Green Building Forum - Mitigating zero floor insulation with EWI apron

Mitigating zero floor insulation with EWI apron

willie.macleod — Fri, 23 Oct 2015 19:06:49 +0100

It's not nylon, it is fibreglass mesh that gets embedded with thin coat renders. It is alkaline resistant, with approx 4x4mm grid. The mesh itself does next to nothing by itself, but once it is embedded in the render it makes a huge difference to the performance of the material with regards to attack from outside. As far as any rodents are concerned it is the same as a concrete wall - if they eat through the approx 4mm cement based render then they can reach the polystrene but I doubt that any rodent will be aware that it isn't a much thicker layer of hard material.

I don't really understand how you did it with dabs. The easy way of doing this well that I did is to;
1) Sand the E/XPS boards and get rid of any surface dusting
2) Use a hawk and trowel, apply appropriate adhesive over the boards - getting good coverage but not too worried about depth (I used Parex Maite - would recommended)
3) Use a 10mm square notch trowel to get even 10mm beads over area you are meshing
4) Cut mesh to size, use trowel to embed mesh. This will show up any low spots which need further Maite.
5) Finish as appropriate. Topcoat/Dash/Paint - but whatever, this layer you have completed will completely change the way the EPS behaves, give it a good kick and you will hurt your toe.....

Mitigating zero floor insulation with EWI apron

fostertom — Fri, 23 Oct 2015 20:04:05 +0100

I see - it's the Maite not the mesh that keeps em at bay - mesh alone won't deter them? Surely Parex describe it as nylon mesh?

Mitigating zero floor insulation with EWI apron

willie.macleod — Fri, 23 Oct 2015 22:42:08 +0100

The Maite by itself does little spread straight onto polystrene - it would crack easily and allow beasts to start tunnelling easily via cracks. The addition of the mesh completely transforms it and it gives a solid finish. Parex just describe their mesh as glass fibre reinforcement, don't know what the treatment is for enabling it to resist the alkalinity. Lots of suppliers of suitable mesh very cheap on ebay.

Mitigating zero floor insulation with EWI apron

fostertom — Sat, 24 Oct 2015 10:47:41 +0100

Thanks willie.

Posted By: willie.macleodI don't really understand how you did it with dabs

means just enough dabs of Maite to hold the naked mesh in place over the face of the EPS.

I'd like to know whether just the naked mesh (as it's nasty-to-bite glass fibre not mere 'nylon') is good enough to deter the beasties.

Mitigating zero floor insulation with EWI apron

teacosy — Sat, 24 Oct 2015 22:09:07 +0100

useful thermal image Gravelld
we are hoping to have deterred the gnawing beasties with cement board and some rather fetching galvanised sheeting. it also had the benefit of creating a level plinth for the above ground EPS.
it's all a bit too new to be able to report back on its effectiveness though.
Ps. all credit for this to an02ew

Mitigating zero floor insulation with EWI apron

teacosy — Sat, 24 Oct 2015 22:09:45 +0100

another pic

Mitigating zero floor insulation with EWI apron

teacosy — Sat, 24 Oct 2015 22:10:06 +0100

and another

Mitigating zero floor insulation with EWI apron

djh — Sat, 24 Oct 2015 22:36:06 +0100

I put paving slabs on edge all the way round. Hardcore underneath of course and 600 mm of sharp drainage gravel outside the paving slabs. But I'm more concerned about squirrels; we had one nest in our eaves at our previous house.

Mitigating zero floor insulation with EWI apron

fostertom — Sun, 25 Oct 2015 09:38:11 +0000

All seems a bit paranoid, expensive

Mitigating zero floor insulation with EWI apron

SteamyTea — Sun, 25 Oct 2015 10:21:57 +0000

Too right to be paranoid, even wildlife has been spying on us for years

Mitigating zero floor insulation with EWI apron

fostertom — Sun, 25 Oct 2015 10:49:56 +0000

Much good it's done em!

Mitigating zero floor insulation with EWI apron

Nick Parsons — Sun, 25 Oct 2015 20:34:49 +0000

That's not a secret squirrel. I could tell what it was straight away.

