deltaman,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function() {
var room = $(".room-block"),
info = $(".block_info");
room.on('input', 'input', function() {
var room_area = 0;
room.each(function() {
var inp = $('input', this);
var area = (+inp[0].value || 0) * (+inp[1].value || 0);
room_area += area;
});
info.html(room_area)
})
});
</script>
</head>
<body>
<div class="room-block" >
<span class="dattext">Высота, м </span>
<input type="text" name="roomh" class="dat" value=""> <br>
<span class="dattext">Ширина, м </span>
<input type="text" name="roomw" class="dat" value=""> <br>
</div>
<div class="room-block" >
<span class="dattext">Высота, м </span>
<input type="text" name="roomh" class="dat" value=""> <br>
<span class="dattext">Ширина, м </span>
<input type="text" name="roomw" class="dat" value=""> <br>
</div>
<div class="room-block" >
<span class="dattext">Высота, м </span>
<input type="text" name="roomh" class="dat" value=""> <br>
<span class="dattext">Ширина, м </span>
<input type="text" name="roomw" class="dat" value=""> <br>
</div>
<div class="room-block" >
<span class="dattext">Высота, м </span>
<input type="text" name="roomh" class="dat" value=""> <br>
<span class="dattext">Ширина, м </span>
<input type="text" name="roomw" class="dat" value=""> <br>
</div>
<div class='block_info'></div>
</body>
</html>