brigthen it up a bit and to increase durability. The only concession I think I'd make is to make sure everything that goes in there- workbench; saw; shelving etc goes on castors so it doesn't scratch up the floor if I'm dragging them around. But that is no real hardship.
Are there any downsides to options 3 and 4 that I am missing?
Thanks!