Bonding a warm flat roof

[Fractal]

Thanks to noseall's advice I've built the structure and deck of my extension roof, and am now ready to add the insulation/EDPM

From checking the forums PU adhesive seems the way to go. I've got a 18mm OSB deck and so am plannning polythenene VCL next, then 130mm Celotex, then 9mm OSB, then the rubber.

Do I bond the VCL to the OSB with PU adhesive, then bond the Celotex to the VCL, then bond the OSB to the Celotex? I'm a bit concerned that bonding the insulation to the polythene vcl won't be very strong.

Is the XR4000 celotex okay as it is the cheapest?

Is any PU adhesive okay like this one?
http://www.roofingsuperstore.co.uk/...sive/insta-bond-insulation-adhesive-62kg.html

Thanks for the help, much appreciated!

 

[Fractal]

Has anyone got an opinion of this, or am I best getting the helical nails?

 

[catlad]

Check the celotex web site it tells you how to do it. I think you will need some ply under your insulation.

 

[Fractal]

I've checked the Celotex website and they show me all the stuff I already know, but what I don't know is what adhesive to use to bond all the layers.
I asked the suppliers of the adhesive I mentioned above and they said it was only for bonding insulation to a mechanically fixed bitumen vcl.

I was originally going to use the helical nails, but in several places on the forum the advice is to bond it rather than nail it.

Can anyone help me with what to use?
Thanks

 

[catlad]

I would have put the 18mm osb3 on top and used large timber fixings.

 

[theoldun]

Tell us what Celotex you have bought. If you have not got any yet then we will tell you which one to buy.
What is the area of the roof?
Give us this information and we will tell you the correct way to install.
Regards oldun

 

[Fractal]

I've not got the Celotex yet, but was think of getting xr4130 since it is cheaper. I am working off the "balconies and terraces" guide on the celotex website since I'm putting osb over the top, and that says to use xr4000
The roof area is about 30m2.

Thanks

 

[theoldun]

The way you have described in your post is not the way to go.
Have read Noseys post and need to ask you a couple of further questions to give you the best way to proceed.
Have you formed a gable ladder all as noesey suggested
Depth of existing joists .
Width of span of the joists.
Maximum depth of firring pieces.
Did you use firring pieces or reducing rips to achieve your fall.
Reason for questions is to reduce depth of facia to a reasonable depth.
We will come back to you, so do not fret.
Regards oldun

 

[Fractal]

Thanks again oldun
I did the ladder as suggested

The joists are 8" x 2" and span about 12 foot
I've used firrings - max depth of these are 4"

 

[hardmetalking]

Are you fixing through the VCL?

 

[Fractal]

It is the VCL bit I'm not sure about.

It seems you can either use the helical nails (and therefore fix through the vcl) or bond everything, but I don't know what to bond it with.

 

[theoldun]

Okay fellow, sorry for extra questions, but wanted to satisfy our-selves that joists were of adequate size for dead load and snow load.
Two options. First the way we do it which is more costly than the second option which is slightly cheaper.
Target U value is 0.18W/m2K. To achieve this we use 126mm Celotex TD4000. TD4000 has a sheet of 6mm ply attached to top of insulation/.
Forget about sticking your VCL down Spread the 1000g poly over the roof area with 200 surplus overhang all round perimeter, if you want to hold it more firmly in place then rattle a hand full of 6mm felt nails through poly into OSB directly above the joists. If you have any joins in poly, give them a 300mm over lap and run 75mm gaffer tape down the join
Lay TD insulation tightly butted across direction of joists and short edges staggered.. Fix with Insofast 18 fixing anchors. Warming, they are very expensive. If you have SDS drill then buy a ISF18 drill bit attachment and screw them in with this , if not just hammer thern in. In a low zone wind area such as Hampshire 6 fixings per board is sufficient, but we would advise 12 per sheet if your joists are 400mm centre.. 4 across each short edge and 4 across the middle. Drill a pilot hole, same size as fixings for all edge fisings, otherwise they can split the 6mm ply. If you were going built up felt you could go straight over this deck now, but with single ply coverings you need a min of 12mm ply underneath the EDPM
We use a further sheet of 12mm ply or OSB for the top cap. We stagger these sheets over the insulation and 6mm ply cap. You may find that some of the dome heads to your fixing anchors are proud of insulation top cap.. If this is the case mark the positions of fixings on back of top cap and chisel a chunk out so that both caps fit tight together. Run a snakey bead of Sticks like ****e round all edges of bottom cap and down the centre and place top cap on and use suitable length of screw every 300mm to to laminate both caps together.
Hope you understand?
Will be back within two days with option 2 and best ways to do your facia.
Regards oldun

 

[Fractal]

Thanks oldun
That was very clear and easy to follow.
I am hoping to avoid buying TD4000 as it seems it is very expensive, and use XR4000 and OSB instead.
Is that similar to method 2?
I've put an 18mm deck of OSB down already.
Thanks

 

[theoldun]

Did not come back to you until we knew you had read first post.
Unfortunately, lot of time wasters on this forum/

Yes 2nd option the same as first if using XR 4000 and 18mm OSB as top cap.
IMPORTANT. Insofast fixings must be accurate to hit the joists and firrng pieces when they go in, so that they do not puncture the VCL above the bottom OSB deck above the insulation..Hope you understand that.
The fixings named are dome headed and it you use these, then sink a 6mm counter hole a touch wider in diameter so that dome head will go down level with OSB top deck.
Facias. Most DIY fans and builders give no thought to depth of facia.
In your instance you would need a a depth of 490mm , which depth you can not get in UPVC, plus you would have no fixing for top of facia.
If you tell us the exact stage your roof is at, we can most probably tell you the best way of getting out of trouble.
Regards oldun

 

[Fractal]

The email notifications were going in to my junk mail, so I didn't realise you'd replied.
Thanks option 2 sounds like the way forward.

I've got the bottom deck on and have already got the OSB for the top deck, so I am ready to order the insulation and fit that.

I was hoping that I could bond it all together as I am a bit wary of managing to hammer the fixings in straight and hit the firrings and joists but I'll just have to be careful.

I thought I could run some wood the same height as the insulation around the edge of the roof to give the fascia something to attach to. Is this not a good idea?
If you can't get uPVC that deep should I get some wood and use that for the fascia?
Thanks again