I notice that some customers don’t put their house number in the address field… (often for dutch addresses)

For dutch addresses (and also all countries where house number comes after the street name) it’s very common, because customers start to enter the street, and Google suggest an address with the correct street name, postal code… So the user select the address before he types any house number and forget about it.

You can add a validation for that at WooCommerce level. If you add this code into your functions.php theme file, the customers won’t be able to validate the checkout form if there isn’t any number in the address 1 field : 

add_action('woocommerce_checkout_process', 'custom_validation_process');
 
function custom_validation_process() 
{
    global $woocommerce;
 
	if(isset($_POST['billing_address_1']) and $_POST['billing_address_1'] != '')
	{
		if (!preg_match('/([0-9]+)/Uis', $_POST['billing_address_1']))
		{
			if(function_exists('wc_add_notice'))
				wc_add_notice( __('You must enter your house number for the billing address'), 'error' );
			else
				$woocommerce->add_error( __('You must enter your house number for the billing address') );
		}
	}
   
    if(isset($_POST['ship_to_different_address']))
    {
        if(isset($_POST['shipping_address_1']) and $_POST['shipping_address_1'] != '')
		{
			if (!preg_match('/([0-9]+)/Uis', $_POST['shipping_address_1']))
			{
				if(function_exists('wc_add_notice'))
					wc_add_notice( __('You must enter your house number for the shipping address'), 'error' );
				else
					$woocommerce->add_error( __('You must enter your house number for the shipping address') );
			}
		}
    }
}