Help with SIP selection

[Hackermatack]

My next project is a new woodworking shop and I would like to timber frame the walls. It will be a extremely simple building 24' by 32'. The shop portion will be 16' x 32' with the remaining 8' being a open storage shed. The roof will be a engineered truss from the local supplier. I have built several timber frame structures and I really love being inside one, the shop is a retirement project. I could very easily stick frame it insulate the crap out of it and call it good but I really want some posts, knee braces, and a couple scarf joints to look at. The only thing holding me back is how to sheath it and insulate it. All but one of my post & beam projects except one were either cold buildings or in the case of the hunting camp minimally insulated. This one must be insulated because it will be on a radiant slab with propane heat. The ceiling is easy because it will be on the bottom cords of the trusses and cellulose is cheap. Thinking about using some sort of insulated panel for the walls, the wiring can easily be surface mounted in conduit and the building only has 3 small windows on the south side and one door. I would really like something close to a r-35 any suggestions for a system that would not break the bank.    

[Weekend_Sawyer]

I used Foard Panel in New Hampshire for my timber frame in WV.
They were good to work with and while SIPs arent cheep they had the best pricing I could find. They also have an installation team but my builder knew how to install them so I didn't need them.

good luck
Jon

[Brad_bb]

I'm surprised, especially since you've timberframed before, that you don't just want to timberframe the whole thing- bents?  

I prefer to put up the frame and stick frame the walls on the outside of the posts.  I like using SIPS for the roof, and spray foam the walls.  Plywood on the outside of the framed walls. Spray closed cell foam first (hire it done), it is also a moisture barrier.  Then spray closed cell foam over that.  In a 2x6 wall you do not need to fill the cavity to get the high R-value.  I have the electrical in the wall (as you need to in a house), so doing it this way allows the electrical to be changed easily.  As you build I've found you do change things as you go along.  It also allows easy changes or additions later.  When you do sips on the roof, you need sheathing on the timberframe first, then an air space, then sips, then another air space, then your roofing.  For sheathing I've been using T&G for the ceiling.  For drywall, you'll need either rafters closer together, or a grid to attach to. If you do go with engineered trusses, and I'm assuming you'll put a flat ceiling so you won't see the trusses, you can use plywood for your sheathing.  You'd still want a space for air between sheathing and sips in my opinion.  This space can also be used as a chase to run conduit for wiring for ceiling mounted lighting, and for getting electrical from one side of the roof to the other for lighting.

Again, since you have the ability to timberframe, a full frame would be much more open and pleasant I think.  It would be the cost of the timbers or finding logs and paying someone to mill them for you.  What wood species are you planning?

With sips, you can choose urethane, or expanded polystyrene which will need to be thicker for the same R-value as the urethane.  I like Murus sips.


 

[logman]

General Panel in Johnson City, Tn has the best prices I have found.

[Hackermatack]

I'm surprised, especially since you've timberframed before, that you don't just want to timberframe the whole thing- bents?  

I prefer to put up the frame and stick frame the walls on the outside of the posts.  I like using SIPS for the roof, and spray foam the walls.  Plywood on the outside of the framed walls. Spray closed cell foam first (hire it done), it is also a moisture barrier.  Then spray closed cell foam over that.  In a 2x6 wall you do not need to fill the cavity to get the high R-value.  I have the electrical in the wall (as you need to in a house), so doing it this way allows the electrical to be changed easily.  As you build I've found you do change things as you go along.  It also allows easy changes or additions later.  When you do sips on the roof, you need sheathing on the timberframe first, then an air space, then sips, then another air space, then your roofing.  For sheathing I've been using T&G for the ceiling.  For drywall, you'll need either rafters closer together, or a grid to attach to. If you do go with engineered trusses, and I'm assuming you'll put a flat ceiling so you won't see the trusses, you can use plywood for your sheathing.  You'd still want a space for air between sheathing and sips in my opinion.  This space can also be used as a chase to run conduit for wiring for ceiling mounted lighting, and for getting electrical from one side of the roof to the other for lighting.

Again, since you have the ability to timberframe, a full frame would be much more open and pleasant I think.  It would be the cost of the timbers or finding logs and paying someone to mill them for you.  What wood species are you planning?

With sips, you can choose urethane, or expanded polystyrene which will need to be thicker for the same R-value as the urethane.  I like Murus sips.

I agree a full on timber frame would be nicer but the building will be kept above freezing all winter and heating the extra cubic feet in the roof would serve no purpose. To keep costs in line trusses with a ceiling on the bottom cord with blown in cellulose will save considerable cash. As for timbers they will be whatever I can find growing on the property probably cedar for anything that touches the slab and a mixture of balsam fir, white spruce, and white pine for the remainder. When we built my sons house 15 years ago we did the walls like you describe from the inside out, the bents were 12' and we hung drywall on the posts the put the 2x6 framing on and screwed the drywall to it from the inside. The electrician wired it from the outside before insulation and sheathing. I will be hiring a couple carpenters to help on this build at 68 my balance on the roof ain't what it used to be and I heal pretty slow so keeping it simple will also save labor cost. I will mill my own timbers, put them up rough and green. Good enough for me and it will probably never be a church. 

[Brad_bb]

You don't need to put the posts directly on the concrete.  Use a square 1/4" thick plexiglass plate slightly smaller than the post (so you won't see it when finished) and drill a hole in the center  and 4 other screw holes and screw it to the bottom of the post.  I use timberlinx to attach the post to the concrete and it will go through the hole in the plexi and a hole you bore in the bottom of the post.  At least one way to keep wood from touching concrete.

If you hadn't considered it, I also recommend you use a vapor barrier under your concrete floor.  When we're back filling the foundation we use road gravel that will compact and level.  Then you can use a layer of ag lime which is much finer to smooth the surface and then your 10 mil vapor barrier, then another layer of ag lime, then road gravel or loose gravel with no fines.  The ag lime will protect the vapor barrier from puncture.

[Hackermatack]

Oh it will have vapor barrier, I'm doing a Alaskan slab with in floor hydronic radiant. 

[Don P]

Don't discount doing it wrap and strap with 4x8 foam sheets as opposed to sips.

[Hackermatack]

This is something I had considered. I can buy 4 x 8 x 4" polyiso foil faced at local the cash and carry discount building supply for $30/sheet i'm just not sure of the best way to install it. I could vertical board over the timber frame with pine shiplap for a nice interior workshop finish then apply the foam. I guess this would mean strapping over the foam and screwing through to my wall purlins with perhaps 8" screws?

[Don P]

Here's the tech report;
https://www.fastenmaster.com/tl_files/fastenmaster/download/TER1009-01_20131218_HDLOK_Attach%20Cladding%20Wood.pdf

[Hilltop366]

I would use a wide sill plate to overhang the sill plate out flush with the strapping to help support foam and strapping and keep insects and critters out.

[Don P]

I've done that and have seen TF'er's rely on that to support SIPs. An engineer pointed out that it is in tension perp to grain so don't call it support, find that elsewhere. It is a good thing just can't be relied upon as a bearing.

[Hilltop366]

Yes good point, along with, not instead of good fastening.

[Hackermatack]

If I were to use this method I would simply pour the slab oversize and allow the foam to rest on the concrete and the slab edge insulation to make a continuous thermal break, but the siding and strapping would still lack support. With the screws at nearly a buck each I guess the screws would be close to a grand. It still may be the cheapest way I just need to do some math to see. Finances may dictate that I simply stick frame it and forget the timber frame, it is definitely the least cost option for labor and materials. Some good information here thanks.