Should Sill Overhang Over Foam Insulation? - Construction - Contractor Talk

Should Sill Overhang Over Foam Insulation?

 
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Old 04-20-2019, 03:45 PM   #1
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Should Sill Overhang Over Foam Insulation?


Hi guys,

I'm a licensed GC here in MN and will be embarking on my first NEW build which also happens to be my personal residence. As a remodeler for many years, my foundation expertise is limited to what i've been reading and basic construction practices.

Anyways, As a GC i will be subbing out most trades and i could always ask them and will be asking them but would like opinions of others.

So my question, In MN we are required to insulate poured foundation wall from head to toe. so basically from bottom of footing to the sill plate. I attached a picture i found on the internet which would mimic exactly what i plan to do. My sill plate (2x6) will be hanging over at least 2 inches to cover foam. I see no other way around it? Take a look at picture and give me your thoughts. is this common practice? i certainly don't want from to sit past the sheathing as i foresee rotting of sheathing
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Old 04-20-2019, 04:18 PM   #2
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Re: Should Sill Overhang Over Foam Insulation?


Don't know others thoughts, but I would want a lot more then a 2x6 sill plate in that situation. Only gives you 3.5 of the plate on the concrete wall, which is placing the anchor bolt real close to the out part of the wall.

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Old 04-20-2019, 06:04 PM   #3
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Re: Should Sill Overhang Over Foam Insulation?


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, which is placing the anchor bolt real close to the out part of the wall.
If you’re lucky and your foundation guy doesn’t place it too far in so it misses the plate altogether.


I’d put the sill even with the outer edge of the crete wall.
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Old 04-20-2019, 07:36 PM   #4
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Re: Should Sill Overhang Over Foam Insulation?


I would set it so my sheathing edge is even with the foundation foam.
Then when you put your siding on, it protrudes past the foundation foam.
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Old 04-20-2019, 11:37 PM   #5
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Re: Should Sill Overhang Over Foam Insulation?


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I would set it so my sheathing edge is even with the foundation foam.
Then when you put your siding on, it protrudes past the foundation foam.
But if water ever got behind siding it would find a way behind sheathing and foam. But I suppose a flashing would prevent that
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Old 04-21-2019, 03:36 AM   #6
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Re: Should Sill Overhang Over Foam Insulation?


Have you considered using the rigid foam on the whole exterior? It will be costly but will payback pretty quickly.
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Old 04-21-2019, 05:59 AM   #7
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Re: Should Sill Overhang Over Foam Insulation?


First, I would use a 2x8 for the sill.

Your diagram shows the insulation on the exterior. Is that code in MN? Insulating the foundation is standard. Also has to be done to comply with the 2012 Energy Act. It is extremely rare for me to see insulation on the exterior of a foundation. It could be because we are in different climates.
Insulation from footing to sill is on the inside.
Also, it only shows 1 1/2" of foam which is way less than required.

As to your question, "Is this common practice"
Since I don't see insulation on the exterior, in my area I would say it's not common practice.
To see siding overhanging foundation. Yes it is common practice and has to be.
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Old 04-21-2019, 06:01 AM   #8
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Re: Should Sill Overhang Over Foam Insulation?


Generally, that foam stops at the grade. 2" required her I believe.
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Old 04-21-2019, 06:10 AM   #9
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Re: Should Sill Overhang Over Foam Insulation?


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Originally Posted by JRremodelers View Post
But if water ever got behind siding it would find a way behind sheathing and foam. But I suppose a flashing would prevent that
Yeah, flash it.
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Old 04-22-2019, 01:25 PM   #10
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Re: Should Sill Overhang Over Foam Insulation?


That is one of the worst details I have ever seen - like others said 2x8 minimum & flashing. No I would not overhang the foam below at all - sorry I can't find the one shareable detail I had on how to do this but I found 2 others online that while not the best are more workable than above:

https://i.pinimg.com/originals/07/af...4514facd73.jpg
https://i.pinimg.com/736x/22/9d/8d/2...2003ebb552.jpg

I would have full termite shield shown in one pic but would have sill shown in other which lines up with edge of concrete // especially as in your climate you need exterior foam sheathing all the way up the walls to (yes you do need the break)
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Old 04-22-2019, 04:10 PM   #11
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Re: Should Sill Overhang Over Foam Insulation?


most flash it
1- 1/2" is not enough to meet the energy code that is in your drawing unless your putting some inside the wall also
some jurisdictions wont allow you to "cantilever " the sill plate out like that. it moves the bearing point out off the foundation and they dont like that

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Old 04-22-2019, 08:35 PM   #12
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Re: Should Sill Overhang Over Foam Insulation?


Should use a sill plate to equal the thickness of the pour and foam.

With ICF, they allow the sill to meet the edge of the ICF around here.
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Old 04-22-2019, 09:29 PM   #13
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Re: Should Sill Overhang Over Foam Insulation?


icf they allow plate to hang flush to outside here to, but that's only 2"
energy code says you need 3" of foam on foundation (r15)
most try to put it all on the outside so they are not forced to drywall the basement walls

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Old 04-22-2019, 11:06 PM   #14
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Re: Should Sill Overhang Over Foam Insulation?


The top row of icf is tapered so the sill isn’t resting on 2” of foam
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Old 04-23-2019, 08:41 AM   #15
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Re: Should Sill Overhang Over Foam Insulation?


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Originally Posted by Donohue Const View Post
icf they allow plate to hang flush to outside here to, but that's only 2"
energy code says you need 3" of foam on foundation (r15)
most try to put it all on the outside so they are not forced to drywall the basement walls

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ICF -2.5 per side for a total of 5" of foam.
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Old 04-23-2019, 09:20 AM   #16
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Re: Should Sill Overhang Over Foam Insulation?


but not at the top

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Old 04-23-2019, 10:02 AM   #17
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Re: Should Sill Overhang Over Foam Insulation?


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Originally Posted by Donohue Const View Post
but not at the top

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All the ones I have ever messed with where. Like so many things are a lot of different options.

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Old 04-23-2019, 03:42 PM   #18
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Re: Should Sill Overhang Over Foam Insulation?


right lots of different ones, I dont really do many icf's, not sure why I always think it a 2" foam

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Last edited by Donohue Const; 04-23-2019 at 03:49 PM.
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