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Housing - Renovation: Venting a uninsulated wooden floor when all external walls are insulated ?

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  1.  
    • CommentAuthorjamesingram
    • CommentTimeAug 1st 2023 edited
     
    Hi,
    I know we've been over this one a few times.
    Tell me again why I can't block up the vents to a cold uninsulated suspended wooden floor when I've dropped EWI and cavity wall insulation down below dpc.
    I know I'm not suppose to due to condensation, but if I don't the ventilation will just undermine the rest of the insulation.
    It's nice a dry under there. If its made airtight , would it really be a major issue? :smile:
    •  
      CommentAuthordjh
    • CommentTimeAug 1st 2023
     
    Isn't the answer when we've discussed it before "fill the space underneath with EPS beads"?

    As long as there's a void, regs require ventilation, IIRC.
    • CommentAuthortony
    • CommentTimeAug 1st 2023
     
    It is your house…..
  4.  
    >>>>"Tell me again why I can't block up the vents"

    'Cold' will be conducted under the foundations and into the soil below the floor. The EWI can not block this, unless it extends many feet below the ground. The cold will draw moisture vapour down from the house to condense in the soil (this is good).

    If the condensation is not able to ventilate or drain away to somewhere safe, then the air under the floor will get cold and damp and rot the joists (this is bad).

    Vents in old houses are small and get blocked easily, they have no oversite and dry soil is exposed under the floor, so the moisture can quickly soak away and sometimes this is ok, sometimes not.

    So underfloor ventilation just gives some certainty that the moisture has a reliable route to escape, no guessing and easy to inspect.

    The cold bridge from the foundations/underfloor always seems (to me) a disadvantage of EWI, and the equivalent bridge from the roof space down through gable walls. IWI can block these, but can have cold bridges in other places. Maybe a combo would work?

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