Author Topic: 48 x 28 Three Car Garage with Attic  (Read 19703 times)

0 Members and 1 Guest are viewing this topic.

Offline Medeek

  • Journeyman
  • *****
  • Posts: 2,096
  • Structural Engineering
    • The Engineering and Design Firm of Medeek
48 x 28 Three Car Garage with Attic
« on: January 19, 2013, 11:01:10 PM »
Working up a new design for a 3 car garage (48' x 28') with 10ft walls, attic,  six dormers and maybe an alternate apartment up top. 





Like my previous design this one has 6 dormers but I made them just a bit taller because of the larger roof (28' span).   
Unlike my previous design I went with a dropped top chord on the gable ends, I think this is alot better in terms of strength and good practice. 

There are a few more pictures here, for those interested:

http://design.medeek.com/images/misc/

Any thoughts on what could make this design even better? 
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

  • Journeyman
  • *****
  • Posts: 4,608
Re: 48 x 28 Three Car Garage with Attic
« Reply #1 on: January 20, 2013, 04:05:26 AM »
Along the same lines you can drop the dormer gables and frame the overhangs on edge, I'll do both, with shorter, light snow overhangs flat is fine, as they increase or the load increases the hard way is better. If the dormers have level ceilings I calif frame them, less time fussing in the valleys. If cathedraled both inside and outside need to plane, a taller order.

I noticed on a drawing you posted the other day the field framed section around a stair was done differently then I would have. Sheetrockers like to have framing or backup all oriented regularly and in the same direction if possible.

The truss "hats" sit on a truncated truss. As the spans increase and that top flat gets wider it can allow the trusses to twist across from one side to the other, there was a church collapse some years ago. An article was written in one of the trade mags by Frank Woeste (JLC, mid '90's IIRC), I've followed his advice and installed diagonal bracing on that level before the hats but prefer a solid plywood deck... the sprayfoamers hate it when I do that though.

Overhangs should not expose framing, smooth and easy to clean, there are enough insect and bird homes in nature, don't build more into the house.

Exit from apartment to outside, do not exit through the burning garage, maintain seperation and remember that one cannot enter from a garage into a sleeping room. Is that you posting Q's re: detached live in garage design on the inspectors forum?.. if not pm for a link.
« Last Edit: January 20, 2013, 04:40:35 AM by Don_P »


Offline Medeek

  • Journeyman
  • *****
  • Posts: 2,096
  • Structural Engineering
    • The Engineering and Design Firm of Medeek
Re: 48 x 28 Three Car Garage with Attic
« Reply #2 on: January 20, 2013, 11:45:40 AM »
On my previous design I did flat outlookers on both gable and dormers.  This time I left the dormers the same and then dropped the gable end for outlookers.  I figured the overhang on the dormers is a bit less so I could probably get away with flat outlookers also the length of the rakeboard on the dormers is only about 6' long so it should be fairly well supported.

I'm not sure what is meant by california framing, where can I go to get more information on that?

My current dormer framing below:



In my framing model I don't show any of the truss bracing that needs to happen between the main trusses and the piggyback trusses.   I've also omitted some the extra blocking that might be required for the sheetrocking, but most of it is there.



I'm assuming that with the overhangs one would simply frame solid blocking between the outlookers so that there are no "bird" holes as you've suggested. 

With regards to the apartment up top.  I have a door with auto-closer at the base of the stairs, does this meet code?  The framing for the walls around the stairwell is on 16" centers as it should be.  I'm not exactly sure what to do with the bit of framing next to the wall where the base of the studs run into the concrete stemwall, maybe someone can enlighten me what is common practice in that case.







Framing of the landing below as well:

Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

  • Journeyman
  • *****
  • Posts: 4,608
Re: 48 x 28 Three Car Garage with Attic
« Reply #3 on: January 20, 2013, 07:20:26 PM »
Nope, they are still having to exit thru the burning garage. If there is a protected hallway to the service door then you're good. If there is a door into the garage AND if the stairway upstairs dumps into a sleeping room then another door is required somewhere between... you cannot directly enter a sleeping room from a garage. Nice job on the portal framing and long wall bracing sections. Just as a FYI, the stairwell down into the zone of the cold garage is a cold pit, a door up top is not a bad thing. Yeah, it makes an uninviting stairwell. A door off the gable end of the upstairs onto a deck makes a dandy exit as well... and a good hangout.

The stemwall connection looks correct to me.

The dormers are framed correctly for the semi cathedral effect you've drawn. If the ceiling was on the walls I'd drop the dormer header to plate height, run the main roof jacks down to that and sheath the main roof. Then overframe flatways valley sleepers and the dormer roof on top of the main roof sheathing. Widen them, say the opposing middle pair, to ~8' and a bed or bath fit in them.

We end up with bats and bees in exposed overhangs, I fully sheath soffits whenever possible, less places for nesting... that's probably regional and personal bias.

