When you have an ICF wall with a SIP roof, what would be the best top plate material to make the connection for the SIP? A 4x6 sitting inside the concrete portion of the ICF wall with 2.5" of EPS on each side seems like the easiest and greenest option. What about a steel U-channel centered within the ICF form? The steel would be stronger but the thermal bridging makes me a little leery, even though it is thermally broken by 5" of foam.

If known in advance, obviously, I would probably opt for a 2 x 4 on edge, maybe with a mitered edge to insure concrete grip, and place it in the top course of the wall, centered in the concrete. My 2 cents.

There are Prescriptive Methods for ICFs to SIPs from 2008 by NAHB research (and PCA, SIPA, HUD): http://www.quadlock.com/technical_library/third_party/Prescriptive_Method_Connecting_SIP_Roofs_to_Concrete_Walls.pdf

Posted By Quad-Lock on 06 Jan 2014 03:27 PM
There are Prescriptive Methods for ICFs to SIPs from 2008 by NAHB research (and PCA, SIPA, HUD): http://www.quadlock.com/technical_library/third_party/Prescriptive_Method_Connecting_SIP_Roofs_to_Concrete_Walls.pdf

They don't address metal SIPs in the Prescriptive Method but the general concept is there. The key highlights are:

• A SIP screw must penetrate wood top plate by at least 1 3/4"
• 6" oc screw spacing
  
• A 12" SIP requires a minimum 14" long screw
• Max 24" overhangs
  

On my design I will go with a 4x6 since it will be ripped/tapered for the 5:12 roof pitch. It also gives it more area for the screws to grip into. 

Is it feasible to do a non-treated wood top plate and just use a foam sill seal between the concrete and wood top plate?

Are top plate anchor bolts at 12" oc a good spacing schedule to keep the top plate from trying to twist and lift?

Posted By Lbear on 07 Jan 2014 06:50 PM

On my design I will go with a 4x6 since it will be ripped/tapered for the 5:12 roof pitch. It also gives it more area for the screws to grip into. 

Is it feasible to do a non-treated wood top plate and just use a foam sill seal between the concrete and wood top plate?

Code does not require the use of treated wood on top of the wall. I used 2 x 10 Douglas fir with sill seal foam underneath.

Are top plate anchor bolts at 12" oc a good spacing schedule to keep the top plate from trying to twist and lift?

If you can get a good straight 4 x 6 to start with, I think 24" spacing would be enough to keep it from twisting. But, you'll have to look hard to find perfectly straight 4 x 6, treated or untreated. Considering the need for good contact between the SIP and the top plate to assure secure attachment I'd suggest you look hard at something like a Microlam or Versalam beam. Follow the Prescriptive Method for spacing.

You sure 4 x 6 will be wide enough? You need good bearing coverage over the concrete. On a 5:12 pitch a 4" rise requires 4/5 x 12 = ~9.5" width. I think you need to relook that part of the design!

Be sure to stagger the bolts if you do use dimensional lumber.  Otherwise, all of the bolts in the same grain may split the wood.

Posted By dmaceld on 07 Jan 2014 07:26 PM

Are top plate anchor bolts at 12" oc a good spacing schedule to keep the top plate from trying to twist and lift?

If you can get a good straight 4 x 6 to start with, I think 24" spacing would be enough to keep it from twisting. But, you'll have to look hard to find perfectly straight 4 x 6, treated or untreated. Considering the need for good contact between the SIP and the top plate to assure secure attachment I'd suggest you look hard at something like a Microlam or Versalam beam. Follow the Prescriptive Method for spacing.

You sure 4 x 6 will be wide enough? You need good bearing coverage over the concrete. On a 5:12 pitch a 4" rise requires 4/5 x 12 = ~9.5" width. I think you need to relook that part of the design!

I assume they make 4x8 or 4x10 Microlam beams?

I've seen them placing 2x6's for a top plate. I figured a 4x6 would be a better option but like you mentioned, a 4x8 or 4x10 would be better.

Posted By Lbear on 08 Jan 2014 12:16 AM

I assume they make 4x8 or 4x10 Microlam beams?

All kinds of sizes. Go here http://www.bc.com/wood/ewp/guides-resources/guides/Western-US-including-Alaska.html and check out the Glu-Lam and Filler King product guides. Of course, Boise is not the only one who makes them. You will have a challenge getting one ripped with the angle you need. If you do it right you could rip one beam into two plates. Talk to your local lumber suppliers for guidance.

