Anyone else been advised to incorporate compression joints/ movement joints in the render system of their timber frame?

[laurenco]

We're about to start battening, renderboarding and rendering our timber frame... the renderer has been pushing the structural engineer on whether or not we're required to incorporate compression joints into our huge swaths of render, and, having been somewhat vague about the issue, the engineer now advised compression/movement joints ought to go in.

 

I've not found much online, but what I've come across is lines that run down or across the render which would tarnish the design of the house. Has anyone had to incorporate these into their build? Would you share pictures? and does anyone know what the guidance is on these? And whether they're necessary?

[K78]

They are the prevent cracking to the finish on timber frame houses due to seasonal movement in the frame.  

 

Probably makes sense on “huge swaths of render”, unless you go for one of the flexible renders. 

https://www.ribaproductselector.com/Docs/0/13810/external/COL649855.pdf

Edited April 4, 2019 by K78

[nod]

Every 9 mtr 

the joint must run through the cement board also 

[Redoctober]

We have a TF but with a stone exterior, not a render. But, we still needed movement joints. We managed to position ours behind the downpipes and  / or in the corners which helped disguise them somewhat.

[ProDave]

Render onto wood fibre board. Longest run 11 metres. No expansion joints. No cracking of render.  Baumit.com lime render system with Silicon top finish coat.

[Triassic]

I’m planning to put mine in the corners. Should I also be leaving expansion gaps in the battens at these locations?

[Bitpipe]

We have a render issue which may have been caused by lack of compression joints, not sure. It may also have been caused by insufficient fixing of the battens to the timber frame outer skin (panelvent board).

 

The boards under the Parex render are pillowing up as soon as it gets warm causing an unsightly effect.

 

The parex is highly elastic so no risk of cracking but does not look good.

 

Render firm committed to fix it but don't understand the root cause yet and understandably only want to do it once.

 

Going to push to have it resolved this year now that everything else is done.

[Triassic]

I’m about to purchase the render board for my TF. I’m going for the 12.5mm to aid rigidity. I’m fixing these to 50 x 50mm battens which should also help stiffen everything up.

[laurenco]

43 minutes ago, Bitpipe said:

The boards under the Parex render are pillowing up as soon as it gets warm causing an unsightly effect.

 

Oh no, this is awful. I'm pleased they are committed to fixing this. Pat, the Weatherby rep, told me a story about a whole timber frame housing estate down south, which bowed in the heat because the cement/renderboards were butted up too close to each other and should have been spaced with room to expand. Perhaps this is the issue?

[nod]

Belt and braces 

I charge £8 per mtr to supply and install exspansion joints 

Like weeps on brickwork

They are just in case  

[Bitpipe]

Just now, laurenco said:

 

Oh no, this is awful. I'm pleased they are committed to fixing this. Pat, the Weatherby rep, told me a story about a whole timber frame housing estate down south, which bowed in the heat because the cement/renderboards were butted up too close to each other and should have been spaced with room to expand. Perhaps this is the issue?

 

That has been discussed - they are butted up tight but it has been determined that that is per the board manufacturers recommendation.

 

Will see what actually happens...

[Pete]

3 minutes ago, Bitpipe said:

 

That has been discussed - they are butted up tight but it has been determined that that is per the board manufacturers recommendation.

 

Will see what actually happens...

Sorry to hear about this. We used moisture resistant render boards and had to leave a 2 to 3 mill gap between the boards. We have a 27 linear length of boards without an expansion gap/joint as the timber frame designer said no expansion joint was needed and the render board people said that their boards would be ok over this distance. Fingers crossed and all!!

[Bitpipe]

6 minutes ago, Pete said:

Sorry to hear about this. We used moisture resistant render boards and had to leave a 2 to 3 mill gap between the boards. We have a 27 linear length of boards without an expansion gap/joint as the timber frame designer said no expansion joint was needed and the render board people said that their boards would be ok over this distance. Fingers crossed and all!!

 

It took a year or so for the issue to appear, firm are very professional and established - they've committed to fix it but we agreed that best for me to finish landscaping etc first and then they'll return so teeing that up for this summer. 

 

Regarding board gaps, how do you stop them getting fouled by the initial coat of render, are they taped? This was the reason that our guys did not see the need for gaps (and neither did the board manufacturer).

 

I suspect it's a combination of factors, board expansion is putting strain on the batten fixings to the frame and these are flexing, allowing the boards to move.

[Pete]

1 minute ago, Bitpipe said:

 

It took a year or so for the issue to appear, firm are very professional and established - they've committed to fix it but we agreed that best for me to finish landscaping etc first and then they'll return so teeing that up for this summer. 

 

Regarding board gaps, how do you stop them getting fouled by the initial coat of render, are they taped? This was the reason that our guys did not see the need for gaps (and neither did the board manufacturer).

