Cavity wall insulation

[peteuk]

Hi,
Can someone give me some advice please?
I have recently had cavity wall insulation installed and was very surprised when the contractor sealed all my airbricks (apart from 2 which I said were under a suspended wooden floor).
I can see no sign of air bricks inside the house so I assume they are to ventilate the cavity only.
At first I was concerned that sealed cavities may cause condensation so I unsealed the airbricks.
I noticed the insulation did not fill the cavity but seemed to be a thin layer on the internal brick wall only. I thought the cavity would be full.
The contractor has advised that what I can see is normal and that I should reseal the air bricks to prevent damp.
Is he correct? If no-one knows, is there a site to confirm that his advice is correct - I seem to be able to find adverts only.
(The filling is "mineral wool" I think)
Thanks, Pete

 

[BOB NUTS]

Mineral wool is normally full fill. If you have a 50mm cavity and it is only half full or less then your not gonna get the full benefit. I think the guy may be lying to you about the depth thats supposed to be there - which insulation did they use? they should be approved and have test information of their product to say how its used/installed which would tell you if a thin layer is intended. If not you may get problems with cold spots attracting any condensation

I'm not familiar with ventilating the cavities but i would guess that the air bricks may have been to give ventilation to the rooms (but have had the room side air bricks sealed/plastered/wallpapered over due to excessive draughts). Generally superceeded by trickle vents in windows these days.

sometimes they are fitted to give ventilation to a fire or boiler. I think larders used to be ventilated.

If the airbricks to the suspended timber floor have been blocked up you may have a problem in the future with condensation and rotting joists

What height are the air bricks at? (all at low level/below floor level? at head height?)

 

[peteuk]

Thanks for the quick reply Bob. You've made me think I am right so does anyone know if there is some authority I can check with and have it officially inspected?

Fortunately the underfloor airbricks to the wooden floor weren't sealed.
The others seem to be just above the DPC on 3 of the house walls. 1 of these walls also has airbricks just below the roof (it's a bungalow).
The wall of the attached garage doesn't have any.
Thanks again,

Pete

 

[Nige F]

sounds like it was originaly a ventilated cavity.unusual down here in SE,and yes the rockwool should fill the cavity, maybe they rushed the job? Complain to the Firm`s MD to start with.

 

[anobium]

The air bricks should have been sleeved prior to the installation of the insulation. Basically the sleeves are like large pipe cleaners and are just pushed into the edges of the cavity where the air bricks are situated, this then prevents the insulation from weeping out and blocking up the air brick.
Blocking up the air bricks will eventually lead to condensation under the floor and this will in turn lead to fungal decay in the floor timbers
I dont understand the reference to cavity airbricks as this is not standard practice, the only time you should see what appears to be a cavity airbrick is when one is installed in the vicinity of a bathroom toilet or kitchen and extends inside the building to prevent condensation.
A cavity is designed soley to prevent the lateral movement of moisture onto the internal surface.

 

[peteuk]

Thanks for the info Nige / Anobium,
The airbricks under the floor I know to be wood (in an extension) were never sealed.
The survey when we bought the house stated the floors were concrete but I guess the surveyor could be wrong. They could have just been "surfaced" - how could he tell?
Anyway I've unsealed those airbricks too which should prevent any condensation issues (I hope).
So the issues I've got are that:
1). The contractor says I should reseal the airbricks to prevent damp from driving rain
2). The contractor says the cavity needn't be full around the cavity and what I have is normal
3). Having already asked the contractor to revisit the job (when I got the bove advice) where do I go from here to get an impartial 2nd opinion.
Thanks,
Pete

 

[suffolklad]

hi i had rock wool blown into my walls and i regret it it is so patchy some here there and gaps i had to take some bricks out of wall and found gaps behind. the old liquid formeldyhide was better but poisness hey. trouble with rock wool is it catches on wall ties and all the cement on them if it was built poorly. and they say it doesnt suck up moisture not convinced about that either

 

[anobium]

What do you mean when you say seal the air bricks Please explain
Clarify: the cavity does not need to be full around the cavity:

If you have cavity wall insulation all the cavity needs filling whatever type of insulation, otherwise pointless exercise
Also cannot understand ref to floors being surfaced. Is there a space under the floors ,if so more than likely to be timber suspended.

 

[peteuk]

Once again thank you for your replies. Apologies for my ignorance and lack of clarity.

The contractor sealed the airbricks with silicon when he installed the insulation. It is this sealant I removed and which he says I should replace to prevent damp.
I have shone a torch into the airbricks and that is how I can see that the cavity is not full. Obviously I cannot tell elsewhere without removing bricks.

