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Pouring final floor before structure is built

JohnChadwick

Looking to pour the final floor screed before walls, windows and roof is on.

Currently at the stage where radon barrier is laid on top of subfloor. Thermal block is also laid.

Looking to get a dry spell to lay the insulation boards, fix the ufh pipes and pour the top 60 or 70mm concrete floor.

Has anyone done a house this way? In my mind the radon layer needs to be bone dry before the kingspan boards go on and the floor is poured. My thinking is that the moisture has no where to go otherwise.

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Mellor

Is your DPM completely horizontal, or it is up and over the thermal block?

Moisture above the radon barrier will evaporate vertically upwards. The screed has a significantly water content that has to evaporate.

JohnChadwick

The Radon Barrier / DPM is completely horizontal yea.

You mean moisture will evaporate upwards through the insulation plus concrete screed...?

Mellor

https://www.boards.ie/discussion/comment/121512611#Comment_121512611

You said you want the DPM to be bone dry, before you pour the screed concrete. Think about that, you are worried about surface moisture, on a surface that you are going to pour wet concrete. Which will have far more water in it than you are trying to eliminate. Any surface moisture will be lost to the concrete. Technically the water doesn't evaporate, some does but most is used to hydrate the cement. Some near the surface will evaporate in summer. I wouldn't be concerned about surface moisture.

But I would be concerned about that DPM. If it is horizontal, what stops the water coming in straight over the top

JohnChadwick

OK I see. Yes great info, hadnt considered that hydrating the cement will absorb moisture.

On your last point. My thoughts are that the DPC will come down over the thermal block, then over the dpm and form a tray to bring water in the cavity to the outside.

bfclancy2

Put the radon up and over the block, that's the correct way

sydthebeat

Radon membrane should have been laid under the subfloor. That would then give you your upstand at the rising walls which is required by the NSAI certification.

you are leaving the radon membrane exposed during the whole build if you leave the installation of the insulation / UFH / screed to the end. Not a good idea. slippy when wet and will be punctured when items are dropped

JohnChadwick

https://www.boards.ie/discussion/comment/121513778#Comment_121513778

Yes but radon has been done this way now. I agree with having radon above subfloor to be honest.

The top screed plus ufh plus insulation will be installed before proceeding with the building structure. The top screed is then the working surface rather than a slippy radon / dpm.

SodiumCooled

I wouldn't be a fan of many aspects of the build method/order of things outlined but one I certainly would not like my finished floor being exposed to the full construction process it's going to get damaged.

sydthebeat

https://www.boards.ie/discussion/comment/121513917#Comment_121513917

too late now

bfclancy2

put a secondary layer of dpm in, under the insulation and lap over the block, 1600 gauge polythene or something similar

JohnChadwick

https://www.boards.ie/discussion/comment/121513917#Comment_121513917

You know floor will be covered with wood/tile right? What is the damage likely to be here, like things falling on it or the impact of heavy loafing during construction...?

Mellor

https://www.boards.ie/discussion/comment/121513728#Comment_121513728

DPC has forms a tray, which directs water down, but that tray is has a gap to the DPM, so water can pass between the too. Mu preference would be up and over a block or half block. Which is that lapped.

https://www.boards.ie/discussion/comment/121513778#Comment_121513778

I'd assume that any exposed radon barrier, insulation, or finished floor gets covered with suitable protection during construction. But maybe I'm assume too much of a domestic builder. It certainly should, obviously.

https://www.boards.ie/discussion/comment/121513810#Comment_121513810

If it's in above the subfloor, you likely still have the ability to go up and over the thermal block. If this meant knocking out a thermal block its worth it.

mickdw

Woeful detail and not a great idea to attempt to do the finished floor at this stage.

I've seen it work on an housing estate where they got everything in the right position by about house no 20.

JohnChadwick

Thanks Mellor. The thermal block is laid and the radon /dpm is under that as shown in sketch. Is there another solution without knocking out the thermal block. No outer leaf blocks are laid so far.

JohnChadwick

https://www.boards.ie/discussion/comment/121514579#Comment_121514579

This could be the solution. But is the original layer (thats already currently installed) still gonna cause issues...?

