Warm roof condensation risk

[PRB86]

Planning on reroofing my property as the existing tiles are starting to fail and need to get it sorted before I refurbish the interior.

I would like to install insulation between the rafters to create a ‘warm roof’ space but have some concerns with regards to the possibility of condensation forming between the overboarding and the breathable membrane.

My current plan is to :
Install insulation between the rafters
Overboard with 6mm ply
Breathable membrane covering the 6mm ply
Battern up the length of the rafters
Counter battern across the rafters
Install tiles

Appreciate that the overboard may be a bit of ‘overkill’ but I want to stop the birds getting into the loft space.

Is there a risk of condensation forming between the membrane and the overboard ? Any comments or advice would be appreciated.

 

[catlad]

Overboard then batons on the rafters then breather membrane then tile batons gives you a space to vent, over fascia board vent strips will do. 6mm is to thin.

 

[Alastairreid]

Tiles.
Tile batten.
Counter batten.
Membrane.
9mm ply.
Insulation boards between trusses leaving 50mm clear gap between underside of ply and insulation.

soffit vents and continuous ridge vents.

 

[Zeberdee]

Tiles.
Tile batten.
Counter batten.
Membrane.
9mm ply.
Insulation boards between trusses leaving 50mm clear gap between underside of ply and insulation.

soffit vents and continuous ridge vents.

Sounds pretty good to me!

 

[PRB86]

Thanks for the advice I have received it has been very useful.

Sad, I know but I woke up this morning thinking about the roof wondering why are counter batterns sometimes used and sometimes they are not.

I appreciate you will get a better airflow through the roof when you have used counter batterns but the disadvantage you get as I can see it is that the end tile near the gutter sits that much higher up.

Are there specific situations / types of roof when it is best to counter battern or not ?

 

[seasickstevie]

But if it's counter battened, as alastairreid says, the tile battens aren't going to hit the counterbattens are they? I would have thought your additional battens should sit on top of the original spars. (then undercloak, then tile battens).

 

[PRB86]

But if it's counter battened, as alastairreid says, the tile battens aren't going to hit the counterbattens are they? I would have thought your additional battens should sit on top of the original spars. (then undercloak, then tile battens).

If my terminalogy use is correct (?) the counter batterns run up the length of the rafters on top of which the tile batterns run at right angles to the counter batterns.

 

[seasickstevie]

I get yer!

I took it as 'counter' meaning 'perpendicular' (as in horizontal).

 

[Alastairreid]

Are there specific situations / types of roof when it is best to counter battern or not ?

Any roof which has sarking board ply etc over the trusses should have counter battens to maintain an airflow beneath the tiles and allow any water penetration to escape down the felt and into the gutter.
Its common practice in Scotland to board over the trusses due to the more extremes of weather.

The height difference at the eaves is overcome by using a deeper fascia board.
If you have no fascia board ie a stone plinth we would screw lengths of 100mmx50mm softwood to wallhead, the fascia brackets can then be screwed to this.