Green Building Forum - External insulation - any pitfalls?

External insulation - any pitfalls?

jamesingram — Tue, 12 Jan 2010 11:35:54 +0000

Tile or Slate hanging is great for EWI , very easy to do , and as you say preserve the character etc.

External insulation - any pitfalls?

fostertom — Tue, 12 Jan 2010 11:56:05 +0000

I now see that paint removal from stone is prior to covering it up again, in areas that are to be EWI'd - presumably to make it vapour permeable? Otherwise, why bother with paint removal and pointing when it's going to be visually covered and functionally weatherproofed by EWI? in this case, a vapour-check at that back-of-EWI position would be just what the strong-VCL brigade would recommend, so can't be too bad. Why not save your money and leave the paint on (and not bother with repointing) - it won't be a complete vapour barrier by any means.

External insulation - any pitfalls?

bella — Tue, 12 Jan 2010 13:11:50 +0000

Yes, paint off/cement pointing out to a "going to cover it up" standard but to give really good vapour permeability so that stonework surfaces (in and out) encourage movement of moisture in any phase to the surface for evaporation and also insulate and protect from driving rain. Agree that it does not need to be done to the highest standard.

Perhaps slate hanging, with say wood fibre insulation, would be a good idea. Possible at what thickness I wonder? What are the downsides - cost of course but anymore than other EWI? VCL? - Scary! The walls will take a year (??years) to dry out and, even then, I guess to stay dry will always need to evaporate moisture both ways (no damp proof course, two walls unclad, a hillside behind the house, damp generally mild climate).

External insulation - any pitfalls?

headgear — Tue, 12 Jan 2010 13:32:14 +0000

Tom,
Having a vapour seal on the outer face of the masonry is always going to be dodgy, any moisture in the wall from rising damp or internal condensation will have nowhere to go except back inwards or up - wick effect. Of course this particular gotcha places severe constraints on the materials and detailing of the external insulation, it would be wrong to replace one vapour seal with another. The obvious countermeasure is to have a vapour seal inside, adding a whole load more work :-(

I'd want to have a look at the condition of the stone in the walls where they've been sealed, and any joists or wallplates embedded. If everything is in good order then all options are open, if not I would prioritise getting water out of the wall.

The lean to solar is a very good solution, I proposed the same for my client in Snowdonia but it has not yet been tried on planning.

External insulation - any pitfalls?

fostertom — Tue, 12 Jan 2010 14:20:54 +0000

bella, vapour permeability of wall in order to encourage/permit evaporation outward, will only work if using vapour permeable external insulation - that means wood fibre, cork or EPS, all of modest thermal resistance. If Nat Park stipulation restricts thickness, you may be forced to use XPS, PUR etc (foamed plastic) insulation of higher thermal resistance, but vapour impermeable. In latter case, no point in making the wall vapour permeable. In fact, as you're thereby into strong-VCL territory, as I said, the paint layer's in exactly the right place for a strong VCL (not that it will be a v strong VCL).

You say also wall vapour permeability to insulate and protect from driving rain - I don't get that, as the EWI will well protect from driving rain, and in that situation the wall won't be called upon to provide any insulation.

External insulation - any pitfalls?

bella — Tue, 12 Jan 2010 19:25:11 +0000

Posted By: fostertombella, You say also wall vapour permeability to insulate and protect from driving rain - I don't get that, as the EWI will well protect from driving rain, and in that situation the wall won't be called upon to provide any insulation.

Probably not very clear - meant that treatment of wall surface and choice of EWI should both encourage water/ water vapour movement and evaporation (as well as provide weather protection and insulation) so yes woodfibre is on the list. I see the issue on thickness but for the moment come down on the side of encouraging external evaporation rather than higher U-value for same thickness. Maximum possible dryness of the internal layers of the wall seems the number one priority and I am not certain that this can be achieved by using an impervious layer on the outside.

External insulation - any pitfalls?

fostertom — Tue, 12 Jan 2010 19:34:50 +0000

A thought - is aerogel water vapour permeable? If so, very best of both worlds, if somehow used for EWI - at a price!

External insulation - any pitfalls?

bella — Tue, 12 Jan 2010 19:39:02 +0000

Needs to allow water (liquid) absorption and movement as well? ie "wicking"

External insulation - any pitfalls?

fostertom — Wed, 13 Jan 2010 18:31:11 +0000

Hmmm? That's a lot to ask of any insulation - to absorb liquid water - I'd have thought that absolute no-no at all cost - severe to complete loss of inulation value. Unless you mean the hygroscopicity of organic insulants - but that's strictly vapour phase. Organic insulants need to be kept dry (i.e. without liquid content) same as any.

