wood sub floor

[oemodm]

Hello everyone,

I've a sloping concrete floor to insulate & flatten out as a future lounge:

I'd like to build using wood. I may need underfloor space for running services. Its a back up. Also, the situation of the house isn't suitable for concrete truck access. So, wood sub floor structure is an easy way to go.

Here's my idea, floor depth of 100mm:

Stand an OSB board (18mm) on its edge (A), flick a builders chalk line to get the straight line, cut, and fix. Repeat all the way.

Here's detail of how each will be braced, fixed, filled - spaced at 40 or 50cm:

To reduce cold bridging on the OSB, I'll cut small curves into the base:

Is this workable?

 

[Tipper]

It must be simpler to put a proper suspended floor comprising joists, etc in?

Vermiculite or recycled newspaper insulation (Warmcel) is easier to install too.

DPC/Membrane? - ignore just spotted it!

 

[freddiemercurystwin]

WTF! OSB used vertically as structural supports? I've seen it all!

 

[ban-all-sheds]

It must be simpler to put a proper suspended floor comprising joists, etc in?

 

[oemodm]

It must be simpler to put a proper suspended floor comprising joists, etc in?

Sure. I was going to do that. However, I'm only raising 10 to 15cm and would rather just build a lattice of OSB on the original floor. If building a suspended floor, I'd have to build too many supporting points to support the joists every 40cm.

OSB used vertically as structural supports?

Yes, and there are 2 differences compared to OSB I beams:
1 = In mine, the I beam laminate strip is replaced by mounting on a concrete floor.
2 = Mine will be double OSB thickness compared to I beams
Used for reference:

Vermiculite or recycled newspaper insulation (Warmcel) is easier to install too.

XPS fitted between will add to the sideways support for each OSB section. I don't mind the cutting and shoving in place.

Hoping for more constructive guidance or if this is really a terrible idea...

 

[Deluks]

Honeycomb sleeper walls and 4x2.

http://www.uwe.port.ac.uk/floors/rtf11.jpg

Then again you could always level it out and do chipboard floated on xps, (or t&g ply if you want to spend a bit more for better quality)

 

[noseall]

WTF! OSB used vertically as structural supports? I've seen it all!

I know tell me about it.

 

[freddiemercurystwin]

That's entirely different nose, cutting up strips of osb and fitting itsy bitsy angles everywhere to keep em in place though! Jeez, proper muppetery!

 

[theprinceofdarkness]

Thank you for a very informative reply freddymercurystwin.
The problem with using OSB on edge are two fold:- With a I beam the edge of the OSB is constrained by the slot into which it is glued, and if you have a 1/8" dip over 4', then you will have to machine a long curve along its edge, thus reducing its overall height.
Without any height dimensions, it is a bit difficult to suggest a solution. One thing is certain, do not rely on the wood being "true" it will turn into a dog's leg while you watch it!.
Having done this job twice, I would use lightweight blocks cut down to get the correct height, allowing for the mortar courses, with a 1" gap between each one. Do not put any blocks closer then 3" from a wall (ventilation).
One good wheeze is to check out the ceiling, if it is true, then make a gauging stick and set heights against the ceiling. Or set up references on the walls, say 1m above Finished Floor Level- vertical masking tape strips. Gets a piece of cardboard and make a note of the various levels, i.e. block top FFL - 4" etc. hang it on a nail near the door, else it will get lost.
Don't use foam, its expensive and a b****r to fit, use glass fibre, hang some plastic netting over the tops of the blocks before laying the joists (leave some slack).
When using lightweight blocks they will suck all the water out of your mortar mix. So wet them, then smear a thin film of mortar on them, leave for 5 mins, then use with extra mortar for your main course. Or seal the mortar faces with with a 1:5, PVA glue + water to reduce the suction. As the tops of the blocks are likely to be true, I would just sit the joist on them with a bit of roofing felt between, it will even out any small imperfections and will be a sound deadener if the joist warps and lifts of the block.
Frank