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DAMP BELOW PARAPET ON FLAT ROOF - help please!

Discussion in 'Roofing and Guttering' started by hello321, 24 Nov 2019.

  1. hello321

    hello321

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    DAMP BELOW PARAPET ON FLAT ROOF



    Hi!


    Was hoping anyone on here could contribute helpful advice and diagnosis as my family are suffering and the situation is getting us all down. We have a damp problem on our front elevation wall (first floor) which sits below a parapet wall, - the parapet forms part of an asphalt flat roof. The fall of the roof falls towards the affected wall.

    For a while now, damp patches have been forming just below ceiling level occurring within 24 hours of rainfall. There is a strong damp smell which goes away after a few days of dry weather. The wall is a solid wall, but is thick.

    We originally had problems with water streaming down the internal face, and this was caused by a cracked cement fillet. Water was travelling down the rear of the flashings and into our bedroom.

    After this was repaired, we continued to get the damp patches, although the direct water streaming down the internal wall ceased. To try and resolve the issue damp patch issue, new coping stones were added to the affected wall and the face of this wall was also rendered. The flat roof at the junction of the asphalt upstand and wall was treated with torched on felt.

    The issue however still continues. The following was undertaken to identify the cause:

    · A dye test over the felt and asphalt was undertaken. No dye seen on the bedroom wall.

    · A waterproof Upvc plastic sheet was placed over the internal side of the flat roof, covering the coping stones and the render. This was because it was suspected that no waterproof additive was added to the sand and cement render leaving it porous. Neither was a DPC applied under the new coping stones. However, the original slate DPC below the coping stones is still in place and likely to be working as the rest of the wall is unaffected. Moreover, te plastic sheet was inspected and is holding out the rain - the wall is dry. The damp however, continues.

    · The internal wall temperature was tested to identify the due point – and was found to be well above the due point. The room is constantly ventilated. Therefore the issue is not believed to be condensation.

    · There are no gutters around the parapet, there is only one stack pipe which is water free as it takes away smells.

    · The downpipe and outlet for the roof is a good distance a way from the damp issue.

    · The second larger bedroom sits below the opposite side of the flat roof, but is unaffected.


    Really need a solution to this.

    1. It could be that water is going through external face of solid wall. However, it’s a very thick wall. I will put tarpaulin or a waterproof sheet over this side to and monitor.

    2. Could it be that water is somehow getting under the asphalt and moving towards the wall due to the fall? I’m not sure how likely this is.

    Would really appreciate a steer on this. I’ve wasted time and money and not prepared to throw good money after bad.

    Thank you all for reading, please see photos below.


    Thank you.

    Sam.

    Photos

    Google Earth Image showing birds eye view flat roof.

    [​IMG]

    Front elevation - showing area where damp patch is in relation to hopper.

    [​IMG]

    [​IMG]



    [​IMG]


    Above: - photo of wall which has been re-rendered with new coping. Still damp patches are occurring.

    [​IMG]



    Dye test – and also showing Upvc waterproof sheet over wall and new torched on felt. No dye seen in bedroom.

    [​IMG]

    Upvc sheeting which has kept water away from exterior internal face of wall. Damp still occurs.



    [​IMG]

    Showing dry wall after Upvc sheeting placed on top.


    [​IMG]

    Above, photo of wall after rendering.

    [​IMG]

    Above – dye test.

    [​IMG]

    Damp area internal wall front elevation below parapet. Streches across other areas of wall. NB wall on oppsite side o parapet is unaffected. Fall of roof is towards this wall.

    [​IMG]
    Protometer test shows moisture.
     
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  3. Why Not Indeed

    Why Not Indeed

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    Only people who are logged in to Screwfix will be able to see your pictures [I can't].
     
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  4. hello321

    hello321

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    See thumbnails
     

    Attached Files:

  5. catlad

    catlad

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    The rendering on the outside look shot.
     
  6. Notch7

    Notch7

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    Its time for you identify the construction detail of each element that could be causing the damp, then methodically examine each one and decide an order for the remedial work.

    So are we saying the wall construction is a solid 9" from ground to top of parapet wall?

    On the external face of the parapet, there is a horizontal crack in the render at what looks like the same course as the flashing for the flat roof -I wonder what causing that.
    As Catlad says, the render looks pretty shot.


    I would check these:
    -Discharge shoot through wall
    -weathering at abutment with pitched roof, including chimney flashing
    -external rendering / porosity of drickwork
    -depth of lead flashing chase at new rendering
    - weathering between lead lashing and flat roof
    -flat roof

    My guess is you need to start doing more invasive investigation and find the damp -maybe stripping back ceiling where it meets the wall.

    You could do an extended hose pipe test on the external wall -rig up a way to spray the wall for a few hours, but keeping everywhere else dry.
     
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  8. noseall

    noseall

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    Who ever invented parapet walls should be put up against a ...um...parapet wall and shot.
     
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  9. datarebal

    datarebal

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    Some dodgy aspects i see.
    Lead flashing each side of the outlet are cut short.
    Looks like a broken tile needs changing not patching
    if that bit of felt overlay was done with that DIY blow lamp.. forget it..you wont have a consistent bond.
    If you are getting it overlaid do it all..

    Render on the outside requires work, that long horizontal crack looks suspicious

    Coping stone looks nice hanging over like that!
     
  10. You might have to go back quite a way for that :!::)
     
  11. Notch7

    Notch7

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    They are a nightmare, prone to leaking.

    Never a good idea to have a section of brickwork that is external, changing to internal.....asking for trouble.
     
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  12. datarebal

    datarebal

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    Built well with correct tray arrangement then they work
     
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  13. DIYnot Local

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