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Thread: One for the builders and architects

  1. #1

    One for the builders and architects

    I have an question that I would like to clear up. My parents house has a loft that the wind can pass through because the eves are open. The house was built that way.

    My question is two fold:

    1, What is the reason for what I think is called a floating roof?
    2, Would it cause any problems if the loft was sealed?

    What I'd like to do is, insulate the pitch of the roof, board it out, sort out the normal loft insulation and board out the loft. I would want to allow for some ventilation or the roof space but not as much as the is now.

    Would that be a problem and why?

    Thanks in advance for any and all advice.


  2. #2
    if you did seal the loft you could also include a open eves ventilator which would alow air flow and ventilation via the open eves, here is a link regarding it.
    P.s i am not a builder I have been studying civil engineering and construction project managment and had an assignment which required reserch on your above question.

  3. #3
    There are quite a few thing to watch out for if you seal a loft you could cause condensation on the underside of the felt this will in turn rot the timbers and cause damp .
    I know of quite a few people who have "stopped Draughts" and caused Damp, Cavity wall insulation can cause similer problems.
    Before doing any work find someone to advise who Has experiance and not going to gain from doing the work.
    Very often the timbers in the bedroom ceilings are not strong enough to take the loads imposed so you need to be carefull,nailing boards down willknock ceilings down!!

  4. #4
    Its a bit difficult to be very specific here without actually seeing the roof, and I have some problem in visualising the layout, but....

    Whether you can actually board out the loft depends on several things - the structure (size of roof ties, etc) and the access. As you say you would then need to insulate the roof pitch - and also ventilate this for preference and finish it with plasterboard etc. Its also more space to heat. Its much easier to insulate the ceiling and board the top of the ties - if they are big enough. Depends I suppose what you intend using the space for - storage or occassional use really makes it a bit of a waste of time going the whole hog. I boarded my loft after insulating the ceiling and use it for storage and also my reloading and overspill trophy space.

    As Mo said the usual way is to provide some ventilation to eaves so that the roof space is not 'dead air' which is an invitation to dry rot but if you are accessing the space regularly you could probably manage with much less ventilation. Having the wind whistling through is unnecessary.

  5. #5
    You don't say if the building is listed .

    If not you could change the eaves detail by putting a fascia and soffit in plastic upvc with a continous soffit vent if it it a traditional English construction IE tiles onto batons over felt ,with no sarking .

    There are various ways to do a eaves closure fascia and soffit is the easiest .

    You can use kingspan insulation pushed into the rafter space leaving a space on the roof side to vent on the internal side of the roof you will require a vapour barrier of visqueen then gyproc to finish

    In scotland we have to come to the standards of the local authority area which all vary

    At the bottom of this guide is roughly what I'm talking about !if you require further information PM me your details I'll call you

  6. #6
    A lot is determined by the existing roof/ rafter depths , It is rule of thumb to leave a 40mm void below the roofing underfelt and any insulalion placed , sometimes this means fixing insulation board (150mm kingspan or equivelant ) to the underside of the rafters and then screw and fix the plasterboard through the insulation and onto the rafter so in theory creating a void for air to travel through .
    The open eves can be closed of but be sure to add vents at reasonable centers to allow for air flow .
    The upstairs cieling joists are unlikely to be man enough to take excessive use , once again this would be determined by depth , length and location of the load bearing walls below .

    In my experience it is neccessary to have structual calculation worked out by an architech and relevant drawings put in for planning permission as using a roof space for anything more than storage has the potential of being a death trap for the user.

  7. #7
    I have the same kind of roof described in the OP, I thought about boxing it in but leaving a gap all round so the ventilation can go up and over. My main problem is the roof trusses, they are the queenspan type which considerably limit the conversion space, I've sat up there for hours trying to come up with a way of repositioning the supports.... also the joists are only 4x2 so they would need to have 6x2's screwed in along side.
    "It's halfway down the hill, directly below that tree next to a rock that looks like a bell-end"

    Good deals with ~ deako ~ sakowsm ~ dryan ~ 2734neil ~ mo ~ riggers ~ mmbeatle ~ seanct ~ an du ru fox

  8. #8
    Geordie_3 You have a PM


  9. #9
    The house is an ex Telford Development Corporation one built in the early eighties. They only use the loft for storage. As it stands at the moment there is minimal insulation under boarding that my dad put down about 20 years ago. I want to try and help them reduce their heating bills.

    I was thinking of taking up the boards and insulation, replacing the insulation with that space blanket stuff, re-boarding the floor.

    I was wondering if it was possible to reduce the drafts that get under the eves.

  10. #10
    Box in your eves leaving vents in ever 1meter or so then board out the roof space as you described leaving 50mm betwween the insulation and your roofing felt then you will need to remove some ridge tiles and fit the type of ridge tile with built in vents this will allow air flow through your roof from top to bottom preventing condensation building up on the inside of your plasterboard ceiling.If your gonna use it as a room you will need building reg's as well !
    Last edited by 375 mag; 18-02-2012 at 20:18.

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