Best fixing for PIR to OSB sheathing

[MikeSharp01]

The time has come to put the PIR insulation, mainly 40mm thick, on the outside of our timber frame and I am looking for the best anchor system?

 

The build up is I-Joist studs and rafters covered in 15mm OSB. The Insulation is on the outside of the sheathing and fixes directly to it. We can put the fixings on the Joist lines but as structural fixings for the cladding need to go on the joist lines I would prefer to use the sheathing as the anchor point for the PIR. 

 

The range looks vast - the hammer type anchors look to be for Brick / block substrates will they work into OSB? I have looked at "surelino" but our insulation is 40mm and the minimum looks to be 50mm although the fixing is only 35mm long.

 

Any ideas / advice?

[Gone West]

Similar construction to yours but I fixed 100x50mm battens to the outside of the racking, drilling from the outside and screwing from the inside. Friction fit 50mm Rockwool RW6 batts between the battens leaving 50m cavity then cladding.

[LA3222]

I'm using Ejot TKE to fix 70mm insulation to the internal face of my SIP (15mm OSB).

 

Kingspan Tek technical sent me to Ejot who said the fixing needs to penetrate 20mm beyond the OSB. 

 

I wouldn't recommend the TKE as the heads are a type of philips and an impact driver destroys them. If I was you I'd get some 80mm Spax SS screws with a torx head. Job done.

 

I'm using Ejot washers too ...you will need washers of some description, I'm using SBH T 65 25.

Edited October 6, 2020 by LA3222

[Gone West]

Is there any reason why the PIR can't be glued to the racking with a few screws from the inside to hold it in place.

[MarkyP]

If you are cladding then will you be battening over the PIR and fixing battens through to the joists? If so I would just screw fix the pir to osb from the outside clamping 

with a disc washer, if you fix pir mid span between joists then minimal thermal bridge. This would hold up well until battening later. 

[MikeSharp01]

Thanks Guys really helpful @PeterStarck I could go from the inside but would be difficult on the roof and @MarkyP you are right we will be battening over so just fixing down will be the way to got and using washers. Looks like the MARMOX washers and 50mm spax stainless screws @LA3222 will do the trick so will have a play with some of them and see how I go. On the 80mm thick I will need longer screws but same basic approach all good - many thanks. 

[wozza]

1 hour ago, MikeSharp01 said:

Thanks Guys really helpful @PeterStarck I could go from the inside but would be difficult on the roof and @MarkyP you are right we will be battening over so just fixing down will be the way to got and using washers. Looks like the MARMOX washers and 50mm spax stainless screws @LA3222 will do the trick so will have a play with some of them and see how I go. On the 80mm thick I will need longer screws but same basic approach all good - many thanks. 

 

Stainless steel insulation washers (discs) are about a tenner for 100 from "the auction site" - I used loads to hang my PIR under the rafters ?

[Cpd]

15 minutes ago, wozza said:

the auction site

Is this a reference to ebay ? 
 

 

[JOE187]

   I used these to fix rockwool slabs externally with long  corrosion resistant plasterboard screws  until vertical battens were fixed on top of insultion.

 

https://www.ebay.co.uk/itm/PLASTIC-WASHERS-FOR-INSULATION-BOARDS-56mm-Celotex-Marmox-Kingspan/152443658826?hash=item237e59a24a:g:3A4AAOSwSlBY3Qf.