Cavity Wall Insulation - some advice, please?

I'm really hoping that there's someone on here with knowledge of installing cavity wall insulation - I have asked as many questions as I can, but I just don't have the building knowledge to proceed further.

I've moved into a traditional 1930s semi. It's got recent double glazing and a double thickness of (new) roof insulation - but when the wind blows, it's so draughty! I am desperate to have cavity wall insulation - but have run up against problems.

I have had the survey done, and there is a cavity wide enough to support insulation being inserted. However, the survey found some rubble in the cavity - I looked through the fibre optic, and it seems to be building debris/ small pieces of wood, which have fallen to the bottom of the cavity when the house was built. However, because of this, the company who surveyed say that they cannot insulate. They use the cotton-woolly type of insulation that is blown in at high pressure; and they say that any debris in the cavity will cause uneven 'filling', which in turn will cause damp patches.

But my house is cold! Please, can someone tell me: is the problem insurmountable? Is there another form of cavity insulation, e.g. polystyrene, that would work better? And where can I get it? I have repeatedly tried the energy saving trust for information, but they only refer to their approved suppliers.

Thank you very much if you can help!

I can't help you with you main question on insulation, but surely, if your house is that drafty, track down the drafts and rectify those. By stopping the wind whistling through your house you may not then have such a need to insulate.

It is possible to clean out the debris from a cavity. You have to cut out some bricks and use a long piece of 2x1 batten to push the debris next to the holes you cut out. The wall ties can be cleaned off also with this method. The Councils often used to do this before filling.
The problem with filling a dirty cavity is that you will always have cold spots whatever you use.

Thanks very much, Stuart 45... so it IS possible to fill it!

All I need now, is to find someone who is capable of doing that work. You say that the Councils used to do it/do it, when insulating their own properties? Perhaps I could ask their Estates dept?

And is it costly work? Any ideas would be welcome.

Bathjobby: I'm pretty sure the draughts come through the walls! The outside wall is absolutely freezing when the wind blows directly on it. The draughts themselves are worst around the skirting boards (being a 30s semi, they are the old-fashioned, 'high' type) - presumably because they have the biggest 'gap' open to the outer layer of brickwork; and a positive gale blows up from between the floorboards! ( I might be exaggerating slightly; but if you put your hand to the floor, you can feel the cold whistle of air).

I know that a certain amount of ventilation around the brickwork is recommended - but am I right in thinking that the double layer of bricks that form the outside wall will be open at the top, up in the loft? And this could be where the wind is getting in, and working its way around? And that would be cured, wouldn't it, if I get cavity insulation?

Thanks very much for your help.

You need ventilation under the floor to stop the floor joists / boards going rotten. If you have draft between boards you should either get a good floor covering or fill the gaps with sawdust and wood glue and sand level.

Cavity wall insulation retro fitted so to speak has its disadvantages, the cavity is there for a reason and you want to go and fill it up. Apart from not filling the cavity completely causing cold spots and condensation it can compress under its own weight leaving the same cold damp spots on upper levels. You would be better spending your money on decent double glazing if you have none and about 12" of loft insulation to stop escaping heat rather than trying to stop fresh air coming in.

Just my 2cents.

gday2uk said:

You would be better spending your money on decent double glazing if you have none and about 12" of loft insulation to stop escaping heat rather than trying to stop fresh air coming in.

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double-glazing is one of the worst ways to spend your money in the hopes of saving it.

draughtproofing gives the best return pound for pound

insulating the hot cylinder and hot pipes repays in few months

insulating the roof and cavities makes the biggest difference

if you have rubble in the cavities, it needs cleaning out. this is a very labour intensive job so not cheap unless you can do it yourself

Gday2uk: I do have double glazing - and very thick loft insulation, only 18 months old!

I take your point about not filling in the cavity because it's meant to be there. I have heard this argument before. It's just that I hate to be cold, and those homes which are cavity insulated seem so much snugger!

Thank you for the tip about filling in the gaps with sawdust/glue - this is definitely something I can try before I have new (thicker, wool) carpeting fitted to the upstairs rooms. With a good underlay! I appreciate that some of the problem comes from thin carpeting (which I have inherited).

It's also been suggested to me that I remove the draughty skirting boards, fill the gap with expanding polystyrene filler, and then replace them - anyone got any thoughts on this?

Thanks very much to you all for the suggestions. JohnD: I have a condenser boiler, so no hot water tank to lag. But should I also lag all the hot pipework?

It is sensible to lag hot water pipes, and heating pipes where they pass through an unheated and uninhabited space (e.g. under the ground floor, where they are also exposed to freezing)

opinions differ, but some people say there is no need to lag other radiator pipes, since they contribute to the general warming of the house when the heating is running.

some of these people say it because they can't be bothered, of course.

