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Can't figure out what shape of roof to use on extension.

  • 11-11-2008 6:30pm
    #1
    Registered Users Posts: 451 ✭✭


    Hi all,

    First see attached picture....

    roofoptionsit5.gif

    I'm planning on getting a first story extension on a L shaped cross-hipped roof house. My architect has stongly urged me to go for option A as its the cheapest, but I think it looks unusual and I'll loose an existing velux window.

    Option B will cost 25k extra, and will involve a flat roof (which I want to avoid from past experiences), but gives scope for a really big attic!

    Option C is something I just thought of recently...

    Questions...
    1) Is Option C possible, and how much will it cost relative to option A?
    2) Can anyone explain why B is 25K over option A? What exactly plays into it?
    3) Is there any other options available.
    4) Any advice greatly appreciated!!

    Thanks,
    LK.


Comments

  • Registered Users Posts: 2,292 ✭✭✭RKQ


    1) Is Option C possible, and how much will it cost relative to option A?
    Yes - care should be taken to carefully detail the valley between the two roofs.

    2) Can anyone explain why B is 25K over option A? What exactly plays into it?
    It seems to be some sort of (Dutch) Mansard roof - A complete new storey - hence the expense. Seems an overkill to fully remove the roof off the house just to roof a small extension.
    "A" is not practical or possible.

    3) Is there any other options available.
    Possibly, but avoid "B" if possible.("A" is not viable.)

    4) Any advice greatly appreciated!!
    "C" might be the cheapest. Do you have to build the extension in the area shown? There could be better alternatives. Removing the existing roof is a waste of money unless the attic is needed to provide habital rooms.


  • Registered Users Posts: 451 ✭✭LeperKing


    RKQ wrote: »
    Do you have to build the extension in the area shown? There could be better alternatives.

    Yep, that is the only viable place for the extension, it allows for a larger bedroom and main bathroom.

    Thanks for the help.

    LK.


  • Subscribers Posts: 40,566 ✭✭✭✭sydthebeat


    a good quality flat roof constructed properly....

    i realise youve had bad experience with them before, but with the advent of more modern design becoming main stream, flat roof construction has come on leaps and bounds...


  • Registered Users Posts: 451 ✭✭LeperKing


    RKQ wrote: »
    "A" is not practical or possible.

    There was no overhead drawings in his plans, but thats what I think he has planned. He showed me a previous job done, as such...
    pastroofbe3.gif, , which doesn't exactly match, perhaps its a mistake in his drawings.

    Thanks,
    LK


  • Registered Users Posts: 2,683 ✭✭✭Carpenter


    Option c is good But have you any trees beside the house will every leaf that falls stay in there and cause you many probs


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  • Registered Users Posts: 4,076 ✭✭✭gman2k


    If you go for 'C' make the valley as wide as possible, so as you can walk up it and sweep out debris.
    The other two options are impractical.


  • Moderators, Home & Garden Moderators, Science, Health & Environment Moderators Posts: 17,565 Mod ✭✭✭✭DOCARCH


    C is your best bet.


  • Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    B is best - by a mile .

    Simple pleasing shape - which if you frame in structural steel below leaves you with all that clear internal space - which is a major plus . More internal space - the whole point of building in the first place

    Don't be put off flat roofs - modern methods are excellent

    Forget C - concealed valley gutters are infinately more prone to leaks than flat roofs are

    And A - is just odd


    .


  • Registered Users Posts: 2,292 ✭✭✭RKQ


    C isn't ideal but its the best of a bad lot. The size, width, detailing and access to the gutter is critical. It must be easy to clean regularly.

    Option B is a mansart roof. It is an option but it is very expensive to remove an existing roof, install steel structure etc. It has a flat roof element on your plan.The interior of the existing house will be open to the elements during construction - so allow a sum to reslab the ceilings etc.

    It seems excessive for an extension but if budget allows then its a choice. Be careful as its difficult to draw the line once you embark on this path - do you replace electrics and plumbing etc. Would it be cheaper to demolish and rebuild? You will need to rent a property during construction.

    A flat roof over an extension of this size is a viable option. Use a modern material.


  • Moderators, Home & Garden Moderators, Science, Health & Environment Moderators Posts: 17,565 Mod ✭✭✭✭DOCARCH


    RKQ wrote: »
    C Option B is a mansart roof. It is an option but it is very expensive to remove an existing roof, install steel structure etc. It has a flat roof element on your plan.The interior of the existing house will be open to the elements during construction - so allow a sum to reslab the ceilings etc.

    It seems excessive for an extension but if budget allows then its a choice. Be careful as its difficult to draw the line once you embark on this path - do you replace electrics and plumbing etc. Would it be cheaper to demolish and rebuild? You will need to rent a property during construction.

    Agree totally - B is a 'nice' option but totally OTT as to the extent of work required in relation to building a relatively small extension. Once a structural engineer gets his hands on it you might be talking about a complete new roof structure. I'd be more worried about the flat section of roof on top of B than a valley bewteen the existing and new roof in C.


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  • Registered Users Posts: 14,537 ✭✭✭✭Poor Uncle Tom


    If you draw a horizontal line half way between the front and back of the house as shown on your first image. Then mirror the return of the hip as shown on the front section, to the rear leaving a small area of flat roof between both returns to act as a wide flat valley. The area of flat would be relatively small and should be inexpensive to finish in a single skin Trocol or even metal finish. imo best option.


