Depth of marmox to minimise bridging

[JohnMo]

21 minutes ago, G and J said:

Ta.  
 

if I understand your wall build up you don’t have a cavity. So I guess the sub DPC wall is simply thinner across the doorways.

 

What happens with a cavity wall?  In some ways I don’t think it should be any different, but I don’t trust my intuition here.  

The wall is ICF, the wall make up from inside is

 

Plasterboard 

50mm batten

365mm thick ICF block (concrete is inside and insulation outside).

 

This is the sub DPC buildup for the walls, upstand not shown.

 

The upstand at the doorway basically gives continuous insulation around the building - below floor level cavity and across doorways

 

 

 

[Dunc]

@JohnMo you've been very helpful in fondation design (thank you!) - I am using a modified version of yours for my TF build. As @G and J I'm wondering how to detail the threasholds - did you just omit the inner 140mm thermolite at the threasholds and set the doors over the outer block?

[JohnMo]

7 minutes ago, Dunc said:

did you just omit the inner 140mm thermolite at the threasholds and set the doors over the outer block

Just been going through some photos, I actually used 2x 100mm thermolite blocks at threshold (not one, stated previously and 70mm upstand.

 

 

[SBMS]

1 hour ago, JohnMo said:

Just been going through some photos, I actually used 2x 100mm thermolite blocks at threshold (not one, stated previously and 70mm upstand.

 

 

Is that 2x100mm thermolite on top of each other lengthways (ie total ‘height’ of 200mm)?

[SBMS]

6 hours ago, ab12 said:

Interesting setup. Out of curiosity what is th reasoning for using 180mm floor insulation? My understanding is 100mm should satisfy building regs.

 

What U value do you want to aim for on the blocks and is the block below DPC (in which case need to aim for 7N)? Have a look at Thermolite blocks- they do some with good U value.

100mm PIR is a poor u value (especially with ufh) and we are aiming to exceed building regs which in itself sets fairly low standards. 
 

My primary aim is to minimise thermal bridging across the cavity on the thresholds so less about the overall U value and more about minimising bridging.

 

What makes you say a 7N block is required below dpc??

[JohnMo]

25 minutes ago, SBMS said:

Is that 2x100mm thermolite on top of each other lengthways (ie total ‘height’ of 200mm)?

No, on edge, one behind the other.

[SBMS]

22 minutes ago, JohnMo said:

No, on edge, one behind the other.

Does that mean your track sat on a 430mm threshold? How did you get the upstand to butt up against the track -

was there not a drop behind the track and the thermalite?

 

[JohnMo]

16 minutes ago, SBMS said:

Does that mean your track sat on a 430mm threshold? How did you get the upstand to butt up against the track -

was there not a drop behind the track and the thermalite?

 

They are on their edge, you have drawn on the side, flick them over 90 degrees, so threshold is about 215mm wide

 

As shown previously 

Edited Sunday at 20:42 by JohnMo

[SBMS]

3 minutes ago, JohnMo said:

They are on their edge, you have drawn on the side, flick them over 90 degrees, so threshold is about 215mm wide

 

As shown previously 

I get you. Your track doesn’t look 215mm deep though so what did you do behind that bit where your screed went?

 

[JohnMo]

✔️ nearly 

 

Thermolite level with top of screed, so no gap where you show ?

 

Level threshold sits on top, then tiles level the whole lot.

Edited Sunday at 21:21 by JohnMo

[Nickfromwales]

35 minutes ago, JohnMo said:

They are on their edge, you have drawn on the side, flick them over 90 degrees, so threshold is about 215mm wide

 

As shown previously 

The inner course should have been done away with at the openings?

[SBMS]

21 minutes ago, JohnMo said:

✔️ nearly 

 

Thermolite level with top of screed, so no gap where you show ?

 

Level threshold sits on top, then tiles level the whole lot.

Got you so your threshold sits proud of the thermolite basically by depth of your finished flooring (tiles + adhesive)?

[Benpointer]

On 24/01/2025 at 22:40, Nickfromwales said:

If it doesn't, neither of us will wake from our deep sleep tonight, but if possible the two should overlap  

 

Will any of this actually matter(?), remains to ever be documented and evidenced in honesty.

 

For the sake of the polar bears, fit the 100mm is my 2 cents.

 

 

This is what’s in my head. ?  

Wouldn't it be better if the Marmox overlapped the PIR a bit more?   At the moment there's a cold bridge in your diagram where there's only effective 25mm of Marmox between as warm screed and a cold concrete block.  Ideally, surely the Marmox should extend down to the bottom of the PIR.

 

Scrub that - you're not able to lay it in sufficient thickness according to Marmox's own specification:  https://www.marmox.co.uk/file-uploads/Doors___Windows.pdf  

 

 

[G and J]

Crumbs I am learning tons on this site.  
 

