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Old 12-13-2008, 10:42 AM   #1
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I have a guy who wants to heat/cool his attic in preparation for a conversion to a family room. It is fairly large and I am going to put in several ducts to get enough volume up there to meet the needs.

To this end I am going to have to cut into a basement joist to get the duct work up there.

I have looked over all other options that there is no other way to get the duct up there unless I build an outside facade to put the ducting in. Even with that there is only one place I could do that as there are a lot of windows that I have to mess with.

So my question is, does anyone see a problem with going ahead with this plan.

I want to cut the top 6 inches of a 2x10 joist (at 16 inch centers) that will be 14 inches wide and putting in 1/8 metal plate on either side of the joist that would be bolted to the joist in many places.

The duct work has to be 6x14 to get the volume I need up there.

On the other side of the house I will be doing the same thing only it will be a return.

Here is a drawing.
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Old 12-13-2008, 10:55 AM   #2
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Honestly, I wouldn't do it. If you do, you need something thicker than a 1/8" flitch. 1/4" would be more appropriate. It would of course need to be bolted to the joist in a staggered pattern at least every 16" top and bottom. I'd add glue to resist squeaks. The longer that plate is, the better.

I'd also suggest blocking between the joists to give it some lateral prevention since so much material is being removed from the top side...Roll resistance. Under load it will want to twist laterally.

Instead of going to the trouble of notching, have you thought about completely cutting out a small section and headering it off to the adjacent joists? Nothing wrong with doing that in 99% of cases. Just use joist hangers on everything and you're good.

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Old 12-13-2008, 11:02 AM   #3
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Just for my own knowledge; cant you use different size duct work, like 4x16 so less material would have to be removed ?
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Old 12-13-2008, 11:16 AM   #4
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Honestly, I wouldn't do it. ....
Instead of going to the trouble of notching, have you thought about completely cutting out a small section and headering it off to the adjacent joists? Nothing wrong with doing that in 99% of cases. Just use joist hangers on everything and you're good.
I'd have to agree with KCT, don't do it. Even if you tried the flitch plate route (larger than 1/8" thickness), you would be required to have something certified to show that the plate had been engineered and approved for the load and span of the project. Besides, I can't see that working out anyways, based on the supplied diagram.

As KCT stated, the best route is to bridge the opening to create a box. Use the same sized lumber as the joists, with joist hangers. The two connected full joists would have to be doubled up, and the two new perpendicular bridging sections would need to be doubled with doubled hangers. The whole thing would have to be code approved as well, prior to the work....
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Old 12-13-2008, 11:17 AM   #5
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Honestly, I wouldn't do it. If you do, you need something thicker than a 1/8" flitch. 1/4" would be more appropriate. It would of course need to be bolted to the joist in a staggered pattern at least every 16" top and bottom. I'd add glue to resist squeaks. The longer that plate is, the better.

I'd also suggest blocking between the joists to give it some lateral prevention since so much material is being removed from the top side...Roll resistance. Under load it will want to twist laterally.

Instead of going to the trouble of notching, have you thought about completely cutting out a small section and headering it off to the adjacent joists? Nothing wrong with doing that in 99% of cases. Just use joist hangers on everything and you're good.
I could put in a header but only on one side. The furnace side will be filled with the duct work to the attic.

I was going to build a small shelf on the floor and just go around the joist but there is a formal dining room about it and the soffit would look terrible on a nice clean wall that runs for 15 feet with no obstructions. The other wall is a library with floor to ceiling custom made wood book shelves. The owner was not real thrilled with that option.

So would you be good with an 8 foot by 1/4 plate and lots of bolts? I have lots of room to put in lots of iron if necessary.
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Old 12-13-2008, 11:22 AM   #6
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Just for my own knowledge; cant you use different size duct work, like 4x16 so less material would have to be removed ?
Air volume. A 4x14 (can't do a 16 on 16 inch centers) will handle 220 cfm while a 6x14 can handle 460 cfm.

As it is 460 is just barely enough to work and will probably not work on really hot days.
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Old 12-13-2008, 05:07 PM   #7
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Why not a split system?
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Old 12-13-2008, 05:55 PM   #8
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Why not a split system?
Yea, that is an option that I considered. I am still looking at that and trying to figure out if I can get enough air up there.

I might just put in a vent somewhere to the lower floors and let that be the return.
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Old 12-13-2008, 09:31 PM   #9
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Even if you can run a duct and get the conditioned air up to the room. you will have to provide and adequate retuen for it to function well.
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Old 12-13-2008, 09:44 PM   #10
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I would forget the forced air heating and put electric.
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Old 12-14-2008, 01:15 AM   #11
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I would forget the forced air heating and put electric.
Heating is not much of an issue since the heat rises through the house. It is the cooling in the summer that will be the big issue.
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Old 12-14-2008, 01:17 AM   #12
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Even if you can run a duct and get the conditioned air up to the room. you will have to provide and adequate retuen for it to function well.
I am thinking of putting in a return through the slanted wall to the 20 foot entrance. This will move enough air to make it work.
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Old 12-14-2008, 11:05 AM   #13
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Heating is not much of an issue since the heat rises through the house. It is the cooling in the summer that will be the big issue.
I tend to forget the importance of a/c. as I live in the north where heating is the primary concern!

One question that come to my mind, is the existing a/c sized to accommodate the increased load of the the reno.
If it doesn't have the capacity, perhaps a heat pump should be considered!
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Old 12-14-2008, 01:24 PM   #14
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I tend to forget the importance of a/c. as I live in the north where heating is the primary concern!

One question that come to my mind, is the existing a/c sized to accommodate the increased load of the the reno.
If it doesn't have the capacity, perhaps a heat pump should be considered!
It is oversized. I put in a ground loop system for him years ago and he has more cold that he needs. If I remember correctly I have 2000 feet of 3/8" pex at 8 feet deep. He has never complained of not having enough cold to go around.

This just gave me an idea.

I could do a hydronic cooling system up there. Humidity is not a problem....hmmmmm.

I think I have just solved my own problem.
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Old 12-14-2008, 04:27 PM   #15
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I have a guy who wants to heat/cool his attic in preparation for a conversion to a family room. It is fairly large and I am going to put in several ducts to get enough volume up there to meet the needs.

.
Since it's a large room, is there any room to put a small system in the attic?

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