External insulation - any pitfalls?

jamesingram — Wed, 13 Jan 2010 18:46:21 +0000

Tom , interesting article in GBM winter 09 page 39 ," making the right choices for insulation , revisited "
I presume its fro mthe NBT woodfibre side of the fence

External insulation - any pitfalls?

Peter Clark — Thu, 14 Jan 2010 10:03:22 +0000

Posted By: fostertomHmmm? That's a lot to ask of any insulation - to absorb liquid water - I'd have thought that absolute no-no at all cost - severe to complete loss of inulation value. Unless you mean the hygroscopicity of organic insulants - but that's strictly vapour phase. Organic insulants need to be kept dry (i.e. without liquid content) same as any

Alternatively, we could say, with Neil May:

â€˜All natural fibre insulations dry quickly, because of the better capillary mechanisms.â€™

http://www.natural-building.co.uk/PDF/Case%20Studies/Breathability_in_buildings.pdf

Therefore to ensure the insulation is dry as much as possible, make it capillary open so that when it does INEVITABLY get wet, it can dry out faster. This principle is well established in the refurbishment of old buildings is it not?

As an aside, I can see no reason why it does not apply to new build also.

Peter

External insulation - any pitfalls?

bella — Thu, 14 Jan 2010 13:35:44 +0000

Is aerogel vapour permeable, anyone?

I have assumed that the term hygroscopic means water (liquid) holding capacity. And evaporation means the conversion of liquid water to water vapour that can then be carried away by air movement (wind, rising currents, ventilation). I imagine, but honestly donâ€™t know for sure, that absorbing and â€œwicking awayâ€ water must be â€œgoodâ€ properties for materials exposed to moisture (condensation, rain) rather as lime or clay plasters seem to be â€“ or cob or hemcrete for that matter. For example, I think I would feel safer having wood fibre or hemcrete rather that synthetics sitting next to wooden floor joists set into solid walls if I was insulating internally â€“ see GBM vols 18 &19.

What I am not clear about is at what point hygroscopic materials used for insulation (woodfibre, hemp, sheeps wool, shredded paper) when â€œloadedâ€ with water via condensation or rain lose their insulating capacity and what the dynamic sum of effects actually come down to in the relatively wet , and only briefly cold UK climate. Lots of evaporation means lots of heat loss â€“ â€œrun offâ€ i.e. membranes, slates, timber cladding might be a much better property in certain situations. Conundrum â€“ how to arrive at the right combination for the refurbishment of solid walled buildings without sending the planners into a tiz. May be it is easier than I know â€“ or maybe more difficult â€“ certainly expensive!!!

External insulation - any pitfalls?

Peter Clark — Thu, 14 Jan 2010 14:55:07 +0000

Posted By: bellaI have assumed that the term hygroscopic means water (liquid) holding capacity.

The document I linked to above discusses this as follows:

'how water moves through structures (water vapour permeability),

but also about the ability of materials to absorb and release water as vapour (hygroscopicity)

and about the ability of materials to absorb and release water as liquid (capillarity).'

Posted By: bellaI imagine, but honestly donâ€™t know for sure, that absorbing and â€œwicking awayâ€ water must be â€œgoodâ€ properties for materials exposed to moisture (condensation, rain) rather as lime or clay plasters seem to be â€“ or cob or hemcrete for that matter.

That is my understanding too, but there seems to be a lot of disagreement? The only proviso is that we should try to reduce the exposure to water, by roof overhangs, cladding, paint that is vapour permeable but capillary closed etc.

Posted By: bellaFor example, I think I would feel safer having wood fibre or hemcrete rather that synthetics sitting next to wooden floor joists set into solid walls if I was insulating internally

Or insulating externally?

My understanding is that it is best to have a wall that is vapour open, capillary open and hygroscopic, because these all work together to protect the wall from damage.
But,

1. It is best to have a more vapour resistance on the inside and less on the outside, so that water vapour inside the house is unlikely to get into the wall, and what does is going to move outboard and evaporate(if the wall has the three properties)

2. It is important to have a rainscreen of some sort on the outside to discourage rain from getting in.

Slate hanging sounds perfect to me, with woodfibre insulation underneath.

I should point out that I am an amateur with little building experience and trying to find my way through the mass of often conflicting advice here and elsewhere.
This issue of how we deal with moisture and water in building fabric seems crucial to me as we aim for more insulation and draught sealing, but there are definitely at least two 'camps' - natural and hi tech.

