Green Building Forum - EWI System Thu, 30 Apr 2026 06:20:23 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306754#Comment_306754 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306754#Comment_306754 Wed, 11 Sep 2024 20:03:24 +0100 Victorianeco
Primarily because we want to renew the facade anyway, the existing render is traditional roughcast.

What is the best EWI system in terms of overall cost per r-value? From what I've seen all of the K-rend jobs in my area look awful with staining, algae and so on. What is the best finish for a seafront property that will be low maintenance?

We may look to DIY the cladding and pay to have it rendered. Can it go on existing roughcast??

And if we do install ne wiwndows in teh outer insulation layer - can the EWI be added next year or is this just asking for leaks?]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306755#Comment_306755 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306755#Comment_306755 Wed, 11 Sep 2024 21:01:08 +0100 Peter_in_Hungary Posted By: VictorianecoWhat is the best EWI system in terms of overall cost per r-value? From what I've seen all of the K-rend jobs in my area look awful with staining, algae and so on. What is the best finish for a seafront property that will be low maintenance?
The silicon based top coat (decorative render) is a lot less prone to staining and algae growth than the cheaper varieties.

Posted By: VictorianecoWe may look to DIY the cladding and pay to have it rendered. Can it go on existing roughcast??

The EWI can go on the existing roughcast providing it is sound and passes the tap test. (If you tap it and it sounds hollow then it is coming way from the wall) Any area that fails the tap test has to be removed but re-rendering is not needed as you just use a slightly thicker bead of adhesive for that area.

Posted By: VictorianecoAnd if we do install ne wiwndows in teh outer insulation layer - can the EWI be added next year or is this just asking for leaks?

You can put the windows up in advance of the EWI (leaks minor or major of either / both air and water will happen) but the biggest concern I would have from renovating experience of several houses is that next year in the scheme of renovations inevitability slips to 2 -3 years and there is no such thing as temporary !!.]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306757#Comment_306757 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306757#Comment_306757 Wed, 11 Sep 2024 21:10:23 +0100 Nick Parsons Graphite EPS unless you like wood-fibre or cork (I do) and want to pay a lot more (I did!)


**''From what I've seen all of the K-rend jobs in my area look awful with staining, algae and so on. What is the best finish for a seafront property that will be low maintenance?''**

Render, seafront, tricky. Staining tends to arise from poorly-detailed 'protruberances'. Avoid them and you've gone part of the way. Ask the system provider to suggest something for your specific situation.

''**And if we do install ne wiwndows in teh outer insulation layer - can the EWI be added next year or is this just asking for leaks?''**

Don't put the windows in the 'normal' position on a reveal to the brick. Do the window-in-plywood-box thing and stick them out. Tape DPM with air-tightness tape to the frames and back to a smooth-rendered strip which you make over the roughcast.

Yes, you can probably do over roughcast, but for fixing use the full-perimeter and 'domino' method of fixing rather than full coverage. Definitely use mech fixings too, in my view. Remind me how wide your cavity is (IIRC you were going to fill that. If it's over 50mm and you are going for 100 or less EWI a condensation risk analysis is even more important. I'd get one done anyway, but the 'rule of thumb' two-thirds/one-third rule comes in. If, for example you had a 100 cavity, filled with gEPS, and you did 50EWI, the inside of the outer skin of masonry could get cold enough for condensation to occur. The other way round and it'll be more 'tucked up snug'.

Yes, you can DIY, but I would advise going on someone's course. Go down below DPC level into a French drain.

I have used EWI Store on a number of occasions, though many other suppliers exist. They do trg too, tho' not sure if in Wales.

**Ah, was typing while P-in-H posted.]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306759#Comment_306759 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306759#Comment_306759 Wed, 11 Sep 2024 21:25:22 +0100 Peter_in_Hungary Posted By: Nick Parsons**''What is the best EWI system in terms of overall cost per r-value?''**
Graphite EPS unless you like wood-fibre or cork (I do) and want to pay a lot more (I did!)

