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Loft Ceiling Joist Query

Discussion in 'Floors, Stairs and Lofts' started by nthused, 17 Mar 2009.

  1. nthused

    nthused

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    Hi all,

    New on here and finally got round to posting. Bear with me as this is going to be a long one.

    I’m going to create a secure loft area to store items that are currently in my spare bedroom to allow the spare bedroom to be used as a bedroom and not a store room. The loft is better suited to storing things than the bedroom.

    I’ve teetered on creating a new ‘habitable’ room but for many reasons, all discussed in detail on other posts in this forum, I’m not going to do this. I’ve a very good appreciation and respect of what the "approved documents" are advising, but my loft is strictly going to be “for storage” and as such there will not be any windows, electrical sockets, heating or rafter insulation. Just a 3.9 x 3.9m floored area, one light fitting, accessed by a timber loft ladder from 1st floor landing and possibly lined with plasterboard. The lack of a window, heating, insulation and electrical sockets will hopefully go some way to show any party concerned that this is definitely not an attempt at an “illegal” or “unauthorised” conversion.

    My questions surround the existing structure of the roof and what I can best do with it to assist the ceiling joists - and probably aimed at the SE’s who post on here.

    It’s a traditional cut, hipped, semi-detached roof, around 8m x 6m with 220x75 purlins bearing in the party wall to meet 220x50 hips with 100x40 joists and 75x50 rafters at 400 centres.

    I am planning to line from the ridge down to the top of the purlins and create a new stud wall in front of the party wall. This is purely for the purposes of keeping the area clean and free from ingress of anything with wings/legs and general dust and dirt. I’m not planning to insulate and will keep the “cold” roof throughout so, if anything, the lining will be dust/spider traps at best. The gap between the rafters will still be ventilated though, in case any moisture should get through and be tempted to condense in the wrong places.

    The question I’m leading up to is regarding the ceiling joists and what I can add, to best improve what is there already. I fully appreciate why new beams and joists are normally specified for conversions, on the chance that I might want to perform recitals of music on one of my many grand pianos, to my extended family visiting from across the pond! However, all I need to do is store some light to medium weight items and at the same time avoid popping the nails through the plaster out of the ceilings below.

    So here we go.
    My house is circa 1960 and does not have any continuous central spine wall. 1st floor (floor) joists run from the party wall towards the side of the house (it’s a semi). I suspect these joists are also bearing on the wall separating my lounge/entrance hall and dining room/kitchen, but have not confirmed this.

    Anyway, all of the 1st floor partition walls are constructed of a single skin of brick and do not appear to continue from any ground floor partitions, so these all appear to lie on beams supported from below and offset from below..

    Now in my loft, the joists run from back to front (approx 8 metere span) and are joined/overlapped on these partition walls. The wall tops look not to be officially bearing the joists but a combination of mortar, plasterboard and plaster has made the ceiling joists surprisingly rigid over their combined span. This is the same all round for the other 1st floor walls. In some places the joists are actually resting on the brick tops.

    The loft floor (ceiling joists) do not have any other structure apart from purlins all round to and between the hips and timber hangars down to every other ceiling joist from them. Considering that there is a completely clear space of 3.9 x 3.9m in the middle of the purlin area the joists are surprisingly rigid – which I put down to a combination of the joists firmly hanging from the purlins and them resting (unofficially) on the 1st floor partitions.

    I would like further to increase the rigidity of the ceiling joists and have a plan to do this. My ultimate questions are regarding cross battening, but first I need to advise what I’m going to do.

    I will use 50 x 50’s or 75 x 50’s to run at right angles to current joists. At each intersection on top of the original joists I will both screw and glue them to each other and will run the joists from party wall out to the rafter feet at the side of the house (using bolts and toothed timber connectors at the join). Once done, I will board out the internal floor area (just 3.9 x 3.9m) with either chipboard or better still, routed-out to T&G ply. I’ll screw and glue the floor to the joists and glue the T&G’s also. So effectively making a rigid deck.

    Here are the key questions.

