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Flat Roof - installing Fibreglass over existing felt roof.

  • 09-06-2020 7:38pm
    #1
    Dazzy
    Registered Users, Registered Users 2 Posts: 594 ✭✭✭


    I have a 40sqm flat roof covered with felt which I am replacing with Fibreglass. 

    One company has recommended putting the new Fibreglass roof directly over the existing felt. So the insulation,  OSB and then Fibreglass over the felt.

    Has anyone ever done this? Is it a good approach or likely to cause problems?
    It will reduce the labour and removal costs of the existing roof so that makes it appealing.  


Comments

  • #2
    Calahonda52
    Registered Users, Registered Users 2 Posts: 13,028 ✭✭✭✭Calahonda52


    how old is the roof?
    whats the insulation?
    how will the OSB be fixed?
    https://www.enviroplyroofing.co.uk/should-you-create-a-warm-roof-or-a-cold-roof/

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



  • #3
    Dazzy
    Registered Users, Registered Users 2 Posts: 594 ✭✭✭Dazzy


    Calahonda52 wrote: »
    how old is the roof?
    whats the insulation?
    how will the OSB be fixed?
    https://www.enviroplyroofing.co.uk/should-you-create-a-warm-roof-or-a-cold-roof/

    The roof is about 20 years old and in good condition under the felt. I can walk on the roof and it feels secure. It will be checked before going ahead to make sure.

    The insulation will be flat roof insulation boards - 100mm.

    OSB will be secured by screwing into the existing joists below the existing roof.

    Thanks for the link.


  • #4
    Toby22
    Registered Users, Registered Users 2 Posts: 122 ✭✭Toby22


    Hi,

    I have a friend who is a roofer and is replacing fibreglass roofs that are less than two years old. He said fibreglass should only be used on small areas. I can give him your measurements and pm you his opinion.


  • #5
    Dazzy
    Registered Users, Registered Users 2 Posts: 594 ✭✭✭Dazzy


    Toby22 wrote: »
    Hi,

    I have a friend who is a roofer and is replacing fibreglass roofs that are less than two years old. He said fibreglass should only be used on small areas. I can give him your measurements and pm you his opinion.

    Yes, please do.


  • #6
    Shaunoc
    Registered Users, Registered Users 2 Posts: 521 ✭✭✭Shaunoc


    Toby22 wrote:
    I have a friend who is a roofer and is replacing fibreglass roofs that are less than two years old. He said fibreglass should only be used on small areas. I can give him your measurements and pm you his opinion.

    Probably means weren't installed right....


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  • #7
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    Shaunoc wrote: »
    Probably means weren't installed right....
    Lots of People and some builders don’t understand the difference between a ‘cold roof, and warm roof’ construction - it’s worth a google, to appreciate the requirements of ventilation with a ‘cold roof’

    Also Some fibre glass products are not UV stable, and we don’t tend to put ballast, paving or greenery on our roofs in Ireland.


  • #8
    tabby aspreme
    Registered Users, Registered Users 2 Posts: 4,126 ✭✭✭tabby aspreme


    Would fixing a new roof over the old one, be increasing the risk of dry rot, chances are after 20 years a felt roof will have some dampness, even though it may not be visible


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