how to install floor joists in loft conversion?

WANT TO INSTALL NEW FLOOR IN LOFT CONVERSION TO MAKE FLOOR STRONGER

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  • 1 decade ago
    Favorite Answer

    We have just finished doing ours. What we had to do is put new joists along side the old ones. You will be amazed at how much the old ones will have sunk in the middle. Don't consider using them for anything other than continuing to hold the ceiling up. Don't nail into them.

    Our spans were in the region of 10 to 12 ft and we had to use 200mm x 50 timber. Try and buy the lot in one hit and have them "Justified", They will all arrive at the same size which makes everything from then, on very easy.

    You will need two joists where a wall is to sit on it and always think about what you are going to nail your new floor to.

    You will need two together either side of the stair opening as well.

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  • ?
    Lv 4
    3 years ago

    Loft Conversion Floor Joists

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  • 1 decade ago

    If the loft is to be converted into a habitable space, the first thing you must do is get Building Regulations consent [in the UK]. This will require a full specification of the works, which means you will need to engage a construction professional.

    If the work is just to enable the space to be used for storage, there are a couple of things to consider:

    1) If the existing roof consists of pretrussed rafters [rafters framed up with metal plate connectors using small sections - typically 100 x 50mm], you will probably not be able to do anything unless you can establish that you have an intermediate load-bearing wall since these rafters are designed to span the full depth of the house - typically 8m. Additionally, no members of these roofs should be cut or removed. However, small areas of these roofs can be boarded for the purposes of taking lightweight storage.

    2) A roof which is carpentry constructed of individual members is more amenable adaptation since it will probably have an intermediate load-bearing wall which can be used to support additional joisting. Again, none of the existing members should be cut or removed - without getting advice from a structural engineer. Again for lightweight storage, loft boarding on the existing ceilings joists would probably be adequate.

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  • 1 decade ago

    You have to determine what you have now (possibly the bottom chord of a truss). IF you have a trussed roof, you can not disturb any member of the truss.

    If you have a standard ridge and rafter system, then it is possible to install flooring joists (perhaps in-between the existing ceiling joists), determine the bearing points present for the span or spans (very possible there is a load bearing wall somewhere in the structure you can make use of). Just remember the end of the joists MUST be supported by a bearing wall. Once you have determined your spans, do the math to figure the lumber dimension. Keep in mind the roof sheathing air circulation requirements, when installing the joist and the new insulation in the rafter voids.

    Hope this helps . .. . .

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  • Saul
    Lv 4
    4 years ago

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    You would need to infill the joists with floor joists. The joists you are looking at are ceiling joists - designed to hold up the ceiling. 4x2 is small even by ceiling joist standards so i'd be carefull about boarding out and storing stuff on it. Floor joists will be minimum of 8x2 inches. You will need planning permission and building regs to do that.

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  • 1 decade ago

    the new joist will all most certainly go the same way as the ceiling joist ..that is from wall plate to a load bearing wall...to carry a floor always go at least ..half the span plus one ..so a 10foot span will need at least 6 by2 joist at no more than 400mm centres ..a 12 foot span 7 by2 and so on ..use green chipboard flooring ..glued at edges and the boards screwed down ..you will need a noggin mid span on joist ..you will wind up moving cables and pipes to get joist in

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  • Bilbo
    Lv 7
    1 decade ago

    First off get a structural engineer to look at this. (You are probably looking at ceiling joists at the moment). He will advise on size and grade oftimber and location of fixings since you need to be careful not to overload other parts of the structure, and he/she will do the necessary calculations for approval as necessary.

    This is not a diy job - but neither is it particularly difficult if you understand exactly what you are doing. Get an engineer invoved for you own and everybody else's safety, not to say peace of mind.

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  • GeeCee
    Lv 7
    1 decade ago

    You have to put in new ones to "float" the new floor above the existing ceiling joists, check your head room .

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    5 years ago

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    5 years ago

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