Help with Sarked Roof Detail, Membrane and Velux Windows in Roof

[Paulgwat]

Hi all,

 

I am looking for some help in understanding where i might be going wrong here.

 

We purchased a Potton timber frame and they supplied the attached detail for how the roof should be constructed for the 2nd floor (these are bedrooms and bathrooms with a wall height at the edge of the room of 1.5M and a sloping roof until 2.4M).

 

We have followed the drawing, installing the counter battens as indicated on top of the sarking board and then installed the vapour barrier (Rhinovent Pro) over the top of the counter battens with the 10mm droop as indicate in the install instructions for the membrane.

 

Battens have then been installed on top of the vapour barrier to allow installation of solar panels and roof tiles.

 

We are basically revisiting this as we have issues with water somehow getting in either via the Velux windows or through the membrane itself (to our knowledge there are no rips or tears in the membrane) and running down the sarking boards and finding its way to the wall plate.

 

So my questions are 

1. Have i bought a rubbish membrane? What should I use instead?

2. Detail from Potton calls for Kingspan Nilvent (or similar) but all of the information on Nilvent says it should be laid on top of the sarking board and not over the counter battens - which takes precendence here?

3 Does anyone have specific information on how to install a velux window on a sarked roof with counter battening, as we couldn't find anything.

 

I am sure I have left out a bunch of relevant info, so apologies in advance if i have omitted anything important.

 

Thanks in advance 

 

Regards

 

Paul

 

 

[Nickfromwales]

Just done 9x Fakros and had ‘input’ as to how / when they went in. 
 

22mm fibre sarking board over 300mm posi joist roof with blown in cellulose.

 

Breather membrane sat directly on the sarking, then 50x25mm vertical rising counter batten, then 50x25mm roof battens laid horizontally for concrete tiles.

 

Zero issues.

 

Manufacturers installation guidelines trump everybody else, including the BCO!

 

The membrane should have been flat on the sarking afaic.

 

You need to get the roofer to expose the heads of these openings, and check how / where water is getting in. If the membrane has this droop then these are just going to become natural gutters, which collect and pool water at the top of any openings / solar PV trays.

 

Poor suggestion from Potton here I’m sorry, but they’ll just blame your roofer. 

[Paulgwat]

@Nickfromwales thanks, I have gone back to Potton for them to review the drawings as have had to put the scaffolding back up to look at this and don't want to have to do it again

[Nestor]

Screen grab from the Kingspan site. Not sure where the 10mm drape on top of the batten would have come from.

 

Is your final roof covering on?

 

I did fit 9 Velux in our roof using the Velux insulation and underfelt collars as well as taping the membrane around the frame. 

 

Near waterproof before I fitted flashing kit and metal roof.

Edited 6 hours ago by Nestor
Spellin!

[Mr Punter]

The membrane should be fine not faulty.

 

As you have sarking and counter battens there is no need for any droop.  As @Nickfromwales says you could have laid the membrane flat on the sarking but no matter.  I suspect the error is where the membrane meets the top of the Velux and the flashing / membrane has not been cut as shown and installed correctly.