Attic joists and purlin issue

Discussion in 'Roofing and Guttering' started by Evren, 5 Jun 2021.

  1. Evren

    Evren

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    Apologies for the long winded thread :(

    We have recently purchased an old house with thick (45cm thick ) solid stone walls.
    The main structure of the house is as you can see in the photo. My question is in regards to the extension roof structure.

    There is a purlin (3" x 8" i believe) going from the solid wall all the way to the valley. The purlin is inside the solid wall on one end but on the other end (by the valley ) the only support it has is a piece of timber attached to 3 other rafters from the main (double pitch roof /photo attached)


    I understand these houses had originally slate roof tiles which were commonly replaced by heavier concrete ones in the 70s & 80s and as you can see this caused a bit of a sag in the extension roof.

    Now my first question is ,is this support enough for the purlin on either end ?
    If not what can i do to fix it ?


    IMG_4078.jpg






    IMG_4631.jpg


    Now the 2nd issue i have is about the joists halfway along the purlin and the purlin itself.
    For some reason ,it looks like 3 of the ceiling joists were cut and joined into a piece of timber that is then joint to 2 joists going in to the wall after the cut joists number 1 & 3 .

    IMG_4648.jpg

    Also as you can see there is the chimney breast to the left of the cut ?! joists .
    Some closer shots here

    IMG_4622.jpg

    IMG_4625.jpg



    Now to add to the misery , the purlin along this part has sagged which i am assuming is due to heavier tiles and the length of the purlin itself (around 25-30 ft) and where it sagged there is a timber jacking structure that i believe is built at some point to support the sagged purlin from underneath.
    By the way the joists here are joined to the roof rafters at the other end , which are resting on solid wall.


    IMG_4640.jpg

    here is a photo of the purlin showing the sag

    IMG_4637.jpg

    Surely ,It cant be right having the weight on 3 joists being passed on to 2 other joists which already have weight on them.
    So my 2nd question is ;

    How can I resolve the issue with the 3 cut joists ? Is there a way to sister some timber to them using strong metal strap and thick bolt and nut setup to pass the weight of these 3 joists back into the solid wall / chimney breast ?




    50096.jpg

    Many thanks in advance for reading this .
     
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  3. blup

    blup

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    It's common for joists to be "trimmed" around a chimney breast and the weight transferred to a doubled up joist either side (assuming the calcs allow for this).

    The sag in the purlin (and its remedy) should be checked by an experienced builder or an SE, and BCO approval to works sought under a building notice. You might need a steel.

    The purlin in the wall is above a window.

    You need an SE (or experienced builder) on site to advise, and BC approval for any works necessary.

    Blup
     
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  4. Evren

    Evren

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    Blup thank you for the answers

    Do you mean i may need a steel purlin or some steel reinforcement ?

    The purlin is above a window ,and over that window there is a thick timber lintel which i presume to be original. Would this make a difference in terms of the support purlin is getting from underneath ?
    Also the other end of the purlin where it is sitting on a piece of timber attached to 3 rafters . does that look normal ?

    Is there any need for an expensive SE advise if i can get the same from a experienced builder ? Will the BCO be forcing me to get an SE calculations before the work can commence ?

    Slightly legal issue but shouldn't he surveyor pick up on this during the purchase of the property which was end of 2019 early 2020 ?
     
  5. blup

    blup

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    I am not an expert so I can only make observations. But as you point out, the additional weight of the concrete tiles means the roof strength should be looked at, especially given the issues you have identified.

    On a structural survey you would expect the roof structure to be inspected, but typically the surveyor would recommend an expert to advise in detail.

    An SE would not be as expensive as you might think, maybe £500 - 750. Structural alterations need BC approval AFAIK.

    The purlin will transfer the weight of the roof to the wall which has the window directly below it, you would expect there to be a suitable beam to take the load transferred from above. The purlin at the other end is on rafters which should also be checked. It may have lasted for a hundred years or more but the introduction of concrete tiles has increased the load.

    A steel purlin needs to rest on something structural like a wall or another steel, so more likely a steel beam would be appropriate, from which support can be given, directly or indirectly, to rafters, joists and purlin.

    As stated, only an expert on site can properly advise.

    Blup
     
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  6. cdbe

    cdbe

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    Anything would be better than the misguided attempt to support the purlin off the trimmed ceiling joists - a small steel spanning from party wall or chimney breast (if complete to ground) adjacent to flue to external wall. The support at the end off the 3 rafters could be helped by a prop down to the wall below. I'm not sure whether repair work is notifiable.
     
  7. Evren

    Evren

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    thank you both , i will get in touch with a SE in that case.
     
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