Green Building Forum - External insulation - any pitfalls? Thu, 11 Jun 2026 21:48:53 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39482#Comment_39482 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39482#Comment_39482 Thu, 27 Nov 2008 16:23:28 +0000 JackyR
But what I'd really like to know is, How will external insulation go wrong?

How might the installers stuff up in the first place?
What probs happen after insulation? Mould - where? Render cracking off? How does it respond to impact?
External insulation is described as lasting 25-30 years - how does it fail? What do you do then?

Is there anywhere I can see some that's been up for 20 years?

If we fit it, we'll have through-colour render due to difficulty of painting side of house (narrow alley) - what does that look like after 10 years?

All wisdom most gratefully received!]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39483#Comment_39483 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39483#Comment_39483 Thu, 27 Nov 2008 16:35:33 +0000 Peter Clark
http://www.ibp.fhg.de/literatur/fachz/Roz2.pdf

From the conclusion:

'The favourable long-term performance together with an excellent driving rain pro-tection and a high thermal insulation quality are the reasons why ETICS have become so popular in Central Europe. Currently more than 30 million square meters of ETICS are installed in Germany every year.']]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39484#Comment_39484 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39484#Comment_39484 Thu, 27 Nov 2008 16:45:49 +0000 tony
In Germany it is extreemly common. Some concrete panel tower blocks have it in the UK.

Almost no down side -- Not good with impact but how often do we hit housed with things?, surface green algae in damp shaded parts --not a problem, If you are Thames Valley have a look at my ones - whisper for addresses. Installers can mess up round scaffold put-locks/lift height joins. They can also be none too clever thinkers when it comes to pipes and wires so do your own thinking and altering before they come.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39503#Comment_39503 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39503#Comment_39503 Thu, 27 Nov 2008 20:32:36 +0000 BrianR
The insulation should ideally be breathable especially in an old house. There was a fashion a few years ago of spraying on waterproof render onto old houses. Then they discovered the woodwork would rot etc.

You may also need to improve the extraction of damp air inside the house in winter time. More insulation means your walls may be less able to get rid of moisture.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39540#Comment_39540 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39540#Comment_39540 Fri, 28 Nov 2008 00:25:08 +0000 JackyR less cracking of render can be expected, due to decoupling of render from masonry.

Tony, your experience is also v encouraging. Don't think I can make to Thames Valley awhile - maybe in a few years!

Brian, yes, I'd read about drainable cladding systems, which made me wonder how water got behind the cladding in the first place, assuming the roof was extended. Are we talking poor worksmanship yet again?

External breathability isn't on the cards, unless we hack off the Victorian render and 130 years' accretion of every type of paint plus a semi-failed spray render (scraped off where loose during last paint job). We'll probably go for waterproof outside, vapour-permeable (or completely breathable) inside, since interior plaster may need to come off AGAIN anyway :cry: Frankly, the render may be holding that wall up...]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39780#Comment_39780 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=39780#Comment_39780 Mon, 01 Dec 2008 10:47:43 +0000 Peter Clark
http://www.project-oecotop-building-systems.com/download/pdf/02a_breathability.pdf

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42631#Comment_42631 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42631#Comment_42631 Thu, 08 Jan 2009 19:59:56 +0000 JackyR Posted By: JackyRWe'll probably go for waterproof outside, vapour-permeable (or completely breathable) inside
Or maybe not. Ball-park quote for 80m2-ish end of terrace: 12K. Pounds. Sterling.

Think that was PIR, but my brain was leaking out of my ears by then...]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42681#Comment_42681 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42681#Comment_42681 Fri, 09 Jan 2009 10:25:11 +0000 Peter Clark
Its the 'cutting edge' thing, if you try to do something different you pay through the nose. This should be perfectly possible for a local 'jobbing builder' at much less, but they would not do it because its different, or you would not trust them.

This is more common on the continent, would someone come from Belgium, or wherever, at a good cost?

