EWI Advice/Ideas

[Charli]

Small 2-bed semi-detached, solid-wall house, uninsulated concrete floor. No heritage value, no features to keep at all. (the beautiful slate roof has already been replaced with a monstrosity). Very sheltered. No damp showing in house at the moment.

I can't live with having an uninsulated house. Its what I do- I insulate things!

 

I've only ever done IWI before, but this house is already tiny.

I was thinking:

• The block garage will be nominally 'done up' into a nice workshop, it won't be heated but indirect heat from adjacent room is about right. As the side of the garage is an earth bank I would IWI it- 100mm pir, and a new flat roof (100mm pir) with some kind of sunroof/roof lantern/lightwell. Includes blocking up the front garage door. Solid concrete floor, probably cover in rubber matting for workshop use.
• EWI on the gable end of the house- 150mm eps- down to the garage roof. I will extend the house roof to overhang the insulation.
• EWI on the back of the house to dpc level- will need to change the roof to overhang, change the guttering and work around windows (they'll need moving). Would like to go below dpc level, but seems pointless only on the back.
• The front of the house is awkward, there's electricity cables there, a porch, and EWI would make it be offset from the attached neighbours house. Is it worth sorting all of this, or shall I IWI that bit? 50mm pir would fit, with a turnback on the adjacent wall.
• The attached side of the house- downstairs is a gennel- so that’s exterior wall. Upstairs is party wall, so I can ignore that. The gennel is very narrow and I can't insulate externally. But internally its mostly a set of stairs, so not much room there either. I shall have to resort to aerogel IWI or something, working around the stairs. Better ideas welcome here.
• Loft will be drowning in insulation- 300mm (currently 150).

 

I will probably get a professional to model this for me (Recommendations for a thorough job in Derbyshire/Nottinghamshire?).

Or might even learn myself (would a retrofit assessor course be any use?). Its an area of interest, though it would never be a job for me. 

 

I would like to DIY a large amount of it (As I find it great fun, I am capable, and have family tradesmen that will help).

 

Ideas/experience/comments welcome!

 

 

[Mr Punter]

Bear in mind that lots of EWI has been a disaster recently.  Lots of mould, damp and ventilation issues, so this needs to be done meticulously, especially mixing EWI and IWI.

[Charli]

I'd be fitting it myself (would probably get someone else in to render). So as long I understood what I was doing I can spend plenty of time and attention to detail on fitting the EWI!

[Redbeard]

As you say the front looks difficult for EWI with the incoming power-lines. How would you deal with them? Lots of Red Tape there, I guess. Step-cracks above front GF window (are you happy the original problem has been solved before you 'box it up'?), questionable boundary (? - your porch roof seems to meet a line down from next-door's FF window cill, so is that the boundary?) Where, then, does the fall-pipe go once you have EWI'd? I think your idea to IWI may be less fraught.

 

However if you were to EWI the front...

If there is no soffit and you think it would look daft to extend your roof-line only, how do you deal with the EWI projection? 'Industry Standard Capping Details' (bits of bent alu gunged in silicone) have a limited life, particularly if they are of the 'downstand' variety. Measure carefully, outside and in, the height above the window. It is not unknown for EWI to stop before it reaches the height of the ceiling inside, in which case what do you do? If that were left 'un-treated' you could face a strip of mould at the top of the room. Internal 'downstands' can be done. Bring it down well below the line of the top of the EWI.

 

I am probably not alone on here in not regarding 300mm as a huge lot for the loft. Assuming you are not storing stuff in there, and that you are using 'cheap stuff', why not use 400, or even 500mm? You'll only do it once. If you do that you'll probably find the biggest 'shortcoming' is then at the hatch. It's difficult to leave yourself a way in *and* achieve excellent insulation coverage and air-tightness. Get inventive!!

 

I worry about the plan to IWI the gable wall in the garage, certainly at 100mm - with a lot of PIR on a wall giving onto soil. If you look at a Glaser-method condensation risk assessment for PIR (which you can get for free on many manuf'rs' web-sites), and the manufacturer's advice, you'll see that they require you to keep the 'outward path' vapour-open (by removing impermeable treatments inside and/or outside). That's because the VCL on the inside (if indeed it is functioning as a 100% effective VCL) blocks the possibility of any retained moisture in the wall coming back in. As far as I can see, if you block the path  inwards, you have no moisture-loss path at all. I may be wrong, though. Enlightenment welcomed!

 

I've written a lot. I hope it is useful - it is certainly meant to be. A lot of 'thinking-through' to do, I reckon.

 

Do come back with Q's and comments.

 

Perhaps ask Nottingham Energy Partnership (0115 985 9057) if they can recommend an assessor. A retrofit assessor course may well increase your knowledge level (of course I don't know how much you already know) but it will not necessarily (AFAIK) give you access to a measured survey model and software, so while it may help you to make a judgement it will not allow you to spit out 'numbers' - running costs, kWh p.a. etc). You can, of course, do that 'long-hand' if you have time, and I bet there are some free access models out there somewhere.

 

Edit: Re EWI - do not automatically think you cannot go below DPC. You do have to think it out carefully and perhaps use different materials but it can be done - down into a French Drain. Caveats re where does the drain exit, have you just dug below the footings, etc., but with care it can be at least considered. I see countless examples where the EWI Co has dutifully avoided bridging the injected DPC which is 150mm at least above internal GFL - leaving a cold bit just behind the 120-year-old skirting...

Edited April 2 by Redbeard
EWI below DPC

[Charli]

Brill, thanks Redbeard, lots for me to think about there!

 

I'm not overly fond of the 'EWI capping', like you said they have a limited life and I don't really trust them. Would much prefer to extend the roof- I can get over it looking odd if its possible to do so (with the electricity cables, guttering, etc).

 

Much more insulation in the loft also possible- it wasn't a bit I was worried about so I just chucked some numbers towards it. 500mm would fit just fine. In past houses we have boarded around the loft hatch (on top of the insulation), and made a 'box of insulation' that you slide over the hole- above the actual loft hatch. Its untechnical but has worked well so far (I do have a thermal camera to check it!)

 

The soil on the outside of the garage isn't actually up to the wall- it doesn't lean on it. A slim person can get down there from the back garden if they're armed with a hedge trimmer to cut back the foliage, digging out much soil and putting in a new retaining wall is a possibility- though an expensive one. I could do much more insulation in the garage, just it will still be a garage workshop and not part of the house.

 

I'm awaiting some recommendations on retrofit assessors (from NEG, and 'FurbNow'- who came up first on search engines), so hoping to speak to someone soon- given that my plans are quite grand. Unfortunately I don't quite have grandiose amounts of money to go with my ideas. 

 

Other non-insulation plans include solar on the roof (south facing, would be daft not to. There's also an adjacent south-facing polytunnel that already has panels on). Then it has wood-fired central heating and a gas boiler for DHW, I was thinking thermal store to be a bit more flexible, and in the summer enable me to use PV to heat up water. But I've no idea how to size any of this- but the assessor should be able to help with that!