External wall insulation

[Giggorata]

Has anyone got any long term experience of external wall insulation?
I am interested in how it performs over a longer period re heating bills reduction, house temperature differences, durability, cost and maintenance needs (if any)
I have a large cold period house! I'm not sure I could afford the whole house to be done, so I'm also wondering if I could just get the back done, for example, or if you always have to do the whole house.
I’ve done a bit of Googling, but I'm really interested in first hand accounts from unbiased Mumsnetters.

I’m interested in this as well. We are in a Semi and the side single brick wall makes the hallway absolutely freezing. You can’t really see the side much from the street as it’s very close to next door so not that bothered about it looking different.

Just posted on another thread about making an older property warmer and detailed our experience of EWI

had ours done about five years ago - solid walls on top half of detached 1912 house, covered with pebbledash. ground floor is stone faced old uneven cavity walls but in conservation area so had to be left as is.

positive experience, little maintenance required to date. our energy usage has come down by about a 30% since installing it however it was done as part of a ongoing programme of updating the house - replaced old double glazed windows, replaced kitchen and installed IWI in that revamped room, replaced boiler to more modern condensing boiler as moved boiler as part of kitchen revamp. replaced flooring downstairs in a couple of rooms and made more effort to have thermal base floor before tiles/karndean and also draught proof floor/walls draughts.

our house is much warmer and nicer to live in since improving thermal efficiency. EWI was a key part of that - it keeps the upstairs at a much more even temperature and cold corners and cupboards have been largely eliminated. Further works have enhanced that thermal efficiency. The EWI also helped improve the exterior appearance - it went over old fashioned pebble dash and cover some old cracks in the pebbledash.

In financial terms, it has a long payback and is hard to isolate the cost savings but our house is much improved for it and I would do it again if I moved to an older property in the future.

Have a look at a few houses that have been done, we did view one 1930s ex council house that had external insulation - it was awful. Also the disadvantage is that the walls of the house take longer to heat up than internal insulation.
Usually dry lining and insulation is much better, although it does create mess inside the house, before you do that make sure the roof and the rest of the house structure is good.

This is useful
energysavingtrust.org.uk/advice/solid-wall-insulation/

That sounds good @SallyLockheart , was it all around the house and was it expensive to install?

@bahmummbugg it was all around the upper floor and yes, it was relatively expensive but doable in relation to the value of the house. Finding a good installer can take a while - ours came from a company about 80 miles away and we paid for accommodation etc for the team while they did the house. However the total cost was still reasonable comparable to other quotes as I liked their approach and the fact that they specialised in EWI/modern methods of constructions and had worked with older properties in the past too. I suspect the cost has gone up since then as the cost of materials generally has skyrocketed and its a labour and material intensive job.

I have seen it done in other European countries on houses and blocks of flats, and it seems well accepted and not unusual. The manufacturers of insulating slab have fitting systems and instruction packs, and quite likely run training courses for builders.

I supoose problems might arise if unskilled installers made a mistake or missed something due to not having the benefit of years of experience. For example I should think you'd need it under the overhang or eaves to preve to rain entry, and this could be difficult on a gable wall.

I have a slate-hung wall on my house, but the first two metres from the ground are wood cladding to prevent damage if it is bumped or knocked. In Switzerland I watched a house that was being mostly rendered over the insulation, but had stone cladding on the ground floor, presumably for the same reason.

Some people think that insulation causes damp. In fact, it is lack of ventilation, which may occur if old draughts and building defects are cured at the same time. Ventilation remains essential. Warm, insulated walls are less likely to suffer condensation than cold ones.

I've had it done on the back of my house. It definitely makes a difference. That thick selotex is thermally equivalent to a 1.2m thick brick wall Kevin McCloud said. Only downside is that when we wanted to fit external lighting, we had to use enormously long screws.

That’s an interesting review @SallyLockheart
i would also in the main want it done to improve the comfort in the house. I imagine it would very expensive.
Even blasting the heating as much as we can doesn’t heat out hall. That’s with new double glazing and a new front door.

