Ventilation duct in celotex

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Hi folks,

We are in the process of getting a rear extension built with the following sandwich layer:

Finished floor
screed with wet UFH heating
PIR insulation boards
Concrete
DPC layer
Hardcore

We have got some ventilation ducts that are flowing the length of the extension to provide ventilation for the front of the house which is still on joist floors. The builder has created a cut out in the PIR insulation for the ducts and it all looks like a neat job.

However my concern is that the parts where the PIR insulation boards have cut seem to be quite fragile.

Is this the correct thing to do? Or would you recommend doing something else instead?

Thanks!
 
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I would have thought the ventilation ducts should have gone through the concrete slab, in plastic ducting.

What thickness of insulation is left where the ducts are? If there is less insulation here, it's a potential cold spot.
 
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The insulation is 100mm thick, and the duct is 50mm thick, we intend to have 65mm dry screed with wet ufh heating
 
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I've done it (after checking on this forum) as two layers of 60mm insulation. Rectangular ducting is in the 1st layer covered then by 2nd layer of insulation. I'm going with 22m chipboard and it looks quite stable now.
 
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I put mine (110mm soil pipe) in the hardcore/mot with telescopic airbrick risers.
 

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