View Full Version : basement soffit - should I worry about sag?

11-02-2011, 08:11 AM
I'm in the process of framing the soffits around HVAC ducts and plumbing in my basement using this website as a guide - http://www.familyhandyman.com/DIY-Projects/Indoor-Projects/Basement/Basement-Finishing/how-to-finish-a-basement-framing-and-insulating/Step-By-Step#step5. My original plan was to use 2x4's laid flat for the lookouts (bottom of soffits) in order to retain the most headspace in the room. However, I will have some wide soffits (mostly 4', but one at ~6') and I'm worried about sag once the drywall is installed. I have no way to secure the middle of these runs as the HVAC ducts take up the entire space.

What is the maximum length of a flat 2x4 before you have to start worrying about sag? Would flipping the 2x4's on end be my only other option?

11-03-2011, 10:27 PM
Well, how much sag makes you worry? Get yourself a 4' length of 2x4 and put some weight on it - get a feel for how
much it might "sag" under the weight of a little drywall. FYI, the big box stores have large piles of "pre-sagged" 2x4's that
you can pick through. Get yourself some saggy ones and install them with the sag "up", so any sag from the drywall will
bring them back down level.

11-04-2011, 05:06 AM
Maybe I should rephrase the question. I'm not so much concerned as to the amount of sag that will occur, as much as I am what the finished drywall will look like if the framing does sag. Therefore, will 6' 2x4 lookouts laid flat sag enough when drywall is installed to make the finished surface crack or otherwise look like crap (waves, bellies, etc.)?

11-04-2011, 06:50 AM
I think at 6' you will be ok. Make sure to use KD lumber. I have seen an outdoor deck done with 2X4 laid flat on a 6' width. Definitely not a good plan, but all in all they stood up. A little springy depending on how you stepped. It was a little old ladies house, and I suspect the builder did it because she wanted a "look" and she only weighed about 92 pound wet. It worked for her. Anyway, the 2x did not sag from their own weight , over many years. And a little drywall may stiffen it up for you!

11-04-2011, 07:04 AM
You might also look at using steel studs for this.

11-06-2011, 03:02 PM
If you are enclosing large hot-air supply ducts, you may well have cracking at drywall joints no matter what you do, due to
constant large temperature swings.

Gary in NJ
11-06-2011, 04:15 PM
FYI, the big box stores have large piles of "pre-sagged" 2x4's that you can pick through.

Isn't that the truth. You get one usable length for every 10 you touch. When I look for wood at Home Depot the pile on the floor is much larger then the selection on my cart.

I like the idea of using steel studs and 3/8" drywall for this purpose. With such a short span the 3/8 will be fine.

11-06-2011, 05:43 PM
Where do you find 3/8" drywall, there is no such thing where I come form.



Gary in NJ
11-06-2011, 06:29 PM
Sometimes it sucks to live in Canada...

http://www.lowes.com/pd_11725-74265-3848WBT080000_4294858283_4294937087_?productId=300 9486&Ns=p_product_prd_lis_ord_nbr|0||p_product_qty_sale s_dollar|1&pl=1&currentURL=%2Fpl_Drywall_4294858283_4294937087_%3F Ns%3Dp_product_prd_lis_ord_nbr%7C0%7C%7Cp_product_ qty_sales_dollar%7C1&facetInfo=

11-06-2011, 06:39 PM
Yes, 3/8" is common in the U.S., while 1/4" is not so much here in the midwest.

11-06-2011, 07:15 PM
Doesn't suck to live in Canada when you need to visit the doctor or hospital... ;)