I am trying to design a frame for a 22X32 foot, 1 1/2 story with a full plate set on top of a 3 foot kneewall, 4 bents total all 8 x8 posts and 8 x8 beams(?). I would like to use 4X6 whitepine rafters with an open mortise at the top and the same size collar ties. My problem is I know the closer to the center (lower down from peak) the ties are the more they help prevent rafter spread. But that starts to reduce my head space below. The rafters would be just a little over 13 feet long from plate to peak. If I set the ties 3 feet down from peak that still leaves decent head space but I am not sure if that will be a good solid roof. The roof will be an 8/12 pitch with the rafters 2 feet on center and will be covered with Foam panels and then metal for a house in Vermont. Any opinions on this would be welcome. I would rather overbuid some then cut it close as I am cutting my own timbers so within reason a little bigger timbers or closer spacing is O.K.. Also would like to have 2, 6 foot wide gable dorms in each roof, but am not sure if they would affect what I have planned. If my idea seems structurally sound I would skip a pair which on the 2 foot spacing will leave my 6 foot for the dormer. Thanks much for any thoughts.