Peter

External insulation - any pitfalls?

fostertom — Thu, 14 Jan 2010 17:51:07 +0000

Posted By: Peter Clarkto ensure the insulation is dry as much as possible, make it capillary open so that when it does INEVITABLY get wet, it can dry out faster

Oh yes ineed, but that's not to say that the insulation should be intended as a way out for rising damp etc; not that the insulation should be expected to absorb liquid water by 'wicking'.

Anyway, is this moisture in the wall that we're trying to find a route out for really from rising damp, i.e. forever renewed? That's actually rare - what's often called rising damp is usually some kind of condensation and/or penetrating damp. If the latter, then EWI will permanently cure both of those and leave the wall dry, once it's dried out initially.

External insulation - any pitfalls?

fostertom — Thu, 14 Jan 2010 18:07:15 +0000

Posted By: Peter Clarktrying to find my way through the mass of often conflicting advice

Yes, we're in the middle of an evolving understanding about water transfer (as about heat transfer too), when old simplicities are being strongly questioned. This kind of debate is the best way I know - so many unexpected realisations turn up and can bring a flash of clarity.

External insulation - any pitfalls?

headgear — Thu, 14 Jan 2010 21:46:52 +0000

"Anyway, is this moisture in the wall that we're trying to find a route out for really from rising damp, i.e. forever renewed? That's actually rare - what's often called rising damp is usually some kind of condensation and/or penetrating damp. If the latter, then EWI will permanently cure both of those and leave the wall dry, once it's dried out initially."

If there is water in the ground and the wall is dry, the water will travel up the wall by capiliary action ( I think the limit is related to atmospheric preasure - a proper physicist could tell me). Water vapour will travel through fabric by responding to vapour preasure gradients, generally from cold to hot but also from wet to dry. In solid stone walls both processes can be happening simultaneously. How fast this happens depends on the physical properties of the stone AND the mortar.

My priority treatments for a wet wall would be
Drainage
Driven rain protection

External insulation - any pitfalls?

Peter Clark — Fri, 15 Jan 2010 09:22:23 +0000

Posted By: fostertomOh yes ineed, but that's not to say that the insulation should be intended as a way out for rising damp etc; not that the insulation should be expected to absorb liquid water by 'wicking'.

I would like to, cautiously, suggest the contrary view Tom.

Whatever the source of water in the building fabric, it is best if the fabric is vapour open, and hygroscopic and capillary open, because this will promote drying out of the fabric, through the absorption and distribution of water - by the insulation if necessary. If the insulation does not do this, it will hinder drying and promote concentration of the water in some areas of the structure.

Of course, if we do this, we need to minimise the water entry by having an outer rainscreen and hi/lo diffusivity for outside/inside, and do something about 'rising damp' if there is such a thing.

The point is, having tried our best to prevent water getting in, from wherever and in whatever form, when some does we should be able to depend on the structure dealing with the damp, the structure looking after itself to an extent, and that means ditribution of any water through out the wall to prevent concentration and encourage dispersal.

Questioning old simplicities? I feel I am questioning new simplicities and promoting old simplicities.

Is rising damp a particular part of Bella's problem? Why has it been mentioned?

Peter

External insulation - any pitfalls?

fostertom — Fri, 15 Jan 2010 19:37:42 +0000

Posted By: Peter ClarkIs rising damp a particular part of Bella's problem? Why has it been mentioned?

Not sure. She and others seem v concerned to not block escape of moisture from her walls - as if it'll be a forever-renewed ongoing problem (which, assuming no penetrating damp or leaking pipes leaves only rising damp - I think?) rather than just a one-off drying of existing water.

I'm in fact suggesting it's the latter, so no need to make the insulation transport moisture, once the source (condensation, I bet) is stopped by the EWI keeping the surfaces warm, and the old moisture's dried out.

External insulation - any pitfalls?

Peter Clark — Sat, 16 Jan 2010 20:25:45 +0000

Posted By: fostertom so no need to make the insulation transport moisture, once the source (condensation, I bet) is stopped by the EWI keeping the surfaces warm, and the old moisture's dried out.

I don't want to make the insulation transport moisture I want to avoid that, but I would like it to be able to just in case. I don't see hygroscopicity etc. as being a way of dealing with known moisture problems, although i know that is done in some old buildings where no other approach will work. More of an insurance policy to make the building fabric more robust for however long we hope it will be around.