    1. Would there be any great benefit or problems with chamfering and attaching the new cross battens to the rafter feet at the side of the house and then attaching the battens to the party wall? I guess this would only add to lateral restraint, which is a good thing and would help out the binders, but I might be wrong. It would definitely add to the rigidity and effectively create a second, overlaid set of ceiling joists and the outer wall/party wall would be at least be bearing some of the load and not just the existing joists.

    2. What would be the recommended method to attach individual timbers, end on, to the party wall (legally and avoiding a party wall act situation)? I won’t be removing any masonry and at most will be using some type of drilled in anchor. The party wall is full height in brick built right up to ridge height. Is this a risky idea?

    3. Would the cross battens and floor need to be the full span of the loft, wallplate to wallplate, to get any benefit of the “rigid deck” effect? I want to avoid a load of timber just resting on top of the middle of the ceiling joists and adding to the rest of the load being taken by them. If the new timber just runs from the party wall to the outside wall within the 4m purlin area, is this actually increasing the load on the span between front and rear walls to the purlins, where there will be no cross battens to spread things out a bit.

    4. Will I risk transferring too much weight, via the ceiling joists resting on top of the 1st floor partition walls down to the beams bearing them? I’ve no idea what dimensions or material these beams are (possibly joist sistered 1st floor joists) and so any further live load might prove a problem.

    5. Can I safely increase the hangars in number from the purlins to the existing joists without putting too much load on the purlins/hip beams?

    6. As I am not removing any existing roof structure, will all of the ideas given, on the basis of this strictly being a non-habited area, be legal and not in contravention of anything in Part A (for example)? I’m a responsible person and owe it to my family not to put them at any risk or render my house unmortgage-able or uninsurable. At the moment, I’m not going to have my loft converted, so if the above doesn’t look like a good plan, I’m going to leave well alone and find somewhere else to put my stuff!

    Thanks for your patience in reading. I invite anyone to pull the idea apart and comment :eek: . Hopefully I’ll learn something from the process.
     
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  3. noseall

    noseall

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  4. nthused

    nthused

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    cheers for that noseall,

    is that a good :eek: or a bad :eek: ?
     
  5. noseall

    noseall

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    There are few members on the forum who will have the time to read all of your post unfortunately.
    Some will be too drunk to stay interested for long enough. :p

    Fragment your post into smaller, more appealing questions and a response may be more forthcoming. ;)

    I am actually going to read it now.. :LOL:
     
  6. noseall

    noseall

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    I think i get the gist of it now.

    Cross battening will be sufficient for storage.

    Using glue and screws is good.

    It was normal practice in the '60's and early 70's, to build 1st floor masonry partition walls off timber sole plates, that seemed to 'float' and didn't necessarily have walls directly below.

    Fixing to the rafter ends aint gonna do much now. The building has settled and restraint will already be taken up by the existing joists.

    How do you intend getting timbers into the loft to span from plate to plate? Never mind, what you have said about cross battening makes sense, and is adequate for storage.

    Have you thought about joist/ceiling level insulation?
     
  7. nthused

    nthused

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    Cheers Noseall, it might read better after a couple of Jamesons! :confused:

    That's cleared a few things up. I think I will break the points up and post these seperately as suggested, thanks for taking the time to read through it though..

    The rafter ends in question are on the side of the house (hipped) which are just currently nailed to the wallplate. The current ceiling joists are running from back to front so the new battens will be between the side rafters and the party wall. My main idea was that it was OK the attach the battens to the rafters without upsetting them too much? The lateral restraint was just a bonus.

    Getting the timbers in I'll use 4.6m lengths and bolt these together mid span with toothed connectors. Worst case these will have to come through a tile removed from the roof but I think the combination of where the loft hatch is, the landing below and the height of the roof I should be OK.

    How would you suggest I attach the timbers to the compartment (party) wall?

    Insulation-wise I'll use mineral wool or similar at joist level and then lay an additional layer cross ways in the new bettens and on top of the other layer. Under the deck this wont quite reach recommended levels, unless I use a more specialist product. Outside of the deck I should get this up to 250-270mm.
     
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