Workshop flooring construction, last minute doubts

[Some bloak]

After postponing for a long time I'm just getting stuck in to my first new workshop build in an outbuilding. Walls are being covered in a heavy DP membrane followed by 3 x 2 stud/ batten frame, which is then being covered (not in between the battens) in 50mm Recticel, finished by cladding the whole lot in 18mm OSB. So far so good.............

However, I'm not sure about the floor. I've found and followed lots of good threads here about flooring but I can't quite match up any with my proposed method. I want to construct a batten/stud frame out of 3 x 2 (400 centres and plenty of noggins) to the existing concrete floor, again with a heavy DPC membrane over the concrete before I frame on top. I Then want to cover the 3 x 2 floor frame with the 50mm Recticel, then everything covered over with a floating 22mm P5 chipboard. I tend to favour flying all insulation over/on top of wall and floor framing rather than in between to minimise thermal bridging where possible (or is in between or on top of a negligible difference?)

The last minute doubt I have, does anyone think that the Recticel will compress detrimentally onto the 3 x 2 floor frame underneath or will the floating chipboard spread any machine loading sufficiently not to cause any problems?.

The concrete floor dips in the middle and is generally not level, otherwise I would just float the Recticel straight onto the concrete to start with. The 3 x 2 battening method will allow me to pack out where needed to get the floor level, plus the 3 inch depth between the battens will give me a handy service void for bringing any cabling to machine points in the workshop if I choose to. I've thought about some sort of levelling screed, but at 30 square metres, it could be expensive and more time consuming than knocking up a batten frame for everything to sit on?.

Any opinions, ideas or previous experience on this, as always will be gratefully received. Many thanks everyone.

 

[skipdiver]

Level the floor with sand and then do your floating floor. All the 3x2 is pointless in my opinion and it will dig into the recticel.

 

[RobinBHM]

Im not sure recticel all over is a firm enough base for a floor.

Ive often done joisting over concrete oversife for orangeries -easier than screed for a timber floor. We lay 4x2 laid flat and pack them up level. Its important to fill the gaps underneath along the whole length, either with silicone / expanding foam or for big gaps bed down sleepers on mortar.

We then lay 4x2 on top or 6x2 with insulation in between

You could do 3x2 flat to level up, as sleepers say 900mm apart, then 3x2 joists upright at 90 degrees to sleepers

Strip up the insulation to 355mm (or whatever the joist gap needs to be depending on how the insulation is cut. then use the insulation as a spacer to lay the joists. Insulation can be scored both sides with a stanley knife and snapped or ripped with a saw.

 

[skipdiver]

Insulation laid directly on the floor, with chipboard on top is perfectly fine. I've done this countless times including the room i am sat in typing this and also in my workshop.

 

[Some bloak]

Insulation laid directly on the floor, with chipboard on top is perfectly fine. I've done this countless times including the room i am sat in typing this and also in my workshop.

Thanks Steve. I would do this, but the concrete floor is not level, so really the fundamental problem is getting the insulation down in a level fashion so I can float the 22mm chipboard on top. Sand sounds interesting but won't it try and move or disperse a bit over time?.

 

[Steve Maskery]

How uneven is the floor? If it is not too bad, go down the sand route. Where is it going to move to?
My slab was pretty good, no more than 6mm anywhere, and it is 8m square. DPC, 50mm Jablite, 18mm osb, and finally 22mm Caberfloor.
The Caberfloor is excellent, BTW, if you want a good, hardwearing, maintenance-free, non-slip surface, and it wasn't very expensive, either.

 

[monkeybiter]

My ground floor extension was built with solid concrete base, ~125mm insulation then chipboard floating on top. All 'above board' & building regs approved etc; what a mistake, I should have done some research and instructed a change to include joists with the insulation between. There is now floor movement in routes of regular use.
In a workshop with possible regular heavy loading in some areas I wouldn't even consider it without solid support.
Just my opinion based on one experience.

 

[Steve Maskery]

There are different compression grades for flooring insulation.

 

[Some bloak]

There are different compression grades for flooring insulation.

Hello Steve. I looked up the tech spec on Recticel and all they would say is that it has better compressive strength than most others. Anyway, the sand idea has potential if I was able to compact with a wacker plate or something?. Maybe do a dry sand cement mix so it sets up a bit. But then I might as well get into a full blown screed approach if I go down this road too far. Initially I thought a simple but sturdy framing packed out level would do the trick.

I suppose the Op above could have the problems I envisaged if everything was laid on an uneven concrete floor which allowed a bit of flexing- maybe not. I've bought a pile of Caber floor which does look like good stuff, although I wasn't planning on laying it on top of OSB, but nothing wrong with a belt and braces approach though. I must speak to you about your tutorial stuff btw when I get everything fired up.

 

[skipdiver]

Insulation laid directly on the floor, with chipboard on top is perfectly fine. I've done this countless times including the room i am sat in typing this and also in my workshop.

Thanks Steve. I would do this, but the concrete floor is not level, so really the fundamental problem is getting the insulation down in a level fashion so I can float the 22mm chipboard on top. Sand sounds interesting but won't it try and move or disperse a bit over time?.

We used this method when converting a garage to a living space and the floor had a fall on it as garages do. Building inspector approved and no problems we are aware of. Put down the sand, levelled with a big straight edge. DPC, insulation, chipboard, sorted.

If you are going to do it with timber, i wouldn't then lay the insulation on top, rather in between the rafters.

 

[skipdiver]

The sand wouldn't need compacting with a whacker. We just tamped and levelled with a long piece of wood and the insulation and chipboard distributes the weight evenly.

My conservatory i'm in now was done in a similar way. I left the wide concrete path at he back of my house down, widened it into a base and because the path had a fall on it, obviously it wasn't level. I actually levelled it with sand and cement as it wasn't a big area. 3 inch insulation and chipboard, topped off with laminate. Solid as a rock.

 

[Some bloak]

The sand wouldn't need compacting with a whacker. We just tamped and levelled with a long piece of wood and the insulation and chipboard distributes the weight evenly.

My conservatory i'm in now was done in a similar way. I left the wide concrete path at he back of my house down, widened it into a base and because the path had a fall on it, obviously it wasn't level. I actually levelled it with sand and cement as it wasn't a big area. 3 inch insulation and chipboard, topped off with laminate. Solid as a rock.

Thanks for your info.-sand method sounding more encouraging. What sort of depth did the sand have?

 

[skipdiver]

Just thick enough to take out the dips. Doesn't have to be very thick at all. The garage we did had a 2" fall and we just did it 2" to nothing over the length of the floor. 1 to 2 inches of sand should suffice.