You may find it smarter to go with 2 different widths, say like a 2 x 10 with a 2 x 6 on top, both ripped at an angle. Less wood waste that way. Play around with a scale sketch and I'm sure you'll figure out what the smartest way to go will be. If it were me I wouldn't use a 4 x. A 5:12 pitch gives you a pretty flat angle. A 12:12 pitch is 45° in which case the horizontal width of the rip is the same as the thickness.

You could use a treated 2x6 set flush with the top of the foam with galvanized 1/2" anchor bolts every 2' or so. You would need to make a screed for the top of the wall that would leave the concrete 1-1/2" below the top of the foam. Then cut a non-treated 2x10 at the angle you need for your roof pitch on a table saw (what is your roof pitch?) so that the inside edge will be flush with your inside foam (provides a continuous edge for attaching trim, etc.) and the outside tapered edge will be flush with the outside edge of the treated 2x6. Set that 2x10 on top of the treated 2x6 and hit with a hammer on top where each anchor bolt is to make a mark. Use a 1-1/2" wood bit to drill holes that will slip over the anchor bolt nuts. Then glue and screw the top 2x10 to the treated 2x6 using construction adhesive and 3" deck screws. Cut or grind off any anchor bolts that extend above the top of the wood. Then take a saw or electric charcoal starter to cut the outside foam at the same pitch as the tapered edge of the 2x10.

Posted By dmaceld on 08 Jan 2014 02:03 AM

All kinds of sizes. Go here http://www.bc.com/wood/ewp/guides-resources/guides/Western-US-including-Alaska.html and check out the Glu-Lam and Filler King product guides. Of course, Boise is not the only one who makes them. You will have a challenge getting one ripped with the angle you need. If you do it right you could rip one beam into two plates. Talk to your local lumber suppliers for guidance.

You may find it smarter to go with 2 different widths, say like a 2 x 10 with a 2 x 6 on top, both ripped at an angle. Less wood waste that way. Play around with a scale sketch and I'm sure you'll figure out what the smartest way to go will be. If it were me I wouldn't use a 4 x. A 5:12 pitch gives you a pretty flat angle. A 12:12 pitch is 45° in which case the horizontal width of the rip is the same as the thickness.

I called and they said they can do a 6x8 or 6x10 in Douglas Fir. This would be easier to rip at a 5:12 pitch (22.62*) and I would probably like to place EPS foam on both sides of the top plate (exterior facing and interior). This way I can run stucco all the way up to the roof line where the SIP attaches. It would thermally break the top plate also by having foam on both sides of it.

Have you thought about what you will use to cut a 5:12 pitch taper on the top side of a 4x6 or 6x8 or whatever? A typical 10" table saw with the blade tilted at 22.6 degrees will only cut ~2.75" deep. This will only give you a bearing surface of ~3" wide (the flat part of the 5:12 taper cut that will be in contact with the SIP). Even a larger 12" table saw will only give you a depth of cut of ~3.375" at 22.6 degrees. This would result in a bearing surface of ~3-5/8" wide.

Posted By arkie6 on 09 Jan 2014 09:47 AM
Have you thought about what you will use to cut a 5:12 pitch taper on the top side of a 4x6 or 6x8 or whatever? A typical 10" table saw with the blade tilted at 22.6 degrees will only cut ~2.75" deep. This will only give you a bearing surface of ~3" wide (the flat part of the 5:12 taper cut that will be in contact with the SIP). Even a larger 12" table saw will only give you a depth of cut of ~3.375" at 22.6 degrees. This would result in a bearing surface of ~3-5/8" wide.

I was wondering the same thing. I was hoping Lbear would come to the realization of the challenge on his own!

Maybe I am missing something here, but why bevel the top plate?  Why not use longer screws and then spray foam the gap?  Since he is in an earthquake region, the SIP may need to make full contact with the top plate.

Posted By Alton on 09 Jan 2014 01:21 PM
Maybe I am missing something here, but why bevel the top plate?  Why not use longer screws and then spray foam the gap?  Since he is in an earthquake region, the SIP may need to make full contact with the top plate.

If he doesn't bevel / taper the top plate then the SIP will only rest on the extreme outside corner of the top plate.  I think he is planning on using a metal skinned SIP and I would concerned with crushing at that localized point if it was carrying the entire weight of the roof plus potential wind/snow/ice loads.

Posted By arkie6 on 09 Jan 2014 01:58 PM

If he doesn't bevel / taper the top plate then the SIP will only rest on the extreme outside corner of the top plate.  I think he is planning on using a metal skinned SIP and I would concerned with crushing at that localized point if it was carrying the entire weight of the roof plus potential wind/snow/ice loads.

