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insulate suspended floor above cellar

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This topic contains 1 reply, has 1 voice, and was last updated by  Roger Harrison 4 years, 9 months ago.

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    Roger Harrison

    Hi, I’ve read through the postings and tried to determine as much as I can regarding the following issue. I’m not sure where to go with this, and some of the postings seemed to be a bit contradictory. So here goes:
    I’ve moved to a 1890’s, brick-built, end-terraced property, no cavity wall, and with a large cellar. i’m starting to do what retrofit I can where possible, but over the next few years as a it will take while plus ££
    I want to insulate the floor of the lounge which is above the cellar. The cellar has the gas combi boiler in it (which maybe evidence towards the end of the posting). My ideas so far are:
    (1) fill spaces between floor boards with decorators caulk
    (2) use expanding foam and/or mortar to fill gaps/defects in wall between the timber joists
    (2a) but what to do with the three airbricks? as I’ll be filling the joist-void with sheep’s wool – do I block/brick-in the airbricks? or, as part of the end of this posting, do I fit a telescopic-style bend to bring air from the air-brick down into the main room of the cellar (i.e. below the cellar ceiling)
    (3) bond three layers of 20mm Gutex, to create a 60mm board and overcome thermal bridging by boarding the internal wall between the joist-space and then extending to about 60mm below the bottom of the joist. Use expanding foam to then seal the board around the joists
    (5) wire a ceiling light with adequate flex, and with a batton to then later hold the light fixing (and for the wire to be then placed through a small hole in the Gutex ceiling board)
    (4) use 100mm of sheep’s wool as insulation between the joists, and butt up against the underfloor of the lounge, using battons to keep in place as necessary
    (5) create a cellar ceiling use the 60mm Gutex and screw this to the joists
    (6) fill the joint between the Gutex placed on the wall and then the ceiling using decorator’s caulk (or ?? tape), and use the Caulk to fill in around the light flex pulled through the board

    (7) What should I do with the existing air-bricks – would I normally block these off, now that the joists are filled with the sheepswool etc? or use a telescopic tube as I’ve mentioned, to bring the outside air, to then into the main part of the cellar itself?
    (8) given that in-time, I will be fitting MVHR to the main house, will the sheep’s wool be airtight enough? or do I need to fit some sort of membrane anyway, either prior to putting in the wool (i.e. directly underneath the suspended floor boards) or, prior to, or after fitting the Gutex boarding?

    But I also need to do something for air ventilation in the cellar. The cellar is moist/humid with moisture coming through the brick floor and walls (basically it stinks!). The cellar has the boiler in it too, which will remain there. It won’t be a proper room but used for occasional storage if at all.
    (9) will bringing air flow into the cellar from a telescopic air duct fitted to the existing three air-bricks be sufficient to create an airflow? I assume it wont because it currently stinks and is humid, so insulating the cellar ceiling will make that worse
    (10) will fitting one or two, vent-axia style bathroom extraction fans, with an automatic humidity-sensor on-off control be adequate?
    (11) or do I need more of a robust dual air intake/extractor exhaust style system
    (12) or shall I fit an expensive, heavy duty dehumidifier? (I’d love to get the cellar tanked but that’s way off budget and ability – plus the MVHR exchanger will probably go in the cellar in due-course reducing the likelihood of ever using the cellar as a proper room.

    This is my first posting on this type of issue, so I hope I’ve done the DIY community proud! Hopefully there is enough detail here so that I can try and get some straight talking advice, in terms of the steps to follow. I based the above on the posts that I’d read and which seemed to make sense.



    Roger Harrison

    sorry I forgot to say that, when I am fitting MVHR, that the cellar itself will be sealed from the ‘warm’ side of house, by fitting an airtight door, or floor hatch at the top of the cellar steps.

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