Reinforcing a T&G floor in a wooden outbuilding

[FunkyJive]

I have a new tanelised 18ft x 9ft workshop with a wooden floor (22mm T&G on timber bearers), situated on a concrete base. It is internally partitioned so as to present a 12ft x 9ft space to be used as a hobby office/studio.

The office will have heavy desks, chair(s), and server rack with castors, and recording equipment so creaky flooring is to be avoided as far as practicable. I would like the floor to be generally flat and very strong.

I'm minded to use 5mm foam (foiled and moisture barrier) on top of the existing T&G floor, and then lay sheets of 18mm structural spruce ply on top of that.

Carpeting will be placed on top of the flooring sheets for improved sound and thermal properties.

So, my questions as follows...

1. Is this a sound idea in principle?

2. May there be any damp/ventilation concerns due to the proposed moisture barrier, or should I let the floor "breathe through"?

3. Should the ply be allowed to float (allowing for differences in natural expansion/contraction relative to the underlying timbers exposed to the outside air), or should I screw the ply sheets down at intervals to keep the floor "tight" and solid?

4. Will I need to provide expansion gaps between the ply sheets (of 1.8m x 1.2m) and between the floor and the wall timbers? If so, what should I allow?

5. Am I worrying needlessly and should I simply screw 'everything to everything at regular intervals to rigidly lock the materials together?


Apologies if answers are obvious to those'in the know', but it's been (and still is) an expensive project, in for the longer term, and I really don't want to be the cause of floor damage or premature failure !


Thanks in advance.

FJ

 

[FunkyJive]

This question has been answered in another DIYnot forum category.

Thanks for looking though


FJ

 

[freddiemercurystwin]

What are you proposing to stop the damp entering the floor? Any membrane used will need to be beyond the reach of your screws! The expansion issue is a moot point and you should ignore it. Just screw it all up tight with plenty of screws.

We assume the bearers beneath the floor are at reasonable (400) centres?

The carpet will add next to no insulation BTW. Without any insulation it will be fairly cold.

 

[FunkyJive]

Thanks for that

Following your recommendation, I'll drop some foiled/damp-proofing membrane and thermal underlay beneath the carpet (i.e. above the ply), and seal the proofing against the wall draught sheet.

I'll screw the ply sheets directly to the T&G timbers. The main bearers are at 400mm centres, though I'll also drive some longer screws all the way through to the bearers as-well - A bit OTT perhaps, but that's just me

Once the floor's down I'll get cracking on the walls - Expanded 50mm polystyrene (foiled) for the cavity, then the plastic sheet draft seal (mentioned above), and then (probably) 15mm Gyproc MR panels for the walls and ceiling. Hopefully it will be much cosier then.

I'm hoping that's the right way to go. Doubtless you can tell this is my first serious outbuilding undertaking, so please excuse me if I've overlooked anything obvious.


Thanks again,

FJ

 

[mointainwalker]

For the work/cost involved , it would be worthwhile putting polystyrene between the floor bearers too.

 

[FunkyJive]

Thanks for your suggestion.

The building's already down and the bearers run lengthways to the building, though probably not impossible if I were to feed in polystyrene strips from one end to lay flat on the concrete if this is what you meant? If so, would this cause problems from restricted underfloor ventilation?

Please forgive me if I'm misinterpreting the term 'bearers' and you're referring to polystyrene sandwiched between the existing T&G floorboards and the added ply sheets above?

All experienced suggestions most welcome before I drive in all those screws

Thanks again.

FJ

 

[mointainwalker]

I meant wedge the PS between the bearers so that the floor when laid would be in direct contact with it. Since you are beyond this stage , it is no longer practical.

If you have enough space to place it on the existing floorboards after your membrane, that would be fine.

 

[FunkyJive]

A good suggestion that didn't occur to me at the time. Noted for future builds though, so thanks again.

All the best,

FJ