Mitigating zero floor insulation with EWI apron

mike7 — Fri, 30 Oct 2015 20:39:15 +0000

Here's an image of isotherms showing the temperatures in the ground below a floor slab (top left) with some perimeter insulation. (Steady state, 2D ie.cross section of a long narrow building. LH side is centre of floor slab)

Each band of colour indicates a drop of 1C from 20C inside to 10C ambient.

Mitigating zero floor insulation with EWI apron

mike7 — Fri, 30 Oct 2015 20:49:40 +0000

Now here's the flux pattern for the same set-up:-

You can see how the flux path gets longer for heat setting off from further away from the edge of the floor. As the pathway widens the temperature gradient drops and so the isotherms will further apart. Interesting how the flux path closest to the bottom of the insulation actually narrows, so the heat flow round this corner is high.

Mitigating zero floor insulation with EWI apron

mike7 — Fri, 30 Oct 2015 20:51:50 +0000

...and here's the two together:-

See what I meant about the lines crossing at right-angles, and the pattern being made up of curvy squares - OK mine are a bit rectangular, and some angles are a bit off right, but it was a struggle to get them that good.

Mitigating zero floor insulation with EWI apron

mike7 — Fri, 30 Oct 2015 21:02:47 +0000

And here's one with no perimeter insulation:-

Mitigating zero floor insulation with EWI apron

gravelld — Fri, 30 Oct 2015 21:13:22 +0000

Thanks Mike. I've never read one of those diagrams but it still looks like an enormous improvement; the external wall with skirt appears to contact that first dark red line, yet without it's the blue or get line, a further 3-4Â° drop.

10Â°C ambient means ground temp right?

Mitigating zero floor insulation with EWI apron

mike7 — Fri, 30 Oct 2015 21:42:34 +0000

Posted By: gravelld10Â°C ambient means ground temp right?

Correct.

From my xl iterations I got the following figures for heat loss in W/m2:

................................................Centre area avg............1m perim avg ...........overall average
Dry ground no perimeter insulation............1.35 .........................3.85.......................2.0
Dry ground 1.5m x 200mm insulation .........1.2............................1.95.......................1.5
Dry ground 1.5m perfect insulation............1.1............................1.35.......................1.15
.
Wet ground no perim ins.........................4.5............................10.9........................6.2
Wet ground 1.5m x 200mm ins..................3.95...........................5.5.........................4.15
Wet ground perfect ins..........................3.65...........................4.8.........................3.9

I used conductivities of 0.6 and 2.0 for the dry and wet ground, and Vol Sp Hts of 1.6 and 3.4.

Makes a big difference whether the ground is wet or dry!
The average overall would be worse for a real ie 3D building as there would be more perimeter per unit central area.

Edit: Oops 2 errors in last column corrected.

Mitigating zero floor insulation with EWI apron

jamesingram — Sat, 31 Oct 2015 15:03:35 +0000

I do this , seems to work ok , though wouldn't bother with the XPS now , just use EPS

Mitigating zero floor insulation with EWI apron

jamesingram — Sat, 31 Oct 2015 15:10:37 +0000

heres a little sketch , with cavity wall you could do the same at ground level
(ok not perfect like a passive slab)

Mitigating zero floor insulation with EWI apron

wookey — Sun, 01 Nov 2015 15:28:44 +0000

I know we've had this discussion several times, but what (James) has caused you to change your mind about EPS rather than XPS underground?

Mitigating zero floor insulation with EWI apron

djh — Mon, 02 Nov 2015 10:24:09 +0000

Posted By: jamesingramheres a little sketch , with cavity wall you could do the same at ground level
(ok not perfect like a passive slab)

I'd be tempted to make the shingle deeper than the underfloor EPS and put a French drain at the bottom of it unless the ground drainage is naturally very good.

Mitigating zero floor insulation with EWI apron

jamesingram — Tue, 03 Nov 2015 12:27:36 +0000

yes djh . as in photo. Shingle to the bottom of the slab
Wookie. well mainly Tom comments on here and ive no concerns regarding eps degrading or taking up any problematic amount of moisture