Homeowner here in Portland, OR. We are replacing the foundation/slab under our old Portland bungalow and installing radiant hydronic in the slab for the finished basement. We're trying to preserve as much square footage as possible relative to the necessary slab edge insulation/framing standoff, and we're trying to be as efficient with the under-slab insulation as we can to avoid unnecesssary depth of excavation. Two main questions: 1. What is anyone's opinion of using this 30mm R10 phenolic foam product to insulate the slab edge perimeter, and extend it all the way up the walls? https://www.kingspan.com/us/en-us/product-groups/insulation/insulation-boards/kooltherm-k9-internal-insulation-board (1a - any chance the phenolic foam board could be used under the slab as well?) 2. Have been reading a lot about the ongoing debate over slab vapor barrier below or above the insulation. Above (between vapor barrier and slab) seems to make the most sense. If instead of one of the more expensive purpose-built grid systems (Rapid Grid, Crete Heat, etc), we do a conventional setup of PEX zip-tied to a metal grid - if the vapor barrier is placed on top of, say, EPS boards, how does the installer avoid putting holes in the vapor barrier when they're walking around on the grid tying down the PEX? Thanks in advance for any wisdom - this forum's been incredibly helpful already.

Homeowner here in Portland, OR. We are replacing the foundation/slab under our old Portland bungalow and installing radiant hydronic in the slab for the finished basement.

We're trying to preserve as much square footage as possible relative to the necessary slab edge insulation/framing standoff, and we're trying to be as efficient with the under-slab insulation as we can to avoid unnecesssary depth of excavation.

Two main questions:
1. What is anyone's opinion of using this 30mm R10 phenolic foam product to insulate the slab edge perimeter, and extend it all the way up the walls?
https://www.kingspan.com/us/en-us/product-groups/insulation/insulation-boards/kooltherm-k9-internal-insulation-board
(1a - any chance the phenolic foam board could be used under the slab as well?)

2. Have been reading a lot about the ongoing debate over slab vapor barrier below or above the insulation. Above (between vapor barrier and slab) seems to make the most sense. If instead of one of the more expensive purpose-built grid systems (Rapid Grid, Crete Heat, etc), we do a conventional setup of PEX zip-tied to a metal grid - if the vapor barrier is placed on top of, say, EPS boards, how does the installer avoid putting holes in the vapor barrier when they're walking around on the grid tying down the PEX? Thanks in advance for any wisdom - this forum's been incredibly helpful already.

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Made your post more readable for you....this forum sucks for new posts....

Insulating the foundation on the outside would be preferred for me. That gives you the thermal mass of the walls to help maintain temp in the house and doesn't take up internal sqft of the house. Have you though of doing an ICF basement and then you can just screw drywall to the ICF and you are done.

I don't think you are going to put may holes that matter in the plastic. You can tape over then before the pour but some holes aren't really going to matter, the cement will just block the hole.

I do the method you talk about tieing the pex to the wire mesh in the concrete. I have done this on 2 houses. I like using rebar ties to hold the pex as apposed to zip ties and other methods. Rebar ties are quick and cheap.

I put the plastic under my insulation, I did research that but don't remember why I chose to do it that way and don't see a big advantage either way.

As far as the Kingspan stuff....I really don't care to use the newest stuff like that on expensive projects....

If you are going to drywall anyway then it is not needed and you can use readily available XPS.

I am just not familiar with that product at all...

Newbostonconst’s advice is consistent with what we prefer as well. For new construction, we typically do crushed rock, self-compacting pea gravel, 10 mil vapor barrier, 4” Nudura HydroFoam, PEX, rebar held off HydroFoam with Hercules rebar chairs (they fit perfectly on the HydroFoam knobs) and then pour the concrete. If we have client who wants to go with cheaper EPS insulation than HydroFoam, the process is essentially the same except we place the PEX on top of the rebar and use plastic zip ties.

Having the PEX higher in the slab improves hydronic radiant efficiency by about 1-2%. Having the PEX lower in the slab on the EPS insulation gives it more protection from rebar sharpies and from getting damaged by the concrete crew during the pour.

