I own a 15 year old house with cavity walls, double glazing and standard depth (joist deep) loft insulation. Boiler is a fairly recent combi condensing jobbie.

Chap knocked the door yesterday attempting to flog mineral wool CWI for a stupidly cheap grant assisted £79. Took his leaflet and googled CWI pros and cons. Jury appears to be out on the benefits of CWI, particularly if wind driven rain passes through the outer brickwork and causes damp. I live in the fairly soggy west of Scotland, so probably won’t take him up on it.

Anyone have any experience of CWI or other ways of cutting energy bills? PV panels, deeper loft insulation, wear a vest and jumper?

Yea got CWI on the same sort of deal, vast difference in heating bill for last winter.
At the price they are doing it for its a good deal, they can also do or top up your loft insulation if it needs it to.

There are loads of scare stories about CWI but a succesful installation is mostly down to choosing the right material and correct installation.

I`d look at the National Insulation association website for approved installers.

The reason that insulation is cheap at the moment is that the utility companies stand to be heavily fined if they don`t reach their carbon reduction targets laid down by government hence they are throwing money at insulation by way of funding.

Friends of mine in Galloway have had solar panels on roof for hot water for years – they say it makes a huge difference in cost. Don’t know numbers obviously.

The full fiull is dependant on location. there are issues over the country with hot spots where CWI isn’t really the done thing. Whe you have it done the contractor will have to make a building regulations submission so the building control authority will approve the insualtion type.

Just taken up the offer from British gas of free cwi and loft insulation for duel fuel customers. Came round to check the wall and was surprised that there wasn’t insulation already in there. Apparently all houses built since ’87 should buy law have some in.

cwi at 79 is a snip.. 119 on my north manchester house.

Following this thread I started yesterday:

http://www.singletrackworld.com/forum/topic/anyone-know-anything-about-wireless-central-heating-stuff

we are also considering cavity wall insulation. I didn’t realise it was as cheap as it is with all the grants available. Definitely going to look into this before winter sets in!

CWU seems a bit like laser eye surgery. Great results for most people most of the time but if it goes wrong……

CWI like laser eye surgery? Nope. More like ‘insulation for your walls’. 🙄

insulate your house as much as you can – you get more payback quicker than any other heat-related upgrades. If you have wind-blown rain that penetrates bricks you probably live on Cape Wrath.

TT – t’was but an illustrative comparison!

Just get a multi fuel stove and burn stuff!!

My attic insulation was only joist deep so I topped it up with a second layer crossways then last Autumn a third layer so it is now something like 750mm deep. The stuff has never been cheaper if you look around for deals. The house is fantastically warm.

75cm of insullation? jesus. I guess you don’t have much ‘stuff’?

5lab – Member
75cm of insullation? jesus. I guess you don’t have much ‘stuff’?

That was my thought. We’ve got a shallow pitch to our roof, so I have to crouch even at the highest point. Most of the floor is boarded. Anymore insulation will mean having to take the boards up, or squishing more insulation into the space under the boards which presumably doesn’t really make the insulation any more effective (possibly worse)……

We did our loft with a foot of mineral wool, previous stuff was thinner than the joists, presumably it was thicker but sagged down maybe?

Made a massive difference even at the end of the winter so should easily pay for itelf this year.

Looked at CWI, but its a flat so would need the whole block to sign up.

Check out polypearl platinum – looks to be the best.
Will not wick moisture through the Cavity

275mm is recommended amount of roof insulation. And get your walls done, it will work and save you money. End of really

Was about to have this done but the installers wanted to drill a 4″ hole in the warmest room of our house where the coal fire is.

Sounds stupid so we passed on the offer.

I too am in the damp west of Scotland. Have decided not to go for CWI despite the cheapness. The houses in my estate have frankly terrible roughcast so there is no chance the walls are completely watertight.

Neighbours who have had it done have not yet reported any dampness but also have noticed no decernible difference in internal heat levels or reduction in energy usage. Mind you, the last two winters have been brutal.