So, @JohnMo, i think this is the arrangement you have:

 

And I’m assuming you don’t have condensation on your door cill , which is where i want to be (hence the interrogation - sorry!).

We will have facing bricks instead of the outer of the two thermalite blocks.  Does this mean I’ll need to do something else to prevent condensation?

 

 

[JohnMo]

Yes the bottom layer of blocks is just normal concrete blocks.

 

No condensation.

 

Just done a couple of thermal images

 

The door sill is aluminium, outside is 5.5 degs. Aluminium is showing 13.3 degs, but never seen any damp.

 

 

This is our lounge window, done the same way as doorway - the window goes to the ground and no aluminium threshold. In the same area it's 19.1 degs.

 

[G and J]

43 minutes ago, JohnMo said:

Yes the bottom layer of blocks is just normal concrete blocks.

 

No condensation.

 

Just done a couple of thermal images

 

The door sill is aluminium, outside is 5.5 degs. Aluminium is showing 13.3 degs, but never seen any damp.

 

 

This is our lounge window, done the same way as doorway - the window goes to the ground and no aluminium threshold. In the same area it's 19.1 degs.

 

That's exactly where I want to get to.  Thank you.

 

Hmmmmm, do I need something special above my top plinth brick?

[Dunc]

1 hour ago, G and J said:

We will have facing bricks instead of the outer of the two thermalite blocks.  Does this mean I’ll need to do something else to prevent condensation?

 

 

would a layer of compac foam at the top of the facing brick be beneficial in diagram 2?

[Russell griffiths]

 

just to confuse the situation a bit more I did this on an icf build. 
500 kpa   Xps. 
 

 

[SBMS]

9 hours ago, G and J said:

Crumbs I am learning tons on this site.  
 

So, @JohnMo, i think this is the arrangement you have:

 

And I’m assuming you don’t have condensation on your door cill , which is where i want to be (hence the interrogation - sorry!).

We will have facing bricks instead of the outer of the two thermalite blocks.  Does this mean I’ll need to do something else to prevent condensation?

 

 

Are you doing a level threshold? Can you change your facing bricks for thermalite or marmox at the top?

[Nickfromwales]

Lose some of the inner, upper thermalite block. Move the PIR upstand further out.

 

Thermalite can be cut with a wood saw or multi-tool, so make a staggered top edge and keep the coldest part of the thermalite away from the tiles.

 

Then install the Compacfoam (purple) and that's a wrap  

 

I also think your tiles would fracture along that suggested line, given the distance of the dissimilar materials they would have to travel over to get to the door  

[Nickfromwales]

 

 

 

EDIT. PIR upstand should travel a bit further down, eg past the screed some more, but you get the idea.

[G and J]

4 hours ago, SBMS said:

Are you doing a level threshold? Can you change your facing bricks for thermalite or marmox at the top?

Good thought. Our front door is our part M access door so there I could use thermalite blocks instead of plinth bricks. 
 

we have a rear door and patio doors where the plinth bricks will be visible as both have a step down immediately outside 

[G and J]

1 hour ago, Nickfromwales said:

I also think your tiles would fracture along that suggested line, given the distance of the dissimilar materials they would have to travel over to get to the door  

That was one of the aspects I was worrying about.  It feels like this requirement is conflicting with the requirement to avoid cold, condensey aluminium cills/frames. 
 

Removing some of the thermalite blocks thickness, maybe even to the extent of the PIR up stand being partly under the cill, sounds like a good plan. 

[Nickfromwales]

6 minutes ago, G and J said:

That was one of the aspects I was worrying about.  It feels like this requirement is conflicting with the requirement to avoid cold, condensey aluminium cills/frames. 
 

Removing some of the thermalite blocks thickness, maybe even to the extent of the PIR up stand being partly under the cill, sounds like a good plan. 

AS long as the PIR and the Compacfoam meet, you can keep more of the block. Will be a less harsh 'temperature transition' then as the threshold wont be as cold internally as the block.

 

This is how I do most jobs, unless there's a bloody good reason (stubborn penis architect usually) to not do so.  

 

6 minutes ago, G and J said:

to avoid cold, condensey aluminium cills/frames. 

Just make sure you seal / foam the interior section of the threshold VERY meticulously, to stop any unwanted cold airflow, as alu is a PITA with condensation. 

[G and J]

OK. Maybe there is another way to look at this.  
 

Insulative block under cill to limit bridging has got to be a no brainier. 
 

Insulative upstand round perimeter of screed similarly a no brainier. 
 

But what if I let the screed touch the aluminium cill?  Yes it will cause more heat loss than needed. But the screed will warm the cill, reducing or eliminating condensation on the cill. 
 

I think condensation would be harder to live with than a tiny increase in heating load.