Cavity Wall - wet outer leaf query?

ArdDonagh

Can anyone tell me if the inside of the outer leaf of a cavity wall should be wet. I have a new house and have recently had problems with water trapped in the cavity. The builder has taken out a window on the ground floor and believes that the water may have been coming through it. However I noticed that when a block was removed on the inside of the bedroom directly above this window, the brickwork inside the cavity on the outer wall is really wet (not just damp). The builder says this is normal. Is this normal for this time of year (and the gable end of the house is facing the prevailing weather). I am concerned that the water may be coming down through the cavity from the roof. The cavity is also pumped with bead. I would really appreciate any help.

Poor Uncle Tom

ArdDonagh wrote: »

Can anyone tell me if the inside of the outer leaf of a cavity wall should be wet. I have a new house and have recently had problems with water trapped in the cavity. The builder has taken out a window on the ground floor and believes that the water may have been coming through it. However I noticed that when a block was removed on the inside of the bedroom directly above this window, the brickwork inside the cavity on the outer wall is really wet (not just damp). The builder says this is normal. Is this normal for this time of year (and the gable end of the house is facing the prevailing weather). I am concerned that the water may be coming down through the cavity from the roof. The cavity is also pumped with bead. I would really appreciate any help.

The main premise of design in relation to a cavity wall is that the outer leaf is constantly wet and you design the inner leaf so they don't physically touch in any form.

It is unlikely the wet/water is coming down through the cavity from the roof as the cavity is most likely closed at eaves level. If the cavity side of the inner leaf is not also wet it is likely that you see condensation on the coldest surface of the cavity as the inner leaf will be heated from the rooms and the cavity insulation will prevent the heat passing to the outer leaf, but the moisture will then condense on the blockwork or brickwork surface.

Also, you say the house is new. If the inside of the house was finished in a wet plaster finish (scud coat, one or two scratch coats and a finish of skim coat) then it is likely the process would have brought over 1,000 litres of moisture into the shell, a lot of which would have soaked through the floor to the radon/DPM course and is being released into the house/cavity slowly and will show up as condensation or apparent damp until such time as it has all been removed. The use of a dehumidifier is advised in cases like this.

This time of year is the worst for condensation/damp issues.

RKQ

ArdDonagh wrote: »

Can anyone tell me if the inside of the outer leaf of a cavity wall should be wet. I the brickwork inside the cavity on the outer wall is really wet (not just damp). The builder says this is normal. .

The Builder is correct. The outer leaf is always wet, especially if it has any brick (clay is permable). Uncle Tom is correct.

Cavity construction was developed for a reason - our damp winters with heavy wind driven rain.

Hopefully your insulation bead can withstand these normal conditions. IMO a cavity wall construction should not have fully cavity insulation. Check the IAB cert from your Insulation Installer / manufacturer.

MacTheKnife1

RKQ wrote: »

....The outer leaf is always wet.....

....Cavity construction was developed for a reason .....Hopefully your insulation bead can withstand these normal conditions. ...a cavity wall construction should not have fully cavity insulation.....

Whoahh!!! I thought eco bead or polypearl were IAB approved. Do you doubt their usefulness??? I was going to use them, would hate to think they were a bad idea?

RKQ

MacTheKnife1 wrote: »

Whoahh!!! I thought eco bead or polypearl were IAB approved.

An IAB cert is a good start. I've given my opinion and explained why.
We must all make our own way in life....:) We all have choices. Maybe google the topic or read some documents on a well known insulation manufacturers site.

Time will tell..... I remember when asbestos was a miracle material, used in everything!

ArdDonagh

Thank you Uncle Tom & RKQ - that is a relief:D. The cavity is not closed off at the top but there in no indication of water coming through the roof (all the rafters are dry) and the membrane under the tiles is bone dry.

Re the EcoBead - it is bone dry also. There was yelllow fleece type insulation (sorry, dont know technical term) around the window and this was soaking. That has been removed now. The water was coming in through the window as the DPC was all "in a ball" in the cavity. The water was then lodging on the DPC and coming through the wall as damp.
Thanks again.

ArdDonagh

Thanks VERY MUCH for that info - its a big relief.

Mellor

MacTheKnife1 wrote: »

Whoahh!!! I thought eco bead or polypearl were IAB approved. Do you doubt their usefulness??? I was going to use them, would hate to think they were a bad idea?

IAB cert doesn't mean do what you want with it. Its not a free pass.
It may for example set a situation where its ok, like rendered blockwork but not brick

Carlow52

Poor Uncle Tom wrote: »

The main premise of design in relation to a cavity wall is that the outer leaf is constantly wet and you design the inner leaf so they don't physically touch in any form.....

Would you expect the inside of a 215mm hollowblock, or a 215mm solid block wall to be equally wet?

Poor Uncle Tom

Carlow52 wrote: »

Would you expect the inside of a 215mm hollowblock, or a 215mm solid block wall to be equally wet?

Proportionally so, yes.

Carlow52

Thanks for that, which might explain my last observation in this thread
http://www.boards.ie/vbulletin/showthread.php?p=58140355#post58140355

Poor Uncle Tom

Carlow52 wrote: »

which might explain my last observation in this thread

I haven't read that thread yet. Anyway, the thing to be avoided at this time of year is interstitial condensation which accounts for a lot of moisture in cavities anyway, imo.

RKQ

Carlow52 wrote: »

Thanks for that, which might explain my last observation in this thread
http://www.boards.ie/vbulletin/showthread.php?p=58140355#post58140355

Don't really see the connection.
Condensation is a problem this time of year but wind driven rain is known to wet the other leaf, thats why cavity wall construction was developed.

Poor Uncle Tom is correct, I too would expect the inside of a 215mm hollowblock, or a 215mm solid block wall to be proportionally wet - depending on render is abit fool hardy in IMO. I seen it all too often.