These instructions don't seem to be working ...
Copy system/expressionengine/utilities/offline.html to your web root folder (the same place you have your main index.php file).
Rename offline.html to index.html. Now your visitors will see the “offline” page while you update your site.
In your ExpressionEngine Control Panel, go to Tools ‣ Data ‣ Clear Caching. Select All Caches and click Submit.
I add the index.html file as it says here but my sites home page remains?