Stud walls on first floor concrete

[SB2023]

Hi all

I am shortly putting up stud walls in our icf new build.

We have done full concrete slab for our first floor on a metdeck. It will have insulation, ufh and screed (same as ground floor).

I plan to build the stud walls before screeding due to soil pipes, ufh etc etc.

I am curious, is there any need for damp proofing or even a block course for the stud walls?l on the first floor? I assume no dpc as this is first floor so no damp...but maybe need it for the screed (I will have it over the insulation).

Then build stud walls entirely of timber rather than a block course underneath?

Thanks for you thoughts!

 

[saveasteading]

52 minutes ago, SB2023 said:

build the stud walls before screeding

yes that's wise, for strength too as the insulation is the weakest component.

I would expect that the floor is designed on this assumption.

No dpm required.

Nail the sole plate direct to the concrete. I wouldn't stop for doors, as you can measure and cut precisely later,

 

However, it is worth a sheet of polythene over the insulation before screeding. Even if you have taped all the joints impeccably, there is a risk of  a gap, especially at the wall interface or of tape sticking to a shoe.

You do not want to see the insulation floating to the top of the screed, and the small investment is worth it.

[Conor]

I'm assuming you're putting down 50mm insualtion, UFH pipes, then liquid screed. In that case there will be a polythene sheet laid on top of the insulation and lapped up the side of the walls prior to pouring. Are you going to board the walls first as well? I would, means screed drying time is not a constraint.

[nod]

Always put dpc under studs when they are directly on to concrete 

Don’t ask me why We put metal studs down on office blocks and BC always want to see 25 either side 

[SB2023]

Thanks all, some good points here and actually, yes I should check with building control too.

Will definitely have a sheet over the insulation as apparently the foil can interfere with the ufh pipes.

Nice call on boarding the walls first....

Really useful, thanks everyone.

 

[MortarThePoint]

26 minutes ago, nod said:

Always put dpc under studs when they are directly on to concrete 

Don’t ask me why We put metal studs down on office blocks and BC always want to see 25 either side 

 

Interesting, I have been putting DPC under my stud walls, but wondered how overly cautious I was being. They don't extend 25mm either side though, just a 100mm DPC under 4x2. On the first floor, I have timber sole plates under my MF partitions which basically brings up to level with the top of screed. Screed was then poured before framing (MF) and boarding.

 

The DPC rule may be more critical if proceeding at pace and there is a chance whatever the sole plate is going on is still high in moisture. I pressume you don't put DPC under purely MF partitions.

[nod]

23 minutes ago, MortarThePoint said:

 

Interesting, I have been putting DPC under my stud walls, but wondered how overly cautious I was being. They don't extend 25mm either side though, just a 100mm DPC under 4x2. On the first floor, I have timber sole plates under my MF partitions which basically brings up to level with the top of screed. Screed was then poured before framing (MF) and boarding.

 

The DPC rule may be more critical if proceeding at pace and there is a chance whatever the sole plate is going on is still high in moisture. I pressume you don't put DPC under purely MF partitions.

Yep Under the MF also 

One of my pet hates constantly telling people to dpc under studs on solid floors We have to take them up if they are missed 

[bassanclan]

4 hours ago, nod said:

Yep Under the MF also 

One of my pet hates constantly telling people to dpc under studs on solid floors We have to take them up if they are missed 

Surely there's a dpm below the concrete anyway?

[saveasteading]

6 hours ago, nod said:

Always put dpc under studs when they are directly on to concrete 

Any idea why? Or if it is so written, or just something they ask for from habit?

I don't recall ever doing this on a dry floor.

[nod]

It’s always in the bill of quantities 

I can see the logic of not fixing timber directly to the floor 

I think with metal its just one of those things they like to see 

[Susie]

I think MF is metal framing, I will eventually build my wood studs, foundations start April hopefully. The floor build up from concrete will be 200mm insulation, UFH and 55mm screed. Do I need a DPC below the wood? I have seen the studs built from the concrete before UFH and also after the screed so it’s insulated below which is best?

 

[JohnMo]

15 hours ago, SB2023 said:

Will definitely have a sheet over the insulation as apparently the foil can interfere with the ufh pipes.

The reason for that sheet isn't as you describe. That sheet is to stop a chemical reaction between the aluminium and screed. The chemical react forms hydrogen bubbles in the screed. The sheeting also acts as a barrier to stop the screed getting under the insulation and floating it on top of the screed.

[MortarThePoint]

1 hour ago, Susie said:

I think MF is metal framing, I will eventually build my wood studs, foundations start April hopefully. The floor build up from concrete will be 200mm insulation, UFH and 55mm screed. Do I need a DPC below the wood? I have seen the studs built from the concrete before UFH and also after the screed so it’s insulated below which is best?

 

 

200mm of insulation for the First Floor feels massively excessive to me.The concrete that insulation is sat on is in the heated envelope (unless over a garage) so is already warm. A well insulated house is going to have a low UFH flow temperature (e.g.35C) so thick insulation is a waste of money. Ground Floor sure, but not first floor. Insulation on first floor is only for responsiveness and zoning as far as I can guess.50mm would be plenty for that.

 

Just seen your not the OP so presume you're talking about Ground Floor

Edited January 7 by MortarThePoint

[Russell griffiths]

7 hours ago, Susie said:

I think MF is metal framing, I will eventually build my wood studs, foundations start April hopefully. The floor build up from concrete will be 200mm insulation, UFH and 55mm screed. Do I need a DPC below the wood? I have seen the studs built from the concrete before UFH and also after the screed so it’s insulated below which is best?

 

I think you need to start another thread for this with diagrams, the original post is about first floor stud walls. 

[SB2023]

As the OP, just to clarify I am talking first floor. Definitely dpc on ground floor concrete slab under studs as designed where I will be using concrete block and mortar as a base. 

Upstairs I will have about 20mm of insulation on the concrete slab just to stop some of the ufh heat travelling downwards in the slab. I think the heating will be rarely used upstairs anyway.

Thanks for correcting me on the chemical reaction @JohnMo.

[John Keith]

I guess you've already done it now but for anyone else...I'll add a link. Underside of sole plate should be at or above ffl apparently?

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-3-internal-walls/6-3-5-load-bearing-timber-walls/

Edited September 23 by John Keith

[saveasteading]

I hadn't seen that clause. I suppose it is generally a good idea to be above all potentially damp zones.

But our steel shed has a structural concrete floor on a dpm. We aren't breaking it up. On it will go 150mm pir then a screed. 

On our steading we also poured a slab and built on that. Bco didn't stop us. 

 

So our sole plate is going to be 220mm below FFL on a dpc.

As it happens we had thought of first laying a kerb, either pc or insitu concrete. But then we thought "why".

 

Any good explanations?

 

We could just call it something other than sole plate. 

[Canski]

2 hours ago, John Keith said:

 

I guess you've already done it now but for anyone else...I'll add a link. Underside of sole plate should be at or above ffl apparently?

 

That seems new. It is however for load bearing walls only. You can’t build a load bearing wall on top of PIR.