I have never found that the graphite EPS worth the additional cost - if you can manage with the extra thickness of standard EPS to get the same U value. Of course that is with prices over here so YMMV.]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306767#Comment_306767 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306767#Comment_306767 Thu, 12 Sep 2024 19:44:40 +0100 Victorianeco
The one area (extension) has 80mm cavity batts]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306769#Comment_306769 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306769#Comment_306769 Fri, 13 Sep 2024 10:26:28 +0100 Peter_in_Hungary Posted By: Victorianecohe one area (extension) has 80mm cavity batts
The cavity batts should be against the inner face with air flow outboard. Probably not possible to additionally fill this cavity nor stop the air flow so putting EWI on this probably won't add anything other than cost.

Posted By: Victorianecothere must be a point of diminishing returns to cost when EWI'ing?

There is but it is a calculation of personal choice. The cost difference is going to be the additional thickness of the EPS as all other costs are the same. (over here EPS is priced /m3 so 200mm is twice the price of 100mm)]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306770#Comment_306770 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306770#Comment_306770 Fri, 13 Sep 2024 12:00:12 +0100 Victorianeco
It's only really 2 smaller elevations anyway, so I guess if scaffold is up and we're looking to re-render it must have a benefit in EWI'ing?

A quick look on EWI store suggests....

Rockwool External 120mm - £39.83m2
Rockwool External 90mm - £34.98m2

XPS 100mm -£22.64m2
XPS 60mm - £17.32m2

EPS 240mm -£36.67m2
EPS 120mm - £19.58m2
EPS 100mm - £16.64m2
EPS 60mm - £9.89m2

So definitely cheaper to buy thicker for all materials in UK but there must be a maximum thickness where marginal benefit of extra depth comes into play?

EPS looks the winner in terms of cost mind.... I'd imagine as with most people cost is the biggest factor]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306772#Comment_306772 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306772#Comment_306772 Fri, 13 Sep 2024 20:25:50 +0100 djh Posted By: Victorianecothere must be a maximum thickness where marginal benefit of extra depth comes into play?Yes there is, but as PiH already said, its a personal choice. Once you've gone beyond whatever you're required to do to meet regs it all depends on your own goals and your assessment of how much its worth to meet those goals.]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306773#Comment_306773 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306773#Comment_306773 Sat, 14 Sep 2024 02:22:46 +0100 wookey
Better is to work out the whole plan with PHPP and you can easily model different thicknesses/costs and tradeoffs, with better windows/roof/floor allowing lower wall U-values, to decide where you want to end up, or just pick a standard like AECB level 2 or EnerPhit and design to that.

I'll second everything Nick P said. Except that I favour using structural insulation (alma vert/compacfoam) for mounting windows in the EWI, rather than plywood boxes - but both methods work fine if you get the details right. The silicone render is great.

I did 160mm/200mm woodfibre+silicone render (and XPS below ground) (on a similar with-cavity detached building but inland/East Anglia so a lot drier). XPS is annoyingly high-carbon but otherwise great. EPS is significantly cheaper and easier than WF but you will spread plastic bits everywhere. WF will give you loads of thermal mass/decrement delay and excellent breathability but you don't really need the latter if you have a cavity and working DPC. And you may not need the former if you don't have overheating issues.]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306805#Comment_306805 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306805#Comment_306805 Sat, 21 Sep 2024 07:08:26 +0100 fostertom
EPS, as well as being cheapest, has great tech advantage of zero capillarity (no 'soaking up' or 'soaking in', is its own DPC, unlike wood fibre), as well as ready and complete re-drying when/if it does get wet, by interstitial condensation or hydrostatic pressure (standing flood water).

Wookey, XPS (and all cellular plastics) is worse not better than EPS below ground - tests show that it does in fact gradually absorb water but then never re-dries. Of course, mustn't be in standing trench water/water table, hence Nick's recommendation of french drain, but that won't save you from flood water - nothing will!]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306811#Comment_306811 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306811#Comment_306811 Sat, 21 Sep 2024 19:23:37 +0100 Victorianeco EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306816#Comment_306816 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306816#Comment_306816 Sun, 22 Sep 2024 23:59:43 +0100 fostertom EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306818#Comment_306818 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306818#Comment_306818 Mon, 23 Sep 2024 08:23:03 +0100 Victorianeco
Can you really screw into structural foam and get a good fixing on say doors 3m wide?

I'll get a picture up of my facade and highlight some queries

Thanks]]> EWI System https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306822#Comment_306822 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18192&Focus=306822#Comment_306822 Mon, 23 Sep 2024 15:17:33 +0100 fostertom http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18174&page=1#Item_11]]>