We have an early 1960s bungalow that has been extended and was built on a slope.
The airbricks of the original house are in the course immediately above the damp proof course. (On one wall - the one at the top of the slope - there are also airbricks near roof level). The floor appears to be on the same level as the damp proof course and therefore lower than the air bricks. When I bought the house the surveyor said these floors were concrete although I have since been told that someone may have surfaced the original (wooden?) floors (with concrete?).
The extension has air bricks 1 course lower than the original air bricks so it appears they are below the suspended wooden floor. These airbricks were never sealed because I told the contractor the floor was wood (I can’t see wool behind these but I think it is ok because behind would be the under floor space)

Your replies again make me think the job has not been done correctly. Is there an impartial body that can inspect it and advise what needs to be done?

Cheers, pete

 

[anobium]

The contractor sealed the airbricks with silicon when he installed the insulation. It is this sealant I removed and which he says I should replace to prevent damp.
I have shone a torch into the airbricks and that is how I can see that the cavity is not full. Obviously I cannot tell elsewhere without removing bricks.


Your replies again make me think the job has not been done correctly. Is there an impartial body that can inspect it and advise what needs to be done?

Cheers, pete

Pete I am still confused with this reference to sealing the airbricks. What the installer should have done was to remove the air bricks prior to installing the insulation and fix the sleeves or cavity brushes around the open cavities were the airbricks were situated. This then stops the insulation from blowing out at these points and and blocking the aperture.
On completion the air bricks are refixed the cavity brushes remain in situ
Dont worry about the airbricks being above the internal floor level. in some respects this is better as the periscope effect provides better air flow to the under floor area. Obviously the inner leaf of the cavity will be open below the floor
If you want an independent body to check the work I am sure that there is an organisation for cavity wall installers, your local council should be able to help

 

[PatrickD]

I'm as confused as everyone else here. The airbricks first. Are they like waffle cakes with square holes in them and if so, where did this 'ere contractor put the silicon. In each hole? If he did, did he say why?

Patrick

 

[peteuk]

Thanks again everyone for your support.
And I'm sorry I haven't explained myself well.

I think the description of airbricks like waffle cakes is a good one. I've just checked 1 brick - 12 square holes (2 high 6 across)

The contractor put the silicon in each of the square holes.
He said it was to prevent the insulation material from coming out of the holes - they do it all the time.
I removed it because I started to worry about air circulation and then discovered the lack of insulation behind the airbricks. (My worry was that it would come out).
When I questionned it, the guy who'd installed the insulation said I didn't have to worry about the air circulation, that they always block up the holes in the air bricks, and that I should redo it because otherwise the insulation could become damp (in driving rain). The lack of insulation material behind the airbricks was ok because it happens sometimes round the airbricks and that is normal.

Now I know there should be no insulation behind the airbrick because the steps described by Anobium should have been followed. However I also know the installer certainly didn't remove any air bricks.

Will it help if I tell you the installers name? They are a countrywide organisation according to their website and were the name I was given as a local installer to qualify for a grant. (I've not mentioned it until now in case the site rules forbade it)
Thanks again.

 

[BOB NUTS]

I would be shocked (and appalled) if somone laid a concrete floor on top of a suspended timber floor - its likely to make the situation worse (maks the timber joists suport more load)

Its highly likely that your suspended timber floor was replaced with a concrete one at some stage. I think youd know by 'feel' if you had a timber floor - if not lift the carpet and have a look.

If you have a concrete floor with a dpm then you wouldnt need to ventilate the void below the floor.

Can you 'poke' through the airbricks and find solid material?

 

[anobium]

Pete if you got a grant for the insulation you should report your concerns to the council and they will have to investigate the standard of workmanship .

 

[peteuk]

Dear all, Once again thank you all for your patience and support.

The floor looks like concrete and sounds like concrete. But when we lifted old floor tiles in the utility room it sounded hollow and looked wooden in some areas of the middle. Unfortunately I didn't think to explore or care about it then and the floor’s been tiled over again since. (A floor is a floor, or it was – and the surveyor had said they were concrete. Could someone have used “levelling compound” rather than concrete above the wooden floor?).
If it weren't for Anobium's comment that airbricks are not usually just to vent cavities I wouldn't be worried about the floor.
Even so since the airbricks aren't blocked it sounds like I don't have a problem now. Does this sound right?

If so, I think my only concern is with the quality of the cavity wall insulation, lack of insulation round the airbrick lack of sleeving etc.
Although my insulation cost was reduced because it came with a grant the council passed me onto an agency to claim it. It will be interesting to see whether or not they are interested, especially as I can’t really say there is a definite problem.

Bob, I can see the wall on the opposite side of the airbrick with a torch. I will try to see if I can detect something below it in the cavity tomorrow. (Or at the weekend if it's too dark or I can't find some wire to check with).

Thanks again,

Pete