How to attach shed porches to timberframe with stress-skins

[KentT]

Ex-lurker here...

I'm in the process of planning a small timber frame retirement home and have a construction question -- and yes, I have two of Tedd Benson's books and have read them...

I'm looking at enclosing the frame with stress-skin panels, and I want to put shed porches on at least two sides (perhaps three).  But, I can't afford to timber frame that much porch area, so I'd like to do the 8' or 10' wide shed porches with conventional, stick-built rafters or trusses.  I have some related questions those experienced with TF building.

1.  Can I simply attach a plate to the OSB skin, using a combination of liquid nails (or equivalent) and screws through the stress-skin into both the the main posts (and using shorter screws into the skin), in order to attach rafters?

2.  Must there be a girt behind this porch rafter plate, between the posts, or will a combination of attaching to the main posts and the OSB skins suffice for a plate to support rafters over an 8' to 10' span, on something like a 3:12 pitch?  I'll be building in Tennessee so no super-heavy snow loads.

3.  Can anyone provide resources (links, books, etc.) that would address these type construction questions, or building a hybrid TF/SIP type house, since I also want to use SIPS to box in a bathroom and closet on one of these porches, putting a full basement foundation under only that bump-out section. while the remainder of the porches will be on standard deck/porch footing pads and supporting posts.  I want the TF looks, but budget drives the requirement to keep it small and combine it with more conventional methods.

Thanks!
Kent

[Jim_Rogers]

Well when these types of questions come up I usually say to the person asking the question to such as your attaching the rafter ledger to the outside of the sips surface to check with the panel company and see how they would recommend you do it.

I've had some consultations with my sips provider and they don't want to just bolt a ledger to the outside of the side with a through bolt to the inside girt.
The reason they don't want this is that the bolt creates a hole through the sips and that can lead to many problems. Such as the hole can elongate over time with settling and open up a larger hole. The thermal break is bad as the point where the bolt changes temperature from warm to cold will create condensation and this will be inside the sips and may cause some internal rot to the osb.

In one design, an internal girt will be glued inside the sip for the outside ledger to attached to.
Then this internal ledger will be supported by two internal posts, if needed, inside the sip itself. But these internal posts won't be the full thickness of the foam.
The sips company engineer will decide if the internal posts are needed or not....

Jim Rogers

[KentT]

Thanks, Jim, for the prompt response.  I hadn't thought of the potential for condensation inside the SIP, and the potential for rust/corrosion, etc.  I knew I'd be creating a thermal break, but thought since it was on the outside of the post that it wouldn't totally destroy the insulation envelope.

At least you're implying that what I'd like to do is possible, though it may take some extra engineering with the SIP.  That let's me proceed with trying to sketch out a potential design to proceed with...

Thanks again! 

[moonhill]

I would check with the manufacturer as per Jim's suggestions.  I recall faintly, panel houses using joist hanger attached inside to the panels for floor systems, that is something an engineer can speck.  The company should do this for you.

Kent, are you cutting a frame or having it cut?

Tim

[KentT]

I would check with the manufacturer as per Jim's suggestions.  I recall faintly, panel houses using joist hanger attached inside to the panels for floor systems, that is something an engineer can speck.  The company should do this for you.

Kent, are you cutting a frame or having it cut?

Tim

Tim, I plan on having it cut.  Though my brother has a WoodMizer, it'll likely be limited to producing board and batten, and such.  I live in Massachusetts, but am retiring back home to TN, so distance is a real complicating factor.

Now that you remind me, I have read of them putting joist hangers in SIPs for SIP-only construction-- you'd think they could put something similar in them to hang 2x rafters from also...

[witterbound]

I worked on a home once that had notches cut in the top of the SIP walls.  6x10 rafters sat in the pockets in this hybrid part of the house, and ran up to a timber ridge beam.  I think this kind of thing is pretty common. 

[Jim_Rogers]

When I toured a house being constructed of sips without any timber frame or stud walls they used joist hangers to support the floor trusses.
Like this:



The hangers were attached to a 2by that was over the top of the wall panel. There was another 2by at the top of the wall but between the two sheets of osb. So each wall top had two 2bys one internal and one over the top of both the side osbs. Then the hanger went over the top of the top one so that both osbs served as supports for the hangers.

Jim Rogers

[KentT]

Jim,

That looks almost exactly like what I'd need.  Thanks again!  Again, all this tells me that it can be done via conventional methods instead of timber framing.

I'm playing with the concept of a 28x36, four bent/three bay main floor, 1.5 story common-rafter frame, solar tempered, with a shed porch along the entire north (36') and west (28') sides.  The master bath, W/I closet, and laundry would be in a 24x 8' or 10' SIP-enclosed bump-out (with foundation) onto the shed porch on the north side.  This would leave a 12' shed porch on the NE corner for a covered entry, with the 28' porch on west end shading the house from the hot summer sun.  The second floor on that north side would be either a full-width dormer, or a salt box frame design.

Then, if the budget can handle it, a small gabled porch (i.e. screened in breezeway) on the East end connecting to the 2-car, stick-built garage.

i simply can't afford 64' x 8' (or 10') of timber framed porch, especially when its either exposed to the elements or hidden in a bath or laundry -- that's what prompted the questions...

You guys have been super helpful!    I wish there were more info on TF/hybrid/SIP construction available -- or if there is, I wish I could find it!  :D

Kent

[VT]

http://www.sips.org/

Try here

VT

[Jim_Rogers]

Kent:
Keep asking questions here.
I may have some answers.....
Don't know until you ask......

Jim

[witterbound]

Don't rule out a timber framed porch.  It might not be that expensive when a timber frame company is cutting the rest of the frame, and they sure do look nice ....

For your bathroom bumpout, if you're going to use SIPs, the SIP roof will just sit on top of the 3 SIP walls, I'd bet.