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Sun Room Addition Lateral Analysis/Design

Sun Room Addition Lateral Analysis/Design

Sun Room Addition Lateral Analysis/Design

(OP)
I have be asked to design a one story 20' x 12' sun room out of wood.  It will have a gable roof with a mean roof height of 15'.  The sun room is to be placed the back of a two story brick veneer house.  It will be located in a 100 mph wind zone.  The client wishes to have the sunroom built on a c.m.u./brick perimeter foundation wall in order to get the sun room floor to match the existing house floor level.  I do not wish to attach the sun room to the brick veneer on the house.  Therefore, I am at a bit of a loss as to how to provide adequate lateral bracing and foundation anchorage for the sun room as the client wishes have the walls for the most part consist of windows with 6x6 posts between.  Could I get some input on how to approach this one?  

RE: Sun Room Addition Lateral Analysis/Design

There are really only two ways without shear walls:  rigid frames or braced bays.  With wood, rigid frames probably won't work, especially with only 6x6 posts.  That leaves bracing in some of the bays.  Diagonal braces, either T-C diagonals, or tension x-braces, may be a solution, provided your client doesn't mind the look.  Otherwise, you may be looking for a different material than wood.

RE: Sun Room Addition Lateral Analysis/Design

Another way is to utilize a special roof diaphragm to cantilever off the main house.  This will require a flat ceiling in the sun room, special connections to the main roof, possible special framing within the main roof/ceilng to distribute the shear and moment from the sun room diaphragm-cantilever, and a check of the diaphragm deflections to ensure adequate rigidity.

Also, since you have very little "wall" lengths, you should check the wind uplift on all those posts between windows and provided engineered tie-downs at the roof and foundation level.

And one further thing...chasing down the load path....be sure to check that the post holddown uplift forces are fully developed down to the footings.  With msonry block foundation walls, you could possibly anchor bolt into the top course and not develop the vertical rebar in the wall to hold-down the top course.

 

RE: Sun Room Addition Lateral Analysis/Design

I have used JAE's solution for these types of additions.  Workr just fine - actaully builders have been kind of doing it that way for years.  Now we must prove they were correct and design the connections.

RE: Sun Room Addition Lateral Analysis/Design

(OP)
Thanks for the responses.  I find them helpful.  However, I will not be able to tie into the roof of the existing house.  It is a two story house and I am designing only a one story sunroom addition.  Is it possible to remove portions of brick to tie into the existing house structure  to tie the sun room to the existing structure (say at the top and bottom wall plates).  Or does this addition need to be built as a free standing structure butted up to the existing brick?

I think I may be able to talk the client into allowing me some wall space in the corners, therefore, I may be able to use the APA Portal Frame construction.  Any thoughts would be appreciated.

RE: Sun Room Addition Lateral Analysis/Design

May be you can fix some colums to a stiffer roof, then tie the columns to the foundations, and then (if permissible) the roof to the main structure of the house, or add some complementary structure to make it work.

RE: Sun Room Addition Lateral Analysis/Design

Can't you tie your sunroom roof diaphragm back into the floor diaphragm of the main house? With the description you have provided, this can not be designed as a free-standing structure as you do not have adequate room for frames on you sunroom walls.

RE: Sun Room Addition Lateral Analysis/Design

(OP)
Thanks KBVT.  That may be possible, but I am unsure of how to tie into the existing structure framing - I would need to penetrate the existing brick veneer.  I don't know how to do this adequately to carry the imposed loads and loading the brick veneer and avoiding water penetration issues.

RE: Sun Room Addition Lateral Analysis/Design

KBVT is on the right track.

You would need to punch holes into the brick at the additions "chord" locations (top of the new walls at the juncture of the new walls to the existing walls).  Then some means of tying the new roof chords back into the floor framing (hopefully the floor joists are perpendicular to the existing exterior walls).  This may require some partial demo of existing interior ceilings, etc. to get attachment to the floor diaphragm.

 

RE: Sun Room Addition Lateral Analysis/Design

You could also go to a pole footing scenario here at all the walls, to include the juncture with the house.  The 6X6 could be steel tubing if necessary, either embedded into the foundation or bolted to it to gain fixity.  

I have done this in the past coupled with short 2 to 4 foot high plywood shear exterior walls to decrease the pole bending length.   

Mike McCann
MMC Engineering

RE: Sun Room Addition Lateral Analysis/Design

Personally, I would avoid attaching to the house.  Too fiddly.  Like Mike, I would look at a steel solution, with the steel posts both embedded and connected rigidly to steel header beams.  I think I could convince my clients that this is the right solution, but I don't know your client.

