Subfloor joist. Does it need replacement?

Discussion in 'Carpenters' Talk' started by Learnedd, Dec 16, 2019.

  1. Learnedd

    Learnedd New Member

    Hello,

    I have a 1920s semi detached property with a wooden timber subfloor.i decided to go have a nosey to check if all the air vents were open and not blocked and timber joists were not rotten or have any play in them. I have had this property a couple of years now.
    The crawl space is about 2 to 3 foot deep with lots of rubble and soil which is damp. I noticed what appears to be a vent pipe and i believe this maybe asbestos? It is directly under the living room gas fireplace in the crawl space below. There is also one below the dining room. The previous owners did have what is called a back burner box which was removed from the fireplace along with the copper tank which was in the bedroom. We now have a combi boiler with new radiators.

    My question what is the purpose of the pipe under subfloor?
    Does it go up all the way in the chimney and out?
    Do i need to have it removed or should i cover it up and leave alone?
    It goes into the brickwork so would not be straightforward to remove? Just thinking because its asbestos and health implications.
    There is some play in one of the joist however it goes right in to the brickwork next to kitchen wall which has no crawlspace to get to.
    Should i spray this with anything to stop any rot? I did notice that the joist ends had been stained with something, perhaps when they were first put there when house was built?

    Your kind advice would be appreciated. I will upload a few pictures of the crawl space and the pipe in question.

    Cheers

    Ian
     

    Attached Files:

  2. jackelliott07

    jackelliott07 Active Member

    Even if it is asbestos, asbestos is only dangerous if disturbed - if under your subfloor, not likely going to cause any issues. I'd just leave it.

    Joist looks fine to me - somebody else may say otherwise
     
  3. Learnedd

    Learnedd New Member

    Hello,

    Thank you for your reply i will leave the pipe well alone.
     
  4. KIAB

    KIAB Super Member

    Wouldn't worry about asbestos pipe,leave it alone.

    But, a suspended floor needs good through ventilation,so make sure air bricks are clear of crud.
     
  5. Learnedd

    Learnedd New Member

    Thanks Kiab,

    I will leave the pipe alone.

    There is a big draft under the subfloor so plenty of cross ventilation. I noticed a gap around the skirting where it meets the floorboards all the way around from looking underneath. Anything you can recommend for filling this from below as i do not want to take up my laminate above or take off skirting boards.There is a draft coming up from below.

    Thanks
     
  6. jackelliott07

    jackelliott07 Active Member

    How big is the gap?
     
  7. Learnedd

    Learnedd New Member

    The gap is uneven but i would say the majority is 5cm gap.
     
  8. jackelliott07

    jackelliott07 Active Member

    5cm? are you sure? that is a huge gap

    Some pictures might help set the scene
     
  9. Mr Rusty

    Mr Rusty Screwfix Select

    difficult to see but is that a brown dust in pic #3? on the joist and brick. if it is could be a little dry rot.
     
  10. Learnedd

    Learnedd New Member

    Hi Jack,

    Some of the floorboards go right up to the brick work and others have a big gap and stop short of the brick work. I could possibly take a pic later
     
  11. Learnedd

    Learnedd New Member

    Hi Mr Rusty,

    You are correct there is brown dust on the brick and joist. There is a little play in that joist when i try to move it.

    Do i need to spray the joist end with something for dry rot up to where it goes into the brick as i cant see the end of the joist?
     
  12. Mr Rusty

    Mr Rusty Screwfix Select

    If it is dry rot under the floor, I would get people in to treat the whole lot.The spores go everywhere and will grow wherever conditions are correct. You can DIY spray but in a confined space you need to be very careful.
     
  13. Learnedd

    Learnedd New Member

    Hi Jack,

    Managed to take a few pics of the gaps between floorboard and wall meets however was not clear so i filled with a bit of foam to give you an idea of the gap size. Whilst i was down in the crawl space i notice my 9x6 plastic air vents are at the same height as my joist and not underneath them. Do the vents need to be under the joist to provide maximum ventilation? I do get air blowing under the floor despite most of it hitting against joist. Pics attached
     

    Attached Files:

  14. Learnedd

    Learnedd New Member

    Any ideas of cross ventilation being compromised where the air vent is the same height as the joist? It appears most of all the air coming through air vent hits the joist.
     
  15. Learnedd

    Learnedd New Member

    Hello Kiab,

    Happy new year an all to you.
    In my subfloor space which is rubble and soil, is there any way i could get better ventilation i.e if i cover the ground with a dpm sheet to stop moisture rising therefore ventilation would work better? The floor is always damp and this gives off moisture. I have five 9x3 air vents all clear but 2 are not entirely under joist height and there is condensation as the bricks are cold and wet.

    Any ideas in what i can do to help either airflow into the corners or like i said lay dpm sheet just over the ground to stop moisture rising?

    Cheers Ian
     
  16. Joe the Plumber

    Joe the Plumber Screwfix Select

    Where is the moisture coming from?

    Is it ground water, or have you got a leaking mains pipe or soil pipe somewhere?

    There's no point in just trying to cover up the dampness (it will find its way to the edges of
    anything you lay on top of it). You've got to find out where it's coming from and then stop
    the source.
     
  17. Learnedd

    Learnedd New Member

    Hello Joe,

    The moisture is coming from ground water as there are no leaks anywhere. So fitting a dpm sheet is a waste of time and would not help as you said.The soil is very damp, no pooling or anything and condensation on the brickworki believe through the moisture rising hitting cold surface.
     
  18. Mr Rusty

    Mr Rusty Screwfix Select

    If the ground is damp I am not sure that not installing a dpm is a good idea - any air movement will tend to take up water from the ground. NHBC standards say:-

    "Provision should be made to prevent ground moisture affecting timber floor construction.

    This can be achieved by either:

    • 50mm concrete or 50mm fine aggregate on a polyethylene membrane laid on 50mm sand blinding, or
    • 100mm concrete."
    I can't see that it will do any harm installing a dpm and may well do some good.
     
  19. Learnedd

    Learnedd New Member

    Hello Mr Rusty,

    Thank you for your response and the information given from NHBC.

    Certainly there are a lot of different opinions on whether to lay a dpm sheet over the bare earth or not.

    One idea would be to lay it down and then keep an eye on it over a few months and check what difference it makes?

    I am thinking to use one of those black plastic heavy guage sheet.

    Any ideas of how to get the airfloor moving under the joist rather than mid joist height as some are now?

    I was looking at telescopic sleeve but they only come as single brick and all mine are double brick air vents?
     
  20. hazymat

    hazymat New Member

    I think this is a fine idea, the only thing I'd add is try to measure the effects of what you test:
    - get a cheap (£10) infrared thermometer and point it at the soil, the joist middles and ends, and also take the indoor temperature. Record as often as you can. Then try and look at what you see, if you are any good with spreadsheets...
    - get some kind of humidity sensor (I know you can get digital ones super cheap online) and monitor for a week before laying a DPM

    Temperature and humidity are the primary things you are trying to control here, so first you need to measure them to know whether what you are doing is working
     

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