Peter

External insulation - any pitfalls?

gjjjohn — Sun, 17 Jan 2010 18:09:15 +0000

In useing external wall insulation there are many points to look out , for instance to apply such a system to a old building with no cavity , brick, stone ,concrete , first check if there is a dpc installed , if not then install a dpc
second check your roof to insure there is no water /damp ingress that my be allowing damp/water to enter the old walls at this point , third if you are not installing a ewis in the complete facade [ perhaps facing stone that is not allowed to be changed by the planers] then ensure that you take steps to stop any damp/water ingress flowing from the unsulatied areas to the insulation facade
Once these steps have been taken you may apply a ewis system with no problems
Regarding breathing problems , there are none in this type of substructure as any of the back grounds i have listed above will allow the water vapour to dispers in a standard heated home [oil,electric, gas ,not open gas flame, ] if your building was old and/or damp when you installed the ewis system there will be some tempory problems with water vapour but these are not large problems and will disapper soon depending on the amount of damp/ water in the old substructure
it is important to rember that each builing type will be differant in applying ewis systems regarding detailing of dpc, new/old bild ,steel/timber frame ,masonry of all the differant types and indeed the cost will differ depending on the back ground , from Â£ 55.00 m2 to Â£ 120.00 per m2 ,

The other main factor in costs are thickness / types of insulation and finishs

regarding finance there are limited grants to be had ,and some very very good tax allowances for industrial buildings

In short go to an approved contractor who will use a eta approved system and can offer a indepant insurance
that is insured to the system and building

any question just ask nb I work In the feild I think I am to say so

from gjjjohn

External insulation - any pitfalls?

bella — Sun, 17 Jan 2010 19:21:56 +0000

I have found the comments here most helpful and illuminating (thank you all) as I try to "take a view", as the lawyers put it, on best options for external insulation (roof and walls) in an 1860s stone-walled building. A few things:

Rising damp : I have some knowledge/experience in chemistry and no amount of "doesn't exist" will convince me that it cannot happen although it must be rare overall if so few of you see it. But if the conditions are right (absorbent materials such as lime between stones, stones laid directly on the ground with a minimum foundation, earth and rubble between two skins of a thick stone wall, water movement generated by previous salt deposition) it must surely happen when/if the ground becomes sodden even briefly. So measures to ensure drainage from footings as rapidly as possible are very important and I still hanker after the means for water to evaporate outwards. I don't think I do have much in the way of rising damp but would I see it? - our predecessor had a 1m band of waterproof cement installed round the ouside walls inside the whole building so I am not going to get much evaporation there.

Damp-proof course - for rubble or random stone walls??? How on earth would you do it? The footings lie about 4 inches below the surface and the walls stand up because of the massiveness of the stone, good construction detail and wall depth of 600mm at the base. Injected damproofing wont work and --- well I don't want to even hink about the alternative. A case of the "cure" being more alarming than the disease. If guarantees for EWI by a registered installer depends on inserting a damproof course first I think I will pass.

External insulation - any pitfalls?

Nick Parsons — Sun, 17 Jan 2010 21:14:49 +0000

''If guarantees for EWI by a registered installer depends on inserting a damproof course first I think I will pass. ''.

I think I am with you there. Some, if not all, EWI firms bridge the dpc -if there is one - (some changing material from porous above to non-porous below), so that if there's any capillary action you've blown it anyway. If there is not a (rising?) damp problem, why take measures to chase the (not a) 'problem' away?

External insulation - any pitfalls?

spoonandfork — Mon, 18 Jan 2010 18:53:58 +0000

"fostertom: part of the EWI deal to really get the benefit, is to also run it as a 'tea cosy' unbroken at the eaves, over the rafter tops. so the roof-finish plane gets jacked up by 150 to 200, crossbattened-over etc for new tiling, and it's simple to extend that outboard to recreate whatever eave overhang you want. That way you can near-enough reproduce the eave detail.overhang you had before (or improve the appearance in v many cases)."

can you clarify this? this approach involves;

remove all roof tiles, battens, gutters and soffits.
run EWI up wall and over roof, right up to ridge
new soffits (to achieve good overhang), felt/batten/tile, guttering etc

that right?

External insulation - any pitfalls?

jamesingram — Mon, 18 Jan 2010 21:30:06 +0000

I was presuming just making sure wall and ceiling insulation joined up would achieve the required complete insulated envelope. ?
this could be done by just lifting the first few row up from the gutters ,
also adjusting the rafter feet, sprocket to allow thicker EWI as discussed earlier.

External insulation - any pitfalls?

fostertom — Tue, 19 Jan 2010 01:05:34 +0000

Posted By: spoonandforkthat right?