I reinsulated my attic. Usual story of hardly two inches of loose fill. Now at least 400mm deep cross laid rockwool. Made a huge difference, especially noticable upstairs.

B&Q are doing rolls of recycled plastic bottle insulation for £3 each. That’s so cheap you would have to be daft not to buy some.

I do think that having a good check for draughts on a windy day and doing someting about it makes a very worthwhile difference. Ok, your not going to achieve Passivhaus levels but it all adds up.

750mm?! My ‘zero carbon’ schemes only have 450mm. Don’t need to insulate my house this winter, I’m off to globalti’s house armed with shorts and t shirt

Check out polypearl platinum – looks to be the best.
Will not wick moisture through the Cavity

we have silver bonded bead, read the horror stories, managed to get an installer to do it part grant funded, most insisted it couldn’t be done but we persisted

If you have wind-blown rain that penetrates bricks you probably live on Cape Wrath.

You obviously don’t live in Lancashire. All brick and stone work is porous unless treated. That was why cavity walls were first built in the west of the UK, as a barrier against penetrating damp.

With the wind behind it you can literally have water running down the inside of your walls if you have particularly porous bricks like we have. My garage is a single skin construction. Not long after moving in I rested my hand on the wall during a storm and relaised the water was running over the back of my hand.

Apparently all houses built since ’87 should buy law have some in.

Not true, first we’re talking building regs, not the ‘law’. Secondly the walls need to achieve a certain U value, you don’t need CWI to do this. Because of the porous bricks our house is built from the builders had to use thermalite blocks instead of standard breeze blocks to achieve the insulation required without compromising the cavity.

CWI must be OK for most people but personally I wouldn’t touch it if you’ve porous walls, live in soggy west or high up (i.e. 1150ft where I am).

Hey, don’t shoot the messenger 😀

My house is an ex council, built from shuttered concrete. Walls are very thick, but obviously any insulation needs to go on either side. Local council have insulated some of their remaining homes by cladding in 50mm to 100mm of polystyrene, then rendering. I had a quote from the firm doing it (who said was same as council were paying), & it was nearly £9k. I have about 350mm of loft insulation. I did a calc on the walls saving 25% & was over 40years payback. Having spoken to those who have had it done they say its made a small difference.

I told the wife I was going to start collecting polystyrene in any shape, & gluing it to the walls…

http://www.energysavingtrust.org.uk/Home-improvements-and-products/Home-insulation-glazing/Cavity-wall-insulation might be a good source of info.
And as stumpyjohn says look for the U value, the lower the better.
well-insulated walls: 0.25 W/m²K;
poorly-insulated walls: 1.5 W/m²K

I did a bit of architecture at uni way back and the building engineering lecturer was firmy anti-CWI. Most older houses use galvanised ties between inner and outer walls. Cavity wall insulating can retain condensation and lead to the ties rotting through and the wall bulging.

I used 21mm wood panelling with an air gap behind it on the inside. 4cm interior space lost. You can use 10cm rockwool backed palasterboard. Both good solutions on houses without a damp proof course as they allow the wall to breathe. If the wall has a good damp proof course then insulating on the outside with polystyrene or one of the latest eco-materials is an option.

Wood on the inside has the advantage of eliminating the “paroi froid” (I don’t know how to translate that but it’s like the cold you feel when standing next to a single-glazed window). You feel a couple of degrees warmer next to a wood wall at the same temperature as a brick or concrete wall.

I sell EWI and insulated render for a living.It`s expensive but the only solution for lots of older properties with solid single skin walls.(7m such properties in the UK.)
Insulating the wall externally removes the risk of cold bridging,keeps all of the building fabric warm,dew point moves to the outside of the wall so no condensation risk and you can add up to 200mm insulation if you want to bring your house up to Passivhaus standard.

Best considered if you want to reclad or remodel your exterior,particularly if you were considering re-rendering an older property anyway.

