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Old 03-19-17, 02:37 PM   #1
buffalobillpatrick
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Default 18" Wide Foam Insulated Threshold Ideas ?

On my new house build, I'm getting bids on having my footers & walls formed & poured.

Standard practice is to pour the slab out through the doorways to the outside.

This would be a Very bad way to do this with a radiant heated slab in climate zone 5. Lots of heat would be wasted.

I need to come up with an 18" wide threshold. It needs to span the 8" concrete stem wall on outside + 6" of EPS foam & then 4" over the slab on the inside.

It needs to be strong, durable, look good enough.

Ideas?

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Old 03-19-17, 11:10 PM   #2
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This is about my favorite door sill detail for concrete walls: door sill dtl | 363 HOUSE Though I would get in touch with the architect before using it and see how well it has held up. regardless of what you do there is always going to be a thermal bridge at the door sill, but that detail seems to me to be the best at minimizing it.


Also why are you running in floor heat? Yes in floor heat feels great, but for it to be effective (with toasty warm floors) you need to have a certain amount of heat loss from the building envelope. If you are building a well insulated and air sealed house then the required floor heat takes it out of the toasty warm range and into a range that is only a bit higher than air temp, and getting floors to air temp (will feel a bit cool but not cold) is easy.
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Old 03-20-17, 10:51 AM   #3
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Thanks DEnd,

I'm very familiar with radiant heated homes with good and not-so-good enclosures.
This new house will be my 4th radiant system design & install. Cold to very cold climates.

I just sold my 1st install that I lived in for 15 years. When it was 0*F outside, the floors were 76*F = about 12 BTU/H/FT^2 with room temperature of 70*F, had to wear house slippers.

Your diagram is a 2 surface solution.

How durable is your 3/8" cement board across the top of the foam gap?

I like the granite, but I'm unsure.

I would like to find a 1 piece solution.

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Old 03-20-17, 11:23 AM   #4
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I need 3x deep thresholds 18" x 38" , 18" x 72" , and 18" x 84"

An idea:
A 1.5" thick PVC board built-up base (Lowes) (strong for moving appliances into house).

On top, Porcelain tile or smooth top rocks, like a shower base might have. Stuck in a base of Mold resistant silicone, this has been used with success in showers.

Thermal conductivity (W/mK)
PVC = .19
concrete = 1.5

concrete conducts heat about 7.9 x PVC

Last edited by buffalobillpatrick; 03-20-17 at 12:52 PM..
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Old 03-20-17, 08:49 PM   #5
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Quote:
Originally Posted by buffalobillpatrick View Post
I just sold my 1st install that I lived in for 15 years. When it was 0*F outside, the floors were 76*F = about 12 BTU/H/FT^2 with room temperature of 70*F, had to wear house slippers.

Your diagram is a 2 surface solution.

How durable is your 3/8" cement board across the top of the foam gap?

I like the granite, but I'm unsure.

I would like to find a 1 piece solution.
That's my point exactly, if the floor is cool enough to need to wear slippers then you aren't getting the main benefit of warm floors. The other benefits are had at less expensive price points, allowing you to spend that money elsewhere. That said it's your house, so spend your money where you want to spend it.

The cement board should be very durable in that installation. What would cause wear (aside from scratches), is movement of the board. In that installation the board is fully supported by the foam, so there shouldn't be any movement allowed. The major possible cause of failure would likely be foam shrinkage, but using the correct foam (highish psf, low shrinkage) would likely mitigate that problem. Like I said contact the architect first though.

I don't think I'd use PVC in that context. The issue is that you have different expansion rates that will be bridged by tile. I worry that the tile would crack . There are doors that have a tile seal on the bottom of the inside part of the threshold. If you took the PVC to that point that would alleviate that problem. Click image for larger version

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Old 03-21-17, 09:39 AM   #6
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DEnd I see that u r in NC

Way different from cold Rocky Mountain climate zones 5-7 with 6-9 month heating seasons.

Here, Radiant heated floors are the most comfortable, along with low gas bills, (no A/C and ducts required)

On my Neighbors big log home, (low average R-value with much infiltration) the floors had to run 85*F when it was cold & windy outside, feet were warm, but the Propane bills were high.

