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insulation, roofing, venting

tcarlin | Posted in Energy, Heating & Insulation on March 1, 2008 06:40am

hello all,
a little background to start, i bought a brick home with a mansard roof, built in 1890. in cincinnati, ohio. and have been undertaking a major renovation. and have a couple questions about the roof and insulating it.
first existing conditions- i have taken off all the plaster so i can see everything and this hopefully gives me the opportunity to unsulate it properly. the steep portion of the roof is slate. the “flat” portion is rubber. when i bought the house i had a roofer look at the situation and he told me the slate was in good shape and the rubber was ok. but since then (6 months) i have had several tears and small holes show up in the flat roof. the roof looks like this. the steep sides are 2x4s then the ceiling joists are arched to direct the water. i would say from about 4 or 5 inches on the side to about 9 or 10 in the center. covered by probably 1 x 6 pine boards then a metal roof then rolls of rubber (or maybe epdm or something i don.t know the details) that are about 4 feet wide. so the roof is about 20 feet by 40 feet so there are a lot of seams. the roof guy noted that it was odd for the metal to still be under the rubber but it seemed ok. but since the holes and tears showed up i was wondering if that metal layer could be causing a problem and do i need to redo the roof. i patched the holes with some tar product for the time being to stop the water dripping inside.
insulation- since i only have 4 inches on the sides and about 10 in the middle i want to look into foam insulation since you can get so much more r value.
also there seams so be a debate on here about venting if you use foam. any thoughts. if i did vent i am not sure how i would do this. can i run a ridge vent down the center of a “flat” roof? do i need to put some kind of pop up vent inbetween each joist? if i didn.t have to vent that would obviously make this much easier.
sorry for being wordy. thanks for any advice.

Reply

Replies

  1. MikeSmith | Mar 01, 2008 06:51am | #1

    how about you try it this way ?

    101617.1 

    hello all,
    a little background to start, i bought a brick home with a mansard roof, built in 1890. in cincinnati, ohio. and have been undertaking a major renovation. and have a couple questions about the roof and insulating it.

    first existing conditions-

     i have taken off all the plaster so i can see everything and this hopefully gives me the opportunity to unsulate it properly. the steep portion of the roof is slate. the "flat" portion is rubber.

    when i bought the house i had a roofer look at the situation and he told me the slate was in good shape and the rubber was ok. but since then (6 months) i have had several tears and small holes show up in the flat roof.

    the roof looks like this.

    the steep sides are 2x4s then the ceiling joists are arched to direct the water. i would say from about 4 or 5 inches on the side to about 9 or 10 in the center. covered by probably 1 x 6 pine boards then a metal roof

    then rolls of rubber (or maybe epdm or something i don.t know the details) that are about 4 feet wide.

    so the roof is about 20 feet by 40 feet so there are a lot of seams. the roof guy noted that it was odd for the metal to still be under the rubber but it seemed ok. but since the holes and tears showed up i was wondering if that metal layer could be causing a problem and do i need to redo the roof.

    i patched the holes with some tar product for the time being to stop the water dripping inside.

    insulation- since i only have 4 inches on the sides and about 10 in the middle i want to look into foam insulation since you can get so much more r value.

    also there seams so be a debate on here about venting if you use foam. any thoughts.

     if i did vent i am not sure how i would do this. can i run a ridge vent down the center of a "flat" roof? do i need to put some kind of pop up vent inbetween each joist?

     if i didn.t have to vent that would obviously make this much easier.
    sorry for being wordy.

     thanks for any advice.

    edit:   pictures would really help

    Mike Smith Rhode Island : Design / Build / Repair / Restore



    Edited 2/29/2008 10:52 pm ET by MikeSmith

    1. MartinHolladay | Mar 02, 2008 08:59pm | #2

      Ah -- return of the Paragraph Length Police !

      1. MikeSmith | Mar 02, 2008 10:41pm | #3

        whadda ya think ?.... work for you ?Mike Smith Rhode Island : Design / Build / Repair / Restore

  2. Piffin | Mar 02, 2008 11:12pm | #4

    Thanks mightily to mike for the help.

    I got abnout two inches into all the jumble and was ready to give up on trying to read it as everything ran together.

    A closed cell faom job would be ideal for this. It needs no venting to do it right. And rubber or modified roofing gets installed regularly over unvented roof spaces.

    From your description, you probably have a torch down modified bitumen roof if it is dark colored or black. Modified is tyupically 39" rolls. The heat of torching it to melt it to stick would have left some black tar-looking ooze at seams.

    but mod-bit rarely shows the cracks and holes you describe.

    EPDM is a rubber roof material ( just like an inner tubne) that typically comes 10' to 20' wide and minimizes seams. I suppose it is possible a DIY cut it down smaller to make for easier access if he was a one man show. Doing that over an older flat seam metal roof could result in the situation you describe, especially if they used the thinner kind.. The down side is that EPDM is NOT compatible with tar. That means that the material you used for temporary patches could be eating away at the membrane weaking it as we speak.

    Or you could have one of the PVC or other new products out there. It would take a few good photos to be sure.

    To re-roof over this, I would use a slip sheet of roof insulation board mechanically fastened and then a glued EPDM sixty mill. Go right over what you have if I understand it right and if the decking is solid.

     

     

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