Bubbling under new Sarnafil roof install

22 Mar 2023
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United Kingdom
Hi All,
Have just had a new extension built where the roof is Sarnafil…
Part of the roof is accessed through a bedroom sliding door onto the balcony roof…
A couple of questions I have..
From the pictures attached you can see what looks like “bubbling” under the Sarnafil which suggests to me it is not stuck down? Builder says this is “normal”

Secondly is Sarnafil mechanically sound enough to be formed on the step of this outside door… which will obviously see traffic through the door and onto the balcony?

Thanks in advance for any advice.


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There should be a threshold on top that you step on, to protect the membrane. What does the door cill detail show? The bubbling is not right assuming it's a hot welded membrane.

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