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Air tightness membrane piercing


cwr
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Hi all

 

Part of our roof make up is to be, from inside: plaster, plasterboard, 25mm service void (25mm battens) 60mm PIR, air tightness membrane, rafters with 125mm PIR between.

 

Builder questioned this as the air tightness membrane will be punctuated in multiple places by the fasteners that hold on the battens, 60mm PIR  and the membrane itself. 

 

Is this a fair point or will it all be ok as the screws/nails self seal the holes they make? 

Thanks

 

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interesting that the air tight membrane is going behind the 60mm PIR. I was planning on filling the rafters with mineral wool, then putting 80mm PIR and THEN adding the VCL. that way any off-gassing from the PIR is all behind the air tight membrane and not off-gassing in to the house.

 

crazy paranoia or sensible?

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3 hours ago, Thorfun said:

interesting that the air tight membrane is going behind the 60mm PIR. I was planning on filling the rafters with mineral wool, then putting 80mm PIR and THEN adding the VCL. that way any off-gassing from the PIR is all behind the air tight membrane and not off-gassing in to the house.

 

crazy paranoia or sensible?

 

Very sensible approach IMO. You have the opportunity to repair the VCL if it gets damaged too. 

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16 hours ago, cwr said:

Builder questioned this as the air tightness membrane will be punctuated in multiple places by the fasteners that hold on the battens, 60mm PIR  and the membrane itself. 

 

Sounds like you have the right  builder :) 

Make sure there is always air tight tape available on the build, and hammer home the point that it is great for the membrane / airtight layer to not be damaged etc but if it does then PLEASE can the guys just put some tape on afterwards to repair / seal up any such punctures. Explain that the house will be AT tested at the end and that any and all compromises will become apparent, just some will be very hard to rectify at that stage.

Best they know it's not the death penalty to damage it, but it will have huge repercussions for you if they don't just quickly fix it in the same moment.  ;) 

 

Also, +1 to the membrane being the first thing you see, with only the battens atop. Just refreshed the page and saw those comments.

Probably worth noting a provisional AT test should be done before any boarding goes on anywhere. You'll be stuffed to fix it retrospectively.

Edited by Nickfromwales
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That all makes sense. Only thing I'm thinking is if the VCL is between the battens and 60mm then fitting recessed led lights might be tricky. I was otherwise planning on cutting a disc out of the 60mm PIR where there are lights so that's there's a localised 85mm void. 

A v slight comprises on the insulation, but overall a tiny %.

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16 minutes ago, cwr said:

That all makes sense. Only thing I'm thinking is if the VCL is between the battens and 60mm then fitting recessed led lights might be tricky. I was otherwise planning on cutting a disc out of the 60mm PIR where there are lights so that's there's a localised 85mm void. 

A v slight comprises on the insulation, but overall a tiny %.

With a run of wool in the void at the rear of the pockets I would really not lose any sleep here. Just make sure there is an extra bit stuffed in at each hole when you fit the lights.

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23 hours ago, Thorfun said:

interesting that the air tight membrane is going behind the 60mm PIR. I was planning on filling the rafters with mineral wool, then putting 80mm PIR and THEN adding the VCL. that way any off-gassing from the PIR is all behind the air tight membrane and not off-gassing in to the house.

 

crazy paranoia or sensible?

That’s how I see it. How would you fix the membrane?

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51 minutes ago, MortarThePoint said:

+1 for the VCL inside all PIR. What fixings are you using for the plasterboard though?

In my mind there will be battens for a service void and the plasterboard will fix to that. So the real question is how to fin the battens through the PIR and in to the rafters?

 

and to answer that please see the previous answer

 

2 minutes ago, Thorfun said:

I’ve not thought that far ahead!!

 

?‍♂️

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3 hours ago, MortarThePoint said:

……do you have a link to one or some?

https://www.cef.co.uk/catalogue/products/4501996-8w-led-downlight-white-4000k
 

These are the 4000k daylight aka natural white ones I’ve been fitting lots of lately. 
Also find the following…

https://www.cef.co.uk/catalogue/products/4471520-8w-led-downlight-4000k

non fire / acoustic shallow depth fittings, 

 

and 

 

https://www.cef.co.uk/catalogue/products/4471505-e5-4-5w-led-fire-rated-downlight-4000k

 

shallow, fire and acoustic rated fittings. 
 

These need bezels to go with them, and I’ve been buying Matt white mostly to match the ceiling paints. 

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I have a 25mm service batten in vaulted ceilings. I've bought a few of these lights for evaluation:

 

https://www.screwfix.com/p/aurora-slim-fit-fixed-round-led-downlight-500lm-9w-100-240v/1906p

 

Above have alloy body and given off a nice diffused light, but are non dimmable. The CEF ones Nick quoted are a good price, but spec does not say if they are dimmable. If anyone knows of similar recessed shallow flat panels that are dimmable, please share a link.

 

The alternatives are these which are dimmable, are switchable warm/cool white and also give off a nice diffused light:

 

https://www.screwfix.com/p/lap-indopro-fixed-fire-rated-led-downlight-satin-nickel-450lm-9w-240v/8969x

 

...but the above need to be tested in the void available as they are bang on the depth limit.

 

P.S. VCL is the taped surface of PIR for us.

 

 

Edited by Hilldes
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4 hours ago, Hilldes said:

I have a 25mm service batten in vaulted ceilings. I've bought a few of these lights for evaluation:

 

https://www.screwfix.com/p/aurora-slim-fit-fixed-round-led-downlight-500lm-9w-100-240v/1906p

 

Above have alloy body and given off a nice diffused light, but are non dimmable. The CEF ones Nick quoted are a good price, but spec does not say if they are dimmable. If anyone knows of similar recessed shallow flat panels that are dimmable, please share a link.

 

The alternatives are these which are dimmable, are switchable warm/cool white and also give off a nice diffused light:

 

https://www.screwfix.com/p/lap-indopro-fixed-fire-rated-led-downlight-satin-nickel-450lm-9w-240v/8969x

 

...but the above need to be tested in the void available as they are bang on the depth limit.

 

P.S. VCL is the taped surface of PIR for us.

 

 

I’ve used those lights before- they’re good :) 

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3 hours ago, TonyT said:

Would it be easier to increase the thickness of the timber service batten?

I think you are right, I've not done a calculation, but I suspect going from 25mm deep battening to 50mm would not lose that much headroom/usable floor area. Right now, roofing batten (25mmx50mm) is though substantially cheaper than alternatives.

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5 hours ago, Hilldes said:

I have a 25mm service batten in vaulted ceilings. I've bought a few of these lights for evaluation:

 

https://www.screwfix.com/p/aurora-slim-fit-fixed-round-led-downlight-500lm-9w-100-240v/1906p

 

Looks to need a minimum 40mm void depth though (extract from manual PDF at bottom of Screwfix specifications tab)

image.png.8bebb6c3f97205999d3ee0d3345ef8de.png

 

This one is thin but can't see a void spec and could be low quality:

    https://hartingtonheath.com/product/i-lumos-led-6-watt-round-recessed-lighting-panel-ultraslim-ceiling-light/

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