What EWI for 1930s solid brick (215mm) wall home

[tanneja]

Hi all,

 

Major renovation of our 1930s semi-home but will have lots of original external wall retained.  Currently have 15mm internal plaster / 215 solid brick / 20mm external render for U-value around 1.8.

 

Builder concerned by prospect of EWI any chunkier than 70mm, (probably to sync with adjoined neighbour / not take up all the soffits overhang / not have windows set undesirably far back) but hopeful I can push him on that.  I see that 120mm of PIR would get us down to 0.18, but obviously PIR is phenomenally expensive.

 

70mm PIR (seems to be max thickness of a single sheet) seems to get us to 0.29.

 

Can anyone steer our thoughts to how to make insulation more affordable, and perhaps what U-value to from a comfort perspective?  If PIR is the only option given our thickness restrictions, and we are looking in the territory of 140m2, where will we get access to the best deals?

 

Many thanks

Edited July 22, 2020 by tanneja

[MikeGrahamT21]

Majority of people use Graphite EPS, for cost vs performance.

 

70mm will get you to 0.38U, however bear in mind that at the minute you are probably around 2.2U, rather than 1.8U you suggested, thats still a massive improvement.

 

You can go over the amount you have available in your soffits, but in my opinion this is when it starts looking horrible.

 

Before

 

After with 70mm EPS

 

After with 100mm Kingspan K5 Phenolic

 

Hope it helps in making your decision.

 

Regards

Mike

[joth]

What are you doing at the wall-roof junction? Will you have an insulated pitched roof too?

 

We are doing this (insulating the roof to create a warm loft),  but didn't want to have deep fascias and skinny soffits, as have extended the height of the rafters (to make a deeper roof section to insulation between), cut off the original rafters at the junction with where the EWI will go but extended the new rafter extensions over to create a new roofline with deeper soffits.

 

This probably doesn't fit into the brief for "reducing the cost" mind you. 

 

[Russell griffiths]

I didn’t think you would use pir for external insulation, I thought it was all EPS if you intend rendering it. 

 

Also so don’t be to tied up with u values, you need to look at the whole build, no point having 1m thick walls and poor airtightness. 

Better to get it all good than some excellent and some aspects poor. 

[Ferdinand]

You can PIR in any thickness well, beyond 70mm up to and including say 150mm or even 200mm.

 

eg Celotex to 200mm

https://www.celotex.co.uk/assets/handy-guide_nov18.pdf

 

The insulation material is a relatively small amount of the cost, and my advice is to really work on the detail and ask lots of questions.

 

I have looked over the years at EWI on half a dozen different houses and always ended up doing IWI, underfloor insulation and loft insulation instead.

 

That is probably not what you want to hear, but you will need to be doing the project on the basis of comfort as well as economics.

 

Happy to comment and point you to resources.

 

Ferdinand

 

Edited July 23, 2020 by Ferdinand

[Onoff]

@MarkyP did similar and I think @oranjeboom too...

 

 

[Mr Punter]

EPS is tried and tested.  There will be a sweet spot on thickness and it could be the 70mm your builder suggests.  Normally stuck on plus some mechanical fixings, then thin coat render / mesh.  Moving the windows outwards towards the insulation is helpful.

[Ferdinand]

Having said what I said, on my latest reno I fitted extended window and door sills to all the new 2G windows to allow for future EWI if required.

 

However for a small 3 bed bungalow experience with the tenants has shown all energy bills running at around £55-60 per month having just done the normal things (UFI, loft, decent 2G, careful detailing) well, so there is not enough saving left to justify that much more - and as it is a rental I would need an extra benefit to do it.

 

Much of this reno is on the forum search "Little Brown Bungalow".

 

F

Edited July 24, 2020 by Ferdinand

[tanneja]

@MikeGrahamT21 you are so right, 2.2 currently, my mistake.  I am struggling to guage the difference in comfort that 0.38 (EPS) and something around 0.2-0.3 (Kingspan K5) would mean in real world terms, and whether the extra cost would be justified if we plan to stay here for 20 years.

 

@Russell griffiths that is reassuring to say not get hung up with U values.  It is such a prominent subject when reading the glazing board here, in reality I ave no sense for what will be the better insolator from low / high outdoor temperatures.  I guessed that building regs set the levels as low as they have for a reason and so was looking to get close to extension or even new build regs.  Any further sense you can talk into me is appreciated.

 

 

@Mr Punter you would be my builder's best mate to agree 70mm would be sufficient.  Our budget is blown to pieces through a very wet start of the year and the virus, is EPS is still a responsible choice for the long term given it's U value, my builder would be enthusiastic take a two day course on it and then try.