Its never going to be as cheap as cavity fill though ,as material costs are higher unless you are lucky and happen to be in a designated C.E.S.P. area and are eligible for masses of utility company funding.A small amount of funding is still abvailable in other parts of the country,though all of that may change in the next year or so when “green deal” arrives and these sorts of measures are likely to be more heavily incentivised and 0% pay as you save scheems come in.

Experience so far in most cases indicates heating savings of 30% though that depends obviously on existing level of insulation and construction and what the exact external wall insulation specification is.(We have done a house to CSH level 6 with a 0.12 u value.)

Also woth bearing in mind if you are considering taking up multiple measures such as EWI/CWI with solar/PV and or double glazing that these tend to ramp up available funding.

How much Jolly Green? My next door neighbour went the EWI route and the bill was 30 000e for a house that’s about 9mx9mx6m. Even saving 30% on the heating bill it’s never going to pay for itself (he’s a lumberjack and gets free wood anyhow)in the lifetime of my neighbours. They say the house is much more comfortable though, damp has been eliminated and it looks rather pretty. Excellent for eco-warriors who don’t much care how much it costs.

I’ve just remembered another CWI anti from my lecturer, the temperature gradient across the wall is insufficient to drive moisture out of the outer wall bricks, nor enough to prevent freeze and thaw either. The result is freeze and thaw destruction of the outer wall.

Most people would probably see better savings upgrading their windows. New regs came into place last year setting minimum standards. Old UPVc windows are no where near as efficient as modern ones and glass coating technology has come on a lot.

Another anti CWI comment I picked up when researching it was cold spots due to uneven fill. This can lead to colder points on the internal wall which can lead to condensation whihc in turn leads to damp patches.

Some useful, fairly balenced info here.

Some good points on CWI there, Edukator and Stumpy.

We sell render aswell as insulated render and we have revised our reccomendation for render thickness recently due to housebuilders and the BSI advice on weather resisatnce for full fill cavities in some areas ,penetration for the very reasons you suggest.

Having said that my parents house had CWI carried out by a reputable installer,and it made a significant difference and they expereinced no problems.

As always pros and cons but a bit of education helps determine whether its right for you and to avoid the pitfalls.

There is actually a map published by BRE showing which areas should not use full fill or have thicker render to improve weather resistance depending on the regularity of driven rain.So thats most of the west coast of Scotland then…..!

At the moment EWI does have some significant advantages over CWI or internal insulation,such as no need to move out whilst work is done,ability to achieve much lower u values,no condenstation,cold bridging risk/no temperature fluctuations through the wall,no reduction of interior space,to name but a few.However, yes there is a high capital cost (typically £60-80 per m2 as a very general ballpark)unless it is subsidised ,when used as a retrofit measure.

In most cases,it is being used on social housing where there are grants available,the client is looking to overcome other issues with internal condensation/cold briding as in a lot of post war prefab housing,or where the client is looking to remodel or facelift their house aswell as the insulation benefit.

If the existing walls have painted render or poor brickwork it is often cheaper to put a layer of insulation over and render them,than to pay the labour to remove the existing render and dub out/make good,if you were re-rendering anyway.

We are finding more and more EWI being used in new build where part L is ever more difficult to achieve and some builders are moving to single skin blockwork construction with external insulation as a means of achieving low u values.

Agree about the difference decent double glazing makes too.Incredible the difference living in a 100 year old terraced house with double glazing to one with draughty old sashes!

Much food for thought. Thanks all.

Unlucky enough to live in a cesp area more like.

Another thing about cwi is making sure the cavity is clear before installation.
Any cr*p at the bottom of the cavity can lead to moisture transfer once the insulation is in. Good installErs use a camera thingie (Boroscope?) to have a look first. Still need to drill a hole.

Draft proofing any major cracks in the building fabric will make a big difference too and is cheap to diy. Just be careful not to do too good a job as you need enough ventilation to get rid of moisture.

Things like the loft hatch. Door seals, letter box, window frames etc

Any cold air coming in = hot air being lost elsewhere