DIY Home Improvement Forum banner
1 - 20 of 26 Posts

·
Registered
Joined
·
152 Posts
Discussion Starter · #1 · (Edited)
I'm adding a master suite addition to my Charlotte, NC house that will come out 16' and be 32' long.
Ceiling/roof will be 2x12" x 16' long rafters. Obviously there is no room for collar or rafter ties with this 12:1 slope Triangle Rectangle Font Pattern Metal
Product Rectangle Azure Slope Font
. Is this arrangement structurally sound? I need to follow code for 2018 NorthCarolina Residential structures. I really want to avoid having to hire a structural engineer and paying another $1300 towards this project. (had to do that with a solar pergola I installed last year).

I had to install knee braces on my pergola, but I'd like to avoid doing that in a house as it would look stupid. Should I use specific metal ties like this one:?
Property Light Green House Architecture
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #3 ·
Well, being above the frost line your slab may move...is that a problem for your addition?
the ground doesn't freeze in charlotte, nc so it's not a problem. there will be a 12" deep footer not shown in sketch as well. I am asking more about the framing.
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #4 ·
I will be using R38 dense fiberglass batts in the ceiling which will leave about 1" of space between it and the OSB roof sheething. code requires R38 be used.
 

·
Naildriver
Joined
·
14,195 Posts
Your framing seems substantial enough. We can't see the front to know how it all will be tied together. A side view isn't much. In addition how will the room be vented? Having insulation up there with no ventilation will present moisture problems. Air must move over the insulation and vent to the atmosphere. You may want to consider spray foam insulation since it has such a low pitch. You will have a snow load problem at 1:12, and wicking of water will take place unless you use precautionary measures. What type material will the roof be, and how will it be tied into the main house?
 

·
Registered
Joined
·
328 Posts
You need ventilation between every bay (inlet air and outlet air.) Suitable ventilation does not look practical here. Foam baffles in each bay won't help here because there is no ridge to put a ridge vent onto to provide outlet air. I second the suggestion to spray foam this, because then you won't need to provide ventilation.
 

·
Registered
Joined
·
7,046 Posts
Weak spot feels like those 2x4s against existing house. I would want stronger rafter connections to the house, I think. Removing some of the existing roof and connecting new rafters to old rafters and using old wall to support new roof. The metal hardware is sometimes used as reinforcement against hurricanes and such. It's good to use reinforcements but compare the cost against such insurances against heavy wind forces. Also not sure about rafter spacing. Your rafter span maybe max for 2x12. Which case I would go for 16" spacing. Not sure. If 24" spacing is ok, at least use 5/8 or 3/4 ply. You must use roll roofing and it must go under the shingles at least 36". Or at least above your snow. I would take the roll roof 36", cover the overlap with ice shield for nail holes then reshingle.
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #8 ·
In addition how will the room be vented? Having insulation up there with no ventilation will present moisture problems. Air must move over the insulation and vent to the atmosphere. .... What type material will the roof be, and how will it be tied into the main house?
well there will be a 1" gap between the R38 batts and the osb roof sheathing. if that doesn't meet code I can tack on a 2x2 or 2x4 to raise it higher. spray foam is too expensive and the roof will be TPO membrane glued to the osb sheathing.
here is front view of house. addition will go in rear corner where windows where phtooshopped in. drew up this 3d render of just the addition
 

Attachments

·
Registered
Joined
·
3,702 Posts
1/12 slope is asking for trouble. Can you lower that end wall and place a closet there where lower ceiling height isnt an issue? Or raise the high side of the roof and have it die into the surface of the existing roof.
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #10 ·
Weak spot feels like those 2x4s against existing house. I would want stronger rafter connections to the house, I think. Removing some of the existing roof and connecting new rafters to old rafters and using old wall to support new roof. The metal hardware is sometimes used as reinforcement against hurricanes and such. It's good to use reinforcements but compare the cost against such insurances against heavy wind forces.
I looked up spans on internet table and 2x12 on 24" OC easily spans 16'. Yes I will be connecting new rafters to the exsisting home's cathedral ceiling trusses. Yes this will be ontop of the exsisting old wall. I do not plan to build a new wall against the old home wall. unless code people say it is necessary.
Also not sure about rafter spacing. Your rafter span maybe max for 2x12. Which case I would go for 16" spacing. Not sure. If 24" spacing is ok, at least use 5/8 or 3/4 ply. You must use roll roofing and it must go under the shingles at least 36". Or at least above your snow. I would take the roll roof 36", cover the overlap with ice shield for nail holes then reshingle.
it might snow 1" every other year in Charlotte. I have 40sheets of 3/4" ply I got off facebook for $6 a sheet, pre pandemic should of got more. seems like a waste to put on the roof, was going to use it as flooring.