I wonder how much NBT would quote you for their woodfibre and lime render 'breathable' system? It might be worthwhile looking at some other quotes, I would be interested to hear what they say myself.

Elsewhere on the forum, someone is offering to run courses in external insulation DIY!

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42786#Comment_42786 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42786#Comment_42786 Fri, 09 Jan 2009 22:16:40 +0000 JackyR
I'm not a payback fiend, but £12K cladding when the house only cost £120K?]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42846#Comment_42846 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42846#Comment_42846 Sat, 10 Jan 2009 19:55:39 +0000 Gotanewlife
Oh and as I understand it - 10 or 20 year gurentees increase the cost of the product hugly because the law requires the provider of the guarentee to under-right it externally and since the external insurance provider hasn't the faintest what the risk is they just assume it will fail!!!! I'm sure that is the gist of what I read....on a solar panel supplier's site I think.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42859#Comment_42859 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42859#Comment_42859 Sat, 10 Jan 2009 21:23:09 +0000 caliwag
We are in a short term world...try this (no I have not used it and know nothing about the company) you will never get your money back from messing about with expensive technologies...just stay comfortable, and keep the bills as low as possible...phew

http://www.mgcltd.co.uk/Products/Thermal_and_Acoustic_Insulation/SEMPATAP_THERMAL/]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42860#Comment_42860 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42860#Comment_42860 Sat, 10 Jan 2009 21:42:52 +0000 Immac Thermal resistance: 0.158m2 K/W
Resistance of untreated wall: =1/2.1 = 0.476
Resistance with sempatap: =0.476 + 0.158 = 0.634
U-value with sempatap =1/0.634 = 1.58 w/m2K
Calculations are for a solid brick wall.

How would this compare to celotex as an internal insulation product on a solid wall? I would prefer to extenally insulate but there's only a 12" gap between our house and the neighbour - can't really work in the space. Sempatap seems like a doddle to put up. I know it would make a difference and I could do it myself - but is it actually worth it? Costs for the material are £158 per 1m x 12.5m roll plus vat and delivery, plus sealant of £13 for two rolls and £26.45 per roll adhesive. I want something I can put up myself that's economical, but I want it to be effective too.

Any ideas anyone?
Many thanks.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42913#Comment_42913 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42913#Comment_42913 Sun, 11 Jan 2009 23:37:22 +0000 wookey
You'd be much better off spending slightly less money on 50mm celotex and separate plasterboard, or for about 25% more bonded PUR/foil/plasterboard (e.g. Kingspan K17). Obviously if you really can't lose 60mm of space then the more expensive PIR boards (K18) are a bit thinner or you can just choose thinner size. even 20mm PIR/PUR will be about 4 times as good as a layer of sempatap.

Putting up the boards yourself is easy enough. Bit tedious fitting round windows etc but not hard. I've done it before with foam-backed wallboards, and am just about to do it with plain celotex+plasterboard. I looked at Sempatap whilst checking out options.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42916#Comment_42916 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42916#Comment_42916 Mon, 12 Jan 2009 00:06:48 +0000 JackyR
The insulation (materials + labour), was in the region of £7500 for 80 m2 semi. Obviously depends on roof edge, doors & windows, etc.

Render (materials + labour) would be around £5000.

Labour comprised approx 2 men x 17 days.

Previous supplier had similar total, which didn't include scaffolding, but said price per m2 might come down for a larger area. Also current economic circs might mean suppliers willing to drop prices. This guy also said cost - and failure areas - were in the detailing.

Conclusion: EWI is incredibly expensive unless you are already completely re-rendering, in which case it's just very expensive...

And I think I'd like it done properly, if at all, to last as long as Tony's in Thames Valley. Sometimes that ha'pennorth of tar just ain't worth it.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42920#Comment_42920 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42920#Comment_42920 Mon, 12 Jan 2009 02:15:07 +0000 rumi_ecobuilder
Rumi here Im male by the way, not that it should matter.

