Exterior Wood Fibre for SIPs

[davidc]

Might there be any compelling reasons not to consider one of the external wood fibre sheathing products for use on SIP constructions such as the one offered by EWI Pro? I have posed a question about wood fibre on timber frame but wondered if there might be particular considerations for SIP ?

[scottishjohn]

you mean sheathing or cladding --

sips would only need cladding on outside--

 

which means sips panels,membrane, then batons and cladding on them ,

same as you do with a TF house  

you need a membrane and gap what ever you use for outer skin  for either system

[jack]

14 minutes ago, scottishjohn said:

you mean sheathing or cladding --

 

I think he's taking about sheet wood insulation products like the one @ProDave used.

[dimpsy]

https://www.weberhaus.co.uk/eco-friendly-homes/wall-system/

It's what one of the German house builders do as a standard wall construction.

[ProDave]

That is the system we used, wood fibre on a timber frame and render direct onto the wood fibre.

 

I am not entirely convinced I would recommend this. I am not convinced it is going to last.  We had an issue in the first winter with the render along the bottom edge of the garage wall, the top layer "blew".  That has been re done and so far okay.   But SWMB pointed out (when the sun was at just the right angle to show it) we appear to have a "blister" on the east wall of the house now.  So at some point that is going to have to be repaired.

 

The trouble with repairs like this, they are never going to be completely invisible.  And one is losing confidence that the whole lot is going to last a long time. Or not.

[davidc]

I see, thanks.

 

So @ProDave , do you feel that you may otherwise have been more ready to recommend the wood fibre sheathing if there had been a gap been that and whatever the final render sits on ? 

 

I had never seen the weberhaus system before, I wonder how they prevent the possible blistering (assuming they do).

[ProDave]

I was attracted to the direct render on wood fibre system because it means the entire wall make up is insulation of some form. I wanted to avoid pointless cavities that have to be ventilated so anything outside the cavity contributes almost nothing to overall insulation.

 

I wasn't expecting "issues" and the problem now is who to "blame" and how to fix it to be sure it won't happen again. At the moment SWMBO thinks the whole lot is going to fall off within a few yeas.

[Jeremy Harris]

3 minutes ago, ProDave said:

I was attracted to the direct render on wood fibre system because it means the entire wall make up is insulation of some form. I wanted to avoid pointless cavities that have to be ventilated so anything outside the cavity contributes almost nothing to overall insulation.

 

I wasn't expecting "issues" and the problem now is who to "blame" and how to fix it to be sure it won't happen again. At the moment SWMBO thinks the whole lot is going to fall off within a few yeas.

 

Might the issue be caused by the relatively large temperature swings you get?

 

IIRC, you were seeing night time temperatures that were below -10°C and I can imagine that the render, with the insulation underneath, may be going from well below zero at night to a fair bit higher when the sun rises and shines on it first thing in the morning.  We've found that it's the east wall of our house that has the greatest weathering by far, and I believe this is due mainly to the clear skies and bright sun early in the morning.  The more exposed west side is no where near as weathered as the east side.  Also, I've found that we've had more movement in the cladding on the east wall, which again tends to indicate that it may be this wall that sees the highest night/day temperature variation.

[ProDave]

10 minutes ago, JSHarris said:

 

Might the issue be caused by the relatively large temperature swings you get?

 

IIRC, you were seeing night time temperatures that were below -10°C and I can imagine that the render, with the insulation underneath, may be going from well below zero at night to a fair bit higher when the sun rises and shines on it first thing in the morning.  We've found that it's the east wall of our house that has the greatest weathering by far, and I believe this is due mainly to the clear skies and bright sun early in the morning.  The more exposed west side is no where near as weathered as the east side.  Also, I've found that we've had more movement in the cladding on the east wall, which again tends to indicate that it may be this wall that sees the highest night/day temperature variation.

The big failure we had in the first winter was along the bottom of the garage wall.  It happened when we were away for 2 weeks over Christmas so we did not see the weather conditions that caused it..  But when we got home there was thick ice all over the parking area.  My speculation was we had deep snow that had piled up against the bottom of that wall (and that is the point the render is closest to the ground) and as that thawed and re froze, moisture got in at the bottom and then blew.  The thick ice we came home to was the last of the thawing and re freezing snow.

 

At that time there was no garage door on, so the inside of the garage will have been just as cold as the outside, so unlike the rest of the house, that garage wall will have been a lot colder.

