Cavity wall insulation.....

[Christian and Beccy]

Not sure if this is in the right section, couldn't see one more appropriate anyway!!!

We have a 3-bed detached Bungalow, built in 1929. It is red-brick and the mortar is very crumbly (is that limewater based?). We are going to get it rendered as the brick-work is not in great condition. I will post separately about that.

Anyway, we are looking at Cavity wall insulation, but I am worried about 2 main things that people have told me.

1. Damp bridging - I guess this means that damp can travel across the insulation media, causing problems inside?

2. Plaster blowing inside - I have been told that there is a danger that the pressure used could blow the plaster off the internal walls? I am further worried about this because of the crumbly mortar.

So, is this type of insulation a good idea, what should we go for and what pitfalls can I expect?

 

[diyisfree]

Hi,

I had cavity wall insulation about 5 or 6 years ago. The rear wall that gets pelted with rain sufferd once we had it.

The dining room wall had mould growing, the kitchen wall also had mold growing and a MASSIVE colony of wood lice (leather jackets)

I built an extension last year and when i broke through the twin skin wall i found alsorts living in the lower 3 feet or so, Worms, woodlice, lots of insects and so on.

Last year i removed lines of 3 bricks then left 5 and so on and removed what i could from the worst effected walls, all seems to be ok since then. To be honest, i cant really say we noticed a difference (warmth wise) but im sure there must be.

A neighbour near to me up the road also had it and her wall that got driving rain also suffered. Her hall landing and stairs were a real mess. In the end she had plastic UPVC cladding put on the gable end to sort it. Looks a mess in my opinion but it was the cheapest method for her.

I say no, dont have it but its your choice.

 

[masona]

Cavity wall is design for keeping the rain off the inner wall and ventilation, if it was me I wouldn't bother, although there're some happy people with it.

 

[JohnD]

I suppose it must depend on the condition of your walls. My house is reasonably modern, no water penetration or damp. If you have faults you need to get them fixed first (except rendering, which will look better done afterwards to save it being drilled).

I had the blown fibreglass insulation because it is a tall building, it is said to be less prone to damp bridging. It also does not swell as it sets like the foam can and does not have any solvents that some people are sensitive to. However I believe it is more expensive.

There was some left over which was outside in the rain in a bin, when I lifted it out of the water, although it had been immersed, it was not even damp, the water just fell out of it as through a sieve or colander.

It made a substantial difference to heat loss. At the time I would run the heating morning and evening, if I came home at lunchtime the house would be cold. After having the walls done, if I came home at lunchtime, the house would still be comfortable. The bills went down too.

You often get a "special offer" to install cavity insulation from the gas or electricity company (I ordered mine from Brit Gas who sub-contracted it to Saxon; was a very nice job, all cleaned up afterwards) which gives you some reassurance that it will not be a bodgy job by some flybynight, and you have someone to complain to if anything goes wrong. I also got a BG guarantee and interest free credit.

It was not expensive and well worth having.

 

[Nige F]

before rendering I would get the condition of the wall-ties checked and remedied if necessary and then have the walls blown with rockwool and then render ........there`s a company www.cavitytech.co.uk down here but something similar in Norfolk could be found ........had it done on my last 60`s semi ...........bloody marvellous noticed the difference straight away ........John, they`ve not used foam for years

 

[diyisfree]

John,

Not sure what the stuff was they put in mine. Was white and looked a lot like shredded fibres. Definatly wasnt rockwool

I have seen some stuff that looks like a white expanded foam but when you touch it it disintergrates to powder at the slightest touch.

Guess there are lots of types out there. maybe get in touch with the installer and ask them a few questions and mention stories and experiences other people have had.

Good luck

 

[Christian and Beccy]

I have just had a local firm round and they have said that they will use 'Walltherm' Blowing Wool. They aren't worried about the quality of the brickwork and mortar in terms of their work and they said that damp-bridging isn't really a worry with this product.

They are talking sub £400 for the job.

Does that all sound reasonable?

We have others coming round, including a company on behalf of our energy supplier, so this is a start.

 

[Fluffster]

I had my end of terrace house cavity filled with the blown wool for £256 through warm front, apparently everyone earning over £15k pa pays that amount with the gov grant topping it up.
It is free if you are oap/dss or have a dependant under 16 in the house.
Pete

 

[Christian and Beccy]

By pure coincidence, it's that time of year again (almost to the day from when I started this thread!) and guess what? We still haven't done anything about the insulation that I asked about above.

So, I would welcome any further opinions on whether or not this is a good idea. I have posted elsewhere on this forum about the troubles we are having getting our bungalow to be warm (despite what I feel is a competent heating system) and really am keen on doing something about it, though I realise that Cavity wall insulation is something that I imagine is almost beyond reversal, so I want to make the right decision.

Help!!

 

[JohnD]

yes.

hurry up and get on with it

I hope you have done your loft.

 

[Christian and Beccy]

yes.

hurry up and get on with it

I hope you have done your loft.

There is more we can do in the loft, we know that, but our bungalow is still work-in-progress, so it's not practical to add to the 4" of insulation that is currently there. Eventually, I had planned to lay joists the other way and top the insulation up to 10", which I know will make another significant difference.

For the moment though, I am just trying to ensure that by insulating the walls that I am not making a grave mistake which cannot be reversed.

 

[JohnD]

Procrastination is the thief of

 

[noseall]

Procrastination is the thief of

....getting stuff done.

 

[noseall]

when cavity walls were first used, their function was to prevent damp ingress, and had little to do with insulation, though this was a handy bi-product.

hence the use of air bricks at high and low level points around the building. this caused a movement of fresh air through the cavity, thus keeping damp at bay.

air is only an effective insulator when it is stagnant. air that moves over a surface will cool that surface.

closing up the air vents only caused the problems of damp to re-occur.

the solution was to remove the air by filling the cavity with insulation.

good but not perfect.

the ideal cavity is one that has a limited air gap, say 25mm AND has insulation also, say 75mm.

 

[diyisfree]

homebase as an offer on at the moment for anyone wanting loft insulation,

100mm, 150mm or 200mm rolls of the space blanket gear (the one that is foil wrapped)

Buy 1 get 1 free £14.00 so works out £7.00 per roll. noticed it today..

Ok carry on, sorry just thought it was a good deal.