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Loft Conversion Questions

Discussion in 'Floors, Stairs and Lofts' started by gill0s75, 15 Oct 2019.

  1. gill0s75


    15 Oct 2019
    Thanks Received:
    United Kingdom
    Hi all, just in the final phases of planning a loft conversion, I am not going to apply for building regs but will be building to the regs, the rationale being there is an extension at our house that wasn't signed off when built (long story) and therefore I will need to get indemnity insurance if I ever sell it any case.

    Im looking for general thoughts of my plans, is there any mistakes I've made, anything I've just missed, any help much appreciated.

    The total loft dimensions are 2.68m x 7.97m, the plan is to only convert one half of the loft (its all we need) the other half will remain as storage only. Height at mid point is 2.4m.

    Image 1 shows the layout of the loft with the half in Yellow planned to be the loft room and the white half left for storage. There are 4 purlins in total that are not ideally placed but actually don't stop the space being usable the lower purlins sit 500mm from the floor and the upper ones sit 1600mm from the floor. The usable space i.e full height space will be 2.4x2.3m.


    Image 2 shows the construction of the centre beam which spans across a supporting wall.


    The joists run from the centre joist which is very meaty (10x3) to the gable wall, there is no adjoining neighbour on this side, so no party wall. The current joists are only 6x1 so the plan is to place new joists in between them in the half Im converting, Image 3 attempts to show this. I plan on fixing a 8x2 C24 to the gable wall with M12 threaded rod resin bonded into the wall and then hanging 8x2 joists from this on long leg hangars on the other side these will hang from the central joist mentioned above (10x3) one. I'll double up around the stairwell.


    In terms of staircase I am able to place a straight staircase which will be 39.8 angle which I believe is compliant to the regs also my measurements say I'll have min 2.0m at all points on the stairs. Tread will be 250mm and Rise 208.6, width 620mm.

    With regards the insulation Im working on the belief I need to achieve 0.18w/m2 for the roof and 0.30w/m2 for the walls, the plan to tackle this in four-ways.

    1. Between the rafters, the current rafters are 60mm deep x 50mm wide. So the plan is to rip some 38x63mm CLS down to 38x50 and then attach to rafters to increase their depth to 98mm, this will allow me to have 50mm air-gap and then 40mm of celotex. I haven't worked out how to attach the CLS yes but was thinking to gorilla glue, screw and use some jointing plates at intervals???

    2. Over the rafters, the plan is to use 90mm celotex which I will then cover with 12.5mm plasterboard

    3. Gable Wall, the plan he is to use 100mm Insulated Plasterboard dot and dabbed on to the gable

    4. Dividing Wall, so my belief is this part of the loft will be classed as cold storage but needs the wall between the two to be fire rated, I planned on a stud wall lined both sides with 12.5mm plasterboard and insulated with 100mm mineral wool

    If I've got my calculations right the above will achieve a U Value of 0.167w/mK for the roof overall, 0.27w/mK for the gable wall.

    So long post and I've done my best to include a good overview any thoughts?
    Last edited: 16 Oct 2019
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