simple_xml_load_string and xml attribute types

I am working with an API at the moment, that accepts XML in a request, however the atrributes of that XML have to particular formats (string, int, boolean, dateTime etc). An example of my XML is as follows,

<Property>
    <Address>
        <AddressLine1>str1234</AddressLine1>
        <AddressLine2>str1234</AddressLine2>
        <AddressLine3>str1234</AddressLine3>
        <AddressLine4>str1234</AddressLine4>
        <PostCode>po75xa</PostCode>
        <RoyalMailReference>str1234</RoyalMailReference>
    </Address>
    <PropertyType>DetachedHouse</PropertyType>
    <NumberOfBedrooms>3</NumberOfBedrooms>
    <YearBuilt>1970</YearBuilt>
</Property>

The XML is stored in a Laravel view that load in like this,

$xml = simplexml_load_string( View::make('samplerequest') );

I then send the request to the API (it is via SOAP), the request I get back shows eve that actually gets sent shows every attribute is a string. How can I define what type each attribute is? Or will will simplexml_load_string() cast everything into a string?