My kitchen remodel featuring removing a wall to open up space turned into more than I had planned on my 1840s farmhouse. I had to remove the inadequate ceiling joists in the side room otherwise of the wall and noticed zero collar or rafter ties above. All the framing is structurally firm oak or chestnut and not bowed. Rafters are true 2×4 spaced 24”oc with lengths of 8’4”. Roof is a 7/12 with a 1x ridge board at height 4’ above top plate Room size is 14’x15’.
I would like to raise the ceiling from the original 8’ to a new 10’ and had thoughts of installing a 2×8 or 2×10 tie on each rafter at 10ft which is half the height of roof rise and would span close to 8’ total length to nail into the rafters.
In order to accommodate the most insulation I need to pad out or sister each rafter. My question is, would a 2×6 on edge underneath the existing rafters with plywood sandwiching the two together, nailed into the top plate and studs and then into the rafter tie without running the full length to the ridge board, be adequate enough? Or would that have an adverse affect on the roof structure.
Or should a 2×8 or 2×10 sister each rafter and run full length?
Thanks
Replies
Might help if you make a few sketches.
were the ceiling joists you removed installed in a way they kept the walls from spreading out due to the roof load? if so, you are contemplating replacing rafter ties at the top of wall level with ties that are further up, (which reduces the span capacity of the roof rafters), and also hanging more structure from the midpoint of the rafters.
It would be best to consult an engineer.
best plan to understand based on examination of the structure, and considering the location, and roof load requirements.
https://codes.iccsafe.org/content/IRC2018/chapter-8-roof-ceiling-construction
can help you understand the impact of raising the ties up the rafter. (but since your modified structure does not use current graded lumber, the specific numbers and spans will not show up in the tables.)
“[Deleted]”
I have made some different sketches to scale. The ceiling joists I removed were 2x4 spanning the whole way without any bracing. Some butted and sandwiched with plywood to complete the span, some just twisted right out and most were only nailed with on or two nails. Structural engineer has been contacted but may just lower the ties into the bottom 1/3 from the halfway point to lower the ceiling down 8 inches and increase the effectiveness of the rafter ties
The boards you removed were holding the walls from moving away from each other due to the roof loads.
If you decide to avoid the expense of an engineer, I would suggest you select additional rafters to carry the load, considering your tie location, run them all the way to the peak, and use framing connectors to secure them to the top plate of the wall (in both the vertical and horizontal directions.) and make sure the existing rafters are secured to the top plate and the new rafters as well. (You can make the new rafters lower than the roof, to allow for insulation and venting space.)
An important part is that these framing components have to keep the walls from moving away from each other, which is critical for the continued life of your existing roof. If you fail to do this, a heavy load (think a couple feet of heavy wet snow, for example) immediately or lesser loads over time will push the walls away from each other, and allow the roof to fail, falling on what and who ever is inside at the time.
Your engineer will likely come up with a lower-cost solution.