With EWI the devil is in the detail. Buildings, mainly dwellings, are a very in my experience, unless meticulously built, a mix of very poorly fitted relatively products which are relatively incompatible. Most of th buildings I have added insulation to the outsde of had poorly fitted windows and doors which generally ere very drafty, along with poorly sealed gas flues, extractors and other throught tha wall systems. All were being rerendered and had between 50-100mm of polyeurothane and render added to their exterior.

I am very aware that costs are a big issue, and towards trying to reduce costs we ave been starting to move towards providing altenative cladding systems including prefabricated rendered panels.

I think the best way to keep the costs under controll is not to render the whole building. The cost of applying the insulation is low for use with a cladding system. For applying render there needs to be a high number of fixings, 18/sqm the mesh has to be stainless as do the profiles.

Getting your local builder to work to a technical spec might be possible, but I think there would be the added cost and necessity of employing an architect to supervise the installation.

As I said before the devil is in the detail:
1. Windows, doors, roofs, vents, flues, cable entries, draisn and DPC.

2, Insulation Materials, Natural, bidegradeble, Breathable, CO2 Nuetral or not

3, Render, Lime or Lime polymer fibre or sand/cement with lime added for flexibility.

4, Cladding Systems - high or low tech?

And finally thickness, 75-100mmis more cost effective than 25-50mm. because the difeerence between the 2 is 200-500 quid.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42936#Comment_42936 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42936#Comment_42936 Mon, 12 Jan 2009 09:31:58 +0000 Peter Clark
I am wondering if we can make it seem more sensible, in some circumstances, by considering the advantages. Does anyone know how to estimate or calculate a rough idea of financial savings?

External insulation is of use in draft proofing as well as insulating, also there is cold bridging (avoiding), is it really possible to get to a 'no heating required' situation? In a new house, or major refit, there would be savings in heating system installation, even if the boiler was needed but smaller, and less pipes and rads? Then the ongoing savings on fuel use.

If you avoided the expense of a central heating system and just put in a woodburner, that would save thousands?

If you saved 30% of fuel, that would easily be £300 annually, but that implies 40 year payback, how long does EWI last?
Or 50% might be £1000 per year in a bigger user? payback then 12 years?

Anyone have any reasonable, justifiable ballpark figures?

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42937#Comment_42937 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42937#Comment_42937 Mon, 12 Jan 2009 09:43:15 +0000 Peter Clark
Thanks for the detailed cost breakdown, bearing in mind it is just an example.

Posted By: rumi_ecobuilderI think the best way to keep the costs under control is not to render the whole building. The cost of applying the insulation is low for use with a cladding system.


Interesting, what effect would cladding instead of rendering have on your cost breakdown?

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42977#Comment_42977 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42977#Comment_42977 Mon, 12 Jan 2009 13:33:46 +0000 tony External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42989#Comment_42989 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42989#Comment_42989 Mon, 12 Jan 2009 14:38:02 +0000 Peter Clark
It does not have to pay back, but spending 12K on doing it will be easier if there is a personal benefit as well as an environmental one. Therefore more people will choose to do it.

Is there a personal financial benefit that mitigates against the high initial cost, if so how much do you think?

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42993#Comment_42993 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42993#Comment_42993 Mon, 12 Jan 2009 15:29:22 +0000 James Norton
Conservatories
Garages
New drives
Re-pointing
New windows
Decorating
New kitchens

etc etc

J

('course that doesn't mean that you have £12K spare to spend in the fisrst place.... :sad:)]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42999#Comment_42999 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=42999#Comment_42999 Mon, 12 Jan 2009 16:26:04 +0000 Peter Clark
Conservatories and garages have other obvious benefits, and so we can ignore the payback. But what is the other obvious benefit, to me, of paying for EWI?

