Increasing air flow through air bricks

Discussion in 'Builders' Talk' started by total amateur, Aug 24, 2008.

  1. total amateur

    total amateur New Member

    I've got a damp problem underneath my wooden floor in the back reception room - proven by slugs etc coming through cracks. Probable cause is prximity to a river (200 yards). Joists and floor is fine for the moment, although it has all clearly been replaced within the last 10 years so I suspect there is an historic problem here - caused by the ground beneath being constantly damp. I have two airbricks on the wall that faces south east and two on the wall facing north west. All are clear. I'm wondering if a faster flow of air underneath the floor and through the air bricks would help, and if so, how to achieve it.

    For example, what if I had a pipe over the mouth of the south-east facing air bricks, and run it up the flank wall. As that wall gets a lot of sun would that create an 'up-draught' which in turn would increase the air flow underneath the boards?

    Another thought I had was putting a vent in the chipboard floor, but that would just allow the slugs in, I suppose?

    I have telephoned four builders to come an give a quote, but only one turned up and he started talking about putting a dpc in the chimney breast - which surprised me as I thought that was not recommended. Hence me turning again to the very helpful blokes on here

    Thanks in advance
  2. doing a bit

    doing a bit New Member

    just fit more air bricks for better ventilation, check the floor joists are on a dpc layer where they cross the supporting walls to stop damp penetrating
  3. total amateur

    total amateur New Member

    Thanks. The two outside walls are about 15ft long. How many should I have on each wall (two on each at the moment)
  4. " I've got a damp problem underneath my wooden floor in the back reception room - proven by slugs etc coming through cracks."
    Cracks! where?

    Maybe they they are coming up from the 'solum'

    Sounds like an old house built too low, near to 'the water table' what's the solum like? any DPC treatment?
  5. doing a bit

    doing a bit New Member

    check what the cowboy says and fit a couple more on each side, ask local bco if they have any ideas , might help and its free
  6. total amateur

    total amateur New Member

    The main crack is on the hearth, where the corner is crumbling. It feels damp to the touch. Anyway - because of that there is a gap of a couple of inches between the main part of the hearth corner and the chipboard flooring. It is an old house (about 100 years) so the fact that the flooring is chipboard suggests that this is not a new problem.
  7. total amateur

    total amateur New Member

    By the way, there is a DPC that I can see on the outside. The only damp is in the chimney breats and hearth which is on one of the internal dividing walls (between the back reception room and the kitchen)

    PS - someone asked what the solum's like. What's solum? How can I tell what its like?

    Thanks for all your help
  8. The 'solum' is the ground under the joists. Older type properties are unlikely to have a solum treatment, in newer properties the solum is sealed with tar (bitumen) or a thick plastic sheet is installed a DPM, and concreted over this stops dampness from rising up,

    Good idea if you checked your solem, pick up some of the material/soil in your hand,and check if it contains much moisture.

    There could be other problems like your chimney, although can't see that causing slugs, also check the solum for tree roots.
  9. total amateur

    total amateur New Member

    The solum does feel damp. Also, on the north-west side of the room I have three air bricks in a 4 metre run, but on the south-east side I have only two air bricks in a 6 metre run. Rather than putting in an additional air brick can I just drill a few holes in one of the external bricks. I mean - isn't an air brick just a brick with holes?

    On Midnight's other point, there is no sign of tree roots.

    Finally - I've discovered that I might be encouraging the slug problem myslef by putting down pellets through the gaps. These do kill them - but they also attract them in the first place, so should only be used outdoors.

    I am sure I need more airflow, but I am not sure that just another airbrick or two would make that much difference.
  10. You could definitely do with improving the through ventilation, particularly on the longer wall, although I wouldn't go drilling through the walls as you suggested, could be a problem in the future when you come to sell. Are the exterior walls stone?

    Damp solums give off a lot of water vapour, some worst than others depending on the water table, also different ground levels inside the property to the outside ground can exacerbate the problem.

    I personally would consider installing a DPC under the floor, not a nice job! although not that expensive to do and easily within the limits of most DIYers.

    The reason I mentioned tree roots was because of the slugs.
  11. Airbricks should be installed every one and a half meters minimum.
  12. total amateur

    total amateur New Member

    OK - price agreed with a builder to repair the chimney stcka and install more airbricks. All DIY'able but I only tend to do it myself if I can't find a builder who gives me confidence. Pleased to say that today I did.

    Let's see if that solves the problem. If not, it might be midnight's suggestion of a dpc under the floor. Do you mean a chemcial injection one, or something else?

    Thanks to all for their help
  13. surfersue

    surfersue New Member

    Our bungalow has airbricks on two opposite sides. 5 one one side and 4 on other. 1 of the 4 is unusable due to venting from subfloor into small conservatory. We have blocked this off on advice of building regs helpline. We have had an aibrick added to one end of gable end nearest the side of house where airbrick into conservatoty is. We have been advised that this will aid ventilation of subfloor and not create any issues by the person we spoke to. Does this sound right
    What is bco..and will this be who we spoke to. Do they come out to property if asked to.?

    As far as we are aware our wooden floor is suspended on staggered brickwork above a concrete base. The airbricks enter the void below the dpc. We are told that as its a 1990s build with no visible issues that the above would be ok.
    Last edited: May 15, 2017
  14. Greentram

    Greentram New Member

    Plastic louvre airbricks have a much larger free area than clay ones: 215x140 - Stadium 12500mm2, clay 2900mm2
    surfersue likes this.
  15. surfersue

    surfersue New Member

    I should explain too that the gable end has no other airbricks and there are none to the opposite end. The conservatory is on wall opposite the side with 5 airbricks.

Share This Page