Marmox Thermoblock under SIPS?

[Post and beam]

I understand the logic of using Marmox under a brick and block wall system.

Is it of benefit under a SIPS construction ?

Any insights gratefully received as always.

[JohnMo]

There is a possibility of a cold bridge at the location of the blockwork under dpc and the insulation of the SIP. The interface being the timber plate the SIP sits on. This could rot over time, or so the theory goes.

 

I was going to use Marmox blocks for timber frame build, instead decided to go ICF build, in the end used Thermolite blocks instead.

 

Ask the SIP company for advise, don't ask with a leading question, just ask for general advice on foundation blockwork and ask a general question about any cold bridges in that area, see what they come back with.

[Nickfromwales]

I’m currently on a SIP’s type build (TF with 140mm PIR infill) and Marmox was the obvious choice there, plus under the large sliders. Also for the rising intermediate internal walls. All of these are significant cold bridges.
IMO you should 100% go with this detail, with the top of the Marmox finishing above ToC, but I am assuming this is not on a raft foundation? 

[Post and beam]

Hi Nick

This will be Block and beam, 150mm insulation, UFH/screed. The Sips panels are 187mm thick  for the U. 15 that i have chosen.

[Nickfromwales]

  On 23/06/2023 at 13:05, Post and beam said:

Hi Nick

This will be Block and beam, 150mm insulation, UFH/screed. The Sips panels are 187mm thick  for the U. 15 that i have chosen.

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Yup. Pretty much what is on site at this project. 
30mm PIR upstands against kicker blocks, and Marmox on top / immediately under TF sole plate. 
AT tape starts at 1st 100mm layer of PIR and then top layer and joints taped / foamed again for belt and braces. Internal AT membrane then comes down and gets taped to the tape already on / across the Marmox blocks.

PIR updstands hidden by internal service battens + PB + skim. 

[Post and beam]

approx £2k for the outer perimeter then i think. Internal walls will add to this sub total.

 

Ouch!

 

[Dave Jones]

marmox are a very cheap option for a traditional build to delink the slab.

[Post and beam]

  On 24/06/2023 at 15:50, Dave Jones said:

marmox are a very cheap option for a traditional build to delink the slab.

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Do you mean that you think £2k is cheap or that it would be less in some way for a traditional build?

[JohnMo]

  On 23/06/2023 at 21:04, Post and beam said:

approx £2k for the outer perimeter then i think. Internal walls will add to this sub total.

 

Ouch!

 

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And if your not careful with the design you could still have a cold bridge.

 

Do you have a drawing you can post of the current design?

[Nickfromwales]

  On 24/06/2023 at 17:13, Post and beam said:

Do you mean that you think £2k is cheap or that it would be less in some way for a traditional build?

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£2k to effectively kill cold bridging for a 6 figure project is negligible, aka ‘cheap’ in the grand scheme. Compacfoam / other would need pricing to get an effective comparison here tbh, so it’ll be down to your own diligence to surmise what is best / perceived ‘cheap’ etc. 

  On 24/06/2023 at 17:31, JohnMo said:

And if your not careful with the design you could still have a cold bridge.

 

Do you have a drawing you can post of the current design?

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Yup, agreed. Sectional drawings would help, as we’re currently drawing conclusions from what info is available here. 

[Post and beam]

Not at the stage of sectional drawings yet. I have the elevations and floor plans that were required to get planning. I dont think thats what you need to evealuate this. This is a Potton SIPS and Post&beam

[Post and beam]

  On 24/06/2023 at 22:53, Nickfromwales said:

£2k to effectively kill cold bridging for a 6 figure project is negligible

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I agree just wondered if there was a difference in some way between using it on a SIPs project and a brick construction. The £2k is more than i budgeted because i did not realise i need wider Marmox than i thought.

I think i will get more value from this than i would spending a similar amount to upgrade from a .15 to a .14 U value build. Which is one of the Potton options.

[Nickfromwales]

  On 26/06/2023 at 08:15, Post and beam said:

I think i will get more value from this than i would spending a similar amount to upgrade from a .15 to a .14 U value build

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Yup, unless you plan to live until you're 136?  

[Dave Jones]

  On 24/06/2023 at 17:31, JohnMo said:

And if your not careful with the design you could still have a cold bridge.

 

Do you have a drawing you can post of the current design?

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here is what i am using albeit with block and beam but its the same.

 

 

the full guide is here https://www.marmox.co.uk/uploads/catalogue_gallery/33/datasheets/ThermoblockTechnical2019.pdf

 

[JohnMo]

But a sip on block and beam, looks nothing like the marmox drawing.

[markocosic]

Not built like this before.

 

Thinking out loud though:

 

Treated sole plate.

 

Sip /sole plate starts at structural floor level.

 

Insulation and floor screed raise raise floor level (fill in between SIPs) and eliminate sole plate thermal bridge. 

 

Airtight the poly under the screed to the walls.

 

Done?

 

Airtightness avoids drawing in loads of moisture from outside during heating season.

 

The sole plate dries to outside via ventilated rainscreen. Just like the rest of the sip. And indeed the floor insulation.

 

Where would you need marmox?

 

Useful on door openings perhaps.

 

Can't see it being useful elsewhere. Lifting the sole plate will surely make more of a bridge (1*45 mm through wall) than the OSB otherwise would (1*11 mm down through floor insulation) especially once that sole playe has been fastened down?

 

For rot I would worry more about joints between sip panels and especially those at roof level where stack effect will try to drive moisture through the gaps in a far more concentrated way than you might otherwise get with a stick build. Top layer of roof sandwich then turns to Weetabix.

[SlivenClod]

  On 23/06/2023 at 16:23, Nickfromwales said:

Yup. Pretty much what is on site at this project. 
30mm PIR upstands against kicker blocks, and Marmox on top / immediately under TF sole plate. 
AT tape starts at 1st 100mm layer of PIR and then top layer and joints taped / foamed again for belt and braces. Internal AT membrane then comes down and gets taped to the tape already on / across the Marmox blocks.

PIR updstands hidden by internal service battens + PB + skim. 

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I am just about at this stage and having "discussions" with my builder. Please can you sketch this out please so I fully understand it. I would be very grateful.

[Nickfromwales]

This is the actual job. 

Those couple of pics show the aerated kicker blocks with the blue Marmox atop, and then the 2x soleplates sat directly onto the Marmox. 
I’ll see if I can sketch out the AT detail. 

[Dave Jones]

already linked it earlier. the shed spec is in their tech doc