Peter]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43001#Comment_43001 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43001#Comment_43001 Mon, 12 Jan 2009 16:40:36 +0000 James Norton Posted By: Peter ClarkBut what is the other obvious benefit, to me, of paying for EWI?

Well just the same as a conservatory really...

Your house looks nicer
Its a nicer internal environment
and because of those value is added to your house.

But also you get the added value from...

Lower fuel bills*
Reduced C02 footprint

J

*Use a free SAP calculator, Knauf do one. Compare current condition vs EWI, condition this will give you an idea how much energy you save multiply by cost of fuel. Don't compare this with fuel your current bills just price the difference between the two options this way losing heat by user action cancels out, also. For simplicities sake, assume your compound interest in investment is equal to the compound % rises in fuel costs - in reality the latter will outstrip the former but that gives you a margin for error. In reality there will be other knock only like higher surface temperature of internal walls leading to lower acceptable average room temp for same heat loss, and also positive effect on heat loss through reduced infiltration.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43003#Comment_43003 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43003#Comment_43003 Mon, 12 Jan 2009 16:49:36 +0000 caliwag It must be cheaper than Celotex internal bacause of reduced labour, and fiddling around openings etc...and way cheaper than external (how do you deal with bay windows, service pipes, eaves and ground level, window ingoes in a typical terraced house?) OK I agree if you have the whole row to refurb from scratch, but that's a serious grant job (if you get everyone to agree), and it may be cheaper to flatten the lot anyway...payback must come into it...people buy cars, sofas, TVs, HiFis etc etc without considering payback because they throw them away and seem to be happy to do so...rightly or wrongly.
Everyone is looking for a quick, cheap comfort fix (viz plastic double glazing...instant comfort...OK looks crap, not cheap, but still selling), so once Sempa gets going it'll be a winner, regardless what we think or say. I'm a fan of MHVR and tight draught stripping but that's not going to win any friends...the government doesn't even know that exists]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43011#Comment_43011 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43011#Comment_43011 Mon, 12 Jan 2009 17:33:33 +0000 TheDoctor
a 10mm layer on your walls IS going to mess with your skirtings / facings etc.

how many of you have skirtings and architraves that are 25mm+ thick?
you would need at least that before the Sempa layer makes them look god-awful.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43014#Comment_43014 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43014#Comment_43014 Mon, 12 Jan 2009 17:46:17 +0000 PaulT
If it is an isicyanate (Urethane/polyurethane) then these can release VERY toxic gases; Although I will not comment on this specific product.

The last time I looked at an polyurethane interior wall lining it had to have a plaster skim coat for fire protection.

If you are going to that trouble you may as well do it properly and dry-line (In my view), (or using insulating paint that is inert) - two ends of the spectrum.]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43015#Comment_43015 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43015#Comment_43015 Mon, 12 Jan 2009 17:48:29 +0000 James Norton
don't even think about it 10mm of EPS will do nothing for your insulation but will just create a perfect environment for mold behind it...! god knows why its being sold as a way of eliminating mold!]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43016#Comment_43016 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43016#Comment_43016 Mon, 12 Jan 2009 17:49:27 +0000 JackyR
New thread for Sempatap discussion?]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43017#Comment_43017 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43017#Comment_43017 Mon, 12 Jan 2009 17:53:03 +0000 jamesingram is stainless mesh required in all locations , agree with stianless profiles etc.

Jim]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43018#Comment_43018 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43018#Comment_43018 Mon, 12 Jan 2009 18:00:48 +0000 James Norton Posted By: JackyRNew thread for Sempatap discussion?

Please God no.....]]> External insulation - any pitfalls? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43022#Comment_43022 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3025&Focus=43022#Comment_43022 Mon, 12 Jan 2009 18:25:31 +0000 Arnold
I said no because it will stop my property from breathing. In fact I asked them why they were recommending it. the lady I spoke to could not answer.

I am intending to ask my MP about this same issue.]]>