I finished the cleaning and have started staining the cedar siding. I always seem to do my house painting on the hottest week of the year -- three times now...

Anyway, many of the planks have curled outward, leaving gaps beneath, and many of the nails have pulled out so that the boards are rather loose. Is this normal behavior of cedar or a consequence of 7 years without maintenance?

I expect to replace the nails they already have at the lower edges with longer or ring shank ones just to pull in the loose boards, but I don't guess there is much to be done with the curl. I'm afraid they'd just split. Anything else I can do?

 

So we can blame this heat wave on you?
The siding will split if you force it too much. Make sure you use galvanized nails. What type of stain are you using? It's always a good idea to caulk any splits in the wood but you need to determine if it will interfere with the stain. Could you post a pic or two of the trouble spots?

 

Now that I am looking, it does not seem to be as bad as I thought. Perhaps the fact that I have had dinner and it's only 95° now... But here are a couple of photos of the more obvious areas. What I am wondering is mainly about how much of a gap between the layers is acceptable? Since the next higher row normally lies flat over the previous one with continuous contact, at what point should I begin to address it?

 

I don't know that there is much you can do to correct the bowing siding other than replacement
You don't want to caulk the bottom of the siding and nailing it back down is almost guaranteed to split the wood.

 

We recently had a log home to remodel and their gable siding was much worse than this, necessitating a 90% replacement. On the lesser affected boards that were still cupped somewhat, I predrilled holes and put in color coordinated 2" decking screws, just to the point of putting tension on the boards. It seemed to help with the pull out without splitting the boards. I knew if I nailed them back with squirrelly nails the would split. Time will tell, I guess.