RE: Sun Room Addition Lateral Analysis/Design

This might be the most over-thought post I have seen here for a while.
You're making a sunroom addtion into nuclear power plant design.
Meet with the possible builder. Any builder with half an ass will be able to provide plenty of insight as to how you can actually build the room.
This type of addition is nothing new or special. You can't do ALL your engineering on paper.

RE: Sun Room Addition Lateral Analysis/Design

One learns by discussion.  Therefore, discussion is good.

Mike McCann
MMC Engineering

RE: Sun Room Addition Lateral Analysis/Design

true-
Dont know why I shot off like that.
Sorry...it was pathetic on my part.  

RE: Sun Room Addition Lateral Analysis/Design

It is probably because prior to being an educated engineer, I was a builder...and a builder of many additions like this one.
I know one thing, building an addition like this that is an order of magnitude more robust than the house is neither prudent nor logical...unless you are trying to hold the existing house in place.  

RE: Sun Room Addition Lateral Analysis/Design

Stillerz,

In no way are any of us giving advice to build the sunroom more robust than the house.  Building an enclosure 15' high with nothing but glass for walls is entirely different from building a two storey brick veneer house with lots of intended and unintended lateral stiffness.

RE: Sun Room Addition Lateral Analysis/Design

All,

All apologies...not sure what my problem is today.
I am not even sure I read the original post thoroughly.
Please accept my apologies.

Regrets

RE: Sun Room Addition Lateral Analysis/Design

Stillerz,

Apology not required, but accepted.  We all have our days...

RE: Sun Room Addition Lateral Analysis/Design

Stillerz - keep poking your opinions in here, though.  Lots of "thinking out loud" is good.

 

RE: Sun Room Addition Lateral Analysis/Design

JAE- Is that a nice thick layer of sarcasm I detect?
If so, I deserve it.

I have done a few home additions similar to this, maybe not to this scale, but I think so.

I have dealt with is as follows:

Where the second floor diaphram is, (or in real world terms, the floor framing, floor joists and rim or box joists) located I would strip some of the brick away.
I would install pieces of LVL that I would call "frieze blocks" for lack of a better term. I would solidly fasten these 4" blocks to he floor framing with through-bolts and adhesive and would also put extra blocking between the floor joists in the existing house to tie this assembly further. I would then do the same in a few spots in the wall above the floor diaphram in locations where the truss will be.
 The first truss to go against the existing house can then be attached to these "frieze blocks" as can the bottom chord bracing, nicely tying the addition to the existing house without relying on a brikc veneer.

This way, the overwhelming majority of the brick can be left in place and the parts that are disturbed hidden nicely.
 

RE: Sun Room Addition Lateral Analysis/Design

no sarcasm.  I tend to do the wrong thing:  speaking before thinking (i.e. thinking out loud) too often myself....so I have emphathy for all who do also.

 

RE: Sun Room Addition Lateral Analysis/Design

Hello,
I assume the eaves height is about 8-9 feet above sole plate level. Would it be possible to use knee braced oak or other suitable hardwood posts, eaves beams and cross tie beams which could act as portal frames. Possibly fixing the base of the posts into the foundations directly or with steel shoes to obtain the additional stiffening effect of cantilever action.
By putting a frame adjacent to the exg house the sun room could be independent or you could chemically anchor the last tie beam and posts to the exg work.
I have designed many similar buildings in the UK but probably not for winds of 100mph.  

RE: Sun Room Addition Lateral Analysis/Design

I don't think cantilever diaphragms are allowed as big as this sunroom is going to be.  Wood cantilever columns don't work unless you bury the post like a fencepost/flagpole footing, or bury it in a short wall and extend them up.

My two cents: use cantilever columns that are steel tubes either welded to a baseplate and bolted to the foundation or embedded in a pier at the corners.

OR

bring the brick up as posts, maybe 12x12 columns at the corners and use those as cantilever columns.

OR

Convince the client to deal with a little less open-ness and use Simpson Steel Strongwalls, 12" should do the trick

The existing house will take 1/2 of the lateral load, attach with a ledger

Good Luck wayniac3
 

RE: Sun Room Addition Lateral Analysis/Design

i love this post discussion.. lmao!

its true, the design of such structures is really a pain the rear sometimes once you put pen to paper.  i wish we could say in our calc package "build like theyve been these things forever but make sure you have a good contractor"...

i love it when i happen on to a house built 70 years ago with an old timer contractor... up in the attic for instance, and i cant figure how the heck the stick framed roof isnt falling down on my head.. and he says, "ive never seen it built any other way.. it aint goin nowhere..."...in other words.. "you silly engineer with your silly pen and paper..."....haha!  good stuff

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