Does my lab head need to be a co-author on my manuscript?
In many of the lab sciences it has become customary, and even required, that the PI of the lab is a co-author on all papers produced by those working in the lab, usually as the last listed author. 

It would probably be thought unusual if you were to break this "tradition". It might even cost you in your relationship with the PI in the future. 

The rationale for this is that the PI has probably done the work to get the lab funded and sets general direction for the work in the lab. Many of the ideas generated by those working there may come indirectly from others, including some insights from the head. 

I don't know if this is the situation in your lab, but suspect that it is since you are asking the question. In such cases it is probably wise to go along to preserve the collegial relationships that can benefit you in your future. 

You may question the fairness of this, and many do, but if it is required by the meta rules, you are a bit stuck. Ask your colleagues in the lab what is the proper approach. If they say to include the head, and you would rather not do so, then I'd advise asking the PI for permission to publish a paper on your own. I'd follow the advise given if for no better reason than self protection. 



I'll note that in some labs many people are listed as co-author even though they have little contribution to the intellectual content of the paper. But they, in some way, enable the work and so are listed as co-authors.