When you open up a typical wall that has been, so called filled with blown insulation, you find large gaps have formed on the blind side of wall ties. So the filling is useless as an insulation as heat always goes to cold and all that happens is you block the movement of heat in one place and it moves to the next weak link.
Cavity walls were re-designed in the late 18 hundreds as many houses of that time had wind blown rain coming through the walls. This still happens today!
If you fill a cavity with this yellow string, it merely transmits the damp across the cavity making the inner wall damp.
Damp walls equal a good transmission path for heat to cold so, the problem is made worse and your heating bill goes up.
A better idea is to follow the lead of modern office blocks and factories, where they have a water proof skin, either glass or steel to stop the wind and rain with polystyrene or similar underneath.

I strongly disagree with PerryOne

It has made my house warmer and cut the fuel bills.

as the inner walls are warmer they are less prone to condensation, not more.

it has not caused damp to jump from the outer leaf to the inner. the wool is water-repellent and if you throw it in a bucket of water it is not wetted.

if there were gaps in the filling, it would not cause extra heat to jump through these gaps. It would be like wearing a jumper with a hole in it. Your skin under the hole might be cold but the rest of you would be warm.

I think iv'e had eperiencies in a way. The house i'm in now, ex coucil, was insulated, 20 years ago, with the blown "wool", never had a problem, i personally believe in having a cavity.

My previous council house had damp under the front window, you know what councils can be like, 6 months wait, with kids anyway, pulled inside wall down (very easily!), cleaned the wool out, quick brick up, paid the plaster and never had a problem.

And john, i don't believe wall insulation does have a big effect on the bills, could be me and other factors, but i am pretty tight, draughs and giving free heat away are not me

We had one of these - very draughty and cold when we moved in.

I guess you have a bay at the front, on both floors with no windowsills upstairs?

It is probably no more than a 2x2 timber frame with plasterboard on the inside and the cladding on the outside, in the floorspace there will be nothing on the inside.

I fitted windowsills in the bedroom and boxed in beneath them filling the box with insulation. Mote insulation around the bay in the floorspace. Boxed in above the window downstairs (to match cavity wall thickness) and again filled the box with insulation. Depending on the design you may not be able to do much above the bedroom window (our bay was under the eaves overhang so the space above was insulated.

This alone halved the heating bill.

Cleaning out a cavity can be time consuming and tedious. It is not always successful. If you have solidified mortar down there you will not be able to shift it with a piece of wood, iron bar or any other normal means. The only way that I have found to break up solidified mortar is to use a .410 shotgun!

Cavity wall insulation will not make your house less draughty. The draught you are experiencing is likely to get under your floor though the air bricks. I wouldn’t recommend blocking these off unless you want a rotten floor.

As stated before the best bet would be to properly seal the bottom of your skirting board to the floor before you try anything else.

Thanks very much for your comments. The problem is, I can see both sides of the argument! I am concerned about what would happen if the material settled over time, or left a gap..however, I have spoken to many people who have filled the cavities and are sure that their houses are warmer for it, and have not experienced any problems. Perhaps, i should say, 'thus far!'. In the history of housing, we have only used cavity insulation for a relatively short time.

But, bearing in mind your comments about cleaning out the cavity, maybe I am going to accept that it's a job I can't do.

Very interested in your comments IJWSE15, about the bays. Yes, I do have two bays, and they are some of the draughtiest places! But they do have windowsills - although I would suspect, as you say, that it is only plasterboard beneath, then a (draughty) gap to the outside. But the outside is fronted with Accrington Brick - I would have thought that would be more weather-resistant than just cladding.

Although it's difficult to pick out one area - there are so many, when it's windy! The bathroom is a particular nightmare - wind seems to work its way in through the fittings for the sanitaryware, there is a terrible draught through the bath panels and around the loo. The old airing cupboard in the bathroom is another draught magnet - although I cannot see any obvious gaps.

The worst one, for me, is the bedroom on the back of the house - without a bay, but above a bay to the living room, with a tiled, sloping roof. Maybe there are gaps beneath the flashing to the bay? But when the wind blows directly against the wall (which it often does, it faces southwest), it's sooo draughty!

Any further ideas on how to cut down the draughts in those two areas would be much appreciated.

take up some floorboards and gave a look. you will find gaps round pipes, bricks, joists, and where a bay roof meets the wall.

you can do a lot of good by stuffing insulation wool into the gaps.

I would formerly have said fibreglass as used in lofts, but I recently came across white fibre rolls made of recycled plastic, not glass, which are much better to work with as they do not shed irritant dust and fibres which make your skin, eyes and throat itch.