Home Forums General Discussion Underfloor ventilation and moisture barrier Reply To: Underfloor ventilation and moisture barrier


Kat – totally agree with Ian and Ian. I think it is a waste of time and money to install insulation and vapour barrier until you have addressed the moisture.
Two suggestions to check / act with respect to external moisture.
1. If the brick wall has been laid by a bricklayer then there will be weep holes on the bottom course… about every six bricks the vertical mortar joint is left out / scrapped out, to allow moisture running down back of bricks to exit externally. You need to get them to check that the peepholes haven’t been blocked… or worse still filled up with soil where garden may have extended to wall… then all that happens is soil in weep holes act as a wick and allow moisture to be sucked from soil into warmer house.
A brick wall is a wet wall system… hence the cavity. Even fired bricks will absorb moisture and more so if (as Ian suggests) the mortar has deteriorated.
Source of moisture is more likely to be failed head flashings above doors / windows… metal flashings are installed at head / foot of windows to divert moisture away from interior of wall. So check above above doors / windows that these flashings re still in good condition.

2. You need to find the source of moisture which is external to the wall / house…if there is soil touching floor / brick wall, the moisture will find path through the brickwork.
Get the owners to dig a DEEP field drain below the level of the floor and ensure it runs down to a stormwater drain… free draining material at base of drain, nova flow pipe and then at least 100mm of free draining material… then weed mat and soil. Deeper the drain the better
Hydraulic pressure can be enormous and water under pressure from outside will find a path into dwelling… you need to get the water away from the wall.

Once drain has been installed… and wall has dried out… may need to wait till next summer, then you can do something with vapour barriers and insulation. Unless you address sources of moisture then insulation / vapour barriers will be temporary sticking plasters and may make the situation worse.

Good luck… and happy to have phone conversation if you can send pictures.