Find Install directory and working directory of VSTO Outlook Addin; or any Office Addin

I found the answer here, full credits to robindotnet.wordpress.com.

//Get the assembly information
System.Reflection.Assembly assemblyInfo = System.Reflection.Assembly.GetExecutingAssembly();

//Location is where the assembly is run from 
string assemblyLocation = assemblyInfo.Location;

//CodeBase is the location of the ClickOnce deployment files
Uri uriCodeBase = new Uri(assemblyInfo.CodeBase);
string ClickOnceLocation = Path.GetDirectoryName(uriCodeBase.LocalPath.ToString());

I've had a similar problem and solved it the same way as described by Christoph, I would also like to know whether there are any alternative ways of doing this but if you don't find anything here's an example

1)Create a custom actions library with the following InstallerClass

using System;
using System.Collections;
using System.ComponentModel;
using System.Configuration.Install;
using System.IO;
using System.Linq;
using System.Xml.Linq;
using Microsoft.VisualStudio.Tools.Applications;
using Microsoft.Win32;

namespace Setup.CustomActions
{
    [RunInstaller(true)]
    public partial class AddCustomization : Installer
    {
        static readonly Guid solutionID = new Guid("d6680661-c31e-4c24-9492-5919dc0uagt5");
        public override void Install(IDictionary stateSaver)
        {
            string installPath = Context.Parameters["installPath"];
            if(!String.IsNullOrEmpty(installPath))
            {
                AddTemplateToAvailableTemplates(installPath);
            }           
            base.Install(stateSaver);
        }

        public override void Rollback(IDictionary savedState)
        {
        }

        public override void Uninstall(IDictionary savedState)
        {
        }

        private void AddTemplateToAvailableTemplates(string installPath)
        {
            //The example below is very basic, put in checks to see whether the registry key already exists and so on
            RegistryKey key = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Office\14.0\Common", true);
            RegistryKey acturisKey = key.CreateSubKey(@"Spotlight\MyAppInstallPath");
            acturisKey.SetValue("InstallPath", installPath);h);
        }
    }
}

2)In the setup project create a key on the Install custom action which points to the install directory:

If you need more info or would like to download the source have a look at this msdn post by Open Xml MVP Wouter Van Wugt titled "Deploying a Visual Studio 2010 Tools for Office Solution Using Windows Installer"