ExtractZip and read-only files on the destination

Hi All, i'm usin FastZip ExtractZip  form powershell like below. THe prolem is that when one of the destination files has read-only attribute set unzip fails with acces denied exception. Is this expected, is there any workaround for this?

function Expand-ZipFile($ZipFileName,$Path) {

$zip = New-Object ICSharpCode.SharpZipLib.Zip.FastZip

$zip.ExtractZip($zipfilename,$path,[ICSharpCode.SharpZipLib.Zip.FastZip+Overwrite]::Always,$null,$null,$null,$fals)

}