 

@Onoff thank you for the post link, I had read it but when i saw the thickness I would need with EPS to get to a U value approaching regs (not that regs are necessary for me as this isn't on the extended part of the house, but still seemed sensible to shoot for that).  Maybe falling short, at around 0.38, will still be fine and compliment the plans for 3G and "relative" air tightness around the house.

 

@joth I have no idea.  Our roof is being entirely taken off and starting over due to previous poor workmanship.  I will be speaking to my builder and read what I can on here about how EMI is managed at the intersetion with roofs.  Will also need to see how it is managed with respect to the DPC and around window and doorway returns, I assume it means bringing the frames of these to the edge of the existing blockwork meaning the EWI forms the entirety of returns .

 

@Ferdinand thank you for those remarks.  We are going for underfloor insulation and loft, but IWI is less favourable given we have a minimal footprint already.  I will look at what thickness of internal insulation would be necessary to get to the equivalent insulation of 70mm EPS or PIR.

 

To all, sincerely appreciate this input, will continue to read other posts, but any more advice would be graciously received.

[A_L]

2 hours ago, tanneja said:

I am struggling to guage the difference in comfort that 0.38 (EPS) and something around 0.2-0.3 (Kingspan K5) would mean in real world terms, and whether the extra cost would be justified if we plan to stay here for 20 years.

 

Starting with U=2.2, going down to U=0.38 saves about 45kWh/yr per m²  and going down to U=0.2 saves about 50kWh/yr per m² in central England. (Full SAP model)

[MarkyP]

it was two or three years ago now but when I did my EWI my research concluded that EPS was the best product. There had been some issues with PIR boards warping post installation under EWI, many major system suppliers dropped them and only support EPS, mineral wool or wood fibre. Worth checking out the green building forum for EWI threads, there's been some very comprehensive discussion over there over many years and there's some really good advice. I'd caution use of PIR unless you can be sure of a comprehensive manufacturuer backed warranty (even these are very dubious in my opinion). Even 70mm EPS will make a huge difference in relative terms (if you can go thicker then do, you dont need much soffit overhand and deep recessed windows look good in my view). Could you manage to sequeeze in 90 or 100mm EPS? Since my EWI the walls no longer feel cold and the temp variations in winter are much lower. You'll also note that when the heating goes off, it isn't freezing cold 40 mins later! Whatever board you use, make sure they install them well - I actually did a course in EWI (to learn how to apply the render, I can plaster a bit so it was pretty easy to pick up) But on the course, we did a morning doing some boarding and instructor actually said if you have any large gaps, fill them with basecoat! I challenged this and he sulked for the rest of the course but doing this is really bad, it creates a cold bridge, but worse it will mean that the render may dry unevenly (heat loss path will show the joints in the render) and in the long run there are examples of the joints staining through the render, I would guess because differential algae growth on the facade due to variable moisture content of the render. You want all joints to foam filled and also use thermally broken fixings recessed below surface with a cap of EPS to close - they work brilliantly and remove the cold bridge and also remove the risk of a fixing "grinning through" the render if sat a bit proud.

 

Not sure what lambda you are using to calculate the u-values but worth checking you are looking at enhanced (graphite EPS) which is considerably better than standard, in the order of 0.031 (vs 0.038) from memory. Also worth noting that EWI grade EPS is cut from aged blocks to ensure dimensional stability - I used a mix of Kaycel EWI EPS and also some EPS supplied by Baumit. But be careful to ensure it's stuff for EWI. Do consider taking EWI down to the top of the footings (builder may not understand this or may be terrified of doing things below DPC so you might need to do some research and show some details) but do a search for plinth EWI (again masses of disucssion on GBF). Many of the large system suppliers now have details for plinth, the taboo of going below DPC seems to be fading which is good.

 

Chose render carefully - your builder will likely plump for the cheapest acrylic finish coat unless you specify otherwise. Typically you will see a basecoat in two passess with a mesh embedded but then a thin coat finish. Worth paying a bit more for a silicate premium mineralic thin coat finish in my opinion (most manufactuers give this option) - it is a nice matt/mineral finish and can be readily painted with mineral paint in the future, otherwise you'll be looking at a film based paint over silcone or acrylic once it gets tired. Also silicone and acrylic can look a bit plasticky in my opinion. Also consider the grain size as well, the standard grain sizes again can look a bit tacky. I used Baumit nanopor fine - 1mm grain size and lovely flat matt mineral finish. 