@Waterdropsdown pm if you would like a bit more info

We used 12mm cork slabs fixed to the walls and then rendered with lime plaster. So from the outside/inside it still all looks exactly like every old georgian house does. It is pretty expensive, we paid probably 100k, but for cosmetic reasons we would have needed a lot of plaster work anyway. Follow on costs also include all new window sills where work was done externally/new window seats and panelling within window reveals where work was done internally. I don't think we'll ever recoup the money, but it gets much warmer inside now. So even if we still use roughly the same amount of gas and wood, we now definitely get more comfort/heat inside.

12cm - 12mm wouldn't do much, sorry.

Thank you everyone for your replies.

Front of our house is cold but that's because it has two bays and a tiled wall roof under the bay (technical term anyone) so not much use doing the front. I am interested in this too for the side of a semi detached house but am rather nervous of finding a contractor. Problem here is the guttering and toilet pipes etc come out so needs to be done properly. So many cowboys out there. If you have had it done, would you be willing to share area and company names?

The tile-hung bay is usually very cold. Often it is practically a false wall with a wooden frame, tiles on the outside and plaster on the inside. Has practically zero insulation and is draughty. It is fairly easy to improve, either when the inside is being redecorated, or when the tiles need to be replaced.

From the inside, you pull off the plaster, clean, treat the timber with preserver, pack between the timber studs and the floor/ceiling joists with mineral wool insulation (which also blocks the draughts, but can breathe), possibly add a layer of PIR slab on the inside followed by foil-backed plasterboard on the inside, plaster skim and redecorate. You might add noggins to support radiator brackets. Usually add a few new electrical sockets on the inside of the bay when it is open. This makes a big improvement. If working from the outside you do much the same but add a breathable membrane under the tiles to block draughts and water penetration, and you need not replaster. You may add new leadwork to throw off rain, and if you are putting in plastic windows, strengthen the structure to replace the strength of the original frames.

My parents had it done about ten years ago on a 1930s semi. They replaced the windows and boiler at the same time. The difference was noticeable literally from stepping through the door, the house felt so different with that damp cold feeling gone.

I know it was expensive, they did it more for comfort than to reduce bills and didn't expect to turn a profit from it. They remain delighted with it though.

@PigletJohn that's really helpful. Nothing came up on a Google so was a bit lost and of course would need to use a contractor who knows what they are doing. Maybe roofer or builder.

We only had a small area done at the back, which is North facing. The rest of the back was being enclosed by an extension.
Before the back of the house for black mould in various places, since the extension and insulation this has gone completely.
That was 50mm thick polystyrene with render over the top.

Re down pipes and waste pipes, don't they need to be removed before the work is done and later repositioned to take account of the increased wall thickness? So you can't inhabit the house while there's no toilet facilities and connecting the repositioned pipes to the drains is extra work and expense.

Yes, that's a good point. Though the new pipes should really be put in place before the old ones are cut away.

It's especially important that any cables are not concealed. I was advised of a case where the electricity supply cable to a sub-post office had been rendered over, and somebody later put a drill through it. The supply is effectively unfused and the cable burned away like a Roman Candle.

Outdoor plumbing is common on older British houses.

If you ask the major suppliers, like Knauf, Kingspan and Celotex, they may have a list of trained installers. They should certainly have an online brochure or installation instructions you can read. I'd prefer Foamglas but I don't think it is generally retailed in UK.

We have a 1930s ex council house with external insulation. It was fitted before we bought, it must be over 20 years old now. Our windows need replacing, they're an older style double glazing with the black rubber trim. Our house is warm in winter (just floor boards or tiles downstairs so we lose heat for that aesthetic) and beautifully cool in summer. We have no damp problems. It hasn't needed any maintaining.

Would there be any point in having 6mm insulation or would it need 10mm minimum? I know one poster wrote that 10mm is pointless but I think it is standard. Does anybody else know what they used on solid brick?

Bear in mind that cavity wall insulation is around 60mm or 100mm thick.

Where I have seen external wall insulation applied in Europe I think it was 100mm.

Frankly, I think 6mm or 10mm is wasted effort.

@oreste do you mean 10mm or 10cm?

Oops, cm!
@PigletJohn What is the idea thickness in your opinion? There is not much scope for extending past the wall. The roofer thinks he can only add one length of timber realistically.
Would internal wall insulation be a better option otherwise?