Render on Renderboards..tell me why I shouldn't

[SuperJohnG]

I'm now at the point of getting the Architect to start on my building warrant drgs and hence have some key decisions to make to freeze everything. 

 

We are still between SIPS and TF and this will figure itself out in the next week or two when I talk with my two shortlisted suppliers. 

 

I have decided to go with an insulated foundation from KORE after I now have prices and I have a good plan together to achieve this on a semi DIY basis with experienced trades where required (I.e. pouring the concrete). 

 

We will have a white render finish externally, likely to be K rend silicone or similar (with Siberian larch on our main kitchen living area) , however I  have spent weeks toying back and forth on whether the outer skin will be render on block work or on render board. 

 

I am based in West coast of Scotland...so it is pretty wet, it gets windy but we are not very exposed, surrounded by trees mostly but we are in the middle of our big say 1.5 acre plot. 

 

I would prefer it do on render board for  the following reasons:

 

1) Simplifies the Insulated foundation with no external ring beam required - cost saving of approximately £2-3k overall.

2) Easy to fit render board and I could DIY the battens if I wanted to, theoretically should be quicker.

3) No wet trade required (which is hit and miss here as I don't have anyone I know specifically)

4) No requirement for lintels etc above windows.

5) From what I can gather - blockwork will end up more expensive.(I haven't gathered all the costs to compare them yet, this is perception so far)

 

However before I take the final step and confirm render board I am trying to identify potential issues that I can foresee and niggles in the back of my head. Some are justified  some aren't. Listed below:

 

1) Render on render boards has a higher tendency to crack - I have seen this mentioned regularly. However I think it's a red herring and linked directly to bad application and workmanship. If you follow the instructions and undertake careful detailing I am sure this cannot be true. I fully intend to find the best tradesmen I can for applying the render. 

2) High street Mortgage lenders - less likely to lend against not having a blockwork outer skin? would I be limited and not able to a access the best rates?

3) Buildings insurance - As above, would I see increased premiums? limited options?

4) Blockwork is just more sturdy - This has to be correct, but really is this just in my mind? I am struggling to understand what difference I may actually notice?  

5) Decrement delay - The only technical issue I can see might be that I would get a better decrement delay with blockwork, which is helpful for those hot days, especially considering I am aiming for high levels of airtightness. But not wildly a problem I would think..this is Scotland after all. 

 

So is there any other reason i shouldn't do it?

 

thanks.

 

[ProDave]

It would be interesting first to see if this issue was ever resolved:

 

 

[SuperJohnG]

13 minutes ago, ProDave said:

It would be interesting first to see if this issue was ever resolved:

 

 

@ProDave this was one that had played on me initially I think. But I had put this down to technical issues with that specific house and the battens rather than it being a fundamental problem with render on tendrbkard and TF  houses. @Bitpipe did it all get resolved in the end? I'm assuming now it's summer again youll have some feedback? 

[Bitpipe]

Had agreement in principal last summer from the contractor to replace the system with a view to doing it this summer but Covid has hit and I need to chase him again - last spoke 6 odd weeks ago as they were restarting operations.

 

Fundamental issue is that their batten did not overlay the structural ribs in the TF outer wall (which were marked) so at least half of them were just screwed into Panelvent (i.e. MDF) and the fixings have failed.

[SuperJohnG]

Thanks @Bitpipe certainly helps rule it out as a problem to be concerned about. Interesting I'm assuming it being battened to SIPS OSB skin not a problem. 

Edited June 28, 2020 by SuperJohnG

[Bitpipe]

50 minutes ago, SuperJohnG said:

Thanks @Bitpipe certainly helps rule it out as a problem to be concerned about. Interesting I'm assuming it being battened to SIPS OSB skin not a problem. 

 

Hmm - can only speak from my own experience but I'd be worried that the OSB skin on its own would have the same issue I had.

 

The render board batten fixings carry a lot of deadweight, the render board - 2 coats of render and the top coat. Plus they need to resist the thermal expansion / contraction cycle of the boards in summer and winter.

 

My issue took 18 months to come to light as the fixings slowly worked their way loose.

[Becca]

I know you're busy with your build @SuperJohnG, but wondered which route you chose?  We're in the east of Scotland and my thoughts about render carrier board + render and render on blocks mirror yours, but will add that I prefer the look of rendered boards and no lintels.  From my pricing, blocks and render looks cheaper, even taking the cost of the ring beam on the KORE foundation into account.  The prices I'm getting for thin coat render applied to render boards is about £12k. ?

[SuperJohnG]

@Becca I stuck with render on boards. I'm only just doing foundations. But should be getting someone to do the render in the 3-4 months. 

 

I can keep you updated once it's planned. But I was getting quotes for 10k to supply and fit render system. That's assuming I have had the house battened and boarded out. 

[Andreacaine9]

On 28/06/2020 at 15:35, Bitpipe said:

 

Hmm - can only speak from my own experience but I'd be worried that the OSB skin on its own would have the same issue I had.

 

The render board batten fixings carry a lot of deadweight, the render board - 2 coats of render and the top coat. Plus they need to resist the thermal expansion / contraction cycle of the boards in summer and winter.

 

My issue took 18 months to come to light as the fixings slowly worked their way loose.

What length of stainless steel screws have you used? We have fixed STS cement board to SIPS but are now worried we haven't used long enough screws

[Bitpipe]

10 hours ago, Andreacaine9 said:

What length of stainless steel screws have you used? We have fixed STS cement board to SIPS but are now worried we haven't used long enough screws

 

I left that to the contractor, not a decision I wanted to be part of. There are usually specs from the render system on the screws required, pull tests etc.

 

In my case looks like the underlying render board has failed also, seems to be a known issue and NHBC have removed cover for MgO boards, none of the render systems recommend them now (but they did when our system was installed).

 

Still working on a resolution.

[IanP]

@SuperJohnG how did it work out for you with the tender boards?

Curious to know, as I too are on the west coast and at the same position you were when starting this thread. 

I'm undecided as yet if better to go for a solid outer skin over sips or use render board.

Got about 80m2 to render and about 150m2 to clad in wood.

Even considering using facing bricks and block under cladding and not have to go to the expense of tender after reading some of the comments on here.

 

Anyone got any m2 budgeting figures for methods mentioned?

[SuperJohnG]

Went perfect and looks mega. (Don't have a pic to hand). You can look on out Instagram self_build_ayrshire

 

I used knauff aquapanel boards and TC15 k rend silicone render. 

 

It was expensive but I think worth it. I paid approx 50 sqm to have it rendered labour only. Was 25 quid per sqm for material. 

 

Those prices do not include the knauff boards or screws. 

[AliG]

We have done render on renderboards on my parent's house. Main reason was that we were limited on the width of the house and this saved space. Also we have a mixture of wood cladding and render and it makes it easier to see the wood behind the render.

 

Looks great, however the cost of battening the frame and putting the boards on was crazy and I think it ended up considerably more expensive than blockwork would have been.