Blocks and renderboard on a single wall

[Omi]

How do you mix blocks and renderboard on a single wall for a seamless rendered finish?

 

We have the following situation in our build where the big picture window/bifold will have renderboard cladding (green) while it'll be blocks (orange) to either side:

 

The external face of blockwork is 150 mm (50 mm cavity) from the timberframe so that would mean 137.5 mm of battens if we want the 12.5 mm renderboard to sit flush with the surrounding blocks?

 

137.5 mm could be formed using a triple layer of 45 x 45  battens but that doesn't sound right structurally? Is there another way to do this?

 

[Annker]

Make sure that the manufacturer of the render system use confirms how they want it done NOT the contractor.

Weber for example can be very particular that these sort of details are built to their specif detailing, they will be issuing the warrant on the system so you must meet their specification.  

[Omi]

I've run it past our SE and the designer and the recommendation is indeed 3 layers of 45x45 battens:

• Vertical battens fitted to timberframe studs (or 600 centers)
• Intermediate counter-battens fitted horizontally at 600 centers
• Outermost battens fitted vertically again at 600 centers

Render manufacturer's guideline states that the render should not be continuous across differing background materials so I think we'll leave a gap between the blocks/renderboard and treat it the same way as an expansion joint.