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Retro Fitting Dormer Window

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  • 10-08-2020 12:28pm
    #1
    pajoguy
    Registered Users Posts: 802 ✭✭✭


    Hi just looking for some guidance here not any exact designs.
    I have 2 velux windows that are 750mm wide and there is 900mm gap between them.
    I want replace these with 1 single dormer window to span the full width of 2400mm. I am aware that I will need to double if not treble the rafters at each side but would these rafters have to go full length from wallplate to ridgeboard or would it be enough to double or treble the length thats under the sides of the dormer. I dont fancy stripping back the roof from wall plate to ridge board. As I say this there may well be double rafters at the existing veluxes anyway. I should have checked!
    All advice appreciated.


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    #2
    Calahonda52
    Registered Users Posts: 12,346 ✭✭✭✭Calahonda52


    Is planning required?
    What sort of roof will be on the dormer: A or flat?
    What depth are the rafters?
    Any roof purlins?
    It the roof a cut roof or trusses?

    “I can’t pay my staff or mortgage with instagram likes”.



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    #3
    Gumbo
    Moderators, Society & Culture Moderators Posts: 38,914 Mod ✭✭✭✭Gumbo


    pajoguy wrote: »
    Hi just looking for some guidance here not any exact designs.
    I have 2 velux windows that are 750mm wide and there is 900mm gap between them.
    I want replace these with 1 single dormer window to span the full width of 2400mm. I am aware that I will need to double if not treble the rafters at each side but would these rafters have to go full length from wallplate to ridgeboard or would it be enough to double or treble the length thats under the sides of the dormer. I dont fancy stripping back the roof from wall plate to ridge board. As I say this there may well be double rafters at the existing veluxes anyway. I should have checked!
    All advice appreciated.

    Seek planning permission.
    Get roof and dormer designed by engineer.


  • Options
    #4
    pajoguy
    Registered Users Posts: 802 ✭✭✭pajoguy


    Calahonda52 wrote: »
    Is planning required?
    What sort of roof will be on the dormer: A or flat?
    What depth are the rafters?
    Any roof purlins?
    It the roof a cut roof or trusses?

    Planning I can sort out myself. Im in the country and its to rear of property. I know It requires planning but I might go ahead with it now as opening the roof up innivember december isnt appealing.
    Only agricultural land to rear for miles so will speak to landowner and if he is happy I might push on.
    Its a cut roof. 7 x 2 rafters with 9 x 3 purlins at 1.2m above floor joist. I would be pushing out the knee wall to have a floor to window height of 700mm. I would be building the new knee wall the same standsrd as the existing one birdsmouting the purlin to rafter etc.
    Going for an A roof on the former id say.
    My engineer is on holidays for 2 weeks so i will get him to detail it exactly when he returns.

    Thanks for replys.


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