Screed, underfloor heat and bifolds !! Help

[spike66k]

Advice please!
I have a 5m x 4m extension underway.
Got my slab down, with the insulation boards under whacked down type 1 below the slab.
My plans say to put 75mm screed down, BUT no allowance has been made for dry underfloor heating - and the bifold company are due to visit for measurements of exact floor finish, so they can make the doors. My floor tiles will be 10mm. The existing tiled floor in the house and the "slab" are approx 75mm difference at the moment.
1) should I guess at the underfloor heating depth (6mm board to mount it on and approx 3mm for the rolls of ufh). Does this sound about right?
2) Does this then mean I should only put 66mm screed down?
3) for drying and ease of install should I use a "flowing screed"? Rather than old fashioned?
If flowing screed, I would like a very rough guideline of how many m3 I would need - and any recommendation for a company around the Oxford or Aylesbury areas who can do it? ( cash if needed)
Many thanks
Colin

 

[noseall]

Talk with your bi-fold supplier, but they usually have some leeway regards floor finishes. My understanding is that your new screed will finish in line with the existing and this will be your floor level. Additional finishes should amount to no more than 25mm.
Surely there must be a 30-40mm tolerance with the bi-folds for additional finishes?

 

[spike66k]

Excellent question.
I will ask the bifold man today!
Thanks so much.

 

[roboughton]

You don't have to put insulation down as you already have it under the slab BUT it does make heat up quicker, depending on brand of heating element they can be between 3mm so lost in the adhesive up to 10mm so more adhesive required. Remember if you are putting the 6mm boards down you also need some tile adhesive on the back of it too so don't forget to allow for that.

 

[r1flyguy]

You don't have to put insulation down as you already have it under the slab BUT it does make heat up quicker, depending on brand of heating element they can be between 3mm so lost in the adhesive up to 10mm so more adhesive required. Remember if you are putting the 6mm boards down you also need some tile adhesive on the back of it too so don't forget to allow for that.

This is exactly what I have done

Also note that bifold manufactures all have there own type of cill and design and there heights vary too, this is what I found.
Our installers had a set height from the damp course and we worked to that, i.e, the concrete slab was in, doors installed, screed laid to depth required including allowances for insulation board fixed with adhesive, UFH, levelling compound, tiles and adhesive, this has left us with a minimal threshold.

 

[spike66k]

Thanks guys.
You are quite correct, the bufold man has just been and was only interested in the height from the damp course.
I have 58mm to play with, including underfloor heating, screed and finished tiles for the bifolds to fit.
A total of 95mm from the slab to the top of the finished tile : Therefore would you agree that the maths should be -
95mm. minus 13mm tile and adhesive
minus 6mm board to mount ufh on.
minus 3mm rolls of ufh
That equals 73mm of screed needed ( liquid stuff).
Have I forgotten anything in the equation chaps?
Should I slam in another 10/20mm insulation board to reduce the amount of liquid screed ( to help the floor heat quicker through less screed?)
Thanks
Colin

 

[r1flyguy]

Hi Colin

I used 10mm insulation boards below my dry ufh,

Are you tiling over the element as this is more difficult than a nice flat levelling compound?

I'd suggest you go slightly over on your adhesive depths etc,

Are the tiles uniform, is 3mm enough,

Just work out what height you expect to have and this will be your tolerance, the more you use the less threshold to trip over when your drunk in the summer on the patio

 

[spike66k]

Thanks buddy! Will do!
I'm just hearing from liquid screed people that it's wise to have only 50mm screed over ufh. Looks like I'll be putting 20mm insulation down!

 

[r1flyguy]

I had the 'normal' screed floor laid over the slab
Then adhesive to 10mm insulation board
Then primed
Ufh heating mats laid
Then covered with levelit2
Then adhesive & 10mm tile

50mm over a non wet ufh seems a hell of a lot of floor to get the heat through!! Plus the tiles on top.

I may be very wrong though as I've never fitted it before.

 

[roboughton]

I have fit the UFH mat/cable at tile level all screed and insulation is below it. So its...

subfloor - in your case screed
insulation board
UFH mat/cable
tile adhesive thick enough to cover the cable - I also ALWAYS put in a extra probe for the UFH controller

 

[spike66k]

I hadn't thought of screeding under the ufh.
Just got a quote for liquid screed, 5.3m x 3.95m by 54mm £800 cash fitted. Is that reasonable? I thought it would be about £600 cash

 

[spike66k]

Blimey. The underfloor heating bloke has been telling me it needs laying under the screed, and it doesn't !!!!! Just stick it to primer on top of the screed and tile over it. Breakdoen of communication between me and the floor heat company!
Thanks to you guys, I now have a clear picture of what needs doing. I've dumped the idea of flowing screed as its a bit pricey. My builder is nearly 80 years young, so I'm now trying to explain an accelerant will be needed in the screed.
I don't suppose there is a ready mix screed with accelerants in? I only need 1.1 m3
Cheers
Colin

 

[roboughton]

Blimey. The underfloor heating bloke has been telling me it needs laying under the screed, and it doesn't !!!!! Just stick it to primer on top of the screed and tile over it. Breakdoen of communication between me and the floor heat company!
Thanks to you guys, I now have a clear picture of what needs doing. I've dumped the idea of flowing screed as its a bit pricey. My builder is nearly 80 years young, so I'm now trying to explain an accelerant will be needed in the screed.
I don't suppose there is a ready mix screed with accelerants in? I only need 1.1 m3
Cheers
Colin

Check with the UFH he's using but most are under the tile. If you were going to heat all the screed the heat up time would be quite a long wait but then it would take alot longer to cool down so its swings and roundabouts but I bet any electric element would be under tile only I have never seen one that goes in the 50-60mm screed. Are you sure you can go with a wet system?

 

[r1flyguy]

The wet systems are covered with wet screed

If you search you tube for the 'underfloor heating store electric blanket' they have full video demos of how to lay the mats

 

[r1flyguy]