Exactly, that's the reason why I need to rip the top plate at an angle. With a 5:12 roof pitch and a steel SIP laying on top of that top plate with a 24" overhang, with a flat (non-ripped) top plate, the SIP would not lay completely on the top plate. As Arkie mentioned, the SIP would barely touch the top plate and leave a large gap everywhere else.

I will call around to see if the lumber mill might be able to do the angled cut on some industrial machine.

I see your problem.  I was wondering if the metal roof SIPs could be attached to the ICFs the same way that we normally attach metal SIP roof panels to metal skin wall SIPs.  That is, with bent angles inside and outside the wall.  The bent angles carries the weight.  Top plate and long screws not needed.

Another method to eliminate cutting the top plate at an angle might be to slope the ICF wall.  This means that one side of the ICF form would be cut lower than the other to make the 5 to 12 pitch.

Posted By Alton on 09 Jan 2014 05:31 PM
I see your problem.  I was wondering if the metal roof SIPs could be attached to the ICFs the same way that we normally attach metal SIP roof panels to metal skin wall SIPs.  That is, with bent angles inside and outside the wall.  The bent angles carries the weight.  Top plate and long screws not needed.

Another method to eliminate cutting the top plate at an angle might be to slope the ICF wall.  This means that one side of the ICF form would be cut lower than the other to make the 5 to 12 pitch.

I think that would work. It's worth looking at anyway. That way you could use a flat 2 x and have it rest flat full bearing on the concrete. Another idea I had is cut wedges at 5:12 and use a flat 2 x propped up on the wedges at every hold down bolt. Fill in the gaps with foam.

Posted By Alton on 09 Jan 2014 05:31 PM


Another method to eliminate cutting the top plate at an angle might be to slope the ICF wall.  This means that one side of the ICF form would be cut lower than the other to make the 5 to 12 pitch.

This would be my preferred method. Any ICF installer use to doing gable walls should have no problem with it. Either pre cut the ICF panels to slope or place and cut the panels. If pre cutting, order loose panels and webs for this portion. Make up a skate of plywood that spans the to sloped pieces and attach a 2x6 to remove and level the concrete inside the form. Place anchors and install plate with sill gasket after the pour. It may be quicker embedding straps that fold up over the top of the plate.

Posted By FBBP on 10 Jan 2014 09:59 PM

Posted By Alton on 09 Jan 2014 05:31 PM


Another method to eliminate cutting the top plate at an angle might be to slope the ICF wall.  This means that one side of the ICF form would be cut lower than the other to make the 5 to 12 pitch.

This would be my preferred method. Any ICF installer use to doing gable walls should have no problem with it. Either pre cut the ICF panels to slope or place and cut the panels. If pre cutting, order loose panels and webs for this portion. Make up a skate of plywood that spans the to sloped pieces and attach a 2x6 to remove and level the concrete inside the form. Place anchors and install plate with sill gasket after the pour. It may be quicker embedding straps that fold up over the top of the plate.

Alton -

That's a great idea. Here is what I sketched up after I read these posts:



How should I air seal between the Steel SIP and 4x6 DougFir? Would the same sill plate foam that comes in a roll work for the bottom and top of the 4x6 to help seal and protect the wood?

Regarding the EPS foam wedges on the exterior and interior. I want to run Stucco all the way to the top of the wall to the SIP. The rigid EPS foam wedge can be glued and screwed to the 4x6 and then I can tape the EPS joint, cover it with StuccoMax and fiberglass mesh and it should be good to go.

Would I be a good idea to caulk the joint between the Steel SIP and top plate and the joint between the concrete and 4x6, on both the exterior & interior sides, before the EPS wedges are installed (I want an air tight seal)?

Caulking or sill sealer (roll) could be used on both the top and bottom sides of the top plate.  However, caulk on the top side could be messy and slow down installing the roof SIPs.  Sill sealer should be able to fill the gap between the top plate and steel roof SIP unless the roof SIP has thick ridges on the bottom side. 

If the sill sealer has a long life, then the top plate would not have to be treated wood.  (In my area, the code does not require treated wood for this application.)  Maybe Dana1 would know which sill sealer to use.

I think the sill sealer should be attached to the top plate so that sliding the roof panels around during install will not move the sill sealer.

I like the idea of spray foaming the voids on both sides of the top plate.  This would be much faster than cutting strips of EPS to fit.  Foaming the inside will mean that the drywall will have to be attached with longer screws or be left to float free.  My guess is that most drywallers will agree to let the drywall float free at the top since it would be only 1.5" up to the ceiling drywall.

Be sure to get ideas from other people.  Maybe someone has experience with this detail.

Spray foaming each side of the top plate could possibly be avoided if the ICF form could be cut at a 5 to 12 pitch and then the concrete screeded down 1.5" within the form.