De_man

Surely the top screed is too thin? Whatever your engineer is willing to pass, suggest polishing the floor a few hours after pour, take your time and it’ll come good did it in our build no issues used a scraper and the mortar came off easily.

JohnChadwick

https://www.boards.ie/discussion/comment/121516604#Comment_121516604

60 or 70mm is ok for ufh I believe. How do you mean the mortar came off? Where'd the mortar come from?

Mellor

https://www.boards.ie/discussion/comment/121516511#Comment_121516511

Putting a separate piece up and over the thermal block is not going to change the flat path way for water to come in.

You need to have a permeant bonded water barrier upstand from the DPM level. A piece flapped on top is not a benefit.

JohnChadwick

https://www.boards.ie/discussion/comment/121516669#Comment_121516669

Thanks for this.

Could the dpc be bonded to the dpm then? The dpc is not shown great in that detail but its would come down at 45 from the top of the thermal block.

Or would a similar option be to have the DPC just turned down the outside wall when it comes out of the outer leaf. In my mind this would stop water meeting the flat dpm when it rolls down the wall.

sydthebeat

Your cavity insulation is supposed to come down 225mm below the finished floor level.

How will it do this if the DPC is at 45 degrees?

Plus, is it a radon membrane or DPM that has been installed already? These are not the same thing

bfclancy2

https://www.boards.ie/discussion/comment/121516669#Comment_121516669

what i was suggesting was a whole new dpm under the insulation and up over the blockwork, should work perfectly, this could have been achieved just using the radon membrane but wasn't so this is next best solution

JohnChadwick

https://www.boards.ie/discussion/comment/121516845#Comment_121516845

In that theory the dpc need to be at 90 degrees then and tail around under the cavity wall insulation.

The radon barrier and dpm is the same thing in this instance.

bfclancy2

https://www.boards.ie/discussion/comment/121516874#Comment_121516874

well we don't know they are the same thing in this instance, the radon barrier hasn't been installed to perform as a DPM so maybe it is just a radon barrier

JohnChadwick

I still think this can work if the DPC is got right.

SodiumCooled

https://www.boards.ie/discussion/comment/121516874#Comment_121516874

loading up with blocks, being scraped cleaning, blocks etc hitting it general wear from being a site. That’s all on top of the underfloor pipes too.

It’s going to make tiling etc much harder if it’s rough/damaged and will need bits of repair/levelling compound.

do you have your kitchen fully designed also if not how do you know where to leave out UF pipe work under cabinets, an island etc?

mickdw

A complete new layer of dpm up and over block would work as suggested.

Anything else is going to be very messy.

You have that flat path from outside to inside.

You could in theory go over the block with a new piece of radon barrier and attempt to seal it to existing at bottom of cavity but there is no way it would be a success and you would never get the 100 percent seal that you would need given the flat water transfer route you have constructed.

Let the radon as installed perform radom duty which it will as it forms a complete barrier under building and across cavity as required and then start again with a dpm where the only purpose with keeping the internal dry.

JohnChadwick

https://www.boards.ie/discussion/comment/121517117#Comment_121517117

The new Dpm sheet is still not going to solve the problem of the flat radon membrane here though is it. With that theory I still end up with two sheets of plastic flapping against each other. And there is still scope for water to run inside along the flat membrane. Unless they are binded together which is messy.

In my mind the dpc can solve this by coming out the same block as the radon membrane and turning down the wall outside.

bfclancy2

https://www.boards.ie/discussion/comment/121517173#Comment_121517173

what does it matter if the moisture runs in between the two layers, its running into an area below the dpm, which would ordinarily be damp anyway, you are overthinking it

JohnChadwick

https://www.boards.ie/discussion/comment/121517218#Comment_121517218

Very valid point. Thank you

Mellor what do you think about my comment on the dpc. If the dpc comes out the same block as the radon membrane and is left longer so it turns down over it. Doesn't this negate the issue of the flat sheet?

Look here's a picture of my thinking.

bfclancy2

https://www.boards.ie/discussion/comment/121517341#Comment_121517341

no that dpc won't remain in that position, it will be compromised by one of the trades, water will get up under and back to square one, damp proofing only works if the membrane is continuous in my opinion, damp is not hard to prevent but if you try and take a shortcut it'll get you, craft bugger that it is