Update 2:
Helm 3 added support for multi namespaces https://github.com/helm/helm/issues/2060
Update 1:
If a resource template specifies a metadata.namespace, then it will be installed in that namespace. For example, if I have a pod with metadata.namespace: x and I run helm install mychart --namespace y, that pod will be installed in x. I guess you could use regular helm templates with the namespace to parameterize it.
Original answer:
We do not plan on fully supporting multi-namespaced releases until Helm 3.0
https://github.com/kubernetes/helm/issues/2060#issuecomment-306847365
As a workaround, you install for each namespace individually using --skip-dependencies or with dependency conditions