Concrete First Floor.

Quazzie

I'm building a storey and a half house with UFH in both the ground floor and the upper floor. This presents a few question for me.

1. Does it have to be concrete for UFH or is there any other option?

2. What concrete options are there, Block & beam, Hollowcore, Poured in-situ Reinforced Concrete???

3. How these joint to the wall. I've already planned for all downstairs walls to be 215 (9") solid to take the majority of the weight, but do i have to have my external with a 215 internal leaf also. or is a 100 standard internal leaf enough?

If anyone has any sketches or drawings of this junction I'd be very happpy to recieve them.

Thanks in advance for any help recieved.

sinnerboy

1. no - you can install UFH in a timber floor structure

2. For first floor most practical option is usually precast (hollowcore) + screed

3. if first floor is concrete better to make inner leaf 215 thick

You need a structural engineer . You can't make these decisions yourself , even with consulting here .

Quazzie

thanks sinnerboy. I will be engaging a professional when I do it but just trying to arrange figures at the moment so wanted to know my options to way up the pros and cons of each.

rahman

Concrete floor is definitely the way to go.
For external walls 4" is fine for inner leaf. For opes greter than 1500mm double up on lintel for inner leaf. For large opes use a girder.
I put in UFH on top of my concrete floor and its a great job

sinnerboy

rahman wrote: »

Concrete floor is definitely the way to go.
For external walls 4" is fine for inner leaf. For opes greter than 1500mm double up on lintel for inner leaf. For large opes use a girder.
I put in UFH on top of my concrete floor and its a great job

In my experience - not . The structural engineer who is certifying construction will have the last word

YourAverageJoe

Have been told by engineer that 4" is fine for my house which is similar to the ops, although he says it depends on the span sometimes.

Carlow52

Convention standards in the US require a minimum bearing of 3 inches for HC slab on a block bearing { less for steel bearing]

http://www.strescore.com/Technical_Data_files/Plank%20Bearing%20Design%20Information.pdf

The reason it is good practice to go for 215 inner leaf block is that it allows a higher margin for error.

The doubling up of lintels is not good practice either.

Heatherview

Hi Quazzie
What ever you deside dont forget to wrap the floor with airtightness membrane and seal wiith tape. now is the time to do it. See sketch for rough idea.

Heatherview

Technophobe

Hi Heatherview...

Can you expand on this please, as I will be installing a concrete first floor slab also...?
Are you saying that before the slab is placed on the structure, this should be done? If so, any recommendations re product type?

Where does this fit in in the overall scheme of things in terms of Insulation?

The more detail you have the better please...;)

thanks



"Hi Quazzie
What ever you deside dont forget to wrap the floor with airtightness membrane and seal wiith tape. now is the time to do it. See sketch for rough idea"

RKQ

Technophobe wrote: »

Can you expand on this please, as I will be installing a concrete first floor slab also...?

See ProClima web site for good photos of installation of membrane around floor slab(Moy and Siga may have similar photos)

Get proper advice on all structural pre-stressed slabs but from experience 75mm bearing for 150mm hollowcore slab but 200mm slab will require bigger bearing and with a 200mm hollowcore slab I'd use 215mm blockwork.

200mm hollow core over domestic spans may not need a structural screed and could be ideal for ufh - saving on second screed -(structural screed + finished screed with ufh pipes on insulation).

IMO a Double lintel is a mad idea - lintel is prestressed , so two lintels are no advantage.

If using conc lintols then ensure 2 rows of blocks minimum above lintel for necessary compression - see Homebond manual etc.
Otherwise use manufactured & certified steel lintols or steel I-beams to Structual Engineers spec.

Remember Hollowcore are prestressed so the longer the span the more they bow up in the middle - so 100mm block work is fine to sides of slab span as floor may not actually sit on wall!

The OP must get Structural Engineers Professional advice before any on site works. Each structure with have its owns individual issues that must be resolved.

YourAverageJoe

was looking at the detail and was thinking that this means the blocks are not 'stuck' to the slab by cement as the barrier is in between. Does this effect structural integrity?

RKQ

YourAverageJoe wrote: »

. Does this effect structural integrity?

No. The slabs won't move with their weight and once the structural screed is poured the floor becomes one unit. Then the blockwork walls are build on top of it. The wallties tie the block walls together

Think of the airtightness membrane as similar to the block work above and below a standard radon barrier detail - radon breaks joint in blocks but theres no loss of structural integrity! Hope this helps.

Technophobe

RKQ wrote: »

Think of the airtightness membrane as similar to the block work above and below a standard radon barrier detail - radon breaks joint in blocks but theres no loss of structural integrity! Hope this helps.

