CWI in Victorian house

[Bodgit]

My house was built in 1886 and has 2" cavities and an injected damp course. It's built on a hill and is partially below ground level, although you can walk all the way round the outside - nothing is actually touching the walls of the house.

I've had two surveyors round so far and both seem completely disinterested in fitting CWI to the house. Neither seem to be particularly bothered about the DPC, which would be my only concern. One told me that the sash cords run in the cavity (which I know is incorrect), and the second told me that they can't touch it until the "basement" walls have been tanked up to ground level, which also seems like a nonsense, as there is nothing touching the walls. They both told me that they didn't think I'd find a company who would do it.

It seems to me that the insulation companies have a lot of work on and can afford to be choosy - not taking on the difficult or risky jobs.

Does anyone have an advice? Is it worth getting more surveys or are they all going to say the same?

There is one room that is particularly cold - it's an extension and has 3 external walls. The surveyors say that they will never insulate an extension without doing the rest of the house, as they can't guarantee that the cavities are not linked. How do they do this with semi-detached houses?

[dennis]

They bash a hole at the top and bottom of the boundary wall and drop a long brush down the joint. They pull it out when they are finished and fill the holes.

[NT]

You'll probably have gale force winds blowing round that cavity, which evaporates away much of the damp that would otherwise get through the membraneless underground walls. Fill with cwi and you'll more or less inevitably get damp below ground.

There are custom ways to do it, such as fitting a barrier that keeps the cwi out of the underground section and taking other measures to keep that bit dry, then cwi'ing above ground.

Extensions can be cwied separately. Small holes can be made to determine whether there is cavity connection, but usually there isnt.

I cant see any company doing it, this is diy territory. Its far cheaper than half inch PIR board and replaster.

Is your wall is brick or block or stone?

The payback on cwi makes it worth some t-ting around.

NT

[Swift Half]

Thanks for the reply.

So you think that the 'basement' problem is not groundless then? Why would these walls be more likely to get damp than any above ground walls? - I can see they would get less sun and they may be closer to the water table, but apart from that I can't see any difference.

Sounds interesting! Do you think the standard CWI companies would do this, or do I need to go somewhere a bit more specialsed?

I'm pretty sure they cavities are not connected.

In the extension, I have access to the cavity in the loft. I was thinking of the possibility of pouring poly beads down there.

Brick.

I've put internal insulation in place in a few rooms downstairs, which makes a big difference. But other rooms (eg kitchen) are not so easy. I'm really trying to make the two large upstairs rooms more comfortable - they get bloody cold in the dead of winter!

[The Natural Philosopher]

Dont be: NT has a thing about 'damp' and is usually completely wrong..

If the walls have been injected below and above ground level, they wont get damp above the injection layer.

If you have under ground walls, they will get damp unless a method of blocking the damp and/or evaporating it exists.

Normally you would dig down, inject at the wall base, and use a damp proof lining and e.g. poly sheets outside before replacing soil.

Its probably time to either draw a plan of what is there so we can understand better, or get an architect or building engineer involved.

[ARWadsworth]

The brush stays in place. It stops the wool, if it is wool insulation, from migrating into next doors cavity.

Adam

[NT]

Above ground, the walls are exposed to the air and sun. Below ground, due to its age there will be no waterproof membrane, and the walls are directly exposed to permanently wet soil. Water thus seeps into the wall inevitably.

The resulting water content is kept down by evporation from the interior surface, and with a cavity wall construction, evaporation from the surfaces inside the cavity as well. When you fill that cavity you almost completely stop the air flow inside the cavity, and hence the evaporation from the inner surfaces of the wall. Modern constructions always feature a waterproof barrier designed to keep the wall dry.

Also the cavity is a physical barrier to water flow, reducing interior damp further. Filling it provides material across which water can track.

I dont think theres any realistic chance of you finding any company to do it. Its a custom solution. The underground section might be kept dry by for example making 2 holes and piping a dehumidifier up to it.

Doable, though it can be quite time consuming. Worth it though.

that's good news

Yup. CWI will perform better than interior insulation too, as half of the thermal mass of the walls stays inside the insulation. With interior insulation boards you lose the benefit of that mass, which stabilises day/night temperatures.

NT

[NT]

TNP and Stuart reply to most damp in old house related threads with the sort of advice that contradicts the leading authorities, such as SPAB, who have drawn their conclusions from a considerable bank of expert input. When pressed on detail they've been unable to back their position up.

In fairness, TNP's approach to damp in old houses was in widespread use a couple of decades ago, but expertise has moved on, a lot has been learnt about how old buildings handle damp since then, and the advice from SPAB et al reflects that.

NT

[Swift Half]

The point is that the outside walls are NOT in contact with earth - you can walk around the outside of the building. Prepare for ASCII art....

Ground Floor| Ground Level (outside) | ------------+ +------ | |###### | |###### | |###### | * |underground Basement | |###### | |###### ------------+------+

The area marked * is outside the house - you can walk around.

[NT]

Oh I see, I missed that bit. In that case CWI is quite straightforward, no funny solutions needed.

NT