Scorched air heat sucks, dry air, dust bunnies, hot air rises up to ceiling creating a higher heat loss, while feet stay cold.

U r right PVC with large pieces of tile would not work, but small flat stones in a bed of silicone should, maybe

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Old 03-21-17, 10:07 AM   #7
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The main level of this house is a walk-out basement with 8" concrete walls, 10' up from footers in rear 2/3 and with 32" stepped down footers, 12',8" high walls in front 1/3.

Insulation is on inside of walls, 2 x thick: 4' x 8' x 3" asphaltic paper faced Polyiso foam
(Cheap on Craigslist), then 2x4 stud walls with shiplap pine. So walls are 18-1/4" thick.

I want the front entry door to swing in, so it has to mounted at the 2x4 stud layer.

The 6" insulation running down the inside of the stem walls in the stepped down footer area is Type 2 EPS, no Polyiso is used below grade.

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Old 03-21-17, 06:04 PM   #8
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Quote:
Originally Posted by buffalobillpatrick View Post
DEnd I see that u r in NC

Way different from cold Rocky Mountain climate zones 5-7 with 6-9 month heating seasons.

Here, Radiant heated floors are the most comfortable, along with low gas bills, (no A/C and ducts required)

Scorched air heat sucks, dry air, dust bunnies, hot air rises up to ceiling creating a higher heat loss, while feet stay cold.

U r right PVC with large pieces of tile would not work, but small flat stones in a bed of silicone should, maybe
Not having A/C does change the equation somewhat, but not a whole lot. You can go with radiant baseboards, or even a mini-split (and get the benefit of A/C for the few days of the year you "need" it). Also because each of those systems are low mass they are able to more appropriately respond to temperature changes in the house, greatly reducing the chance of thermal overshoot of the set point.

Also the source of the heat in a house has zero effect on the humidity in the house, unless you are burning stuff inside the house air envelope (furnaces are actually burning gas outside of the house's air envelope). House use, air leaks and ventilation strategy determine household humidity. Dust bunnies are ultimately caused by dirt, dead skin, spider webs, etc... a forced air HVAC system can actually help reduce them, as they filter the air removing a portion of the dust that cause dust bunnies.

Yes hot air rises, one of the issues that warm floors help with is the stack effect that is caused by heating the air. However it only helps with the issue it does not eliminate it. The driver of the stack effect is Adding energy, the less energy we add the lower the temperature difference between the various layers, and the larger those layers are. In a totally closed system (ie no energy loss) the temperature will stabilize across the entire system after a short time period after energy is added.

My point in all of this isn't to tell you that you are wrong, but to have you re-examine your choices because there may be a cheaper way to do what you want to do. Why? because the same systems that work for leaky houses don't really work well for highly insulated air tight homes. It's very very easy to throw money at a system and have it just become a problem or never used. I'm just saying take a step back figure out what your floor temps are likely going to need to be and see if the system response times are going to actually be able to meet your needs.

Last edited by DEnd; 03-21-17 at 06:35 PM..
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Old 03-21-17, 06:28 PM   #9
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Quote:
Originally Posted by buffalobillpatrick View Post
The main level of this house is a walk-out basement with 8" concrete walls, 10' up from footers in rear 2/3 and with stepped down footers, 12' in front 1/3.

Insulation is on inside of walls, 2 x thick: 4' x 8' x 3" asphaltic paper faced Polyiso foam
(Cheap on Craigslist), then 2x4 stud walls with shiplap pine. So walls are 18-1/4" thick.

I want the front entry door to swing in, so it has to mounted at the 2x4 stud layer.

The 6" insulation running down the inside of the stem walls in the stepped down footer area is Type 2 EPS, no Polyiso is used below grade.
Well heck that's easy then, you just need to find a door with a wide enough threshold.

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Old 05-07-17, 01:22 PM   #10
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I found some structural strength high density foams to bridge the gap:

Owens Corning Foamular 1000 XPS 100psi

And

6 lb Polyurethane Mix & Pour Foam in stock ship same day | Fibre Glast
125 psi

I could put 1/2" Wonderboard & tile on top of the high strength foam.

I think the Foamular would be easier to use, cut to size & bedded with low expansion Great Stuff, which is about 2# density SPF, I think.

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