Excuse my ignorance on this but can you just confirm that the airtightness membrane is placed on top of the pre-cast slab and then you build up from there etc?

thanks and sorry for being a pest!!;)

Technophobe

Quick question on this....if u have UFH downstairs and given that heat rises...does that mean that even with a concrete 1st floor, that certain amounts of your ground floor heat will ultimately leak upto your 1st Floor

RKQ

Quick reply... Yes.
All heat rises but this will mainly heat the 1st floor, which will take the chill out of these rooms.

It is possible to insulate the underside of the slab.

I'd be concerned about the hollow voids in the slab, if unsealed, allowing warm air into the cavity or wind driven air from the cavity into the voids.

There is an airtightness detail to rectify this situation - wrapping the slab in a breather felt and plastering both ends into the walls above and below the slab. Some people seal the holes in the slabs with plaster or spray foam.

Johnniep

rahman wrote: »

For opes greter than 1500mm double up on lintel for inner leaf.

This is not good practice and should not be allowed on a site.

Technophobe

RKQ wrote: »

Quick reply... Yes.
All heat rises but this will mainly heat the 1st floor, which will take the chill out of these rooms.

It is possible to insulate the underside of the slab.

I'd be concerned about the hollow voids in the slab, if unsealed, allowing warm air into the cavity or wind driven air from the cavity into the voids.

There is an airtightness detail to rectify this situation - wrapping the slab in a breather felt and plastering both ends into the walls above and below the slab. Some people seal the holes in the slabs with plaster or spray foam.

Hi RKQ,

Thanks for the reply and info....
If as Heatherview says above and you added to re Proclima etc, you put in the vapour barrier, does that prevent the heat from leaking thru' from the Ground Floor to the first...?

thanks

technophobe

Bitten & Hisses

An alternative to Hollowcore+screed is to use an easyscreed type of product. (easyscreed.ie). My architect used this method for his own house: timber battens, a layer of plywood, layer of insulated gypsum board with the easyscreed poured on top. He claims it gives good soundproofing and it works better than concrete with UFH, although it is expensive by all accounts.

mickdw

Where did the idea of doubled up prestressed lintels come from? Its crazy but it seems to be getting popular. Some 'Engineers' are insisting on them being doubled up! Ive seen lots of cracks between the lintels when this is done no matter how they are proped during construction.

Technophobe

Heatherview wrote: »

Hi Quazzie
What ever you deside dont forget to wrap the floor with airtightness membrane and seal wiith tape. now is the time to do it. See sketch for rough idea.

Heatherview

Hey Heatherview..

Can I ask what product you used when you wrapped your concrete 1st floor..??

Just for my own understanding, what happens to the membrane hanging above and below the slab? Is this somehow sealed to the internal blockwork and then covered over when slabbing etc?

thanks

sas

Technophobe wrote: »

Hey Heatherview..

Can I ask what product you used when you wrapped your concrete 1st floor..??

Just for my own understanding, what happens to the membrane hanging above and below the slab? Is this somehow sealed to the internal blockwork and then covered over when slabbing etc?

thanks

You use solitex plus, the roofing membrane. It's quite robust and so is less likely to tear when hollow core slabs are dragged across it.

Internally, you tape it to your block work using a fleece backed tape. You then plaster over the tape (plaster adheres to the fleece) and hence you have a good airtight junction.

Alternatively you can fixed it to the block work using expanded metal lath and plaster over it as above.

Technophobe

Hi SAS

thanks for the reply....

Just to check this and for my own info

The Solitex Plus is firstly stuck to the inner side of the internal cavity wall block using the tape you mention, then pulled up the side of the concrete slabs laid for the 1st floor and then taped again to the inner side of the internal cavity wall above the slab?

cheers;)

sas

Technophobe wrote: »

Hi SAS

thanks for the reply....

Just to check this and for my own info

The Solitex Plus is firstly stuck to the inner side of the internal cavity wall block using the tape you mention, then pulled up the side of the concrete slabs laid for the 1st floor and then taped again to the inner side of the internal cavity wall above the slab?

cheers;)

The membrane is fixed to the wall inside.
The membrane travels up the wall and then turns towards the cavity travelling underneath the hollowcore.
The membrane is now brought up around the hollowcore (in the cavity) and back inside above the hollowcore.
The upstairs block work is completed on top of the membrane.
The membrane is then fixed to the inner surface of the inner leaf of blocks.

fuchia

I was thinking of just bedding the hollowcore in morter but this airtight membrane sounds like a better job.