I just checked your span and its at around 24 ft. What's the pitch?

I'm thinking you may not have to sister up the rafters. If you do what I was recommending I would use 2x6's.

I like conans idea of 2x6...you can only span 2x4 so much...2x6 will not need extra supports to carry the 50 lbs per sq foot or possibly more in your area (snow load)(see all the extra support needed on engineered truss) His idea is simple..1 guy can do it and bolting is great idea...im guessing the only thing your roof rafters are good for now is furniture so nailing is out of the question and screws do not have the sheer strength...you can also run a steel strap from your bottom bolt connection at outside wall around plates to connect to outside walls.

Likely your rafters are slung down some. Run a string line and try to straighten out a bit as you stick frame your new truss.

Edited by Connor - August 26 2014 at 2:44pm

B is redundant unless you want a deck above for storage or something...unnecessary material.
You will have to strap the bottom side of C ( 2x4)at middle of span to stop side deflection. Wouldnt hurt to strap the top of C also mid span if you want to over kill it...the connection where the 2 Cs cross is a support point. The 2x6 gives you far more strength than 2x4. C provides the brace that you are thinking B will do therefore B is not needed. The design pushes all the load to the outside walls. If there is not a ridge board at the top and the current rafters just butt to each other you will have to gusset the top of new 2x6 to tie together and block in between each set of rafters. Put new 2x6 rafters right beside existing 2x4 rafters and bolt together. Are your existing ceiling joists under existing rafters or are they beside them.

The sheathing or ship lap ..what ever the sheathed the roof with is the connection between old and new rafters...you wouldnt have to attach new rafters to roof sheathing. You could also use PL premium adhesive when you are setting you new rafters to the old and bolt together.

Edited by Connor - August 26 2014 at 6:05pm

Like in this design, if both 'C' were to meet in the middle, rather than connecting straight across, I wouldn't need such a large 2x6, maybe 14' each.

'B' would act more as a collar tie rather than a rafter tie, offering strength and supporting the connection between both 'C'.

I would not use 'A' but would use both 'D'.



Now, I believe I stand a snowballs chance in hell taking a 2x6 and sistering it to my existing roof rafters. They are a 100 years old and have bowed just a little bit. But they are a full 4" (not 3.5" like todays lumbers, and I believe probably a stronger wood.) And looking at trusses today being made out of 2x4, I'm thinking I should be able to get away with it. The collar tie will prevent any future bowing, right?

There is no ridge beam/board, rafters are butted up to each other. So adding a rafter tie (about 1 foot below the peak) or a gusset plate would probly be a god idea.

Here are some pics of current roof and joists.





Edited by Ice Man - August 26 2014 at 9:57pm

Yes, there is one nearby. I may be able to sneak a few minutes of their time and get their opinion.

It wasn't my intention to go so deep in thought about it here on the forum, my reason for posting about it was to see if anyone had ever had any experience in doing it.

Most of the books on renovations and snippets of information on youtube and on the web don't ever seem to cover aspects of dealing with a house built in 1912.

in your last diagram of truss...dont think you can omitt A
Imagine placing a couple of squares of ashfault shingles at #2 or 4...Conans design is stronger...I get you dont like the length of lumber youll be playing with but youll be stick framing till the cows come home otherwise