AC Insulates Under Floor of 120 Year Old Crawlspace

[AC_Hacker]

Originally Posted by TimSmall

Radiant barriers aren't that useful on upward facing horizontal surfaces, as over time they get dirty and stop working. Also their contribution is pretty minimal anyway...

I would be interested to know your source for this information.

I have come across the following graphic that is from a brochure for Reflectix, a US producer of reflective insulation material. The graphic itself is from research conducted by Penn State, a public research university, that illustrates that in downward heat loss, radiant barriers are very effective, as radiation is the primary mode of thermal loss.

I have also seen the very same information in US Army Corp of Engineering building manuals.

In THIS_POST I did an experiment with a shiny piece of aluminized mylar, and the results were startling.

I'm not expecting results as dramatic as the above, but the principle exists, and the insulation I am using comes with a foil face, whether I want it or not, so I'd be remiss not to use it.

I did inspect my wooden support posts, and they have been in position for about 100 years, and they look like they could easily 'go the distance' again.

Best,

-AC

[AC_Hacker]

Originally Posted by ctgottapee

And unfortunately not as avail and pricey. I'd like to use it too and Menard here started to carry it, but it's almost 4 times fiberglass price. Even more than the expensive denim batting.

Mineral wool is the same price of fiberglass where I live.

Originally Posted by ctgottapee

Any reason you didn't just buy one of the foam spray tank kits and do a 1 or 2" spray underneath?? It's about a $1 a board foot. Might require some planning to move the tanks timely to prevent clogging.

I think that possibly might have been the best way to go, now that I have done all this. The EPS is about $.38 per board foot. Plus, my son (William Hackerson) is really struggling to find a job and pay rent, etc. so this is something of a public works project for him.

Originally Posted by ctgottapee

And I'm confused by the radiant barrier, I thought it was suppose to go on the warm side(floor) of the air space to prevent heat radiation through the air gap??

I'm pretty sure that you need an air gap between the radiating surface and the reflective material. I've seen recommendations of 1/2 inch to 1 inch. But the wavelength of IR is very short (< 1 mm), so I think that the gap can be small.

-AC

[MN Renovator]

Originally Posted by AC_Hacker

Mineral wool is the same price of fiberglass where I live.



I think that possibly might have been the best way to go, now that I have done all this. The EPS is about $.38 per board foot. Plus, my son (William Hackerson) is really struggling to find a job and pay rent, etc. so this is something of a public works project for him.



I'm pretty sure that you need an air gap between the radiating surface and the reflective material. I've seen recommendations of 1/2 inch to 1 inch. But the wavelength of IR is very short (< 1 mm), so I think that the gap can be small.

-AC

I've seen similar recommendations too. I just walked to the kitchen, put a piece of aluminum foil to use as a reflective barrier on the stove and turned the gas burner on. I could hold my hand as close as I felt I could while still being confident that I wouldn't come in contact with the foil, probably 1/4" away and I couldn't feel the heat. It only took about 5 seconds or so with the 12,000 BTU burner on high to glow red and start to curl towards my hand so the experiment was short lived. I felt the heat on my forearm from what was flowing around the foil but it was an effective radiant barrier at close proximity.

I figure long as there is a gap and things aren't touching, you don't have a conductive path and the radiant barrier is effective, of course you'd need to take into account that construction materials especially wood move/shift with temperature and moisture changes but that is easy to account for.

[buffalobillpatrick]

In my current house I installed radiant heated floors. 2 runs of 1/2" pex suspended between each 16" deep TJI on 16" centers (this is not a good method, as I found out later for low temp. Modcon boilers) but it works because of my high insulation levels & triple pane with an outer 4th layer of glass storm windows + 80g buffer tank.

Based on boiler firing rates at design temp. Of 0*F somewhere around 8-10 btus / ft2 / hr.

ICF basement & 8" SIP upper 2 levels.

Radiation & convection moves the heat from the pex into each plenum.
The pex is hung to the subfloor with plastic electrical clamps, but makes zero contact.

About 10" below the pex is a layer of Reflectix. It keeps somewhere around 80% of the heat above it to conduct through 1.25" OSB subfloor + 1/2" cement board + 1/2" of tile & thin set & radiates into rooms above.

After 14 years. I see no degradation over this time. The bottom surface of the Refectix has very low emissivity, so IR don't radiate much downward.

[Mikesolar]

What is the dT on the tubing?

[buffalobillpatrick]

15-20*F loops are 500' (way too long)

It actually heated just fine for 1st 10 yrs. with only 2 X 10W El-Sid low head DC pumps on each zone, probably 3 qts / min flow.

