Ceiling service void batten sizes

[Moonshine]

I am building a warm roof with the air tightness layer going below the roof joists, no MVHR

 

I am going to batten below the joists to allow sevices such as down lighters and fan extract in a bathroom.

 

How big are the battens typically spec'ed as to allow sevices for bedrooms and bathrooms to run?

[DevilDamo]

For a warm roof, the VCL should be above the ply (or similar) deck so is above the joists, not below them. That would mean you could use the joist depth to accommodate downlighters and extract ventilation.

 

A cold roof would be different as any penetrations through the plasterboard is likely to puncture the VCL, which would be positioned below the joists. The service void depth ultimately depends on your choice of fittings and ducting. In my opinion, a min. 75mm void should suffice.

[Moonshine]

9 minutes ago, DevilDamo said:

For a warm roof, the VCL should be above the ply (or similar) deck so is above the joists, not below them

 

Holy sh@t I had forgotten that! That makes things easier!

[nod]

We used the multi foil 

Joists ply multi foil fairing strips 

Then OSB 3

150 kingspan between the joists Then counter baton board with 15 mil duplex 

Leaving just enough room for down lights without crying the insulation 

Seems to work 

[Hilldes]

1 hour ago, DevilDamo said:

For a warm roof, the VCL should be above the ply (or similar) deck so is above the joists, not below them. That would mean you could use the joist depth to accommodate downlighters and extract ventilation.

 

@DevilDamoIs that the case where the insulation is on the outside of the rafters? If not the VCL would be in the same location as the breather membrane? I thought the point of the VCL is to stop moisture from the house interior entering the building fabric.

 

@Moonshine My warm roof spec is from outside: breather membrane, rafters filled with mineral wool, 50mm PIR across inside of rafters, VCL, 50mm service batten and plasterboard. I know 50mm service cavity (+ plasterboard and finish depth) is going to be tight for downlighters etc. but we need every mimilmeter of headroom. Its a 1.5 storey with vaulted ceilings upstairs. Might move the VCL above the PIR to avoid heat damage from downlighters. We will have MVHR but the ducts run up through internal walls.

[ProDave]

Mine must be a "hybrid" though I always think of it as a warm roof.

 

Outside to in:

 

Tiles

battens

counter battens

breathable membrane

100mm wood fibre board

200mm rafters filled with frametherm 35

11mm OSB racking layer

Air tight membrane

25mm battens

Plasterboard and skim

 

25mm battens are just for cables, being a 45 degree sloping roof, surface mount spotlights are used.

 

If it is a flat roof or only a slight slope and you want flush lights you will need more space.  Or use flat panel LED lights that often will fit in the thickness of plasterboard.

[Iceverge]

3 hours ago, Moonshine said:

I am building a warm roof with the air tightness layer going below the roof joists, no MVHR

 

I am going to batten below the joists to allow sevices such as down lighters and fan extract in a bathroom.

 

How big are the battens typically spec'ed as to allow sevices for bedrooms and bathrooms to run?

Don't forget you can use different thicknesses depending on how much space you need in each room. battening at 90deg to the rafters makes it easy to run wiring and if you insulation inbetween  it cuts down on thermal bridging of the rafters. 

 

For my money I'd use 50x50mm battens with 50mm mineral wool inbetween. 

[DevilDamo]

@Hilldes This will help... https://www.bauder.co.uk/technical-centre/design-considerations/flat-roof-design-considerations/thermal-design-insulation-and-consideration.

[Hilldes]

Thanks @DevilDamo that gives the orer of materials as I expected - i.e. VCL inside the insulation and breather membrane outside the insulation. Interesting definitions of cold and  warm roof (albeit flat roofs in the link), that would make may pitched roof a cold roof and I've always referred to it as a warm roof ?.

[ADLIan]

In a pitched roof construction insulation between/under rafters = cold roof construction but warm roof space. If all/majority of insulation above the rafter this is a warm roof construction (& warm roof space)