Sticking PIR to OSB3 on a flat roof

[ToughButterCup]

Attaching foil faced PIR to OSB isn't as simple as I at first thought. Rooting around on Tinternet only shows how wide the choices are: the Internet as shared ignorance perhaps?

 

So I thought I'd ask how BH folk do it.

 

This video is one which admits  that fashions change. Roofers used to use nails, then screws then thermally broken screws and now foam - expanding foam at that.

 

I need to attach 270 ml of PIR to my OSB deck. One layer of 120 and the second 150.

How would you do it?

 

 

 

 

 

 

[Onoff]

I'm reading various: expanding foam - the one for wall boarding, contact adhesive , carpet fitters glue, no more nails type stuff.....

 

???

[ToughButterCup]

Precisely @Onoff. There's no single method. Hence me asking the question on BH.

The video shows my preferred option: squirt it on.

 

I've got some sticky expanding foam: it works for PIR to OSB, but I'm not sure about PIR to PIR, so I'm going to try it out later this afternoon.

Maybe I should use thermally broken screws for the first layer (150ml) and then foam for the second layer.

 

The specification says foil lined PIR. If that's the case, and I need two layers, doesn't it make sense to have single sided PIR ?

(Is there such a thing?) So that the insulation can be laid foil-outwards on the top and bottom sheets.

 

I had no idea such a simple thing, isn't.

[Dudda]

I encounter this question regularly (just out of a meeting this morning on this for a client who's mechanically fixing a Bauder membrane on the laps through the PIR into the WBP deck).

 

One question asks loads of questions. What's the build up on top of the PIR? That's more important. If you've a roof membrane that's mechanically fixed then it will have to be fixed through the PIR to the structure below. What thickness is the OSB? If the structure it's fixing to is the OSB then will the pull out strength be enough? You'll get a stronger fixing from ply and you'll spend ages looking for the structure behing trying to fix back to that. What's the uplift and wind load? If the roof is sedium it's weight will hold it down. If the roof membrane is stuck to the PIR then the PIR needs to have a certain bonding strength. This is easy to achieve and certify by thermally broken fixings at xxx centers but how do you get that from foam? Who's going to certify how much foam you need and sign off on it? 

 

 

[ADLIan]

Check with the PUR manufacturers.

Generally foil faced boards are mechanically fixed whilst those for bonding have a coated glass tissue facing (normally cream/off white in colour). Remember you will also need a VCL on the deck prior to the the insulation boards and you cannot bond to polythene so fully bonded PUR normally goes onto a fully bonded bituminous felt VCL.

[Declan52]

Could you use something like plasterboard screws with washers for fixing the first layer with a few squirts of foam and then use a glue or low expansion foam for the next layer.

 

[jamiehamy]

We put tissue faced PIR onto the OSB deck - OSB>VCL>Insta Stik>PIR>Some super sticky-put-it-on-both-sides-contact adhesive>rubber.

 

Not sure whether Insta Stick is compatible with the foil faced boards however. The insulation and adhesives were all recommended by the EDPM provider. We contemplated using thermal fixings but getting them long enough and actually just getting them was very very tricky - I needed around 200mm and no-one could provide them. Was very odd - the suppliers (Rawl I think in Glasgow) only provide them to roofers.

[ToughButterCup]

4 hours ago, Dudda said:

[...]

One question [...begs...]  loads of questions.

[...]

 

To bloody right @Dudda

I'm going to have to put a good deal more mental energy into working out how  this flat roof  is going to be made to work. It's a nightmare (but not as much so as @Onoff's bathroom)

 

Well at least nobody has accused me of overthinking this one.

[pudding]

On 22/08/2018 at 15:21, jamiehamy said:

We put tissue faced PIR onto the OSB deck - OSB>VCL>Insta Stik>PIR>Some super sticky-put-it-on-both-sides-contact adhesive>rubber.

 

Not sure whether Insta Stick is compatible with the foil faced boards however. The insulation and adhesives were all recommended by the EDPM provider. We contemplated using thermal fixings but getting them long enough and actually just getting them was very very tricky - I needed around 200mm and no-one could provide them. Was very odd - the suppliers (Rawl I think in Glasgow) only provide them to roofers.

 

Bit of a thread resurrection! I'm looking at my flat roof buildup. Currently proposed to use the tissue faced PIR. Which VCL did you use and what glue to stick it on? 

 

Alternatively, is there any reason or issue against installing the VCL under the OSB? So once the flat roof joists are up, lay the polythene VCL over it and then screw the OSB on through the VCL? Seems like this order would avoid any issues glueing down tissue faced PIR, and the VCL still protects.

 

Ta.

[scottishjohn]

you could   buy as sips panels  ?

 thinner layer of PIR between existing OSB and sips panels -mechanically fix no problem 

 you can buy 200mm sips panels ,so maybe one layer of them is enough?

and you know my view on edpm  after seeing the holes crows pecked in it on a flat roof  where they brought up bits of food to eat it 

GRP all the way for a flat roof  

Edited June 8, 2020 by scottishjohn