ICF Insulated Top Plate Offset Cut Worth It?
Last Post 29 May 2015 03:56 PM by FBBP. 9 Replies.
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txICfHomeOwnerUser is Offline
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24 Apr 2015 08:08 PM
Our ICF installer has an option for a 3" OffSet Cut on the Top Plate. He is saying this will provide a better seal between the rafter tails. We have a 6/12 sloped roof and will be using open cell spray foam. Will the open cell spray foam fill the gap? Or is the insulated offset cut a good idea? Extra cost is $650.
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26 Apr 2015 08:54 AM
Not exactly sure what a 3" offset cut is. Is it leaving the inside or outside of the ICF taller? If so, and if the cut off would otherwise be waste, $650 maybe a lot. But how many lineal feet of wall is there? Now if he was skipping the top plate and using Simpson Strong-tie LTA2 to anchor the trusses, that would be a good investment as you would have the ICFs going to the bottom cord of the truss and a much stronger connection.
Brad Kvanbek - ICFconstruction.net
ronmarUser is Offline
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26 Apr 2015 08:33 PM
Got a diagram of what your installer is talking about? The purpose isn't readilly apparent in the name
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27 Apr 2015 12:57 AM
I bolted the top plate to the ICF wall and set the trusses on the plate using Simpson hurricane holddowns to secure the truss to the plate. Then I just cut OSB pieces to fit between the trusses and nailed them to the outside edge of the plate. That closed in the wall to roof gap nicely and gave a surface for the foam spray to adhere to. Because that created a closed space in the eaves on the outside I added vents so the eave space is ventilated. There is no air flow between the eave and attic space.
Even a retired engineer can build a house successfully w/ GBT help!
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27 Apr 2015 10:10 AM
It's something I've done several times. You set the raised heel truss inside the icf walls instead on top. You cut the top to of the wall to match the angle of the rafter
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27 Apr 2015 10:10 AM
It's something I've done several times. You set the raised heel truss inside the icf walls instead on top. You cut the top to of the wall to match the angle of the rafter
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27 Apr 2015 12:40 PM
In total it is about 350 linear feet of wall. The $650 is for cutting the inside layer of foam 3 inches higher than the outer layer. The goal is very similar to what dmaceld mentioned, but using the foam to make the seal instead of cutting OSB/Plywood to close the gap.

We have a brick veener exterior so the thought is to seal the roof to wall with Spray foam and then vent the eaves so the moisture from the air gap can escape on both the bottom and top.

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27 Apr 2015 03:46 PM
What you describe would be arguable slightly better than plywood as an insulation stop. If the inner side of the ICF would otherwise end up cut off and in the garbage, $650 maybe a bit much. But look at it this way, that is about $1.80 lf or $3.70 per truss space if 2' oc. What does it cost to cut and install each plywood piece?
Brad Kvanbek - ICFconstruction.net
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30 Apr 2015 03:12 PM
I have done it and seen it done. Some good, some bad. The bad was truss and carpenters knock foam when setting trusses, I think it works better with rafters. Last one I did was rafters and then SIPS. It was a tight home, it worked out with overall plate height and rafter heel height well. The customer really has to want it though.
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29 May 2015 03:56 PM
A similair setup is to have the trusses made with raise heels and make them 4" shorter then the outside of foam to outside of foam dimension of the building. Apply 2" foam to the the heel of the truss so that it lines up with the outside face of the ICF.
This protects the heel of the truss from thermal bridging and acts as an insulation stop.
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