Sloping lean to roof insulation question

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Hi all,

We are having a sloping pitched roof on our rear extention and the architect has put 100mm insulation between 200mm rafters, then below the rafters a 50mm insulation with vapour control & drywall built in, Kingspan Insulation K17. Then an additional 12.5mm plasterboard on top of this.

I asked the architect if this could be changed to 150mm in the rafters then a vapour control barrier then 12.5mm plasterboard but in his usual 1 line how dare I question him response gave the answer "as per the spec".

So the question is could this be changed as I have suggested or should I go with what the architect recommends? Also is there really any need to add 12.5mm plasterboard on top of Kingspan K17?

Thanks in advance

Paul
 
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Re the extra plasterboard, could this be for fire regs. perhaps.
Re the architect, he is in your employ - ask him - don't be intimidated, if he needs reminding just reaffirm his position in the play of things. If there is a building warranty issue that's something you'll just have to live with I'm afraid...pinenot :)
 
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The 50mm insulation underdraw is to prevent cold bridging or shadowing occurring and is quite pertinent.

As for two layers of plasterboard, not a clue unless there is the need for additional fire protection i.e. 1 hour etc.

Ask your architect for the reasons and remind him not to be so rude. These guys like to feel very important you know.
 
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Im not afraid to ask the architect questions, but I am biting my tounge in the interest of getting the project done. My usual response to such an arsehole would be to tell him in no uncertain terms what I think of him and ask if he had a problem would he like to meet me face to face and be so rude. He will know exactly how I feel once the project is finished and reviews are left on him over the internet.

Currently after asking the same question 3 times, and wording it differently we are back in full circle with a "refer to spec" answer literally that is the extent of his e-mail.

RE the double boarding I have worked on sites on and off for years as a tiler and im now a plumber and bathroom installer. Structural isnt my area of expertise but its unusual for things to be double boarded. Ive run this past my builder and plasterer that I use on jobs and the answer im getting back is that the Architect is an arsehole and covering his own arse, which I pretty much thought anyway.
 
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Noseall,

Thanks for the explanation regarding the cold bridging. That makes perfect sense. Now why couldn't the Architect have just said that in his reply????
 
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