Not sure about what you are asking, but here is a UserControl that has a root visual of ScrollViewer:
<usercontrol x:class="WpfApplication1.UserControl1" xmlns:x="#unknown">
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<scrollviewer>
</scrollviewer>
</usercontrol>