Vulkan validation layer in UE4 is not enabled by default. We can see the codes in VulkanLayers.cpp around line 300:

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const int32 VulkanValidationOption = GValidationCvar.GetValueOnAnyThread();
if (!bVkTrace && VulkanValidationOption > 0)
{
    ...
}

The validation layer will be enabled only if VulkanValidationOption has a proper non-zero value when creating VkInstance. The GValidationCvar is defined at the begining of the same file like this:

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TAutoConsoleVariable<int32> GValidationCvar(
	TEXT("r.Vulkan.EnableValidation"),
	0,
	TEXT("0 to disable validation layers (default)\n")
	TEXT("1 to enable errors\n")
	TEXT("2 to enable errors & warnings\n")
	TEXT("3 to enable errors, warnings & performance warnings\n")
	TEXT("4 to enable errors, warnings, performance & information messages\n")
	TEXT("5 to enable all messages"),
	ECVF_ReadOnly | ECVF_RenderThreadSafe
);

We have several options of validation level, and the default value is 0.

Of course we can assign a new value to GValidationCvar. But make sure it is setted before creating ‘VKInstance’.
Another safe way to do this is add startup argument ‘vulkanvalidation=(xxx)’ to your project or UE4 project property. You don’t even need to modify any codes by this way.

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