  • Registered Users Posts: 28,650 ✭✭✭✭Quazzie


    Would the additional attic space that option B gives i.e potentially an extra 2/3 bedrooms not make it an extremely viable option?


  • Registered Users Posts: 38,833 ✭✭✭✭Mellor


    LeperKing wrote: »
    There was no overhead drawings in his plans, but thats what I think he has planned. He showed me a previous job done, as such...
    pastroofbe3.gif, , which doesn't exactly match, perhaps its a mistake in his drawings.

    Thanks,
    LK
    This one is much more viable than the original option A


  • Registered Users Posts: 451 ✭✭LeperKing


    Guys, thanks for all the responses, I've doublechecked the layouts, and my previous drawings were slightly incorrect. The amount of space the extension is gaining is smaller.....

    correctroofoptionsjv9.gif

    The extra space from B) is very appealing, but I just don't have the need for it at the moment, and I'm not sure I would get the return in house value for it.

    I take everyones point about flat roofs have improved, but I still consider it as a less robust solution than regular pitch roofs. That's just a layman's opinion. :o

    I hadn't thought of gutters been blocked by option C, I presume if its wide enough it should be ok, does it need to have an incline to be pratical?
    1. Which roof would be cheaper C1 or C3?
    2. I like C2 but it looks expensive, is this what you were suggesting Uncle Tom
    Thanks folks,
    LK.


  • Registered Users Posts: 324 ✭✭Slates


    Mellor wrote: »
    This one is much more viable than the original option A
    You would have to be careful with this option due to the low roof pitch it will provide, what product are you putting on the roof ?


  • Registered Users Posts: 451 ✭✭LeperKing


    Slates wrote: »
    You would have to be careful with this option due to the low roof pitch it will provide, what product are you putting on the roof ?

    Tiles, which had me thinking low pitch + wind = problems.

    LK.


  • Registered Users Posts: 2,292 ✭✭✭RKQ


    C1 and C3 will work (IMO Extension is too small to justify removing the whole roof)
    Both C1 and C3 will work and cost a similar amount but C1 is least likely to have problems as IMO it will have 1 hidden gutter and the roof shape is more pleasing on the eye.

    Put a reasonable fall on the gutter, make it 350 to 600mm wide, so its comfortable and safe to walk along, when you brush out fallen leaves etc.


  • Registered Users Posts: 38,833 ✭✭✭✭Mellor


    Of course, I wasn't suggesting it as a good option. its just alot better than the original, which wasn't great at all.


  • Registered Users Posts: 14,537 ✭✭✭✭Poor Uncle Tom


    Yes LK, C2 is what I was suggesting, except with the central gutter emptying onto the the right of the sketch instead of the bottom. It would have worked out well with the first set of sketchs, not so with the second set as it would be very costly, and the central gutter would be about a third up the roof height. RKQ has nailed it above, imo.


  • Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    The new pics could be included in an IQ test: what comes next:D

    For me B is the way to go, no question included in this is the key opportunity to upgrade the insulation/airtightness etc of existing roof and make it all ultra snug

    Is, in B, making the roof come to a point an option?


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  • Registered Users Posts: 451 ✭✭LeperKing


    Carlow52 wrote: »
    Is, in B, making the roof come to a point an option?

    PP would be impossible as it would stick out.

    LK


  • Registered Users Posts: 1,477 ✭✭✭topcatcbr


    sydthebeat wrote: »
    a good quality flat roof constructed properly....

    i realise youve had bad experience with them before, but with the advent of more modern design becoming main stream, flat roof construction has come on leaps and bounds...

    I have to agree with syd. Some situations just call for a flat roof. I think this is one. They are not perfect by any means but neither is an internal gutter. they cause the same amount of problems. The main difference is that a flat roof is far easier to fix than an internal gutter. and far easier to work on. Modern materials will last much longer than traditional roofing pitch or torch/built up felt.


  • Registered Users Posts: 14,537 ✭✭✭✭Poor Uncle Tom


    TC, there shouldn't be any 'fixing' needed for internal gutters. These can be made in 'one run alu' up to 600mm bed widths. All this needs is a sweep out once a year the same as the valleys. I usually get the chimney sweep to sweep out the valleys and gutters on my house just before christmas and give him an extra €20, he has never complained.


  • Subscribers Posts: 40,566 ✭✭✭✭sydthebeat


    TC, there shouldn't be any 'fixing' needed for internal gutters. These can be made in 'one run alu' up to 600mm bed widths. All this needs is a sweep out once a year the same as the valleys. I usually get the chimney sweep to sweep out the valleys and gutters on my house just before christmas and give him an extra €20, he has never complained.

    In my experience there is a danger of slipping slates puncturing the metal...
    I would certainly agree that an internal gutter should be made as wide as possible for cleaning, also a tapered sarking board can be used to create a fall in it...


  • Registered Users Posts: 1,477 ✭✭✭topcatcbr


    TC, there shouldn't be any 'fixing' needed for internal gutters. These can be made in 'one run alu' up to 600mm bed widths. All this needs is a sweep out once a year the same as the valleys. I usually get the chimney sweep to sweep out the valleys and gutters on my house just before christmas and give him an extra €20, he has never complained.

    Thats a good point for a continuous alu gutter. I was only considering a built up lead gutter which would be more common. I never detail an internal gutter in anything i draw where at all possible. when i do it is genneraly less than 1.5m. I dont like them at all.


  • Registered Users Posts: 14,537 ✭✭✭✭Poor Uncle Tom


    Agreed they do equal maintanance.


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