PVC vs semi-rigid to avoid a manifold

[Adam2]

I've an abundance of 150mm PVC duct - bonus from an auction so this is essentially free as I'll never use it all.

 

Considering my ample supplies I was thinking that for the top floor of my house I could use this instead of a manifold + multiple semi-rigid ducts. There's 2 bedrooms and 2 bathrooms so figured a "Y" connector on the supply/extract then run the 150mm duct to the required locations.

 

One concern I've seen mentioned is potential for noise transmission - the ends of the ducts will be about 10m each from the "Y" so about 20m apart. Not sure if anyone has anything at all similar but would be good to hear if the noise transfer is likely to be a real issue with this setup.

 

If I do go this route it'll save 2 x manifolds and about 80m of semi-rigid duct so seems worth looking into (though accept a bit more work on joints and maybe some faff with routing)

 

 

 

[Adam2]

A rough image that may help explain. Ducts come up through a services opening in a dressing room

 

 

 

[Conor]

I've done a load of mine in spiral ducting. Had to as lack of voids for ducts. It will perform very well but it is an absolute pain in the ass to do! If I was doing it next time, 100% semi rigid.

[Adam2]

Thanks - maybe will wait until joists in and take a look at routing 

[Bonner]

I am planning to use 125 & 150mm rigid duct so would be interested in any excess pipe ?

Thought about Y connectors and 45deg runs but threading through posi-joists at an angle doesn’t look feasible. 

[Gone West]

I fitted a 125mm serial rather than manifold ducting system in my last house using rigid uPVC. Fitting attenuators reduces 'cross- talk'. The ducting fitted snuggly through 250mm metal web joists. It does mean the joists have to line up accurately though.