The only issue with having the vapor barrier below the insulation is the potential to trap water between the vapor barrier and the insulation that could delay floor finishing work. Since we either finish concrete slabs by stamping or polishing them, this isn’t an issue for us. If you plan to put hardwood over the slab, this could be an issue for you.

Thanks both Newbostonconst & sailawayrb for those great perspectives.

For both of you: do you ever chamfer the edge insulation so the slab concrete winds up flush with the foundation right at the edge? If so, what gap between the foundation wall and the framing does the owner wind up with? I'd love to not be locked into a 2" standoff if I go with 2" of edge insulation, but not sure how to get around that.

For sailawayrb: any reason you use the Nudura Hydrofoam as opposed to products like Viega Rapid Grid, Crete-Heat, or Heat-Sheet, that give you a similar R value with an inch less total thickness, plus an integrated vapor barrier? Cost, availability, or something else? I'm also in Oregon (Portland area), so trying to figure out who my best bets are for suppliers nearby.

(Sorry about the formatting, not sure how to get these posts to accept my paragraph breaks.)

The page breaks are always screwed up on the first post....some say it is the browser that does it...no worries.

I do ICF foundations and put an inch of insulation on the top of the footing. Then pour over all the insulation and up against the wall. That way there is some type of thermal break every where.

I have found that with a insulated basement floor and walls the basement isn't that cold old clammy the way it used to be.

I currently have a walkout basement with half the wall area exposed(above ground) and rarely heat the basement (even with 3 occupied bedrooms) We have heated floors up stairs and the heat from them radiates up and down so both floors/areas get heated.

I am guessing with a full underground basement I wouldn't need to heat it at all. We are near Ann Arbor Michigan. We have R30 walls upstairs and R80 roof.

Your house sounds like you are keeping the upstairs the way it is for this project, so you will still have heat loss through that structure. There is some dynamics you might want to think about with that setup. Explain the house plan as a whole if you want ideas.

The cost of heated floors is a lot and now after building a super insulated house I question whether I should have wasted the money to do heated floor and forced air(because I still needed AC anyway - We are also Geo). It takes very little energy to heat our house so the floors aren't as warm in this house as was the case in our old R19/R38 house.

Again, good luck and enjoy your project.

Newbostonconst, I can certainly understand your perspective. If you need AC, mini splits become a compelling and complete solution. If you have mini splits, they provide both high efficiency AC and heating too making hydronic radiant heated floors totally redundant and unnecessary. We don’t recommend hydronic radiant heated floor for remodels or when the floor will be finished with hardwood. Retrofitting hydronic radiant floor heating into a place is a very expensive proposition. Hardwood floors don’t feel cold in an energy efficient house and then trying to drive heat through them via hydronic radiant is an expensive poor efficiency game that is best avoided IMHO. I think hydronic radiant floors make good sense when you have new construction incorporating concrete slab floors that will be stamped, polished or finished with tile. In this case, the overall heating system cost is low (usually lower than a forced air furnace system) and the operational efficiency can be made as high as you are willing to spend for it (e.g., a cheap simple boiler versus an expensive air-source or ground-source heat pump system). Given that energy efficient homes need a lot less heat BTU/H, often there is no ROI justification to use the more expensive heat source options. And if you don’t need AC because of your climate and you have an energy efficient design (well-sealed and well-insulated) that perhaps also uses passive solar cooling/heating design methodology and features, you are done.

