I think that pre 2.7 there’s a -6dB headroom by default.
An easy solution is to load your wav file into an audio editor (audacity will do) and use the editor’s Normalize function. In audacity you can set a value for this.
The default in 2.7 is still -6dB headroom. But krixa already said that the output is pretty much peaking at 0dB anyway, so normalising isn’t going to give much of a boost in this case.
The problem here is not peak loudness, it’s perceived loudness. You can increase the perceived loudness of a sound by carefully (or not so carefully) using tools like limiters and compressors, in order to boost the body of the sound and make it more full, while keeping the peaks below a certain threshold. You essentially ‘squash’ the dynamic range of the sound while simultaneously normalising the results, giving you a louder overall signal. But if you push it too far then you end up with muddy crap that has no dynamic range whatsoever and sounds like every other boring piece of shit on the radio, so you should try not to go too crazy with it (unless that’s the specific sound you want, I guess).
A very quick (but perhaps not very elegant) way of boosting your overall levels is to add a Maximizer (Track DSPs > Native > Maximizer) to your master track. Choose a preset such as ‘Master Boost Fast’ and then play around with the Boost parameter until it sounds a bit nicer to you. Depending on the type of music you’re writing it may be necessary to adjust the other parameters to get more subtle results, but if you don’t really understand what you’re doing then you should simply stick to a preset and make small adjustments, otherwise you can easily create a horrible-sounding mess with extreme settings.