Now I have zone valves & 1 Taco 008 high head pump.

[buffalobillpatrick]

About 2 yrs. ago I finished a 450ft2 TV room in basement. I removed the Reflectix above that room. Now that room is heated from the radiant ceiling (floor of room above) It stays about 2*F cooler than room above. It has a bathroom that has 2KW electric supplemental heater.

[AC_Hacker]

Originally Posted by buffalobillpatrick

In my current house I installed radiant heated floors. 2 runs of 1/2" pex suspended between each 16" deep TJI on 16" centers (this is not a good method, as I found out later for low temp. Modcon boilers) but it works because of my high insulation levels & triple pane with an outer 4th layer of glass storm windows + 80g buffer tank.

Based on boiler firing rates at design temp. Of 0*F somewhere around 8-10 btus / ft2 / hr.

ICF basement & 8" SIP upper 2 levels.

Radiation & convection moves the heat from the pex into each plenum.
The pex is hung to the subfloor with plastic electrical clamps, but makes zero contact.

About 10" below the pex is a layer of Reflectix. It keeps somewhere around 80% of the heat above it to conduct through 1.25" OSB subfloor + 1/2" cement board + 1/2" of tile & thin set & radiates into rooms above.

After 14 years. I see no degradation over this time. The bottom surface of the Refectix has very low emissivity, so IR don't radiate much downward.

BBP,

I'm glad your previous system worked, but looking at your hydronic implementation really makes me cringe.

It would be very useful to everyone, if you duplicated this post on the DIY Radiant Floor thread (RIGHT_HERE), with some details about how, knowing what you know now, you would have done your floor design different.

The other details about the rest of the house look just great, what with ICFs and SIPs and 4-layer windows, etc.

Best,

-AC

[buffalobillpatrick]

Yep, live & learn from mistakes. I didn't have the info 14 yrs ago.

[Snail]

The info in this thread is really good. However, there is another factor that nobody has mentioned. Maybe we are unlucky, or just klutzes, but over the decades we have had several “indoor floods”. There was the burst washing machine hose, the unattended filling sink, the dishwasher bearing seal failure and, the latest, a spectacular DIY disaster by yours truly.

In the last case, I turned the toby back on at the end of a day’s DIY plumbing, without checking all the taps were closed. What an idiot! Anyway, I came back after a day off to find water pouring out the bathroom door, the basin tap was wide open, far too much for the basin drain to handle.

Initially, I wasn't too worried. I plugged in an electric fan heater and a dehumidifier and thought that the only long-term consequence would be a bit, OK a lot, of wasted electricity. However, after a couple of days I realised that the exposed chipboard floor wasn't drying a well as I expected.

The floor was chipboard, which I think may be similar to OSB, on timber joists over a crawl space. It was insulated with double-sided reinforced aluminium foil, with a sort of bubble-wrap material in the centre. The foil was stapled up to the bottom of the joists and all joints were sealed with aluminised tape.

I went into the crawl space and decided to have a look at the bottom of the floor. As I tugged at the the foil, a seam split open and I was deluged. There must have been 50 gallons in total up there!

In a way, I was lucky that I blundered. If the foil had remained in place, any subsequent small spillages or plumbing leaks that may or may not have been detected at the time would gradually have built up and rotted out the floor.

I would now personally be extremely reluctant to have any form of under-floor insulation that could hold water in any wet areas, such as kitchen, laundry, toilet and bathrooms. I’d also want to avoid sealing in pipe runs. The insulated-conditioned crawl space approach seems a lot safer. I would imagine that it would be cheaper and easier to do as well. I'd be very interested in any experience members may have with that approach, which is pretty well unknown here in New Zealand. My wife is on at me to replace the foil and I don't want to. She has a point though, polished tongue-and-groove floors look lovely but they are COLD.

The NZ government had a scheme to subsidise retro-fitting house insulation. They refused to subsidise any reflective foil system. Apparently our Building Research Association has surveyed the performance of such systems in actual practice and found that the long-term in-place performance was very poor. The theoretical advantages were negated by installation and dirt issues. It apparently doesn't take a lot of dirt to seriously degrade the reflectivity and thus also increase the emissivity of foil. Anyone who has opened up a crawl space attic or wall cavity in an older house will realise just how mucky things can get (In the NZ environment anyway, humidity cycling between 65 and 90% RH every day all year round).

Another caution. In Australia and New Zealand, a number of installers of underfloor foil-faced insulation have electrocuted themselves. A single misplaced staple can make the entire underfloor live. Be careful with that stuff!