I think our home in southern Oregon is a good example of when to use hydronic radiant heated floors. It is an energy efficient design, single level ICF constructed structure, with stamped concrete floors, in a dry diurnal temperature climate, that incorporates passive solar cooling/heating design methodology and features and uses a wood fired masonry heater in addition to hydronic radiant heated floors. AC is not needed or used and the interior temp never exceeds 68F even after a week of 105F high temps (like this week). Heating monthly cost never exceeds $30/month and that is with a cheap electric boiler. I styled the interior to be “mountain lodge” and the masonry heater, masonry walls, stamped concrete floors (some stamped to look like old wood planks), leather granite kitchen counters/window sills and wood ceiling beams/trim create a feeling of both coziness and permanence. The floors never get very warm, but they never get cold either. I don’t have any issue about that. The floors are pet friendly, practically indestructible, easy to clean with the central vacuum system (which also practically eliminates any need to dust the interior furnishings too) and will retain their appearance forever with minimal maintenance. Construction photos may be found here if interested:

https://www.borstengineeringconstruction.com/About-Us.html

SPDX, we built ICF homes in the Seattle area and more recently in southern Oregon area. However, we are now semi-retired (now mostly do design and not much construction) and we sold our ICF construction braces and tools to Better Builders of Oregon (Jerry Spivey) who build ICF homes in the Portland area. We often do hydronic radiant floor heating designs for their clients, in addition to our other clients. As far as a supplier to the Portland area, I would recommend and try Valley Supply:

https://valleysupply.com/

We used Valley Supply both when we operated in the Seattle area and more recently in southern Oregon. We would often get free delivery by piggy backing on one of their trucks that was passing through our area. The reason we like Nudura ICF and their HydroFoam is largely low cost for a quality product. However, our cost isn’t what your cost would be...we did a lot of business with them. Nudura blocks are good (and again, we especially like their HydroFoam for installing floor heating PEX). So are BuildBlock. So are FOX Blocks. We have used all three over years and we have also used TF Systems which is a vertical ICF panel system. Really, all the major ICF brands are good these days. So what you typically end up using largely depends on the combination of product and shipping cost to get them to your construction site. Since we construct using ICF, we don’t have any need to chamfer the insulation perimeter. We simply pour the slab within the ICF walls which typically have 2.5 inch thick EPS insulation before reaching the concrete core.

We don’t dig footing trenches. We construct our footings on top of a crushed rock (i.e., often called 3/4 minus) engineered pad. Footings are typically 12 inches thick and as wide as the building design requires (often 3 feet or more because of seismic). Self-compacting pea gravel is used to fill the cavity between the engineered pad and to top of footing. And as I mentioned previously, 10 mil vapor barrier is placed over the pea gravel, 4 inch thick HydroFoam, PEX, and then rebar before pouring the slab. Since this is new construction, ceiling height (usually 10 feet) is set by the design and not limited by the floor insulation or anything else. Of course, there are infinite ways to build a home and locality often dictates what makes the best sense. We just never build basements or crawl spaces, our soil conditions are not favorable for successfully digging trenches (e.g., ground level bedrock, huge boulders) and we don’t have any significant frost level to deal with.

Best advice that I can offer, do an integrated design that considers all things. Don't do a piecemeal design as is often unfortunately typically done. Best wishes for a successful project!

Speaking of hydronic radiant design: Bob Borst did the design for my 3000 sq-ft ICF(Quadlock) home on 2 levels in Western Montana a few years ago. I have never reported because our build has taken 4 years since I did all the work myself. We moved into the house earlier this year, and I can finally report on the satisfaction with the result. 1st, Bob’s design was spot on. The layout made installing the PEX easy to follow. His materials list made it easy to source the right components. By the way, Supplyhouse.com was the best and cheapest source of materials. Waiting 3 days for delivery was never a problem. I’d recommend Borst as a reasonably priced, accurate, and well detailed source for getting your hydronic design right.
My gas bill includes $6.50 just to have a meter. But heating our hot water and the house has not presented a bill over $30 from February until now. February was less than $20 to heat the house and less than $5/month to heat water.
I think the efficiency of our house is down to the ICF design, and Borst’s hydronic design. I’m heating the entire house and hot water using a Navien 55k btu mod-con, and an HTP ultra-stor indirect tank.
Many thanks to the Borsts for giving me the confidence to do this on my own and still have a great result.

Thank you Scott! We are glad to hear that your project turned out well. All the best, Gayle.