Lindab Plenum ceiling mounting?

[junglejim]

My MVHR parts have arrived 😀

 I have plvcu ceiling/wall plenums and wondering the best way to mount within the ceiling. The mounting tabs are useful but not sure whether to go direct to the underside of the 22mm egger floor above or whether I need to fit a piece of timber for each one and screw into that. Any advice and photos would be really appreciated. Thanks

[Nickfromwales]

1 hour ago, junglejim said:

My MVHR parts have arrived 😀

 I have plvcu ceiling/wall plenums and wondering the best way to mount within the ceiling. The mounting tabs are useful but not sure whether to go direct to the underside of the 22mm egger floor above or whether I need to fit a piece of timber for each one and screw into that. Any advice and photos would be really appreciated. Thanks

I always put a piece of 18mm OSB between each posi, screwed to the underside of the upper chord, and that gives a flat surface to mount to. 
 

The tabs are a bit soft, so use penny washers with the screws. 
 

Note: I always install 75mm acoustic insulation in before ANY 1st fix or M&E begins, as it’s so much easier to have that lost between the upper chords, and near zero effort to fit it as zero obstacles. Then you have the whole void for services etc.

 

Ergo, the 18mm OSB is requisite to fly over the 75mm acoustic batts.

 

I don’t fix anything (routinely) to the Egger / P5 as it’s “not the done thing”. 

 

Couple of battens for this one as other services too close to use a bridge of OSB, but gives you an idea. 

[junglejim]

23 minutes ago, Nickfromwales said:

I always put a piece of 18mm OSB between each posi, screwed to the underside of the upper chord, and that gives a flat surface to mount to. 
 

The tabs are a bit soft, so use penny washers with the screws. 
 

Note: I always install 75mm acoustic insulation in before ANY 1st fix or M&E begins, as it’s so much easier to have that lost between the upper chords, and near zero effort to fit it as zero obstacles. Then you have the whole void for services etc.

 

Ergo, the 18mm OSB is requisite to fly over the 75mm acoustic batts.

 

I don’t fix anything (routinely) to the Egger / P5 as it’s “not the done thing”. 

Thanks that’s useful. Still trying work out the best build up for my ceiling. The posi joists upper cord is about 45mm and there are regular noggins with the same gap above so thinking maybe 50mm Rockwool rwa45 then MVHR ducts then another layer of acoustic insulation. I feel like the ceiling should have as much insulation as I can get in but realise I also don’t want to be insulating the wiring . I’m probably way off here so really interested in what others do… another steep learning curve! 

 

 

[Nickfromwales]

31 minutes ago, junglejim said:

Thanks that’s useful. Still trying work out the best build up for my ceiling. The posi joists upper cord is about 45mm and there are regular noggins with the same gap above so thinking maybe 50mm Rockwool rwa45 then MVHR ducts then another layer of acoustic insulation. I feel like the ceiling should have as much insulation as I can get in but realise I also don’t want to be insulating the wiring . I’m probably way off here so really interested in what others do… another steep learning curve! 

 

 

We're currently, selectively and strategically, adding the second layer of 75mm insulation between the lower chords, eg where kids bedrooms upstairs are over the sitting room and the TV room / snug, so 150mm total acoustic insulation.

 

Then 15mm sound block plasterboard to finish. I suggested acoustic 'resilient' bars but the preference was to keep the max ceiling heights possible.

 

Go 50mm + 50mm  and the void in between will take the services, as I note you have quite shallow posi joists. FYI you can quite heavily scallop those strongback timbers to allow you MVHR ducts to pass over or under, as long as you leave them complete where possible. You can completely remove a section, just lay replacement timber on top of the lower chord and straddle those two posi's, to keep them 'tied'.