Fixing of wall units

[LinearPancakes]

We have some DIY kitchens wall units to hang. They have 2x wall hanging plates per unit that are first screwed into the wall.

 

Our wall is timber frame with air tightness membrane, 18mm plywood, 12.5mm plasterboard and ~3mm skim. The air tightness membrane is directly behind the plywood, so I don't want to screw in too far and make holes. This means 35mm long screws to account for the screw head protrusion of ~2mm.

 

Obviously this is not a particularly long screw and only 18mm nearest the tip will be really gripping anything. Given they're heavy, slightly deeper than usual (320mm) wall units, I'm tempted to:

 

* Cut away the plasterboard for a rectangular area around where the wall hanging plates will go

* Glue and screw 15mm plywood to this area, leaving a consistent level

 

The extra plywood would bond really well to the existing plywood behind, meaning there's 33mm of really good hold from the combined layers of plywood.

 

But this might be overkill. I'd appreciate any insight.

[Russell griffiths]

Yep that’s the way to do it. 
don’t do little bits of ply though. 
cut a 250mm wide strip the length of all the cupboards. 

[Bozza]

+ I’d do this too exactly as @Russell griffiths suggests.  Personally I’d big screw the new ply strip at the vertical joist locations, though it would go through the membrane it’s clearly going to be trapped and clamped and thus sealed.  Also some good quality no nails along the length too.

 

makes hanging those big units a doddle.

 

 

[markc]

Agree with both of the above, fixing wall units to a continuous ply strip is so easy and curse free. 100x easy and nicer than drilling and plugging etc.

[LinearPancakes]

Thanks so much for the fast responses guys. Great suggestions. I'll run with the continuous strip approach. The existing ply will have been screwed through the membrane at stud locations anyway, so no harm adding a few more.

 

I'll check the brackets & unit to see if I can get away with 18mm ply instead - much easier to get hold of than 15mm. I suppose fire retardant ply would be good here try to preserve the fire performance as well.

[Bozza]

If you go for 18mm if it stands proud of the plasterboard you’ll have to pack out the bottom of the units which will naturally want to pull in at the bottom to the wall and putting strain on the fixings, and making it harder to get nice and level.  Sourcing 15mm ply will make your life much, much easier than faffing around.  
 

I did something with something similar with my DIY K wall units in my utility room, fitted them onto a horizontal batten then had to brace out at bottom.  Big heavy extra high extra deep units.
 

other option would be to put in another lower batten but all extra work like I say having  one 15mm not sitting proud is best option by far.