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Suspended floor requirements

Discussion in 'Building Regulations and Planning Permission' started by James Nightingale, 15 Sep 2021.

  1. James Nightingale

    James Nightingale

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    Hi all,

    I'm looking at DIYing a suspended floor as part of a single internal garage conversion.

    Approximate size is 2.1mx4m so its not a huge area. Just going to be using it for a home office.

    I know I need to install a suspended floor to bring it level with the rest of the house but I'm struggling to find insulation requirements and required thickness of the wood. Obviously with the price of wood i'm trying to keep it as close to spec as possible, don't want any over engineering in it.

    I'm based in Warwickshire in case it varies between counties?

    Thanks
     
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  3. oldbutnotdead

    oldbutnotdead

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    You need 100mm of Kingspan or similar in the floor. How much drop have you got from kitchen to garage? What are you doing with the rest of the garage? Have you checked (if it's a newish build) that you are a freeholder and that there isn't any restriction on the deeds about converting the garage?
     
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  4. James Nightingale

    James Nightingale

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    Hi,

    Thanks, its definitely freehold as we've just purchased it. I'm converting it into an office.

    250mm drop from utility floor down to floor of garage.

    So looking bricking up and putting a window in where the up and over door is. Then boarding up the ceiling and putting insulation on the top of it. Will the baton and board the walls with some insulation though as slim as I can get away with as I need to maximise the space available. The garage has two internal walls (one is original exterior, other is boarded wall to utility. The other two walls are single skin.
     
    Last edited: 15 Sep 2021
  5. oldbutnotdead

    oldbutnotdead

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    You can purchase leaseholds...but if the solicitor said it's freehold that'll do.
    Is it a newish (1990 onwards) build on an estate- if it is you need to check that you actually have permitted development rights.
    Usually a garage conversion is notifiable to Building Control. There's a link here for things you need to consider https://www.planningportal.co.uk/info/200130/common_projects/25/garage_conversion/2
    You still didn't let on how much drop you have from kitchen to garage floor.
    Walls- on halfbrick external walls you'll need at least 80mm PIR, possibly more.
    Ceiling- if there's a habitable room upstairs then fine, otherwise you'll need 270mm of rockwool or about 140mm of PIR.
    Means of escape- if the kitchen doesn't have an external door in it the garage window needs to be an escape window.
     
  6. James Nightingale

    James Nightingale

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    Sorry, meant to say we saw in the docs from solicitor it was freehold. We wouldn't have bought it had it been leasehold.

    Its 1960's I believe. It said 1980's on the info from the vendor but chap over the road said it was definitely 60's as he was there when they put them up.

    Realised I didn't add that bit in so edited post, but probably after you'd already read my response. Its 250mm floor drop between garage and utility.

    Walls - is halfbrick same as single skin? So 80mm on the single skins but what about the existing wall (originally the exterior wall of house). I'm assuming nothing needed for the wall between utility and garage as its just a boarded wall?

    Ceiling - no, won't be habitable, its a single story but does have a pitched roof.

    Escape - yeah remember reading up on that somewhere. The utility leads to the kitchen which leads to the conservatory where there are patio doors so not sure if that constitutes a fair escape route? Either way the window I plan on putting in will span about 1.8 metres width and be quite tall so should satisfy the escape requirements. There will be a door to the hallway as well which will be right by the front door?

    I've added a floor plan as it may help make it easier to answer.

    Thanks
     

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  7. oldbutnotdead

    oldbutnotdead

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    250mm drop, 2100 span. Not quite enough room for suspended timber, you'd need 150 x 50 joists & that doesn't leave 150mm ventilation gap. If you build a dwarf wall up the middle you could use 100 x 50 joists so you'd have 150 clearance, you'll need airbricks in the window wall & through to the utility (if that's suspended timber) or to the outside wall.
    Might be better putting a floating floor in (130mm sand, dpm, PIR, t & g chipboard)
    Yeah half brick is single skin, 100mm would be better. No need to insulate between garage and house wall, you may get damp in that wall unless cavity trays were installed as part of the garage build.
    Roof-270mm rockwool in the loft space then.
    Escape- if there's a door to the hall then that's your primary route out
     
  8. Dereekoo

    Dereekoo

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    47 x 97 C24 at 400 centres ok for 2.1m span?
     
    Last edited: 15 Sep 2021
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  10. ^woody^

    ^woody^

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    Use c16 4x2's and drop a piece mid span to act as a prop if at 400 centres, or at 1/3 span if 600 centres. It would be important to also fit noggins to stiffen the whole lot up.

    At 250 depth you could use quilt insulation, or any of the other types. Full fill would be essential.

    But complete infill with polystyrene, under and between with no gaps will also act to make the whole floor solid with no movement, so no need for noggins.
     
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  11. James Nightingale

    James Nightingale

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    Struggling to find guidance on a floating floor, when you say sand, you just mean loose building sand? Not a concrete mix? Dwarf wall wouldn't be an issue. I've got building regs officer coming out tomorrow for an initial consultation so I can see if they have any specific requirements for my area.

    I can go 100mm if i'm not insulating the other wall then. Would you baton the garage/house wall and board it or is there another way that'd take less room? I imagine with my luck they won't have cavity trays, anything I can retrofit to minimise damp issues?

    Appreciate your help!

    I'm not sure if you're asking me or telling me lol

    From the other posts it looks like I don't have a big enough gap? I'm not too familiar with the rules versus floating and suspended floors. Is your suggestion that this would class as a floating floor and thus not require the same gap that a suspended floor may need?
     
  12. Dereekoo

    Dereekoo

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    Guess I'm really flagging up that Oldbutnot dead ref to 50 x 150 requirement not strictly true as 47 x 97 would suffice
     
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  13. James Nightingale

    James Nightingale

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    Thanks, as you can probably tell i've not got a clue but trying to learn as I go. I may be wrongly assuming that suspended is going to be easier than a floating floor as I can work with joist hangers and lengths of wood but getting a good level on a screed will take more time. Might be cheaper with the price of wood though!
     
  14. IT Minion

    IT Minion

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    A floating floor is where you have the flooring bits sitting on top of a later of insulation. So with your 250mm drop you'd put in something like 200mm of polystyrene and then build the rest of your floor on top of it (chipboard and whatever surface finish you're going with).
    Simple, cheap and meets building regs
     
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  15. James Nightingale

    James Nightingale

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    Thank you, i'm trying to find some youtube videos on it to get a better feel for it but whenever I search for floating floor it just comes back with a load of people laying laminate, whereas what I need is the bit before that! Any ideas what I should be searching for?
     
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