 

Since being repaired that has not re occurred, but the single blister (not yet dealt with) on the west wall of the house is a worry.

[jack]

36 minutes ago, JSHarris said:

The more exposed west side is no where near as weathered as the east side.  Also, I've found that we've had more movement in the cladding on the east wall, which again tends to indicate that it may be this wall that sees the highest night/day temperature variation.

 

Interesting. Our wooden cladding (Siberian larch) has weathered fairly evenly east, south and west. The critical thing seems to be rainwater - you can see a diagonal line down within the deep overhangs showing where rainwater reaches. Sunlight by itself doesn't seem to cause very much weathering - I suspect you need a combination of UV (breakdown) and rain (to wash away the breakdown products) to get the full effect. 

 

In addition to higher temperature swings, is the side that's weathered most for you more exposed to wind and rain? I can't remember the orientation of your house, but vaguely recall that the front faces south-ish(?)

[ADLIan]

The Building Regs (Engalnd & Scotland), advice in Timber Frame Construction (from TRADA) plus other sources all refer to the use of a ventilated cavity behind render systems (on a carrier board) onto TF construction. Render on insulation on the structural frame is not recommended and has not been for many years.

[SlivenClod]

On 07/05/2019 at 09:42, jack said:

 

Interesting. Our wooden cladding (Siberian larch) has weathered fairly evenly east, south and west. The critical thing seems to be rainwater - you can see a diagonal line down within the deep overhangs showing where rainwater reaches. Sunlight by itself doesn't seem to cause very much weathering - I suspect you need a combination of UV (breakdown) and rain (to wash away the breakdown products) to get the full effect. 

 

In addition to higher temperature swings, is the side that's weathered most for you more exposed to wind and rain? I can't remember the orientation of your house, but vaguely recall that the front faces south-ish(?)

@jack is your cladding on to SIPs? I am considering vertical timber cladding onto SIPs and finding it difficult to find details on suitable product, on fixing method and general arrangement.

[jack]

46 minutes ago, SlivenClod said:

@jack is your cladding on to SIPs? I am considering vertical timber cladding onto SIPs and finding it difficult to find details on suitable product, on fixing method and general arrangement.

 

Not SIPs, sorry. Ours is onto battens attached to a wooden frame that hangs off the house to form a 400-1000mm overhang (different depths in different parts of the house).

[scottishjohn]

just fix batons your sips --maybe more  fixings  -so you are not over stressing the 11mm or15mm osb .

Me i would pre-drill the vertical  batons  so i know i am feeling how tight it is in the osb outer skin of the sips then attach cross batons ,then cladding 

so its sips ,then -house wrap then vertical batons the cross batons  then cladding 

I suppose you could just use cross batons -

-but for my taste i would like plenty of air gap behind  and no ledges for moisture to gather on 

 

[Jeremy Harris]

The SIP panel manufacturers produce standard details for pretty much everything, so worth checking, but generally on walls you will need counter battens (not battens) against the SIP outer skin (with  breather membrane behind) and then for vertical board cladding you will need to run battens across the counter battens to provide fixings.  The counter battens are needed to provide ventilation airflow from the base to the top, although some manufacturers may allow the use of ventilation shims behind batten fixing points, rather than counter battens.  Insect mesh or similar will be needed at the top and bottom of the ventilated cavity to keep bugs out, stainless steel industrial pan scourers work pretty well and can often be wedged in place, so a bit easier to fit than mesh.

[Richard 137]

On 07/05/2019 at 08:52, ProDave said:

I was attracted to the direct render on wood fibre system because it means the entire wall make up is insulation of some form. I wanted to avoid pointless cavities that have to be ventilated so anything outside the cavity contributes almost nothing to overall insulation.

 

I wasn't expecting "issues" and the problem now is who to "blame" and how to fix it to be sure it won't happen again. At the moment SWMBO thinks the whole lot is going to fall off within a few yeas.

 

Hi Dave

              you have put here exactly what i have been thinking and trying to sort out over the last couple of months, I am just about to order SIPs house and passive foundation and the only thing i cant get my head around is fitting batten and render board to outside when there are breathable insulation board that increase U value and are easier to install and the mess render system work on. I have looked at the EWIPRO system and thought it ticked all the boxes i had also liked the Baumit open therm EPS system. i know you mentioned you had some issues below so any advice would be very much appropriated.

Regards Richard