New to the forum but a long time looker. After searching this forum for my answer, I was unable to find an exact answer to what I am trying to do so I thought I would post it and see if anyone can help me.
I am adding an addition to an existing house, a gable end addition tying in to the existing part of the house with valley rafters. I hope that is clear enough for someone to get a picture in their mind. The addition is perpendicular to the existing house. The pitch of the roof is 5/12 with a run of 13’6″ on the common rafters. Okay, here is the question:
The original house was built with non-dimensional lumber or rough sawn so when they cut the rafters, they cut an extreme birdsmouth in the rafter, meaning less than 2/3 of the original board is left. I don’t think this creates a structural problem, just a way they did birdsmouth cuts back then. HAP or heigt above plate is probably 2-2/12 inches. In order for my fascia to match the existing fascia when I frame my new addition, my cuts for the birdsmouth will be what they are supposed to be, about 2/3 of the rafter will be laying on the top plate ( I’m assuming) so the question is, do I alter my wall height to accomodate the difference in the birdsmouth cuts from the old to the new or do I make a cut as deep as the existing so they will match? I don’t want to make a cut that deep as I think it is too deep and I want to keep the birdsmouth cuts to a building standard but I want my fascia board to be the same level when I make the turn at the valley.
I hope that is clear enough for someone to generate a picture in their head as to what I am trying to do. If I need to clarify anything, please feel free to ask and I wll try to better explain.
Replies
How much overhang is there?
How much overhang is there, and how thick is the rafter above the cut? If there wasn't too much overhang I would make the cut the same and glue and nail another rafter to the bottom 4' or so to add strength. It also depends on if the ceiling was going to run seamless from the existing structure to the addition. If there was to be a beam or a doorway there anyhow, lowering the ceiling a little bit wouldn't be noticed.
Other options include varying the pitch or the size of the overhang. It's a formul;ae with lots of variables. Take your pick
toj.
Remodeling is one thing-additioins are another. Making the true and new work with the old and ? is the most difficult part-especially when not thought out in advance. Some will frame the walls and then see the problem. Tho it might not be too late to "make it work", it sure would have been easier in the long run to figure this out b/4hand.
If you've got the deck of the addition done and no interior partitions yet, you have the perfect drawing board.
To make the fascia and soffit line up can be shown full size on that deck. You may decide to drop the ridge so that you don't have that problem point to deal with too. It might work better to drop the eave walls so you don't compromise the rafters. By knowing the length and the pitch you can start at the fascia and work your way up as far as the ht. of the new walls. More than likely you may have a full opening into this new addition, but the ceiling hts do not necessarily have to be on the same plane. A beam or faux drop down at that location will break it up.
Sketch it out (I'm no math wizard, so full size on a floor sure works for me).
Note the critical areas like the top of your fascia. If the same width overhang is a prerequisite, you may have to putz a bit to get that right. The bottoms of the rafter after you pass the wall can be adjusted for most any fascia width.
As an example of no figuring b/4 hand. I once had the pleasure of finishing an addition that the brother in law of the customer, threw up. The homowner was quite surprised when I had to add nailers and another subfloor to get the one floor even close to their original. Since the dimension was critical (no step down) nobody thought to if nothing else, cut a damn hole through the wall so they knew the finished floor height.
It would have been a hole lot easier with a bit of planning. Oddly, they could have jumped up a size on the floor joists..............
You can do all the above on a pc of paper hopefully but not necessarily to scale-the numbers just need to be right.
Best of luck.