Screws for wood fibre insulation through batten

[hotnuts21]

HI Guys,

Im fitting 60mm steico woodfibre boards to the outside of the TF. These will be secured in place as per the manufactureres instructions with counter battens (38x50) and the cladding will go onto the horizontal batten also 38x50.

 

Instructions say to use 6*180 screws, but im concerned these will lead to cold bridging?  Although they will be buried in a batten and then covered with another batten.
Would something like the following be suitable?

https://www.aboutroofing.com/insulation-fixing-6-0mm-x-180mm-countersunk-pozi-woodscrews-box-of-100.html

 

Thoughts?

Paul

[Iceverge]

I suspect the screws will make almost no difference. I had a look at this for basalt Vs stainless steel ties for our wide cavity. 

 

What's the total wall make up? 

 

Are the screws into the studs? 

[hotnuts21]

Yes screws into Studs.

Makeup from outside to in

 

Timber cladding
Batten
Counter Batten
Insulation (60mm not 40 as below)
breather membrane
OSB3
Stud.

Makeup diagram below, although the sizes and products are wrong, it gives you an idea.

Edited November 4, 2021 by hotnuts21

[SimonD]

1 hour ago, hotnuts21 said:

Thoughts?

Paul

 

I've installed the woodfibre boards using woodscrews, but nowadays the woodfibre manufacturers are recommending Ejotherm STR H screw-in anchors as they do reduce cold bridging. A few of the eco and passivhaus merchants sell them.

 

HTH

[Iceverge]

I've had a gander. 

 

Our walls were 250mm cavity wall with Stainless steel ties going from inner leaf @ 4/m2 so probably a much worse situation than you are in. 

 

Changing to Teplo basalt ties would have cost an extra €2500 over SS and would have saved...........drumroll.............. €2 per year in heating (2 kWh)

 

It was beyond insignificant in the scheme of things. By improving the airtightness by 0.005ACH per hour we'd have got the same improvement or plugging a leak 3mm in diameter.

 

 

 

[hotnuts21]

Thanks all, I think I will stick with standard screws.

The ejotherm and similar anchors I might use a few to hold the insulation in place before I batten, rather than trying to fix board and batten at the same time, but with the big round plastic head they are not designed to go through a batten, rather sit directly on the insulation, with a batten they will then leave a raised area on top of the timber, causing issues for the other cross batten. Thats kinda why I asked the question in case I was missing some similar fixing without the head.

 

Just got to work out what to do with the board at the dpc level now as we are having a flush patio at the  back doors ?

[hotnuts21]

The other question I have, is when batten and counterbattening, do you use one screw through both battens, or fix the counter batterns first and then a second long screw through both into the stud too?

 

Thanks.

[BenP]

Hi, 

 

We've just today put the final fixing in for our wood fibre sheathing board on roof and wall. 60mm on the walls too. 

 

As you suggested, we've used the Ejotherm fixings to hold the sheathing board back to the timber frame. Typically a couple per board. 

 

We're now in the process of fixing back the vertical battens with Heco fixings (https://www.heco-schrauben.com/screws-accessories/screws/heco-topix/). 180mm perpendicular (straight in) and 200mm at 60 degrees (for suction and sheer). 

 

We ordered the insulation through Ecological Building Systems who organised a fixing plan from Heco. I think you can go direct though. The plan basically says where fixing centres are closer together (i.e. corners of the building). Whereas the middle of the long walls the spacings are much further apart saving on screws. 

 

Couldn't quite believe the cost of the them though.....

 

Pic for good measure.... (every other batten done for now as I'm working through limited stock!)

 

Cheers

[hotnuts21]

@BenP have you used doubled up batten around the Windows to give a 50x50 perimeter? Did you have to wrap them in dpc?

[BenP]

On 19/12/2021 at 21:46, hotnuts21 said:

@BenP have you used doubled up batten around the Windows to give a 50x50 perimeter? Did you have to wrap them in dpc?

 

Hey - sorry for the delayed reply - it's been a busy yet productive Christmas. Remaining windows are finally going in today too!

 

Not quite sure  understand the question.... The double batten you can see it just two close to each other to ensure 600 fixing centres for the cladding and as per the timber frame within. No DPC either although I have decided I'm going to redo some of the battens to leave a small gap so I can introduce a small 'tray' to get any water coming down the membrane away from the window head. 

[MrMagic]

@hotnuts21 @BenP Quick question on your wall makeup - how is this breathable with the OSB on the outside? i.e. if the core stud got wet how would that breathe out?

 

Steico make-up here has no OSB layer - https://www.mikewye.co.uk/STEICO-timber-frame-clad/ (seen the same for pavatex)

[BenP]

Hi - OSB is on that Mike Wye build up - see item 5. 

 

Ours is on the inside of the timber frame as a racking measure for the timber frame. As I understand it, OSB breathes. There are alternatives though that also act as an air barrier....

[MrMagic]

Thanks @BenP - devil in the detail as usual! I guess it was more for @hotnuts21 where the makeup shows VCL on the inside and OSB on the outside... as you say, I guess it must be breathable?

[hotnuts21]

Yes, as above you need an OSB or similar racking board. In these types of makes up it typically goes on the inside as per mike wye.  However it is breathable (although the least breathable of everything in the build up). We decided to add the external wood fibre board as an after thought, so the timber frame was already up and traditional with it on the outside.  It is the point of failure/most likely to get damp/moist, but I spoke to Steico technical support and quite a few others all of who said it was fine to do it the way I did the risk was the condensation analysis, but providing we put a good Vapour barrier on the inside of the wall, it will be fine. 

Which kinda blows my mind because im using OSB for my flat roofs!!

[hotnuts21]

I think this is a more accurate makup of what we had ended up with.