How to work out screed depth

[crispy_wafer]

A question i've been too afraid to ask.  How do you work out how much screed depth is required - so when speaking to suppliers you sound like you have a clue...  At present I've been guessing, and now i'm getting closer to getting it done, I dont want to have too much poured in.

 

Buildup is

block and beam floor

Dpm

150mm Insulation

DPC located 1 block above floor

 

Main entrance door has been installed at the dpc level but has a 15mm upstand.

 

At this point I've no idea what the finished floor layer will be or thickness which doesnt help.  Is there a rule of thumb.

 

[joe90]

Surely this has all been calculated? Taken into consideration for door heights etc, even taking into account tiles or other flooring? 

[Conor]

So basically your threshold is about 230mm above the B&B floor? Take away insulation (150mm), and your left with about 80mm. Allow 20mm for flooring, anqother 10mm for error, and your down to 50mm. 

 

The key thing is the floor finish at the door threshold. 5mm lvt or 30mm limestone slabs?! That'll determine your screed finish level. You need to decide this yesterday.

 

You normally do this on the reverse way, set your thresholds based on a set depth of insulation, screed and floor finishes.

[jayc89]

What screed are you going for? 50mm is generally considered the absolute minimum depth for a liquid screed, 65mm if using sand/cement. 

[saveasteading]

Cemfloor say 

Pouring between 40mm and 50mm of liquid floor screed for underfloor heating is optimal. The diameter of the heating pipe is included in this depth.

 

We are going for 50 as 40 doesn't allow much tolerance for any wobbles.

[crispy_wafer]

The rule of thumb I wanted was to work out depth of screed, I had my assumptions, but as with most things self build no prior experience.  And I'm sure this post will help others in the future too.

 

Fancied resin topped or a microcement, but budget constraints know mean my plans will need to change.  My big concern would have been pouring too much screed for one type finish, then what if in 10 years we then fancied a different type of flooring, I've then got to replace the front door and threshold.

 

Marek

[Conor]

2 hours ago, crispy_wafer said:

The rule of thumb I wanted was to work out depth of screed, I had my assumptions, but as with most things self build no prior experience.  And I'm sure this post will help others in the future too.

 

Fancied resin topped or a microcement, but budget constraints know mean my plans will need to change.  My big concern would have been pouring too much screed for one type finish, then what if in 10 years we then fancied a different type of flooring, I've then got to replace the front door and threshold.

 

Marek

We had the opposite issue. Allowed 20mm for engineered wood flooring. We changed to 12mm laminate at the last minute, so used 5mm wood fibre underlay to bring it up to the right height. You'll not motoce a 10mm gap at the thresholds, so definitely allow for the thickest floor covering you'd likely go for. 

[saveasteading]

Today I looked up the NHBC tolerances for floors. Shockingly tolerant.

The 3mm over a 3m straight-edge is sensible and reasonable. But 20mm overall variation over 6m being acceptable? 

 

Therefore if you are worried about 10mm, as we all should be, then it seems you have to write our own specification.