Cutting birds mouth

[mpls_ham]

I'm ready to start cutting rafters for my cabin and I would like to prepare them at home and haul them up.  My question is this: How much wiggle room will I have when setting the rafters if the width of my parallel top plates vary by one inch from one end to the other?  Will I have a little "play" to work with?

Thanks,
Scott

[MountainDon]

You mean the two gable end walls differ by 1 inch in length, right?



In my experience, limited to a handful of roofs over many years, is that the first set of rafters I cut, is only the test set. They have never been perfect, maybe the upper end angle needs adjustment, maybe the birds mouth needs a tweak. It would be a shame to precut everything according to the calculations or drawings and then find the measurements to be off a tad. With the variance in the building width that could get out of hand. Remember you want the rafter tips to have full contact to the ridge board or you will need to shim. And if the bottom ends don't fit well the soffits become a problem. Many pros will not cut the rafter tails until the rafters are installed. They snap a line and use that to trim the tails so the fascia lines up without waves. My opinion, OMMV.

[Redoverfarm]

I will have to side with Don on this.  If it is realitively close by maybe cut one and then check it with all four corners and see if it will work.  I would be more prone to cut on sight though.

[cabinfever]

I've got to echo the advice so far. Cut the first one, test fit, and adjust. After that, you can use it as template for the rest. I've made enough mistakes at this point that I wouldn't dare commit all of my materials in advance - even if I was sure I had it right.

[mpls_ham]

Thanks....I will cut my two end pairs and cross my fingers.  I don't relish the thought of custom cutting each rafter. 

[Don_P]

Do stringline the walls to make sure they are straight. If the width is 1" wider at one end and you do not alter the rafter pattern the ridge will drop out of level 1/2" or so, the cuts will probably not change angle enough to worry about. But I still cut a test pair before going to town.