Cutting a hole in 2nd floor rim joist
I’m having a company come out to my house next week to install central A/C. The house is your typical 4 BR New England colonial with a 1 story addition off the back.
The issue that I’m having is how to get a supply duct to the family room on the back side of the house. The pitch of the roof is roughly 4/12 and is too shallow for the installers to go through the side of a closet and into the “attic” of the family room. Based on my calculations, it seems that the best option is to drop a supply duct through the floor joist bay (parallel with the floor joist) and go through the rim joist into the “attic” of the family room. The floor joists are 2×12, 16″ OC and I believe they will be using an 8″ duct.
I know there are rules that give guidance for floor joists in terms of the size of the hole and how close it can be to the edge, etc. But what about rim joists? It seems that rim joists are there to keep the floor joists equally spaced and perpendicular. It doesn’t seem like that they provide much structural support.
Is this safe to do? This would leave roughly 1.5″ of wood on top/bottom sides of the hole which is a bit on the thin side. I could strengthen the area by gluing 3/4″ plywood on both sides of the joists. Perhaps another option would be for the installer to use 6″ duct instead of 8″?
Replies
Can you post a photo of the rimjoist? Normally, you're right; a rim joist doesn't always carry a span load, but I would be reluctant to say "cut away!" without a clearer picture.
As far as routing the ducting; most HVAC shops can configure ducting to fit some really oddball circumstances. Basically, the objective is to match the cross sectional area of the ducting to the flow requirements of the design. The shape can be square, round, oval, rectangular and with a variety of turns and offsets, if required, in a variety of shapes.
With that in mind, and a few tricks of the trade by the installers, there are few "inaccessable spaces."
Notchman, thanks for the quick response. I've attached a photo of the area. The photo is taken from the room that is in the main house and is looking into the family room. The blue squiggly line with the words "Hole here" is where we'll likely need to cut a hole in the plaster ceiling to expose part of the joist bay. I don't have a picture of the rim joist itself since I will wait until the installers come on Monday and discuss it with them.
The "beam" is roughly 9" wide (including the two 3/4" trim boards. The depth of the beam is 11 1/2 inches. The span of the beam is ~ 9ft.
The family room ceiling is ~ 4.5" lower than the ceiling of the main house. I don't know what type of framing is in the ceiling of the family room. I suspect that it is 2x4 trusses for 2 reasons: 1) the width of the room is ~20ft and there are no partition walls in the middle. 2) the attic of the main house was framed with trusses although the family room addition was added a few years after the main house was built. (main house built in 1966, addition around 1968).
The wall with the picture of the horse is a bearing wall that separates the kitchen from the living room. On the second floor, the front closet wall in my daughter's bedroom sits on top of this bearing wall. The closet is ~24" deep.
So it seems that the rim joist is adequately supported by the beam and is not carrying the span load by itself. You bring up a good point that the ducting do come in variety of sizes.
Since the family room is where we spend a good portion of our time, I do want to use every option to get a real supply duct in the room. Several fallback options exist. Once is to put the supply register right where the blue squiggly lines in the picture but sort of angle it to direct it into the room. Kind of sub-optimal with the 12" beam in the way. The other option is to punt on this and do the ducting when the upstairs bathroom is remodelled. Then I could build some sort of chase for the duct and it could enter the family room ceiling via the side of the exterior bathroom wall.
With that beam carrying the load (if I'm following you), I suspect the rim joist can be cut out to accomodate the ducting.
But let us know what the installer comes up with....yours is one of those situations that require a little on-site climbing and poking around.