Cavity wall versus dry lining wall

[Alison556]

OK, so our house is pretty old - built around about 1919. It's brick with pebbledashing.

The gas guy who was out servicing my boiler told me that British Gas are currently offering free cavity wall insulation if your gas and electricity are with BG. Only problem is, my upstairs neighbour would have to agree to cavity wall insultation as well.

Working on the basis that she probably wouldn't agree (she's a cantankerous old bugger), I thought about just dry lining the one room that really does get perishingly cold.

The guys that were quoting me for the dry lining job said that I don't want to even contemplate cavity wall insulation because if I fill the cavity, then I risk causing damp because there will be no air flow.

Are they right or are they just trying to ensure that I give them the work for dry lining?

 

[noseall]

Whilst that when constructing a new building, insulating the cavity with say dritherm or celotex etc is by far the simplest way it also means the inner walls are free from 'troublesome' insulation which can cause fixing issues.

However, there have been claims on this very forum that retro' filled cavities, with either foam, beads or fibre-wool has led to damp issues.

I think that these issues have more to do with the condition of the cavity rather than the insulation. By this i mean that the lower part of the cavity (dpc level) has probably been breached by excessive mortar snots falling and gathering. There may also be broad cavity ties that have the same problem of fallen mortar gathering on the metal band.

Also, if you have any vents i.e. suspended timber floor vents or room vents, then you need to ensure that these do not get overwhelmed by the cavity fill. The surveyor that measured ours blathered on about how the lads would sleeve through etc. They didn't. I ended up doing all the vents myself having found most of them were clogged.

So, if you have cavity breach issues then a clear drafty cavity may keep things in check. If your cavity is healthy and clear, and all the vents are adequately sleeved, then i say fill 'em.

It is far better to have the insulation out of the way.

 

[Alison556]

Thank you for your answer.

How will I know if the cavity is healthy or not? Or is that something the surveyor will be able to advise on?

We don't have any damp in the property - just freezing cold walls and I was worried about causing dampness.

 

[joe-90]

If the cavity thing doesn't come off then insulated plasterboard will make a massive difference to the room. Not all cavities are wide enough from that era to be suitable for insulation and will almost certainly have a load of debris in it.

So insulated PB is at least a safe alternative.

 

[noseall]

How will I know if the cavity is healthy or not? Or is that something the surveyor will be able to advise on?

Good question and one i can't answer.

The most practical and economical solution is to fill the cavity, however it may not necessarily yield the best results.

If you are really concerned then engage an impartial professional (structural surveyor) to advise. Lets not forget though there must be thousands of homes that are successfully insulated via retro' cavity fill.

How wide is the cavity? It must be an early example built in 1919.

 

[Alison556]

I don't know how wide the cavity is - I didn't even think we had a cavity to be honest. The internal walls are brick but there's lathe and plaster on the external walls which will obviously take up some room.

I'll see if I can find out how wide the cavity is.

Of course it all depends on whether my upstair's neighbour is agreeable to cavity wall insulation. If she's not, then it'll have to be dry lined.

 

[AronSearle]

I would be surprised if it's a cavity construction.

If you are in an exposed location, don't do it, unless you have a decent roof overhang.

If not, you also need to check the general weather tightness of the construction, penetrations into the cavity need sealing (windows, pipes, flues etc), otherwise water will get in, and may bridge across the insulation.

Remember that most of the people that blow it in are cowboys, I have dealt with a number of cases were they blew it into a cavity frame, without even knowing what type of construction it was. Get someone other than the blow in insulation people to tell you if it's suitable, they will nearly always say it is.

I have dealt with people that have not been able to sell their house after bodged installations, so take care.

 

[ferdinand2000]

I've just had the BG package as I use the Homecare boiler package on a rented property.

They send a surveyor out first, so there's a chance to discuss it with the engineer. I guess they put a camera in to examine your cavities. If it is less than 50mm they won't insulate it.

Your neighbour sounds like my gran who said "ain't having none of that new fangled rubbish here" to a free gas connection in about 1972, as a result of which it is about to cost us £700 extra to get central heating done.

On the 1919 cavity wall; I'm just buying a 100 years+ old semi with a narrow cavity, and the nice neighbour in the other half has just told me that it is too narrow to have insulation. Pah.

So it may be skirtings lifted and cornices down for dry lining as I am refurbing.

Ferdinand

 

[AronSearle]

They send a surveyor out first, so there's a chance to discuss it with the engineer. I guess they put a camera in to examine your cavities. If it is less than 50mm they won't insulate it.

It depends who is sending the surveyor.

If the surveyor is from the company getting paid to insulate, they can be worse than useless. I have dealt with installations that have gone wrong, because the surveyor didn't even bother to check the construction type, because all they cared about was selling the item and getting paid.

Not saying a lot of them are like this, just enough that you need to be careful.


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[Alison556]

It's a bit of a minefield really.

I've seen problems with cavity insultation on these home improvement programmes where they've ended up with hellish damp because the insulation got soaked because of a poor outer wall.

I've noticed a couple of cracks in the harling/rendering so I'm guessing that the wall isn't going to be perfect for insulation.

My neighbour isn't even that old - she's just so bloody lax - she just wants to live in her house and not have to bother with anything.