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RWebb 09-20-2010 10:25 PM

Sistering Rafters/Ridgeboard
I'm in the middle of remodeling the back part of my home. Home was built in 1920. The current roof rafters are actual 2x4's 33" center. Now that's scary. Not sure on what type of lumber is used. It's very dense.

The joist rest on each other where a ridge rafter would be in today's construction. I was going to sister 2x8's to the existing rafters along with addition rafter in between making them 16oc.

Any suggestions on what I can do for addition support. Should I notch below the rafters at the ridgeline and install a beam? I have also read that I can have a welder make a V shaped steel plates to bolt to the top portion of the of the rafters.

I know the first response will to be to consult a structural engineer to size the beams. I would like to hear what are my options.

I would include a picture, but no longer have a server or hosting site.



josephine 09-21-2010 02:43 AM

Dense wood
I have a similar situation, though my rafters are huge. I know I need to drill pilot holes in the dense wood; nails just bend too much without this. The wood could be the hearts of oak. I don't know enough about American Chestnut to know if it could be that.

Gary in WA 09-21-2010 01:56 PM

RW, get a building permit. Then what you are already doing and propose to do will meet minimum safety standard. Your H.O.Insurance will cover the addition with the paper trail and in case ever a problem even after you move out.


WillK 09-21-2010 03:34 PM

What are the rest of the details, overall size of the house (span of the rafters) is it a single story or story and a half, is there an actual sagging problem or is this just a concern, has sheathing been added, is there a knee wall supporting the rafters mid-span or rafter ties?

Rafter ties and/or knee wall may provide extra support AND present problems with adding rafters of larger size, and adding more rafters of the same size might just be adding weight...

My house has 2x4 rafters on 24" spacing, was built in 1917, has had sheathing added... I was concerned about the spacing and span, but I feel okay with it now. The rafters in my house get support from knee walls and ceiling joists that are in the top 1/3 of the rafter so they tie them, and there is no ridge board (which IMHO is a construction aid more than a necessary structural element)

On the other hand, I had 2x4 rafters in my shed dormers at a 4/12 pitch, inadequate ventilation and blown in insulation (along with birds nests in what little vents there were, and previous homeowner taping off of gable vents to prevent said birds) The result was moisture and those rafters didn't have the pitch to run off the moisture, so they rotted and had to be torn off and replaced - which I used as an opportunity to build gable roof over the dormers.

slummy 11-24-2010 11:08 PM

sistering rafters
My 2 x 4 rafters are 24" on center. They support 3 layers of shingles, a layer of cedar and a layer of pine sheathing - that's a lot of weight. So much so that it has cracked several of the rafters.
After consulting buddies of mine that each have twenty plus years of roofing experience I am going to follow these directions;

First replace floor joists from end to end (the entire span in all structural framing is key) Use nail gun and circular for this
Step 2 lay a 2x6 plate across and above the entire span of my attic floor / downstairs ceiling joists
Step 3 climb step ladder, use speed square to measure pitch of roof, set chop saw and cut base plate side of 2x6 sister rafter
Step 4 Have a friend hold base plate flush to floor (I don't need a seat cut - you might)
Grab other end of sixteen foot 2x6 climb step ladder use square to draw a line down from my 1x8 pine ridge plate, cut 2 x6 - lay sister rafter on the ground then
Step 5 use a four foot level against cracked rafter and good rafter to inspect the difference in pitch (get a mental picture of how the good rafter looks)
Step 6 jam a kneewall sized 2x6 between new base plate (step 2) and cracked rafter to take the sagg out of the roof (check pitch with level)
Step 7 from end to end nail up the sister rafter that I just cut both sides of with the nail gun my buddy lent me.

Step 8 remove kneewall from new 2x6 rafters and put them under good 2x4's

Peace out y'all

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