 

(I ran a thread tracking my DIY EWI installtion over on GBF http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15355)

[ADLIan]

The renovation/upgrade of existing floors, walls and roofs is covered by the thermal requirements in Approved Doc L1B (assuming England) which details U-values to be achieved. Building Control do have a degree of flexibility however and exceptions are listed. This type of work however is very badly policed by BCOs, perhaps partly because they're not informed. Lack of proof of Bldg Reg compliance here may affect any future sale of house.

[tanneja]

Thanks @MarkyP and @ADLIan, both very helpful to me and my builder.

 

To gauge where we stand with our building we have a couple of EWI installers coming around to quote tomorrow.  It would seem 100mm of graphite EWI would bring us to the redecoration regs, but the soffit overhang would be a token.  Builder will know more about whether he can have more roof overhand when he takes off the existing in a week from now.  

 

Also plan to visit an internorm seller in the next few days to discuss installation with EWI involved, surely it is something they are used to!?

[MarkyP]

building control should be flexible here, there is scope for them to compromise on insulation upgrades where there are significant limitations that might limit scope to achieve regs. And even 25mm EPS would be a huge improvement over nothing at al so I would be surprised if they wouldnt accomodate less if it was necessary. I cant recall whether with graphite EPS you need 100mm or 90mm, had a feeling it was the latter but maybe the regs have changed since I last looked. Your installer should give you a u-value calc for BC. maybe you already have a BC on the job, a chat would give you an idea. Mine was fascinated by EWI and hadnt seen it before, he took loads of pictures and several of his colleagues came for a look.

 

one other neat feature to consider is using frameseal beads (pic below). These provide a gasket seal to the face of the frame and a mesh carrier for the render, they provide a nice detail for the renderer to work to and a neat finish along with a long term weather and wind seal to the frame, otherwise you'll be looking at rendering up the frame (can be scruffy) and a silicone joint which will fail over time. my renderer hadnt used them before but was converted and now uses them on all thin coat rendering jobs, EWI or not. They arent very expensive and take minutes to fit (self adhesive backing to hold to the frame until render is applied)

 

if using a specialist contractor ask for some detail on the method and the products they are using, there's a lot of detail here and the stuff I mentioned above wasnt done by any of the installers who quoted me so I did it myself using a renderer on a labour basis with me fitting and detailing all the boards and sourcing the best product I could find myself

 

if the soffit is going to be out during the installation, take the EWI up between the rafters and then foam in. You can then run loft insulation up the top of the EWI in the loft eaves

[Ferdinand]

My further comments.

 

1 - When you EWI you seal your 2G in, so you need to do that first or make provision for upgrading from the inside later.

 

2 - It is all about detail, and sweating it. Work your quoters hard with your questions. If one of your suppliers is noticeably more knowledgeable, then it is probably worth paying some extra - I would pay 10-20% extra for a reliable and durable local supplier in whom I had more confidence.

 

3 - You can save a certain amount by removing some of your fittings yourself that need to go back on top of the EWI. Also consider allocating spots where you are going to put things later (eg external lights) and making sure that the mounting points are sound.

 

4 - Personally I would put a priority on going for 100mm or 125mm as the extra cost will be relatively small. I would then consider champfering the window reveals as that makes it less 'blocky'. 

 

5 - If you are going for RHI on your heating, do your initial EPC before anything else.

Here's why - because it is done on the difference, so if you improve then baseline, you get less. This was a couple of years ago, but I think it still applies - check.

 

 

Ferdinand

Edited July 29, 2020 by Ferdinand

[Ferdinand]

6. PS Taking the EW8 down to the fo7ndatiojs is an alternative to insulating under the floor.

[tanneja]

First EWI firm have suggested that the windows are left fixed flus on the front of the blockwork, and that the EWI (Graphite EPS) would be extended over the frame of the window 30mm around all edges.  Part of me thinks could be ok as plan to be Tilt and turn windows, although its losing sight of some of the beautiful frame I plan to pay for with Internorm, and would that get complex with the cill at the bottom?  Is their strategy the most viable / secure relative to bringing the windows (to some degree) into the EWI layer?

[tanneja]

On 23/07/2020 at 23:59, Mr Punter said:

EPS is tried and tested.  There will be a sweet spot on thickness and it could be the 70mm your builder suggests.  Normally stuck on plus some mechanical fixings, then thin coat render / mesh.  Moving the windows outwards towards the insulation is helpful.

@Mr Punter, when you say moving out windows towards EWI, do you mean up to be flush with the face of the solid blockwork, or even protrude a percentage of the window into the EWI layer?  The quote we just had around dismissed the latter entirely saying the fixing brackets are flimsy, not something they recommend at all.

 

How impactful would the technique be where the EWI isn't overlapping the window frame, the window is sat back to be flush with the blockwork, and render is carried back on the return faces of the EWI towards the window?  In this scenario, there would be a rim around the window frame which is essentially render covered brickwork, although it would be quite thin in relative terms (but a fair bit of length if the perimeter of each window).

