h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Well, I'm more interested in the cons really.
I think the pros are pretty obvious: saving money and reducing CO2 emissions.

But what are the drawbacks of getting it done?

Not had it done myself personally here, but my Father had it put in about a year or two back....
He's had the sealed unit replacement windows in the house quite a while, then had the cavity wall done. Where he lives they always used to have a problem with mold on the walls in places, as the house is not far from the marshes and rivers etc... If anything though, since he's had the replacement windows and cavity wall insulation, that 'damp' we used to get seems to have gone too... Can't really see any cons really cept maybe the cost; as it was he got it done for free through the 'warm front' scheme, can you get any help in paying for it; I know a lot of the energy companys seem to keep trying to tell us they're helping people pay for things like loft insulation so maybe they've got some simular reduction in price or help towards the cost for cavity wall insulation too
It does make quite a differnce to the warmth of the house; more noticeble in say spring and autum, where somtimes you'd want to turn the heating on a bit* now the house just doesn't seem to need the heating on so much in those not overly cold but not overly warm periods, of course when its as cold as it is now the heating still needs to be on, but I guess the cavity wall insulation (and replacement windows), are still contributing to a reduceing of the time the heating actually needs to be on for

If you live in the UK, substantial government grants are available (up to 100% depending on age/circumstances) for cavity wall insulation.

http://www.government-grants.co.uk/cavity-wall-insulation-grants.shtml

I'm guessing it's quite expensive if you ask your dentist to do it.

Oo I can get it done for free

Wasn't planning to get the dentist to do it.

A builder bloke who did some work for us said it had made his house warm, but they'd had problems with moisture since having it done 'cos it wouldn't let the house breathe.

I can't have it done here. I have a rather damp cellar (now with added sump pump and bubble wrap) but still it's damp.

It's EXTREMELY messy. To the extent that it would be very difficult to live in the hosue while the work was being done.

Is it messy? I'm sure when my Father had it done they didn't even need to do anything from inside the house, they just drilled into the walls in a couple places outside and pumped it in I'll double check with him, as it was a little while ago now

It might depend on which walls, and whether they can be accessed from outside or inside. I know when I had it done in my last house there was drilling into brick from inside the hall, and brick dust gets everywhere.

>A builder bloke who did some work for us said it had made his house warm, but they'd had problems with moisture since having it done 'cos it wouldn't let the house breathe.<

They did a big piece on this on that Encyclopedia of All Knowledge that is the One Show (on BBC1).

There are plenty of cons, they showed a house that was slowly getting destroyed by cavity wall insulation. In essence, the place was in an area exposed to constant wetness and the cavity wall insulation soaked it all up. Because it was sealed in more or less, it couldn't dry out and so it was all seeping into the walls causing all the problems of damp - breaking up the brickwork, mould in the walls, plaster decaying etc.

Their advice was to get your place properly surveyed to find out if your house is suitable before you do anything.

This wasn't that uncommon a scenario according to them, although I suspect it was as severe a case as they could find.

I have never had problems with cavity wall insulation, either with the installation or the after effects. Just a much warmer house! As long as your contractor is working to the industry standards and his work is guaranteed I would recommend it.

As someone said, there are a lot of people who qualify for a grant towards the costs. Go for it!

The fact that the house can no longer breathe is a serious consideration.

Basically, if you already have damp inside, it can make the problem much worse. There's a thing called a "dewpoint", the temperature at which water condenses out of the air, which depends on how moist it is. (I've explained all that in Post 15 here F16034?thread=7194044 )

If that happens inside the wall, your insulation will get wet, no longer do its job properly, and makes a good host for mould.

There are ways to calculate where the dewpoint will be, and whether it will happen inside the wall. But in most cases, since the wall wasn't constructed to be insulated, you'll have to think about sealing it all - that is, essentially, wrapping the inside of the house in a big sheet of plastic. Then the moist air won't get out. That creates other problems.

To construct a wall for a cold climate, the optimum is either to have the insulation on the *outside*, or to make the materials less dense from the inside to the outside so that the water vapour can be carried away. Or you need to leave a space air can move through between the insulation and the facade - essentially what was happening when they built the doubled-up walls with room in between in the first place!

Also, the insulation they blow in has a tendency to settle over time, and the waterproof, flame-retardant stuff isn't very good for the environment (and the sheep's wool or hemp kind has to be treated to make it more moisture-proof and flame retardant.)

While there are buildings for which it's the obvious good choice, yours might not be one. So don't get "some builder bloke" to do it. Ask someone who knows what they're doing to *recommend a type of insulation* for your specific house, and wait and see whether cavity wall insulation is among the options listed.

I've had two houses done. The second, after retiring, wasn't free but it wasn't far off, either (£99 I seem to remember). In both cases it was well worth it.
Not a lot of dust from drilling (dust collection hoods) outside or in (garage).

The main risk (to a *normal* house) was said to be that of having *bridges* of mortar across the cavity - mortar having dropping onto the ties between inner & outer & getting damp from rain on the outer- so that when filled, the ventilation no longer worked, leading to damp patches inside.

The settling problem was said to be not significant with improved materials & methods.

In neitherof my cases were there any problems that I'm aware of ( about 10 yrs for the first & about 3 for the second).

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Well, I understand you can get proper people to do it for you.

I've just spoken to my father, who is a builder, and he said something about how, if you're unlucky, having it done can "bridge the damp course", and then you've got problems.

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That sounds like the problem my dad was talking about.

The most important thing is to make sure your house actually has a cavity. Not as silly as it sounds as a lot of pre war houses were not built with cavities.

My house in the UK doesn't have a cavity but that didn't stop one unscrupulous comapny trying to convince my wife to sign up for it.

Out here in the tropics we don't have cavities either no real need. Cavities were originally a means of stopping moisture and condensation ocurring.

They don't stop the moisture and condensation, they just give it a safe place to condense - and if you fill it up with insulation, you can get moist insulation.

Those rings on the anchors are intended to help the moisture drip away.

I suspect ~bridging the dampcourse~ means the cavity insulation going below the dampcourse and drawing damp up and allowing it to penetrate walls.

I'm waiting to have mine done. The company did a survey but I know my property is suitable as the adjoined property has already been done, as has the house on the other side. Both are adamant it's worth it.

I have an open fire in my lounge which I don't use, and because of that the insulation company advised I would need to get my chimney blocked off or they would put a vent in the wall - something to do with carbon monoxide being drawn into the room if I ever used the fire. Blocking the chimney would mean I'd be unable to use the fire as the smoke would just come back into the room, and the vent would mean I could still use the fire but there would be no danger of carbon monoxide poisoning. I opted to get my chimney blocked but the builder who did it misunderstood and only capped it so smoke could still escape. He's waiting for the snow to go so he can put that right then I'll be rearranging the insulation.

It's going to cost me just over £150, which I don't think is too bad, and that's without any kind of grant.

Deb