How do I add an Web Application to an existing Web Site? - wcf

Question

How do I specy that there already is the IIS Default Web Site? The Default Web Site must not be uninstalled. I just want to add a new Web Application with my WiX installer.
Unfortunately I didn't find any fitting samples. Everyone always seems to install and uninstall the whole thing.
EDIT:
<Fragment>
<ComponentGroup Id="IIS">
<Component Id="EEE" Directory="WCFFOLDER">
<iis:WebVirtualDir Id="MyVirtualDir" Alias="MyVirtualDir" Directory="INSTALLDIR" WebSite="DEFAULTWEBSITE">
<iis:WebApplication Id="DeploymentWebAppl" Name="MyName" WebAppPool="MyAppPool" />
</iis:WebVirtualDir>
</Component>
</ComponentGroup>
<iis:WebSite Id="DEFAULTWEBSITE" Description="Default Web Site" Directory="INSTALLDIR">
<iis:WebAddress Id="AllUnassigned" Port="80" />
</iis:WebSite>
<iis:WebAppPool Id="MyAppPool" Name="MyAppPool"/>
</Fragment>
How do I specify that there also is an virtual directory? If I put the iis:WebApplication element directly into the Component I get the following error: "The Component element contains an unexpected child element 'iis:WebApplication"
What is the value of INSTALLDIR? I donÄt know where the Default Web SIte has its Directory (propably C:\intpub\wwwroot)
I want to do the same in my WiX installer as in the following C# code I have
using (ServerManager manager = new ServerManager())
{
var site = manager.Sites["Default Web Site"];
var application = site.Applications.CreateElement();
application.Path = "C:\ProgramFiles\.....";
application.EnabledProtocols = "http,net.tcp";
application.ApplicationPoolName = "MyAppPool";
site.Applications.Add(application);
manager.CommitChanges();
}

Answer 1

See the example code here: Install a New Virtual Directory to Default Web Site with WiX.
Rephrasing it: if you put your <iis:WebSite> element inside <Component> element, then the website is managed by MSI and removed when uninstalling. If not, then the website element is a placeholder, and it is not touched by uninstall.