Cracked Roof Topping

[Gercivil]

Hi, I have a problem in one of our apartment project it is about 10 to 15years old. The roof topping have many cracked with a 10 to 20mm vertical movement. In one portion of the roof water leaks, the rain water pass through the adjoining joint of the hollowcore slab.
Our preliminary assessment is that there is a defect with the water proofing membrane, in which, an expansion in the material cause the vertical movement.
Roof Topping Detail:
-50mm conc screed
-800micron water proofing membrance
-50mm polyurethane insulation

I need second opinion to the problem...

 

[Ron]

10 to 20mm faulting is quite a bit, but you probably won't know that until you remove the membrane. At 10 to 15 years old, I would expect your membrane to start having problems.

Unless you have an extraordinarily long and narrow structural dimension, I would not expect that structural expansion caused your issue, particularly after this long. More likely membrane deterioration.

A few questions:

What type of membrane was used?
Is this a protected membrane assembly?
Is the membrane applied directly to the topping slab or is it applied to the insulation?

 

[Gercivil]

We already instructed the contractor to remove all the roof topping and to replace it.
Our provisions:
Layer 1: Sprayed foam of polyurethane, min. 50mmthickness
Layer 2: Liquid protective membrane applied to a minimum dry film thicknes of 800microns.
Layer 3: Protective layer of 100grams/sq. m of geotextile
Layer 4: Grade 20 concrete screeding, min. thickness of 50mm.

Four apartments were built but only this building got problem.

Thanks Ron.

 

[SteveGregory]

Could you have a relatively long span parallel with an adjacent very short span? You might get enough difference in the deflections to cause a problem.

 

[Ron]

Gercivil...I hope you are in an area where there is little rainfall. The system you have described is a very weak waterproofing system.

 

[a2mfk]

Steve has a point. You don't really give us enough info on the exacts to give you any other opinions. What about a sketch of the roof with the direction of the hollow core panel spans indicated? Vertical movement in a roof structure that is causing a leak may require a structural modification, not just an envelope repair/replacement...

 

[Gercivil]

Ron: Actually for a year, I only experieced 7days of rain. The temperature during summer is about 45C-50C.

Steve & a2mfk: The max. span of the hollowcore slab is only 4m. Before placement, we will check the bottom level of the hollowcore slab for deflection.
Also, we haven't find any structural cracks inside the flats that why we rule out the possibility of a structural defect.