It's a line when to go from flat lookouts to up on edge, the math doesn't favor flatways for very long. Now if you box the bottom in with a soffit sheathing and the top has the roof sheathing it's beginning to become more than the sum of its parts. Just a tangent, I've never done it but have thought in hindsight on some of the larger overhangs I've done that I should have installed the twisted hurricane ties from the lookouts down to the wall. It's easy to think of just gravity loads on overhangs, the snow or a fat roofer, but depending on exposure and overhang width the wind can produce really impressive uplift on those exposed edges of the roof as well.

If you can figure out main roof sheathing rows in relation to the piggyback joint and try to move the joint away from a sheathing row's joint it'll help tie the parts together. They seem to like to land break on break.

A PE... what states?
« Last Edit: January 20, 2013, 07:43:28 PM by Don_P »

Offline Medeek

  • Journeyman
  • *****
  • Posts: 2,096
  • Structural Engineering
    • The Engineering and Design Firm of Medeek
Re: 48 x 28 Three Car Garage with Attic
« Reply #4 on: January 21, 2013, 11:49:45 AM »
I'm really starting to like the idea of a deck off of the gable end, simplifies the interior framing, roof framing and eliminates all of those pesky fire code issues.

 So let me see if I have this straight.  If there is a space upstairs used as an office/studio (possibly with 1/2 bathroom) etc... but not a living space or apartment (no bedrooms) then what I have is ok?  If there is a bedroom then I would need to frame a hallway/room at the base of the stairs so that egress to the exterior can be accomplished without passing through the garage.  I thought I'm up on my codes but it seems like I'm always missing something, probably the reason I'm posting on this board.  I never hurts to have some expert eyes take a look at what you've got.

After designing the stairwell I realized as well that even if the stairwell is insulated and sheetrocked it will be cold down (cold air from the attic will tend to the lowest point) there but I would rather leave the top open then have so many doors closing the space off.  However, if there is an apartment upstair and I remove the door from the landing and frame a small room at the base of the landing/stairs then it might make more sense to close it off up top. 

I would have actually preferred to frame the dormers as you suggested but when I raised the dormer height so that dormer top plate height was 8'1" the dormers looked too high to me.  On a larger span roof (higher ridge) I would probably go this route since it simplifies the dormer roof framing.

I don't prefer open soffits either.  When I lived in Utah pretty much everything was closed soffits, usually aluminum soffit and fascia.  Here in Washington the norm seems to be open soffit with vent blocks between the trusses.  Maybe it has something to do with moisture or something, western WA is wet, everything molds out here, including the new dog house I just built, its very annoying.

http://www.facebook.com/home.php#!/media/set/?set=at.10151287833961357.524590.533591356.1452421444&type=1



On my previous shed design I used Simpson Strongtie H2.5A to tie the dormer rafters to the dormer walls.  I will probably use those same ties for the outlookers as you suggest.  Wind uplift can be a factor and should be considered.

You're right my sheathing joints on the roof appear to line up with the piggyback truss joint line, how convenient.  I guess my only thought is to cut the first run of sheathing in half and then it straddles it nicely but then I have a sheathing joint near the eaves which weakens that whole interface.  Not sure how to win sometimes.

I added the hold-downs into the model last night, probably a bit of overkill but it should be secure.



I finally got around to taking the PE exam this last October (Mechanical Engineer, Washington State).  However, I've found over the years I'm much more interested in the structual engineering field and now even architecture.  If I can find the right firm I'd like to work toward the requirements for an SE (structural engineer), two more years of experience and a two day 16 hour exam.

« Last Edit: January 21, 2013, 01:37:17 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Don_P

  • Journeyman
  • *****
  • Posts: 4,608
Re: 48 x 28 Three Car Garage with Attic
« Reply #5 on: January 21, 2013, 07:57:01 PM »
302.5 is where the garage /dwelling seperation codes are. I'm not sure what the interpretation would be if you call it something other than a dwelling... I got busted fair and square, it was an apartment upstairs. But... you're selling plans, a whole different order of responsibility, this isn't a one off. From memory, a flight of stairs, if there is one from the deck, cannot rise more than 12' without a landing. I prefer 1/2 level landings more like 5' apart when possible, don't let the fallee build up but so much momentum. Anyone that says they're fully up on anything past the '90's codes is probably being overly optimistic, I've got the '68's down, I think  ;D. Yup everything I took to WA that didn't mold, rusted. Sheesh I thought we got rain.

