Cavity wall insulation advice

[Eggling]

3 providers - 3 completely different things said so looking for advice from anyone more knowledgeable than me!

We moved into our 1930s semi a couple of years ago. It's a normal 3-bed semi, ground floor extension to the rear, garage and porch added on at some point too. No cavity wall insulation. We do need to thicken the loft insulation as it's not up to the standard, and considering insulating under the floorboards too.

The house is cold, and we are expecting our first baby in a few months so would like it to be warmer before next winter! We decided to apply for the gov green home grants scheme to get the cavity walls done.

Provider 1 said they could do it and house was a good candidate. They drilled into the walls to check the cavity etc. However, they said we would need various enabling works as the drive is concreted right up to the house / tiled right up to the tender at the back and thus presented some issue with the DPC (sorry for vagueness I can't remember exactly). The quote was high to allow for this, green homes scheme are saying it's too high so we have had other quotes.

Provider 2 said no problem, cavity suitable, can do it and no need for enabling works as the air bricks allow for air to circulate. Awaiting quote.

Provider 3 says they wouldn't recommend we do it - said our pointing isn't great and the lintels have come down a bit so it's likely to spill out.

Not sure where to go from here. We can't afford full repointing and lintels replaced, plus hoping to extend in a few years so loathe to do all that now. The house is too cold at present so we need to do something.

We're in the northwest, standard suburban street so not massively exposed to the elements.

Any advice welcomed!! Thanks in advance!

Read this: www.property-care.org/problems-with-cavity-wall-insulation/

I honestly wouldn't do the cavity; I'd upgrade everything else you can, so loft, underfloor, make sure your windows are top notch etc.

I worked in insulation sales many moons ago, and house builders / developers were able to 'over'-insulate one or more areas and not insulate other areas, as long as the construction as a whole met the appropriate levels required to meet Part L. I wish I could remember the technical term for it, but I've slept since then!

Thanks @NoWordForFluffy. It feels like a bit of a minefield to be honest!

It can so easily go wrong and you then get damp / mould. I'd trust the company telling you no, and the one that essentially priced themselves out of the work! The third ones are potentially cowboys.

Is there an EPC for the house anywhere? If so, that will give you ideas where you can improve the property to make it more energy efficient and, presumably, warmer.

Yes it's rated E and one if the recommendations is cavity wall insulation to take it up to C. The extension has a flat roof which we are hoping to replace and get properly insulated when we further extend in a few years.

When we looked into things it seemed that we would probably be ok as not massively exposed to driving rain etc? Is that not accurate?

We'll definitely look at the loft and floor. Windows are all double glazed but a couple are older and stick open a crack so do need replacing.

No, it's whether the construction of the wall cavity is suitable to start with as well. Cavity walls when constructed aren't full-fill, there's an air gap so that the insulation doesn't wick damp into the house, as a starter. But badly-installed retrofit cavity insulation can block the necessary air flow which will also create damp. This is because it's full-fill.

There is a reason there's a massive legal industry which has appeared in the last decade in relation to cavity wall insulation retrofit insulation: it goes wrong LOADS.

I'd do absolutely everything else before retrofit CWI!

Superfluous 'insulation' there!

This house has it done 1979 detached it’s the white fluffy stuff. No problems so far, it’s a lot warmer than the solid walled Victorian terrace before this. A friend has had it done in a 30’s detached , the little grey balls and has had no problems with that.

I don’t think it’s suited to houses in very exposed areas where the wind can drive the rain into the brickwork, also the house ( pointing ) needs to be in good order to keep any water from getting through, but that should be the norm for any house.

It was the balls they were on about (provider 2). We'd read a lot of horror stories but also positive ones like yours @Chumleymouse! It seems a shame to invest in boiler etc and lose heat through the walls, but maybe I'm thinking about it wrong. Really appreciate all the advice!

TBH, I don't know much about the balls. But, if one company has said you need extensive work first and another has outright said no way, I wouldn't trust the third company!

How big are your rooms? Do you have room to insulate from within on the external walls?

The friend had it done during a complete renovation and it was installed from the inside ( blown in ) so he didn’t get all the holes on the outside.
There’s lots of information on the internet about it some good ,some bad but try and do as much research as you can before deciding.

There are stories of people getting damp problems with it , but also stories of successful installations. It’s like you say a bit of a minefield.

You could use insulated plasterboard on all the outside walls as another option if your planning to renovate. You would probably lose about 40mm or so of space on each wall ? Could be worth considering.

Not really, the rooms aren't massive and we've had plastering done since moving in so wouldn't want to have to re-do that. Perhaps when we get the extension done but we're a few years off that.

We definitely need to do the loft and if we can the floor. We are also replacing the back door which currently lets a lot of cold air in. Doing the walls too seemed to make sense, particularly if we could get help towards the cost, but perhaps it's too risky.

Fixing draughty windows and doors will likely have more impact than you realise. My parents' 1930's semi is way warmer with just a new, insulated, front door. Do those and the other insulation and see how it feels then.

A bit of a tangent, but lots of new companies have sprung up since the Government started this big energy grant scheme. A guy near me has started a company and I wouldn’t trust that he actually knows what’s talking about. A complete cowboy who is always starting businesses that then go bust. His very professional looking website advertises the ‘50years experience’ his company has. He’s 25.

Perhaps the 2nd quote is this type - just desperate for the Government cash, regardless of whether it’s appropriate for the house.

It's in the nature of people, and especially newspapers, to talk about the minority of things that go wrong, rather than the majority that go fine.

My house is among the majority. It has none of the building defects you mention, though it is in a coastal location and one side is exposed to driving rain during storms. No damp. The mineral fibre does not "wick" water across because it is water-repellent and not absobent.

CWI cut the heat-loss of the house, and the gas bill, by about 20%

Draughtproofing is the cheapest thing you can do, with the quickest payback, and loft insulation (if you have none) saves the most.

New windows cost so much, and bring so little benefit, that they may never achieve payback. But you might as well do them if your old windows are rotten and beyond repair.

I'd be more wary that companies have said it's either not suitable at all, or only suitable with extensive work. They're the ones best-placed to advise you as they've actually looked at your house.

quite right.

provider 1 sounds good to me, but the work probably needs doing anyway so maybe get it done by a reputable builder when convenient. The defects they describe may cause damp.

Provider 1 would be our choice if we were going to do it, but if we can't get the government scheme to agree to pay then it's out of reach. My worry when they first came back to us is that we'd end up getting a quote from somewhere shoddy that undercut them but the work wouldn't be suitable for our house. It's very frustrating - I did speak to them and it's not that they won't pay for the enabling works at all, just they're saying the quite us too high, but the provider says they can't budge on that so there's nothing we can do there.

Thank you for your advice everyone, lots of food for thought!