Solution 1:

For a 302 Found, i.e. a temporary redirect do:

header('Location: http://www.example.com/home-page.html');
// OR: header('Location: http://www.example.com/home-page.html', true, 302);
exit;

If you need a permanent redirect, aka: 301 Moved Permanently, do:

header('Location: http://www.example.com/home-page.html', true, 301);
exit;

For more info check the PHP manual for the header function Doc. Also, don't forget to call exit; when using header('Location: ');

But, considering you are doing a temporary maintenance (you don't want that search engines index your page) it's advised to return a 503 Service Unavailable with a custom message (i.e. you don't need any redirect):

<?php
header("HTTP/1.1 503 Service Unavailable");
header("Status: 503 Service Unavailable");
header("Retry-After: 3600");
?><!DOCTYPE html>
<html>
<head>
<title>Temporarily Unavailable</title>
<meta name="robots" content="none" />
</head>
<body>
   Your message here.
</body>
</html>

Solution 2:

The following code will issue a 301 redirect.

header('Location: http://www.example.com/', true, 301);
exit;

Solution 3:

I don't think it really matters how you do it, from PHP or htaccess. Both will accomplish the same thing.

The one thing I want to point out is whether you want the search engines begin to index your site in this "maintenance" phase or not. If not, you could use the status code 503 ("temporarily down"). Here's a htaccess example:

RewriteEngine on
RewriteCond %{ENV:REDIRECT_STATUS} !=503
RewriteCond %{REMOTE_HOST} ^192\.168\.0\.1
ErrorDocument 503 /redirect-folder/index.html
RewriteRule !^s/redirect-folder$ /redirect-folder [L,R=503]

In PHP:

header('Location: http://www.yoursite.com/redirect-folder/index.html', true, 503);
exit;

With the current PHP redirect code you're using, the redirect is a 302 (default).

Solution 4:

Did you check what header you're getting? Because you should be getting a 302 with above.

From the manual: http://php.net/manual/en/function.header.php

The second special case is the "Location:" header. Not only does it send this header back to the browser, but it also returns a REDIRECT (302) status code to the browser unless the 201 or a 3xx status code has already been set.

<?php
header("Location: http://www.example.com/"); /* Redirect browser */

/* Make sure that code below does not get executed when we redirect. */
exit;
?>

Solution 5:

From the PHP documentation:

The second special case is the "Location:" header. Not only does it send this header back to the browser, but it also returns a REDIRECT (302) status code to the browser unless the 201 or a 3xx status code has already been set.

so you are already doing the right thing.