You'll probably get pushback calling for ties to lookouts on a typical overhang, not that they're a bad idea at all. The most critical place is the lower corners. If you can keep that corner, the bottom 2 lookouts, down you'll save most roofs from that failure. Dr Bender from WSU was giving a talk and said the sheathing nailing was often the worst on that lower corner, wide spacings and missed shots. Being the only carpenter in the class I had to comment "Try hanging on to the top of the sheet with one hand while out at the end of the roof, looking at the ground, reaching way down to nail off that corner." Actually the OSHA way is to rip the bottom row in ~half and install it from staging. Then get up on the roof and work full sheets. It would help with the piggyback joint but you've already picked up on the problem with doing that. If you're serious and want to work in wood design sign up for one of his short courses and do some networking, I was in a room full of fun jobs... well, and inspectors too. Thinking more, same thing for the "woodworks" series of seminars, lots of regional wood design professionals getting ceu's.
« Last Edit: January 21, 2013, 08:30:28 PM by Don_P »

Offline Medeek

  • Journeyman
  • *****
  • Posts: 2,096
  • Structural Engineering
    • The Engineering and Design Firm of Medeek
Re: 48 x 28 Three Car Garage with Attic
« Reply #6 on: January 22, 2013, 05:58:06 PM »
Here is what I've got for the entryway and the lookouts.  The door on the landing will probably go away since I don't think it is needed.





I'm thinking about taking a series of classes at the UW for structural engineering CEU's

http://www.seaw.org/events_detail.cfm?pk_event=151

However, I don't think these will deal with some of the more practical aspects of wood design, framing etc... I will look into what is offered by WSU and courses by Dr. Bender.

I was looking through the IRC last night about the max number of risers per a single flight of stair but all I could find was the 12' max. rise.  With my stair design I originally designed it with 3 risers to the landing and then the upper flight.  However, after looking at it, it did not seem very "inviting" so I went back to the 2 risers to the landing.  The problem of course is that with 10' walls, 6' stem wall and 2x10 floor joists I am getting pretty close to the 12' max, which makes the stairs quite a climb regardless. 

If I framed the stair outside then I would probably come up with two options, single flight of stairs and one that splits the stairs in about two, with a top landing and U-shaped mid landing.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Rob_O

  • Rural Technician
  • Senior Member
  • ****
  • Posts: 315
  • Fisherville, KY
Re: 48 x 28 Three Car Garage with Attic
« Reply #7 on: January 23, 2013, 07:53:29 PM »
Thanks for sharing your design, I have been "napkin sketching" a simple 24*36 garage with an upstairs apartment using attic trusses but didn't consider the rise of the stairs and headroom requirements... looks like I have some more  ??? to do
"Hey Y'all, watch this..."

Offline Don_P

  • Journeyman
  • *****
  • Posts: 4,608
Re: 48 x 28 Three Car Garage with Attic
« Reply #8 on: January 24, 2013, 04:34:02 PM »


Offline Medeek

  • Journeyman
  • *****
  • Posts: 2,096
  • Structural Engineering
    • The Engineering and Design Firm of Medeek
Re: 48 x 28 Three Car Garage with Attic
« Reply #9 on: January 25, 2013, 11:17:53 AM »
I am amazed at the quality of the software you are running for the illustrations.   Right down to showing truss plates and Simpson ties. . .    I’m surprised it doesn’t show nail heads.

I did notice that there is a continuous header-beam that runs across the top of all the overhead garage doors.   I asked our neighbor-carpenter about it.   He said that this is the new requirement.   I guess it makes sense.   I wonder what the laminated beam for that would cost.

As far as the entry to a sleeping area . . .    Why not just exit the door through the outside wall instead of into the garage . . .   


/.

I use Solidworks (mechanical engineering specific) to solid model most of what you are seeing.  It is generally used by mechanical engineers but I find it works reasonably well with architecture as well.  I also use AutoCad quite a bit for large complex drawings but its ability to do parametric 3D models is quite limited even though it does have that ability now.

The header is actually 3 headers, see image below:



I will specify a 5-1/4" x 11-1/4" LVL for these headers, more than adequate for the 9'-3" span.

The system of extending the header beyond the king studs is called a portal frame and is required as per the IRC.  Notice that the two doors have single portal frames and the leftmost door has double portal framing.  You will also notice that I've doubled up the king studs on the man door and the corners are three studs, perhaps a little bit overboard but I'm going for a design that can be built in a seismic D with wind exposure C, so it needs to be beefy.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline dablack

  • Senior Member
  • ****
  • Posts: 442
  • Rusk TX
Re: 48 x 28 Three Car Garage with Attic
« Reply #10 on: January 26, 2013, 04:14:22 AM »
I'm working on a 26 x 52 four car garage with attic trusses right now.  I went with 32' long attic trusses, to give me a porch type area on front of the garage and to give me a 19' wide room upstairs.  We are putting three bedrooms and two bathrooms upstairs so we needed the room. 

You can check out my build here:  http://countryplans.com/smf/index.php?topic=11727.0

I also had to be careful with stair design due to headroom and a 10' tall side wall.  Luckily, since the upstairs room center is shifted from the downstairs, due to the large porch area, I didn't have to do a landing and can have just a straight run of stairs. 

If you have any questions, let me know. 

Oh, yeah, I'm also a mechanical engineer.

Austin