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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: How much underfloor ventilation is needed

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  1.  
    • CommentAuthordelprado
    • CommentTimeOct 27th 2016
     
    Is there a calculator for this? I have the original holes from my 1920s house, but I am not convinced it is enough.
    • CommentAuthorCWatters
    • CommentTimeOct 27th 2016
     
    Approved Doc C says the free area should be...

    "1500mm^2/m run of external wall or 500mm^2/m^2 of floor area whichever is the greater"

    Page 26 - 4.14b

    https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/431943/BR_PDF_AD_C_2013.pdf

    I think the NHBC recommend the vents are distributed on 2m centres.
    • CommentAuthordelprado
    • CommentTimeOct 27th 2016
     
    Yeah I saw this, but like every building reg I don't trust it at first sight and wondered if there was any wisdom here that means I should do something else?
    • CommentAuthorgyrogear
    • CommentTimeOct 27th 2016 edited
     
    (1) What are the joists made of ?
    (2) Where is the ventilation air coming from (and going to...).

    gg
    • CommentAuthordelprado
    • CommentTimeOct 28th 2016
     
    Joists are timber. Diagram shows ventilation pattern here:

    http://s10.postimg.org/kpgkttc6x/plan.jpg
  6.  
    Block them up and pump with EPS?
    • CommentAuthorSprocket
    • CommentTimeOct 28th 2016
     
    I'm sure I remember someone in here suggesting Leca (or something like that) for this purpose many years ago.
    Can anyone comment on pros and cons?
  8.  
    '' I have the original holes from my 1920s house, but I am not convinced it is enough.''

    Are you convinced it's *not* enough? (And if so, by what symptoms?)

    Since I note your subsequent post re u/floor insulation you are definitely right to question the amount and flow of ventilation air. I (and others - viz a lot of discussion in AECB) find that under-floor insulation applications don't always behave as one might expect them to.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 28th 2016
     
    Posted By: Sprocketsomeone in here suggesting Leca
    This one?
    Not so legible as a jpg - click fostertom and tell me yr email and I'll send you the pdf.
      285Ja-ufloor.JPG
    • CommentAuthorgyrogear
    • CommentTimeOct 28th 2016 edited
     
    I blocked mine up (interestingly, they are / were the exact size as stated in the (so-called...) "guidance").

    Could not understand why they were there: admitting cold air in winter so UFH was working overtime to warm the crawlspace ! and warm air in the summer, rusting up my plumbing and condensing on the (muck) floor !

    So insulated CS walls & house has been *much* warmer & THE CS MUCH dryer ever since !
    (Am now concreting the CS floor...)

    gg

    edited : it is the *CS* that is much dryer (not the house!) (the house has always been dry !) :shocked:
    • CommentAuthorEd Davies
    • CommentTimeOct 28th 2016
     
    gg, have you been monitoring the humidity in your crawlspace?
    • CommentAuthorgyrogear
    • CommentTimeOct 28th 2016
     
    Yes, Ed, although I am not sure how well, or what it all means !

    For past year or more, I have had a weather station (base) in the kitchen, with temp and RH, and a slave transmitter for temp and RH, down in the CS.
    I don't (yet) have a data logger, so my method is to take occasional photos, then copy these to my PC; I then file them by Month, and by Day. I have started grabbing them into an XL file, it is very laborious !

    My aim is to establish a one-year record.
    However, as I see it, the weak point is, I do not have the external RH of the day, against which to compare - for that, I have to visit the local weather station via internet. For example, today our local RH was 84%, and the CS is currently at 83%...

    =========
    Otherwise:

    Lowest CS RH observed = 74% (12 OCT 2016) (Lounge RH = 38% = a very dry & sunny autumn afternoon).

    Highest RH observed = 98% (after 10 days’ absence, no heating on) at 30th Dec. 2015 @ 6 p.m. (Lounge at 16°C and 62% RH, CS at 15°C and 98% RH) (we went on holiday and the house was not heated).

    Prior to blocking the vents, I have no idea what the CS RH was - it was certainly smelly, moist and very uninviting...
    ====================
    I have to confess that my main point of interest is the CS *temperature*, not the RH...
    (I don't live down there !)

    gg
    • CommentAuthorEd Davies
    • CommentTimeOct 29th 2016
     
    Posted By: gyrogearLowest CS RH observed = 74%
    That's not ideal but

    Highest RH observed = 98%
    that's truly scary if it lasts long.

    (I don't live down there !)
    Yet.

    Remembering my father's leg going through the floor of my ground floor bedroom when I was about 6 or 7 due to the joists rotting away after a water leak. The flowing water wasn't directly in contact with the joists (just flowing across the ground) but must have been pushing the RH way up.
    • CommentAuthorgyrogear
    • CommentTimeOct 29th 2016
     
    LOL !

    Actually, I have *concrete* joists !

    gg
    • CommentAuthorEd Davies
    • CommentTimeOct 29th 2016
     
    So, helpful advice to somebody with timber joists to say you blocked your vents up without mentioning that your joists are concrete. :devil:
    • CommentAuthorgyrogear
    • CommentTimeOct 29th 2016 edited
     
    yes, admittedly, My Bad

    Severe apologies for that...
    :shamed:

    However, that admittedly belated parameter does not prevent the OP from consdering blocking *HIS* - depends on how humid his conditions are...

    If the underfloor is an accessible crawlspace, it could be conditioned, by blocking the vents; encapsulating the floor; and insulating the periphery walls, to make a conditioned crawl...

    Air could then be drawn in from the heated volume, and expelled through one of the blocked vents -

    I found this on a blog: http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/70974/What-Is-the-Best-Way-to-Deal-with-Crawl-Space-Air

    "continuously operated mechanical exhaust ventilation at a rate equal to 1 cfm for each 50 square feet of crawl space floor area.”
    (The makeup air entering the crawl space is conditioned air from the house upstairs; since this conditioned air is drier than outdoor air, it doesn't lead to condensation problems.)

    Hope this helps some, and goes some way towards correcting my earlier concrete (non-abstract...) omission :sad:

    gg
    • CommentAuthordelprado
    • CommentTimeOct 30th 2016
     
    Thanks for your thoughts. I am wondering if there is any benefit of laying limecrete along the mud floor in the void
    • CommentAuthorgyrogear
    • CommentTimeOct 30th 2016
     
    Posted By: delpradoif there is any benefit of laying limecrete along the mud floor


    well, that is what I am currently engaged in !

    http://voices.yahoo.com/how-rid-moisture-crawl-space-6367824.html?cat=6

    QUOTE
    “For those that have concrete surface spaces, consider yourselves fortunate. These finished crawl spaces have sealed protection against unwanted water and create much appreciated surface area to stow away several items as storage".

    I suspect that even lime-stabilization would be better than nothing...

    gg
    •  
      CommentAuthordjh
    • CommentTimeOct 30th 2016
     
    Posted By: gyrogearhttp://voices.yahoo.com/how-rid-moisture-crawl-space-6367824.html?cat=6

    That redirects to a generic yahoo front page for me. So I don't have any information except what you posted.

    Neither concrete nor limecrete provide a barrier against damp, so unless there's a damp proof course somewhere I doubt it will reduce humidity much.
    • CommentAuthorgyrogear
    • CommentTimeOct 31st 2016 edited
     
    Hmmm.... apologies for the bad link, I ended up contramoggrifying it with a keyword search - here is a fresh link...

    http://itchyfish.com/how-to-get-rid-of-moisture-in-a-crawl-space/

    gg

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