Is screed compulsory?

40701085

Hi all,
Exposing my ignorance here, I know - but is a ground floor screed essential?

Reason I ask is that the queen wants solid wood floors (standard is 18mm thick I think) on GF. I spoke to the carpenter & he said that it is better to batten out the floor slab, lay some ply and nail down the wood floor (with insulation & pipework underneath to be sure) rather than try to glue the floor onto a screed.

His rationale is that unless the screed is perfectly level, you'll have gaps where the glue won't meet the screed leading to cupping etc & the wood will move. Says he did a fix after a floscreed job recently & even on that system they didn't find all areas level.

Would be glad to have your thoughts on this...

PS How long do you think the boards would need in the house to "acclimatise" before laying?

topcatcbr

40701085 wrote: »

Hi all,
Exposing my ignorance here, I know - but is a ground floor screed essential?

Reason I ask is that the queen wants solid wood floors (standard is 18mm thick I think) on GF. I spoke to the carpenter & he said that it is better to batten out the floor slab, lay some ply and nail down the wood floor (with insulation & pipework underneath to be sure) rather than try to glue the floor onto a screed.

His rationale is that unless the screed is perfectly level, you'll have gaps where the glue won't meet the screed leading to cupping etc & the wood will move. Says he did a fix after a floscreed job recently & even on that system they didn't find all areas level.

Would be glad to have your thoughts on this...

PS How long do you think the boards would need in the house to "acclimatise" before laying?

This sounds ok to me

RKQ

150mm concrete floor slab is compulsory but screed is not, provided slab is smooth and level, preferably power-floated.

Timber floors work well on ply. Aclimatise timber in room for as long as possible - week or two at least. Also ensure slab is dry- circa 25mm per month, so 6 months since slab was poured before laying a board.

Do you still have pipes to lay?

40701085

Thanks RKQ - yeah the slab was poured back around late March.

The plumber hasn't started at all yet. How do you reckon it will affect him?
(Heating will be rads, not UFH in case this helps.)

The one other question that did occur to me was how would I avoid cold bridging with the floor insulation - can the battens be fixed to the slab thru the PU?

RKQ

Not sure what your floor construction is.
However, I assumed the insulation and rad pipes were installed in the floor slab. If this is not the case then a screed may be advisable.

Would need full spec to be able to advise further - re insulation, cold bridges etc!

40701085

em, I think it was something like hardcore, radon dpm etc, then 150mm slab (stepped raft)...and that's all - does this sound right?
I will be talking to the plumber this week as he's due to start soonish so maybe he can educate me further.

If I learn anything more I'll let you know!

RKQ

40701085 wrote: »

em, I think it was something like hardcore, radon dpm etc, then 150mm slab (stepped raft)...and that's all - does this sound right?

No floor insulation?
Floor insulation is required to ensure compliance with the Building Regs. A certain thickness depending on the date of your grant of permission.

A screed will be required to cover the insulation and pipework. I assume a certain height is left for this. What height are the eternal door thresholds above your finished slab?

40701085

There are 6 inches left, so original plan was for 70mm PU, 60mm screed & 18-20mm floorboard. No room for battens here unless the screed is omitted - do you reckon this is a bad move?

House was started late last yr (PP obtained in 2004) so I don't think I'd be subject to the latest building regs, but I want to put down as much xtratherm as I can regardless.

sydthebeat

40701085 wrote: »

There are 6 inches left, so original plan was for 70mm PU, 60mm screed & 18-20mm floorboard. No room for battens here unless the screed is omitted - do you reckon this is a bad move?

House was started late last yr (PP obtained in 2004) so I don't think I'd be subject to the latest building regs, but I want to put down as much xtratherm as I can regardless.

lay battens in screed....

RKQ

Lay battens or hilti nail sheets of ply to dry screed and secrete nail floorboards. Note position of all pipework to avoid puncturing pipes!
(Screed on insulation as described above, pipes fixed to insulation.)

