Problems with how to finish reveal with aluclad windows

[cbk]

I'm about to get windows installed and the fitter has pointed out an issue which I'm not sure how to solve.  House is an ICF build (Isotex) so all window reveals have to be covered in something to hide the blocks.  External finishes are a mix of render (K-Rend Silicone) Stone Slips and Cedar cladding.  Windows are Ratinonel Aluclad and structural openings have been made to the size of the window + 5mm fitting allowance.  Original plan was to fit the windows and then render the reveal up to the face of the window for a neat finish.  Fitter has pointed out that the Aluclad finish may need to be removed for general maintenance of the window and should not be rendered over.  Worse still he has suggested that the render may cause moisture to trap behind the aluminium cladding causing the timber frame to rot!  When done right there should be a slight shadow gap around the edge of the window which adds to the modern look.   

My guess is depth of the reveal will be about 50mm so this is a narrow strip that needs to be covered somehow.  Only idea I can think of is to use an aluminium flashing the same colour as the window that will be thin enough to fit under and aorund the window and then use a stop bead to render up to the edge of window opening.  All sounds a bit fiddly and might end up looking like a dogs breakfast.

 

Any other ideas would be most welcome.

[Simplysimon]

5 hours ago, cbk said:

Fitter has pointed out that the Aluclad finish may need to be removed for general maintenance of the window and should not be rendered over. 

well i'm stuffed then.

5 hours ago, cbk said:

Worse still he has suggested that the render may cause moisture to trap behind the aluminium cladding causing the timber frame to rot!

why do you think the aluminium is there? seriously though, there is fitting instructions which state the gap at the side of the aluminium must not be sealed with mastic/silicone asit's a drain. if you leave a shadow gap are you relying on tape to seal as 5mm is not a lot of clearance. btw, is that 5mm each edge or 2.5mm clearance a side?

[ProDave]

I broke every rule in the book.

 

 

 

This was discussed at length with the renderer.  The basic principle is you do not want render or anything else filling the gap at the side and even worse if render or similar does go down the gap, it could then bridge the gap between the aluminium and the timber.

 

So by fitting a render bead, then rendering up to that bead, you have not breached the gap and it can drain to the bottom.

 

This is not official advice, but the Rationel rep did visit afterwards and did not bat an eyelid or tell me it was wrong.

[cbk]

8 hours ago, Simplysimon said:

btw, is that 5mm each edge or 2.5mm clearance a side?

I think it is 5mm for each edge  but as supplier has gone bust I can't be sure.  Will find out when the fitter starts to install.  ✌

 

Thanks ProDave.  Pics look a neat solution and I can see how this avoids the problem.  WIll discuss with the renderer to make sure they follow the advice and I make sure they don't use any silicone either.  I also have some timber clad walls which can easily follow the same principle.  One wall is clad in stone slips which are about 15mm thick and will be pointed up with sand and cement.  Will need to find a bead deep enough to cope with the depth. 

Edited July 24, 2022 by cbk
typo

[Conor]

The fitter is talking through their hole.

 

Should be done the same way as Dave's. Ours was similar, the renderer used adhesive beads that he stuck to the window frames before putting the base coat on. Fill any big gaps around the window frame with standard Exterior frame sealant.

 

Btw, if you're using aluminium sills, you'll want these fitted before rendering.

[Nick Laslett]

Our render used Window Reveal beads on our aluminium windows from EWI Store. 
 

https://ewistore.co.uk/shop/external-wall-insulation/white-window-reveal-bead-6mm-2-5m/

 

Here is a blog with video that goes into some details. 
 

https://www.beconstructiveltd.com/why-use-external-wall-insulation-reveal-bead/

[Chanmenie]

19 hours ago, Nick Laslett said:

Our render used Window Reveal beads on our aluminium windows from EWI Store. 
 

https://ewistore.co.uk/shop/external-wall-insulation/white-window-reveal-bead-6mm-2-5m/

 

Here is a blog with video that goes into some details. 
 

https://www.beconstructiveltd.com/why-use-external-wall-insulation-reveal-bead/

That looks a really good solution thanks for sharing 

[Stones]

We have an ICF built house with Rational Auraplus aluclad windows.

 

Windows weather sealed to structural timber frame in ICF wall, in our case using a sealant but could as easily have  been compriband. 

 

Render reveals:

 

 

Plastic stop bead hard up against alu cladding. 

 

Timber reveal:

 

 

Timber hard up to alu cladding.

 

This ensures drainage channels behind alu cladding are clear and any water drains away. Weatherseal hidden and protected from elements.