Filling Cavity threshold 150mm

[Jam13Smith]

Hi All,

I've searched the forums and come across a fair few similar situations, but I guess I'm looking for opinions/ knowledge from people with better oversite than myself...
I'm about to insulate the floor of our newly built extension and below is the set up.

Builder doesnt think a fill in the cavity is really necessary, and could very well be correct and more than happy to be told so.

Engineer by trade, so over think most things, and I have concerns that due to it being a high traffic area, the 150mm cavity lends itself to being a weak point? What would you do?

If a fill is necessary, using a DPM to create a trough as other posts suggests then lean mix as below okay?

Many thanks in advance

 

[George_engineer]

I'd do the second one. On a short doorway it is more bother, but for a bi-fold I'd generally not have the innerleaf.

 

[freddiemercurystwin]

Agreed, furthermore you ought to have a vapour barrier under you screed (to prevent any screed seeping through the gaps in your insulation and at the perimeter) lapped up the wall in front of the dpm, lap the dpm up under the threshold, then these days our more conscientious builders are using epdm tape everywhere for good measure.