40701085

Thanks for all the advice - plenty of food for thought..:rolleyes:

topcatcbr

All the described above methods are fine. But the origonal post was "

40701085 wrote: »

but is a ground floor screed essential?

" The answer to this is no

And
"

40701085 wrote: »

Reason I ask is that the queen wants solid wood floors (standard is 18mm thick I think) on GF. I spoke to the carpenter & he said that it is better to batten out the floor slab, lay some ply and nail down the wood floor (with insulation & pipework underneath to be sure) rather than try to glue the floor onto a screed."

There is nothing wrong with this AFAIK. Nobody has said any different so far.

xt40

hi,
you are being wrongly advised about the wood floor.if you go with battens it will end in tears and will cost you unnecessary expense.
there are a number of problems
noise caused by either creaks or the hollow sound you will get from the air gap between the battens. as the wood expands and contracts, it will stretch the nails and it will do your head in, especially in winter.
18mm floor + battens + mdf sheets = a huge rise in the floor. what if it gets grubby and you want to take it up in the future and replace with tiles or carpet. al your doors and skirting will be wrong.


the easiest and best way to lay a solid wood floor is to float it like a cheapo laminate on a sheet of plastic and some foam underlay over a normal SCREED. you absolutely must use floor clamps to tighten the boards together while the glue is going off or else you will have huge gaps and it will look rubbish.
glue 2-3 rows together,clamp,wipe excess glue,wait half an hour and repeat process.

with this method, zero noise,zero rise in the floor and as nothing is actually nailed,glued to the screed, its easy peasy to take up if you want at some later date.

RKQ

We are getting confused here lads.... better read all the posts before jumping off the deep end. I don't want the OP to be confused.

xt47 who said mdf on battens on screed? ("18mm floor + battens + mdf sheets = a huge rise in the floor.)
12 or 18mm plywood on a cement screed isn't a huge depth. Or battens in screed with no ply. Insulation and pipes are protected by screed. Nothing wrong with floating a floor if thats your preference.:)

Topcatcbr the OP was answered above, regarding floor slab compliance!

Originally Posted by 40701085
I spoke to the carpenter & he said that it is better to batten out the floor slab, lay some ply and nail down the wood floor (with insulation & pipework underneath to be sure) rather than try to glue the floor onto a screed."
There is nothing wrong with this AFAIK. Nobody has said any different so far.

How are battens fixed to conc slab ?
Are battens fixed thru insulation board? Topcatcbr can you see the problem with the OP's question? - too little info at that stage to give a definative answer.

Insulation between the battens won't comply with Building Regs! - heat loss thru battens:)

topcatcbr

RKQ wrote: »

Insulation between the battens won't comply with Building Regs! - heat loss thru battens:)

Are you sure about this. I know that the insulation will be bridged but there is a greater depth available to fill with insulation.

Anyhow I would imagine that the floor would be battened and counterbattened to remove any discrepencies in the floor slab and could be insulated between each allowing for minimal bridging where the battens cross.

Id fix battens through DPM/DPC with SS hitli nails into floor slab. I dont see any other way of doing it. No different than suspended timber ground floor (on dwarf walls).

RKQ

topcatcbr wrote: »

Anyhow I would imagine that the floor would be battened and counterbattened to remove any discrepencies in the floor slab and could be insulated between each allowing for minimal bridging where the battens cross.

Id fix battens through DPM/DPC with SS hitli nails into floor slab. I dont see any other way of doing it. No different than suspended timber ground floor (on dwarf walls).

Are we talking battens or floor joists?
If we use 150mm joists as dwaf walls how do we provide cross ventilation?
Wheres our recommended 75mm to underside of joist?

Now I'm getting confused:)

IMO 70mm foil insulation, rad pipes laid on top in armaflex, 60mm sand / cement screed - easy and simple! No cold bridge.

Floorboards - choice of methods -lay plastic dpm, then

• Hilti nail 12mm or 18mm plywood to screed - brick pattern & secrete nail solid t&g floorboards.
• Use semi-solid floor (no plywood required) or
• Float floor on dmp as described above by xt40. (Clamping is critical)