Microsoft has introduced a new optimizeCompilations switch in ASP.NET that can greatly improve the compilation speed in some scenarios. You can read this blog post to understand the overall idea, study a more detailed explanation about Dynamic Compilation here or simply follow these 2 easy steps:

1) Install this hot-fix:

• Windows XP: http://code.msdn.microsoft.com/KB969612
• Windows Vista: http://code.msdn.microsoft.com/KB967535
• Windows 7 – not necessary

2) Update your web.config as follows:

Add optimizeCompilations=”true” to your <compilation …> tag. Below is an example:

<system.web>
....
<compilation debug="true" optimizeCompilations="true">
....
</compilation>
....
</system.web>


And you’re done! Next time you change something inside the App_code or even a dll inside the bin folder you might not have to wait the entire site to rebuild.

Important note: this approach speeds things up but you might get some weird errors when you start changing some code signatures or restructuring dlls.In this case, all you need to do is a simple “rebuild project/solution” inside your Visual Studio to get things straight again.