spray foam is too expensive I would rather just track on an extra 2x4 to make the 2x12 rafters taller. besides I dont' want to block exsisting rear roof vents.
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #11 ·
1/12 slope is asking for trouble. Can you lower that end wall and place a closet there where lower ceiling height isnt an issue? Or raise the high side of the roof and have it die into the surface of the existing roof.
I know first hand because I will tearing out my old 12x12' deck with covered roof above it which leaked. I had used sheet metal roofing that looks like ^^---------------------^^ and it held up ok, it wasn't PBR agricultural metal roofing which is rated for 12:1 pitch. the leak was between the shingles and the metal roofing which I did a half ass job on. TPO membrane roof is rated to be used on a low slope like that so it should work fine as long as I can get it under the shingles a foot or more.
Yes I can get longer lumber to raise the pitch, but it gets expensive.20' long boards will go for $55 each and structural I joists cost $85 each. my 2x12's cost $26 each so we are talking about 2x or 3x the price to raise the pitch from 12:1 to maybe 12:1.6 ? I was actually planning on using 24' rafters and that would give me a 3 ft rise over 16 feet or12:2.5. takes a lot longer board to raise it up just a bit.
Still going to be a low sloped roof that requires some sort of membrane roof so why spend the extra money is my thought? do you have a better idea? thanks in advance.
 

·
Registered
Joined
·
7,046 Posts
As long as you sheathe the framing, I don't think you'll have any problem with getting a permit. And even if low slope, you can use 1.5" baffle against the sheathing and use insulation for 2x10 which should give you adequate r value esp since you don't have long cold days. Check the local insulation rules. If 2x10 is not enough, you can add xps boards to the rafters and drywall over that. Try to frame little overhang so you can hang gutters but also get the soffit intake and take it to the trusses. This will give you some ventilation for heat and enough to get the humidity moisture moving.
 

·
Naildriver
Joined
·
14,195 Posts
there is a ridge vent another 16' up the roof at the peak
Will this addition be vented to the main attic for the ridge vent to work? How will air be introduced into the cavity above the insulation?
 

·
Registered
Joined
·
152 Posts
Discussion Starter · #16 ·
Will this addition be vented to the main attic for the ridge vent to work? How will air be introduced into the cavity above the insulation?
yes, via soffit vent. Dense Fiberglass batts that are R38 are 10.5" tall and I will nail 2x4's on top of the 2x12 rafters to give a couple inches of air vent space. local code requires R38 minimum ceilings.

Slope Rectangle Triangle Parallel Font
 

·
Contractor/Engineer
Joined
·
1,628 Posts
You'll need a permit. If you're the GC, your city may allow you to submit your drawn plans (plus all the other documents) and then they may allow you build once it passes their engineering review.

I've done similar 16X20 with hand drawn plans in a couple of towns. Other towns - no way, need the engineer, etc.
 
  • Like
Reactions: solarroofingpro

·
Registered
Joined
·
152 Posts
Discussion Starter · #18 ·
Other towns - no way, need the engineer, etc.
never understood why an engineer is needed on standard construction practices. I can see needing an engineer for unusual applications, but this seems straight forward to me. maybe to cover thier ass if the thing falls down and kills someone?
 

·
Registered
Joined
·
4,239 Posts
It's up to plan check.
You draw your plans, or have plans drawn by a draftsman or an architect, and see if the city accepts them.
If they do, they will list their corrections for you to do, and will tell you to resubmit the plans.
Please don't look for logic, just follow their instructions.
If they approve your submitted plans, they'll stamp them and assign you a bldg inspector and an inspection card (permit).

BTW, double check the footing depth, rebar schedule and size and type of concrete they call for.
 
1 - 20 of 26 Posts
Top