Screw for 120 mm stud

[Hobbybyggare Anders]

Hello, I am planning to add extra insulation to a roof from the outside with 120 mm wood fiber insulation. To achieve this, I will place 120*45 mm battens on each rafter (with tongue and groove board in between) to create spaces to lay the insulation. The roof has a slope of about 30 degrees. But which screws should I use and how should they be fastened?

Should I use long screws like 200 mm and screw them straight? Where can I buy such screws at a reasonable price?

Alternatively, can I use somewhat shorter screws like 140 mm and screw them at about 45 degrees from around 50 mm up (they should then go 70 mm into the substrate, is that sufficient)?

Or, should I use angle brackets and fasten them with screws about 70 mm?

Or is there another method I haven't thought of?

How closely should I place the screws?

 

[Workingclasshero]

Could korsregla be an option?
45+70.
It might be more expensive but simpler?

 

[Plupp 284245]

I did something similar when I screwed wedges onto a flat roof. They were about 140 at their thickest, I drilled down a bit with a 10 mm and used 6x160, which at that time was available at byggmax at a good price. If this is the correct procedure, I have no idea, but I feel like it became steady. You have to back out the screw and re-tighten it so that the beam really pulls tight. Possibly pre-drill with a 6 mm.

 

[Hobbybyggare Anders]

Could cross battening be an option?
45+70.

I think it will be difficult to cross batten, I plan to use 120 mm insulation boards, and if I change them, I'll have to rethink more than I dare.

 

[Hobbybyggare Anders]

… They were about 140 at their thickest, I drilled down a bit with a 10 mm and used 6x160, …

interesting, what could be the risk with this solution? If you just have a long enough bit holder, you could drill down 95 mm and then screw as if it was a 45 mm stud you’re screwing into. On top of this comes the joint between two asfaltsboard then battens to create an air gap, raw wood paneling, roofing felt, metal sheet. So the risk should be minimal that something could run/fall down the hole.

 

[Finndjävel]

A 160mm screw should suffice, right? You drive the head a few mm into the wood so they'll go in 42-43mm. I don't see why they would need to go in longer than that if the wood you're screwing into is fresh. Look for places that sell screws by the kilo price, and you're sure to find someone who has longer screws cheaply.

 

[Plupp 284245]

Heco 6x160 349:-/100pcs at Jula. That can probably be considered really cheap.