what do i insulate the permiters of my slab with?
Last Post 07 Dec 2015 11:08 AM by sailawayrb. 10 Replies.
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ahrenoUser is Offline
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29 Nov 2015 05:36 PM
I have a poured slab garage. i ran pex for radiant heat. I have it insulated underneat but i'm not sure what to do around the permiter of the slab? Do i just construction glue some foam insulation? what size insulation? I'm guessing 2"? is there a special glue to use? I'm in oregon where the ground doesn't freeze. thanks for any help
ronmarUser is Offline
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29 Nov 2015 11:25 PM
What did you insulate under the slab with? Foam EPS or XPS, just high density like would be used under a slab...
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30 Nov 2015 01:02 PM
Where in Oregon does the ground NOT freeze...somewhere on the coast? EPS is best as it is greener than XPS...and because this is a green building forum... Given that slab heat loss for residential buildings predominately occurs at the perimeter, you should consider using an insulation thickness at least as thick as that used for the under-slab insulation. The hydronic radiant floor heating design calculator on our website provides insulation R-value recommendations (reference Siegenthaler) based on the floor type and the design indoor/outdoor temps.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
ahrenoUser is Offline
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04 Dec 2015 02:00 PM
Thanks sallawayrb, i looked at your calculators, they require a lot of information that i dont know. a lot.

im guessing it should be eithere 2 or 3"

the ground doesnt freeze in eugene or pretty much anywhere along the i-5 corridor. it may frost but it doesnt freeze like it does in wisconsin.
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04 Dec 2015 04:05 PM
R-10 is plenty.

http://www.finehomebuilding.com/design/departments/energy-smart-details/frost-protected-shallow-foundations.aspx
MA<br>www.badgerboilerservice.com
sailawayrbUser is Offline
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05 Dec 2015 10:58 AM
Actually, to obtain the insulation recommendation, you only need to enter the design outdoor temp, the design indoor temp and the hydronic radiant floor type (i.e., enter 0 for Slab-on-Grade, 1 for Thin-Slab, 2 for Above-Floor and 3 for Below-Floor). I will update the software instructions to make this more clear for future users.

The equations used in the software are based on John Siegenthaler’s Modern Hydronic Heating recommendations for MINIMUM insulation R-value. For a Eugene OR design outdoor temp of 26F, a design indoor temp of 70F and for Slab-on-Grade, the recommended minimum floor insulation R-value is R6. Again, since this is the recommended MINIMUM, you could certainly use more insulation than this. Without splitting hairs, a 2” thickness of EPS/XPS is about R10. EPS would be a greener choice.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
ahrenoUser is Offline
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06 Dec 2015 06:45 PM
Thanks, the calculator intimidated me. I appreciate the explanation.

What do you guys usually do to cover the insulation? It'll be a slight eyesore if I bring it up to within a few inches of the siding.
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06 Dec 2015 09:10 PM
There are several ways to detail the perimeter insulation depending on the type of slab that will be accomplished. These links should provide you with some good insight:

Building Science Corporation Slab Edge Insulation

OREC Slab Floor Edge Insulation

You will also note that the OREC requires R15 for residential Slab-on-Grade which, in your case, is higher than the Siegenthaler recommended MINIMUM insulation R-value of R6.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
milnerptUser is Offline
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06 Dec 2015 11:58 PM
interesting from that second link sailaway -

they ADVISE the use of blotter sand between the VB and the concrete slab (as its 'best practice'?) and it looks like it only has to be R10 insulation under slab if its a heated slab. right?
BadgerBoilerMNUser is Offline
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07 Dec 2015 07:46 AM
It is not good practice and the difference between practical advise and theory.

R-10, no sand.
MA<br>www.badgerboilerservice.com
sailawayrbUser is Offline
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07 Dec 2015 11:08 AM
Yes, R10 will be acceptable for the under-slab insulation of your heated slab, but your inspector will still likely require R15 for your perimeter insulation. In residential buildings, the majority of Slab-on-Grade heat loss is via the perimeter. So there is merit in having more perimeter insulation...even though I personally think R15 may be overkill for your location.

The performance goal for hydronic radiant heated floors is to keep the downward floor heat loss to less than 5-10% of the total floor heat gain. So significantly more R-value below the PEX than is above the PEX is what you strive for to maximize performance. The Siegenthaler MINIMUM insulation R-value recommendations result in about a 10% downward heat loss.

We avoid the use of sand (or any fines) which we consider as unnecessary and perhaps even problematic.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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