Internal wall insulation - yes or no?

[orwhrpty]

I'm having some efficiency measures installed in my home through the ECO4 scheme. The installer wants to install SWIP IWI. My property is an 1900's semi detached, with solid brick walls and no cavity.

I've heard too many bad things about IWI. I'd like to hear your opinions on it, and specifically the SWIP system. I'm tempted to just say no, but am I overreacting?

 

[a twig]

I’d also be very tempted to say no to it, the studwork in the system is extruded polystyrene with OSB glued to it and then with mineral wool bats shoved between them.

They then offer a choice of vapour open or vapour closed membrane over the top of that, but then say you wang plasterboard over top of the whole lot, which would somewhat go against the vapour open membrane option… none of it makes sense to me to be honest.

Haven’t used or seen it directly though, opinion is just from trying to make sense of their datasheets

 

[paulc]

Have solid 9" brick walls on the upper half of my house. Every room is monitored with a temperature & humidity sensor and the data logged in an ever increasing database. Two of the upstairs bedrooms and the landing have had IWI installed as part of a long term project to renovate & improve comfort levels. Comparing data from prior to adding IWI and afterwards shows negligible improvements in the rate of heat loss. But external wall temperatures are higher in the insulated room(s), so condensation & mould are no longer a concern (although a better heating system will probably be helping on that front).
The two main things that have had the biggest impact is increasing loft insulation to ~400mm (was originally ~200mm), and fitting decent double glazed windows. Although with the latter, eliminating all the cold draughts that were coming in around the windows (badly fitted in the 1970s, and hinges/seals failing) probably accounted for much of the improvement.

For me, installing IWI as an energy saving measure is not worth while if looking at it in terms of covering the costs through reduced heating bills. On the other hand, it should add a point or two to the EPC which might make it easier to sell the place when the time comes. Also have nice flat walls without any cracks in the plaster which makes decorating much easier. On the downside, mountings for things like radiators and curtain rails need some forethought - I used a 12" high strip of 12mm plywood above the window(s) to screw curtain rails to, and radiators got moved to internal walls.

 

[fernicarry]

Its a bit of a cheek calling it a "system" when majority of the components are off the shelf that anyone can buy at a builders merchant. With the exception of the polystyrene/OSB laminated studs which strikes me as a very odd choice of material for studs. I suppose that's what you have to do to become a "certified" supplier to one of the govt schemes to be allowed to trouser vast amounts of tax-payer's money.

As @a twig says the plasterboard and gypsum skim really aren't what you want on your solid walls. The breathable option might be ok but its actually one of those "smart" membranes that changes its mind between vapour open and closed depending on relative levels of humidity. By restricting transmission of vapour from inside to outside by adding a membrane and making the room more airtight you run the risk of increasing internal condensation. You need to think about increasing "planned" ventilation at the same time. Trickle vents in windows or even mechanical extract/input.

Their installation instructions have the usual caveats -- make sure wall is dry and free of defects. Well doh, and that's where you might need to put the bulk of your focus and money first regardless of the system used. The system won't miraculously make existing problems go away. It might hide them for a while. There was a thread on here a while ago where someone had one of these systems installed onto what sounds like an inappropriate building and the problem had continued unseen leading to it all having to be stripped back out. If your home has no existing problems and is in fantastic condition outside (rainwater goods, pointing, ground levels) then maybe you have nothing to fear.

Also you will need to reinstate or move services after the work -- electrical sockets, radiators. Reinstate cornices, joinery details -- skirting boards, architraves. Sorting out all of that stuff isn't part of the system or the service.

As @paulc says the best possible outcome of using a recognised system is an uplift on your EPC rating as there is a chance of the assessor having a matching tick box. If you home brew it as most of us on here do then its unlikely the assessor will have a clue how to treat it and will probably give you no benefit as a result. This has more to do with EPC not being fit for purpose than anything else. The powers that be deperately want to use EPC as a stick to drive us towards improvement but know that its so laughably inaccurate that it needs major reform first.

There's plenty else written on this forum about IWI if you want to learn about it and make up your own mind on how to proceed.

 

[Aurelius]

Hi
Regardless of the IWI system used, my main concern would be the contractors that are undertaking the ECO grant work. I can't recall the exact stats but there was an article on the BBC recently stating that for EWI grant work, circa 80%+ of installs required some form of remedial work, the figure for IWI was lower but still sufficient to cause real concern. There are a plethora of inexperienced and unethical companies undertaking this grant work, they work at breakneck speed to move on to the next job ASAP. When the work dries up, they dissolve the company and disappear into the etha leaving you with little recall.
Please be careful.