Fixing Celotex to roof deck

Andy7 · 25 Nov 2012

What fixing methods are recommended for fixing Celotex to the roof deck on a flat warm roof?

I guess the vapour barrier will be stuck down with an adhesive on the OSB.
The Celotex on top of that. I've seen some helical fixings, but I'm a little unsure about those and I don't see a lot of information around.
Would a suitable roofing adhesive work or is the only way mechanical?
I get a feeling in my water that a decent adhesive over the surface area will give a good defence against uplift from wind... though wonder about how that would fair against thermal movement.

I'm probably going for the two-layer Wickes underlay and capfelt on top of that... also probably the topic of more questions when I've gotten on top of this detail

Jase750 · 26 Nov 2012

Use a timber frame with celotex between the joists , 150mm joists for 100mm celotex.This will allow you to ventilate your roof. Tack your vapour barrier down, dont glue it. Use ply skin and felt as normal.

ryanhirst · 26 Nov 2012

I agree with Jase on this one!

theoldun · 26 Nov 2012

Joists must be dead 400 or 600 centres.
Do not stick membrane
If you wish to comply with building regs you need 126mm Celotex TD4000, this includes the 6mm ply stuck to the insulation. You can go three layer felt on top, but if you use a single ply covering, then you need an additional 11mm OSB on top of celotex.
Fixings on 6x6 footprint with joists at 400 centres, you will need approx 330 number. We use Insofast stainless warm roof deck screws at approx 75p each. You will need 170mm long to hit firings.. They are not cheap!! Will get them here.
Insulation Fasteners | twistfix.co.uk
www.twistfix.co.uk/
Finally goggle The Celotex Flat Roof Guide and fill yer boots.
Regards oldun

noseall · 26 Nov 2012

ryanhirst said:
I agree with Jase on this one!

Why?

Opting for a vented cold deck method does not make sense.

Warm deck every day for me.

theoldun · 26 Nov 2012

noseall said:
ryanhirst said:

I agree with Jase on this one!

Click to expand...

Why?

Opting for a vented cold deck method does not make sense.

Warm deck every day for me.

Will tell you WHY nose. You know what you are talking about, and understand the construction industry. Unfortunately others do not.

Regards oldun

limerockconstruction · 26 Nov 2012

I replied to another post about this recently, i'm glad someone else has used the twistfix fixings - only found then recently, but they were good - like oldun says, a bit pricy but the business!

I too am with noseall and oldun - warm deck all the way for me

Andy7 · 27 Nov 2012

Brilliant advice, everyone - thanks.

esp. the "don't stick the vapour barrier" bit. (out of interest, why? Tearing die to thermal movement?)

The spec has been warm deck for me for a long time, fell in love with the idea as soon as I understood it. My builder did a warm deck on an extension recently and I didn't really understand why, so when I found the method on Google, everything snapped into place in my mind. It's a really clever method when you think about it.

I'm starting to consider now the idea of using composite materials for the roof. ie 'celotex' with bonded ply.
I was a bit bummed out by the idea of paying about £1 per twistfix, will look for those 75p ones and just bite the bullet. I'm going to have to put off the fancy coffee machine for the office for a bit then - but at least I'll be warm and dry!

Andy7 · 27 Nov 2012

theoldun said:
...but if you use a single ply covering, then you need an additional 11mm OSB on top of celotex.

Sorry, can I just clarify?
Are you saying
Joists > VB(tacked down) > celotex100 > 11mm osb > single ply felt (adhesive)

or was that TD4000 in place of there I have celotex?

thanks,

==========EDIT===============

Scratch that - just read the manual. All makes sense so far. Though I'm weeping over the price of the helical fixers.

waynz · 20 Feb 2014

theoldun said:
Joists must be dead 400 or 600 centres.
Do not stick membrane
If you wish to comply with building regs you need 126mm Celotex TD4000, this includes the 6mm ply stuck to the insulation. You can go three layer felt on top, but if you use a single ply covering, then you need an additional 11mm OSB on top of celotex.
Fixings on 6x6 footprint with joists at 400 centres, you will need approx 330 number. We use Insofast stainless warm roof deck screws at approx 75p each. You will need 170mm long to hit firings.. They are not cheap!! Will get them here.
Insulation Fasteners | twistfix.co.uk
www.twistfix.co.uk/
Finally goggle The Celotex Flat Roof Guide and fill yer boots.
Regards oldun

If you are to fix the warm deck to the firrings would that not damage the Vapour barrier by puncturing it?

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Fixing Celotex to roof deck

Jase750

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