[MikeGrahamT21]

18 minutes ago, tanneja said:

@Mr Punter, when you say moving out windows towards EWI, do you mean up to be flush with the face of the solid blockwork, or even protrude a percentage of the window into the EWI layer?  The quote we just had around dismissed the latter entirely saying the fixing brackets are flimsy, not something they recommend at all.

 

How impactful would the technique be where the EWI isn't overlapping the window frame, the window is sat back to be flush with the blockwork, and render is carried back on the return faces of the EWI towards the window?  In this scenario, there would be a rim around the window frame which is essentially render covered brickwork, although it would be quite thin in relative terms (but a fair bit of length if the perimeter of each window).

Hanging the window out into the EWI layer in its entirety. There are some posts on here about it using steel angle irons to hold the weight of the window, with brackets to support it in place, a very robust solution.

[Mr Punter]

You need to avoid having ANY uninsulated window reveal exposed to cold outside, as the cold will track through to the inside and cause damp and mould issues.

 

You can get around this either by moving the window outward to the frame overlaps the insulation or adding some insulation around the outside reveal - which is often not practical as it reduces the effective opening size.

 

[Ferdinand]

2 hours ago, MikeGrahamT21 said:

Hanging the window out into the EWI layer in its entirety. There are some posts on here about it using steel angle irons to hold the weight of the window, with brackets to support it in place, a very robust solution.

 

You are doing a good job asking questions about all the details.

 

Keep on keeping on. 

 

Your window supplier should be able to talk about extended sills. The last one I did I fitted extended sills to windows and thresholds to doors just in case I want to do EWI later.

 

On 25/07/2020 at 12:19, ADLIan said:

The renovation/upgrade of existing floors, walls and roofs is covered by the thermal requirements in Approved Doc L1B (assuming England) which details U-values to be achieved. Building Control do have a degree of flexibility however and exceptions are listed. This type of work however is very badly policed by BCOs, perhaps partly because they're not informed. Lack of proof of Bldg Reg compliance here may affect any future sale of house.

 

Our local BCO take the view that they seek to encourage any improvement and have people talk to them rather than jumping on people for not doing the EXACT regs.

 

Ferdinand

[Russell griffiths]

When I was window shopping I mentioned to some suppliers at a show that I was going to do the third version in that drawing above. 

They all seamed very glad and gave me a big thumbs up as that really is the best way to mitigate cold spots. 

[tanneja]

@Russell griffiths Do you have the contacts of any suppliers/installers who might consider the south east?  Logically, if the heavy windows (triple glazed Internorm) can be held robustly and it doesn't threaten the airtightness over time of repeated opening and closing, the second and third options are clearly thermally best.  Neither EWI installer today would entertain anything other than the windows being entirely in the brick walls.  My builder likewise thinks I am crazy, I showed him pictures of the steel brackets used on some of the projects here, again thinks I am bananas.

 

@MikeGrahamT21 I must say I don't want to be worrying about the rigidity of any of the windows in their place, and the airtightness being compromised by any movement in the EPS.  I can't seem to find any brackets online.  Would you recommend them over a wood frame or a compact foam frame?  Did I forget to say, budget already stretched!

[tanneja]

@Mr Punter I offer my thanks for those pictures, and I felt I wanted to achieve 2 at the least.  EWI installer seem to have no interest or experience in this approach, interesting standpoint when their product is to maximise thermal insulation, being unconcerned of clear thermal bridges when the client is open to widows being optimised, as they are all to be replaced anyway.  What hardware or installer would you recommend?

[tanneja]

@MarkyP, have read your GBF post of your installation, and seen your windows 60% out of your blockwork.  With the chance to look back at the process, and how the windows are performing, and any other methods of combining windows with EWI, what product would you use to bring windows somewhat proud of the blockwork?  For reference, our internrom windows are 93mm deep, and thinking of 100mm EPS (if the soffit can handle that, will know that next week when the roof details are finalised), curious what % overhang you would do in that circumstance.  Everyone thinks I am mad for thinking of anything other than these heavy expensive windows (that are quite slam-like in the way they open close) being firmly attached in the blockwork.

 

An issue with this window approach is the window company will do fitting and plan to do with expanding tape, but would that have as much value with only a % of the window in the brick?  I would then be reliant on EWI installers to ensure they have some kind of air tight fitting of the EPS to the frame.

 

My builder is amazing, and is happy to do an EWI course to help us do this ourselves if lots cheaper or we aren't confident I would get the finish we want, but we are time constrained too, so its a delicate situation to balance.