 

I suspect it's a combination of factors, board expansion is putting strain on the batten fixings to the frame and these are flexing, allowing the boards to move.

I must admit this did concern me, the fact that you leave a gap and then it is filled when the first coat of render is put on. What type of boards did you use?

[Mr Punter]

Most of the shrinkage movement in timber frame is at floor junctions, so horizontal joints are often specified at this location.  I don't understand why you would need vertical movement joints in timber frame render onto board.

[MarkyP]

I have an 18m run along a wall with EPS EWI and Baumit star contact white (cement/lime hybrid) base coat finished with silicate mineralic thin coat (nanopor fine, 1mm grit). No movement joints and no cracks and  this is with multiple thin sections of render over window reveals which are often where cracks will appear. Choose carefully the finish, acrylic and some silicone thin coat looks cheap in my view, has a plastic sheen nature to it. Silicate thin coat is mineralic and looks far better in my opinion, also could be mineral painted later in life to refresh or change colour while retaining the flat, mineral finish. I was very impressed with Baumit products and technical support.

 

I asked Baumit about expansion gaps and were told none were required. You'd need to follow the recommendations of whoever manufactures your render but the logic Baumit gave me was that they only place expansion gaps where there is a underlying structural movement joint or expansion gap. They said that joint beads placed in elevations where the underlying structural base is continuous are pointless. Your render boards would be staggered jointed, and the basecoat will have a mesh embedded, and the render base coats are polymer modified to allow far more movement than sand/cement. So I think if you needed an expansion gap, you would need to incorporate it through the render board as well to ensure the movement was focused there,  right through the build up.

Edited April 4, 2019 by MarkyP

[Bitpipe]

1 hour ago, Pete said:

I must admit this did concern me, the fact that you leave a gap and then it is filled when the first coat of render is put on. What type of boards did you use?

 

They used Euroform Rendaboard 12mm which was approved by Parex.

 

Contractor thinks that hot air is building up behind the boards and that it's not suitably vented at the top but I think this is off target as the coping sits on a bracket with a generous drip overhang so unlikely to interrupt airflow.

 

[Mr Punter]

Jesus!

[K78]

Wow. No wonder the contractor is not arguing over correcting that. 

 

A bit worrying that you don’t agree with his opinion of what went wrong. I hope it all gets sorted. 

 

I would email pics to parex and see what they think?

 

I was all all set for rendered EWI. Until I looked at older examples on the continent and seen leapord spots from fixings, yellowing and other issues.

 

My current pp has a mix of timber cladding and render. I really hope they let me change to all timber. 

Edited April 4, 2019 by K78

[Mr Punter]

@Bitpipe Is there continuous ventilation at the base of the cladding system with a decent path up behind? Is it just this gable end or other walls too?

[Bitpipe]

12 minutes ago, Mr Punter said:

@Bitpipe Is there continuous ventilation at the base of the cladding system with a decent path up behind? Is it just this gable end or other walls too?

 

 

Yep - batten is 25mm with insect mesh top and bottom. all walls have the effect to varying degrees.

 

At the top of the non gables, the render either finishes within 3mm of the soffit which allowed for alu cladding (the contractor suggested sealing that gap but I never did) or tucks under a grp edged flat roof. The gables have an alu coping but that sits on a bracket and there is a generous overhang and gap so airflow should not be impeded.

 

 

[Bitpipe]

2 hours ago, K78 said:

Wow. No wonder the contractor is not arguing over correcting that. 

 

A bit worrying that you don’t agree with his opinion of what went wrong. I hope it all gets sorted. 

 

I would email pics to parex and see what they think?

 

 

Parex reps have been out with the contractor, not sure if board vendor was there too. Plan is to re-convene this spring with MBC also and see if we can't figure it out.

[Gone West]

@Bitpipe Is it possible to put a temperature sensor behind the Parex boards to see if there is a significant heat build up? I would be surprised if a ventilated cavity behind a white surface would get that hot.

[Temp]

 

5 hours ago, Bitpipe said:

 

They used Euroform Rendaboard 12mm which was approved by Parex.

 

Contractor thinks that hot air is building up behind the boards and that it's not suitably vented at the top but I think this is off target as the coping sits on a bracket with a generous drip overhang so unlikely to interrupt airflow.

 

 

I'm thinking its a combination of not enough fixings and no expansion gaps between the boards.

 

 

 

 

Edited April 4, 2019 by Temp

[Bitpipe]

1 hour ago, PeterStarck said:

@Bitpipe Is it possible to put a temperature sensor behind the Parex boards to see if there is a significant heat build up? I would be surprised if a ventilated cavity behind a white surface would get that hot.

 

This is what the contractor has suggested should be do-able, just need to figure out how.