Vent installation short cut

[Rich P]

Tomorrow I'm going to tackle the microwave vent installation (with my SIL's help of course ). We going to use the rear venting option which will exhaust straight through a 3-1/2 x 10 "pipe" in the exterior wall on which the microwave is installed.

Should be a piece of cake except that I strongly suspect there is a stud someplace in the opening we have to cut. If the stud is centered, it's no big deal as the microwave actually has two blowers, one on each side of the 3-1/2 x 10 opening, so the stud would not interfere with the airflow.

OTOH, if it's in the path of one of the blowers, I either:

Option 1 - just cut the sheet metal to fit around it and not worry about it.

Option 2 - just cut the stud

Because of the clearances, I don't believe there is enough space to open up the interior wall and install a header. The rule of thumb I have always followed for Douglas Fir lumber was the header should be 1" x the length of the span in feet, so this would need to be a 4 x 4 header. This would mean using the top venting option, cutting into the cabinetry above the microwave and trying to route the venting around the problem.

I know what a building inspector would say, but what are the real world problems with Option 2? (This is a 1 story wood frame 30 year old ranch style in good condition.)

TIA for all the thoughts.

p.s. I'm trying to keep this to a 1/2 day project.

[twistsol]

This exact situation was on Ask This Old House last night. You run the potential of the celing or floor above sagging. It realy depends on what is above the stud you are about to cut. If it's a single story house and your on a gable end there is no load to dealwith if you are die gly below a floor joist, you will have bigger problems.

[Rich P]

It's a hip-style roof and a single story house. I figured I would check for ceiling joists and rafters above the opening to see where they are landing on the top plate. The only real load would be from the roof as the ceiling load is just the sheet rock and some blown in insulation. Also, this is the coastal area of California so there are no snow load worries.

[cabinetman]

If there is a stud in line with a rear venting, you might consider venting up into the cabinet, which would give room for a jog to be in the duct. Then duct out the rear of the cabinet.
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[jdon]

Any possibility of fitting an adapter to a round flue, and using flexible pipe to go around the stud?

[Rich P]

Cabinetman,

Yeah I can go that route it just adds time and takes up space in the upper cabinet. The only common venting I have seen is to transition from the 3-1/2 x 10 rectangular vent to a 6" round. This would allow the "jog" via an elbow. I have not spotted a rectangular fitting that would allow this to be done without the transition. I have seen 45 degree fittings than bend along the long side but nothing that bends along the short side. Two 45's for the jog and a 90 to go out the back and I'd be happy but I don't know if these exist as a standard item. I suppose I could get out a pair of snips a butcher up a piece of 3-1/2 x 10 duct?

jdon,

Nope, unless I go up. I have only the space in a standard 2x4 framed wall.

Rich

[cabinetman]

I suppose I could get out a pair of snips a butcher up a piece of 3-1/2 x 10 duct?


Rich

I've had to do that before. Also check to see what's available in pre-made ducting.
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[toolguy1000]

i had the same problem when i did my kithcen. i removed a section of framing like silva did on TOH. it's not really difficult. there is only a small probability that cutting one stud and reframing it will cause any problems during the reframing. it's not like you need to build an interior wall to support the load when reframing for one stud. reframing is the best long term solution.

[cabinetman]

I've owned 4 homes in the last 40 years. I renovated each one with cabinets and appliances. The first home had an exterior wall duct. Since that one, all were interior walls, and I hooked up microwaves as non-vented. To tell the truth, I don't notice a difference to warrant installing them ducted.
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[Rich P]

Wish I had seen this Silva episode. I actually wouldn't "reframe", just cut out enough stud to allow the ducting to pass through (nominally 3-1/2"). The whole thing then is covered when the microwave is reinstalled so interior appearance is not an issue. On the exterior (stucco), the wall cap has a flange that extends past the nominal opening so that trims out that side. A little caulk, some plastic anchors and some screws and the exterior is done.

I was walking the dog earlier and went past a local remodel site where I know the general and his foreman. They were both on site and their take is "cut the stud if you have to". The top plate is a doubled-up 2x4 spanning 32" which is more than enough to take just a roof rafter and/or ceiling joist. If we were talking two stories or some special load, that would be different.

[toolguy1000]

all that's involved in the reframing is spaning the opening created when the one stud is cut with 2x material. it's like creating a small 2 dimensional box in the wall. i'd try contacting TOH and see if they have a link on one of their sites. once you see how realy easy it is, you won't think about trying today's shortcut that comes back to bite you in the future.

[tseavoy]

If it were me, I'd just cut the stud and forget about reframing around it. Houses are a bit of overbuilt. That stud was carrying very little load and the exterior sheathing will serve to carry any load around the opening. Not advising you, but "if it were me" ----

Tom on Marrowstone


"why can't the electrical outlet and the fork be friends?"

[Bill Stock]

My experience has been that it's usually better to just do it. The amount of time I spend dicking around looking for a shortcut is not worth the aggravation. I really hate drywall, but it's not that difficult to do a decent cut and patch job.

[Rich P]

All,

The opening from the back of the microwave is at the point where the overhead cabinet bottom meets the wall. That's the corner where the vent needs to be placed. In order to do anything regarding framing I'm have to pull down the whole wall of cabinets. Realize this is a microwave/hood range combo installed between wall cabinets with a small overhead cabinet above.

Running a 2x4 horizontally between a cut-off stud and the adjacent studs offers little structural help for the load above. All it does is support the edges of the drywall which is not a problem here since the opening is behind the microwave.

The good news is based on my SIL's tests with the stud finder, we don't have a problem. If it turns out we do, I with Tom from further up the west (as in left side of the map) coast, cut the thing and move on.

I'll update this post with whatever happens tomorrow.

Thanks to all for the inputs!

Rich

[Rich P]

Got the vent installed just fine. Turns out there was a stud in the center of the vent opening and another one about 5 inches away, so we cut the center one and notched the other by about 1/2". Left both dampers in place and everything works well.