Yes - roof insulation cd be between rafters too; then the over-rafter EPS cd be thinner, say 100, which wd still kill thermal bridging thro the rafters. The new extension rafter-ends wd sit within the outer 100, fixed to the old rafter tops, or preferrably staggered from same, fixed to noggins between. End result is that eave level finishes about same ht, relative to window heads, having moved up say 100 on the diagonal, but extending further outward to bring rafter ends lower, back to approx extg. level. Hope that makes sense.

jamesingram, that wd work too, except that lengths of rafter/ends still penetrate the insul 'tea cosy'.

External insulation - any pitfalls?

bella — Tue, 19 Jan 2010 17:26:03 +0000

One of the deciding factors in favour of external roof insulation for us is that the roof is open internally with exposed rafters and the original exposed pine sarking boards (so no ceiling) as well as purlins and three A beams, all in rather good condition but with work needed on lead valleys, down-pipes, drains etc etc. The planners want internal insulation (so did our professional advisors) - will keep you all informed of ultimate decision. This discussion is giving us extra confidence that external is the right approach for this particular building. It is interesting that the discussion with the planners has all centred round whether or not it is acceptable to raise the roof not what is the safest/most effective method of insulation. Ultimately the safety and integrity of the roof is the bottom line but with a calculated heat loss of around 6000kW/yr insulation is clearly essential if the building is to have a long term future as our dwelling.

External insulation - any pitfalls?

fostertom — Tue, 19 Jan 2010 18:04:23 +0000

Overwhelmingly, your building demands external over-rafters insulation - it's obvious.

As well as safest/most effective/easiest form of insulation (incl easy to make it thick!), it's clearly best for the building visually, and preserves it best, by leaving your exceptional boarded rafter, purlins and trusses as original - few such must still remain, after decades of ruination by internal insulation.

The resistance to raising the roof surface is ridiculous, knee-jerk, rulebook-bound. Not only will raising it be practically undetectable once completed, if well done, without careful study of old photos, but it seems they've already agreed to a half-measure raise, so why not just allow you to do it thick enough to really do the job for all time, instead of making you want to come back and ask for more thickness in a few years, when the half-measure is shown as inadequate?

Making the roof raise undetectable will be much easier, almost automatic, if EWI is allowed at the same time - the two geometries work together to restore the eaves height to just about what it was before, above window heads, but just 250mm further outboard.

Go for it!

External insulation - any pitfalls?

fostertom — Fri, 12 Mar 2010 16:45:23 +0000

Just come across this on Springvale site http://www.springvale.com/page_view3.asp?InfoID=559:

"Producing one square metre of Platinum EPS at a thickness of 100mm requires 5 litres of mineral oil. Over a period of 50 years the same board saves over 600 litres of heating oil (source BASF)"

That's 50 litres (nearly 11 gallons) of oil per m3 of EPS. That much oil would occupy about one ninteenth of a m3 - so EPS is 1 part oil to 18 parts air!

External insulation - any pitfalls?

Paul in Montreal — Fri, 12 Mar 2010 16:48:15 +0000

Posted By: fostertomThat much oil would occupy about one ninth of a m3 - so EPS is 1 part oil to 8 parts air!

Not quite, it might take 50l to produce 1m3 of insulation, but it doesn't mean that there is 50l of oil in the m3. But the take home is that using oil to make insulation saves more oil than it uses in manufacture - and prevents some oil ending up as CO2.

Paul in Montreal

External insulation - any pitfalls?

fostertom — Fri, 12 Mar 2010 17:18:02 +0000

Posted By: Paul in Montrealit doesn't mean that there is 50l of oil in the m3

I know - artistic license - most of it prob goes as fuel for the process (or perhaps they're not actually including embodied energy?) It just seems a surprisingly large amount of oil.

That 9 gallons of oil contains about 315kWh of energy, or 420 carthorse-hours of work, or an Olympic cyclist pedalling non-stop for 3 months. To make 1m3 of EPS.

Posted By: Paul in Montrealusing oil to make insulation saves more oil than it uses in manufacture - and prevents some oil ending up as CO2

Absolutely - if oil's got to be used at all, it should be for EPS, even more so than other oil-based insulants - but there are non-oil alternatives to even this.

And having used precious oil to make EPS, it shouldn't merely save so much oil as fuel, in its lifetime - it should eliminate oil as fuel altogether, because the tiny remaining heating requirement should be supplied, year-round, by free solar heat, not by burning anything at all.