Basement Framing for HVAC

[jjohnston]

I am planning to start the framing of my Basement. I have a couple questions about HVAC and ducting.

1) Do I need 6" walls to drop my cold air return ducts through (I think code here requres they be ducted, not use the wall cavity)?

2) My Basement has a main cold air return duct that runs the full length of the basement, can I just punch a hole in that and run my ducts down the wall? that main duct seems to go directly over the walls I would drop the duct down.

 

[nealtw]

It is about the square inches, if one cavity in a 2x4 wall is not enough, do 2 cavities or move the stud over for bigger cavity.
I have never seen duct run down the wall for return air. But if you have to cut the hole before you build the wall.

 

[user 4883]

Re: the main, yes you would tie in to that but be sure to install a manual damper in each tie in branch.

 

[jjohnston]

I"m debating having an HVAC company do it... I don't know a lot about HVAC. But if I do the framing, I did confirm with an HVAC place that they do need to put oval ducting down inside the walls now. they said they use a 3.5" oval duct that works in a 4" studded wall. But now my question is, if its 3.5" I would need to cut a 3.5" hole in my top plate, and code says I can't cut more than half the wood out without some kind of metal reinforcement. Can I still do this? I don't know how strong 1/4" of wood on either side of that duct would be.

Also, in framing, I am looking at the below for my top and bottom plate. it says its #2. but my 8' long studs are stud grade. am I OK using #2 grade for my top plates? I'm planning on doing a double top plate.

https://www.menards.com/main/building-materials/lumber-boards/studs/2-x-4-lumber/p-1444422747483.htm

 

[nealtw]

I thought you were talking about return air.
Heavy metal strips for bearing walls, not so important for non bearing wall but absolutely needed to protect wire are plumbing from drywall screws.

 

[nealtw]

I"m debating having an HVAC company do it... I don't know a lot about HVAC. But if I do the framing, I did confirm with an HVAC place that they do need to put oval ducting down inside the walls now. they said they use a 3.5" oval duct that works in a 4" studded wall. But now my question is, if its 3.5" I would need to cut a 3.5" hole in my top plate, and code says I can't cut more than half the wood out without some kind of metal reinforcement. Can I still do this? I don't know how strong 1/4" of wood on either side of that duct would be.

Also, in framing, I am looking at the below for my top and bottom plate. it says its #2. but my 8' long studs are stud grade. am I OK using #2 grade for my top plates? I'm planning on doing a double top plate.

https://www.menards.com/main/building-materials/lumber-boards/studs/2-x-4-lumber/p-1444422747483.htm

Top and bottom plates are usually wet lumber as it is easy to straighten them out as you nail them in place. If you order studs the will be pre cut for standard wall height and cost more. And most times don't fit in the basement. If you have to re cut them you may as well just buy 8 footer.

2 and better is the standard for all home construction.
Sill gasket between wood and concrete, always.

 

[Snoonyb]

What is the intended occupancy of the individual rooms that would require an individual return for each space and what manner are you intending to seal each space so that a centrally placed return would not be sufficient?

If your walls are non-bearing, there is no need for double top plates.

Dimensional lumber, IE., 2X4, is 1.5" X 3.5", and is why the HVAC CO is stating that dimension for their duct.

 

[jjohnston]

I guess my reason for double top plates are, length. max length I can get is 20' for wood locally. So I need to build walls in multiple sections. Code says I need to stager my top plates for strength, so I figured, double wall plate, have the top plate extend 2' past the 2nd top plate, and I fulfilled my requirement.

My basement measures 8'4" from the cement to the bottom of the floor joists above. So either I have a 1" gap or I do a double top plate, and cut the 8' studs down a half inch? but am open to suggestions of better ideas.

Code changed here in Minnesota in 2015, that now all cold air returns need to be ducted. we can no longer use the space between the studs...

For dropping the return air duct down the wall, do I simply leave a gap in the top plate, or try and cut it out? or does the HVAC person do the cutting?

Intended occupancy is 1 bedroom, 1 bathroom, 1 media room, and 1 family room. I think code states that all bedrooms need to have a supply and a return. My media room will be sealed off from the rest of the basement, so its a separate room. Not completely air tight, but as tight as I can get it without going crazy about it.

 

[jjohnston]

Oh, and do I care about premium grade stud vs standard grade stud? its about 60 cents more for premium per stud...

 

[Gary]

Do they say why you can't use the wall space? Not doubting it, just wondering why. I'm guessing it has something to do with fire prevention?

 

[nealtw]

Oh, and do I care about premium grade stud vs standard grade stud? its about 60 cents more for premium per stud...

Not sure what that means but if you are buying pre-cut studs I like the finger jointed ones made out of scraps because they are straighter and real lumber.
They are not to be used for horizontal.
If you are dealing with the big box stores and you are buying pre cut. Measure them. Canadian standard studs are 92 1/4 US standard stud 92 5/8.
They have been known to just sub one for the other.

Do you know how to level down from upstairs so everything is square in the basement.

 

[nealtw]

Oh, and do I care about premium grade stud vs standard grade stud? its about 60 cents more for premium per stud...

OK found a listing for LUMBER and PREMIUM LUMBER, still don't know what that means.
The cheap and standard stuff we use is SPF 2 and better and I suspect that is the cheap lumber but if it is number three, spend the $.60.

 

[jjohnston]

Yeah, it has to do with energy efficiency. all ducts now need to be completely sealed by either welding, adhesive, etc. maximum air leakage can't exceed something like 2% over the entire system.

Its same thing for plumbing. all hot water lines need to be insulated from right out of the water heater, all the way through the walls to the faucet.

 

[Gary]

ahh, that makes sense I guess.

 

[jjohnston]

lol both say stud grade or better. the only difference I could see is one says Species may vary among Spruce, Pine and Fir, the other just says varies from pine to fir. so no spruce in the cheaper ones...

 

[jjohnston]

Not sure what that means but if you are buying pre-cut studs I like the finger jointed ones made out of scraps because they are straighter and real lumber.
They are not to be used for horizontal.
If you are dealing with the big box stores and you are buying pre cut. Measure them. Canadian standard studs are 92 1/4 US standard stud 92 5/8.
They have been known to just sub one for the other.

Do you know how to level down from upstairs so everything is square in the basement.

level down? Umm... I guess not, didn't know that was a thing...

I do know my unfinished basement has its ceiling drywalled already due to the new fire codes

 

[nealtw]

level down? Umm... I guess not, didn't know that was a thing...

I do know my unfinished basement has its ceiling drywalled already due to the new fire codes

Good then the fire stopping between walls and floor system is done. Are your outside walls finished and if not how high is the foundation?

 

[jjohnston]

outside walls are not finished, that will be my first step. I believe the block goes up about 8' 3" until hitting the current drywall, then the space between the drywall and the block has spray foam filling the void. but I will measure to be sure.

 

[nealtw]

outside walls are not finished, that will be my first step. I believe the block goes up about 8' 3" until hitting the current drywall, then the space between the drywall and the block has spray foam filling the void. but I will measure to be sure.

That's ok I was just thinking full height half height or curb.

Best laid plans get screwed by someone else doing a good thing.

We always got there before the drywallers so we fire stopped with the top plate using a 2x8 against the sill plate on top of the wall but your spray foam did that in.
If you have an interior wall near the staircase, work your long lines off that and measure over to the outside and check that for straight and use the 3,4, or 6,8,10 to make sure the other walls are square to that.
We always leave a 1" gap from wall to foundation but with a block wall you can get closer, but not touching.

 

[jjohnston]

I want to do 2" thick rigid insulation again sedan the block, then 2x4 wall framed right against the insulation.