Posted By Dana1 on 27 Oct 2010 01:08 PM
Running the crawlspace warmer without the insulation between the first floor & crawl REDUCES the relative humidity of the crawl space rather than increases it. But sealing all of the air penetrations to conditioned space likely reduced a drying path for moisture getting into the crawlspace through the concrete walls and air-leaks through the foundation sill & band joist. (Those air leaks will be somewhat drier during the winter- the fall/spring warmer rainy periods are typically your worst case conditions in your area.)

68% RH is too high- you WILL get mold conditions on the joist edges (which is probably creating the "bad" air down there). Running the crawl space cooler with more fiberglass between the joists will only make it worse.

Thanks again for your input.  This is a rather huge issue to get my head around.  This is Victoria and most of the trades (insulating and heating) are stuck in a conservative groove.  They do somewhat agree with your reasoning.  I do to.  However, to have those "pros" come in and install as you suggest the bill will be upwards of 6+k.  I doubt we will ever see an energy payback for the rest of our years here (we're seniors).

In the 10 years that we've owned this 30 year old rancher, I've never noticed any standing mold, especially on the joist ends.  This has been with the vents both opened and closed  -- when we purchased the house the vents had been left open for the previous 20 years.  Of course, the R13 insulation was only stapled to the bottom of the joists and the rim joists were not insulated at all.  This had kept the CS relatively warmer than outside -- but at a co$t of heat loss.  All insulation is down on the CS floor right now waiting for a) decision as to what course we will take  b) having a knowledgeable contractor agree to our terms of instruction, cost and date.

A single 200-300 board-foot DIY kit for 2lb foam would be suffient material for air-sealing foundation sill and band joist to ~R6 (1" thickness). Then, sealing the interior face of the concrete with a vapor-permeable silane-based sealer will reduce the flow of ground & rain moisture through the foundation slightly, then putting even an inch (R5) of XPS on the concrete, foundation sill, and rim joist will lower the RH of the crawl space by two mechanisms: The XPS is only semi-permeable to water vapor, and insulating the foundation will raise the average temp of the crawl space. A combination of 1" of XPS + a mini-studwall with R11-13 UNFACED rock wool or fiberglass batting (and no interior-side vapor barrier) would be nearly ideal for Victoria's maritime climate. (Great city, BTW- I love the summers there!) I'm not sure if the nat'l builing code has recognized yet that inerior vapor retarders are far more likely to create than prevent problems in coastal BC- you might have an argument with the code inspector on that one, in which case using 3-4" of unfaced EPS instead of 1" XPS (without insulation in the studwall) would put you in the same R-range and is it's own barrier.

With it vapor sealed at the floor, vapor-retarded and air-sealed at the foundation wall, and kept warm enough the the RH stays well above the mold range on the joists, there simply IS no contamination issues by mixing conditioned & crawlspace air.

As for the Advance Energy research summary you linked to , your nowhere NEAR as cold in winter as places like Flagstaff, but you're also nowhere near as DRY, and they didn't insulate the CRAWLSPACE floors, only the crawlspace walls. In all cases the crawlspace stayed much drier with insulated walls rather than insulated floor. In Victoria the subsoil temps are ~10C, and if you insulate the walls of the crawlspace to ~ R10-R20 and the crawlspace floor to ~R8-10 you'd have the best of all worlds. If you insulated the above space floor to R20 between the joists the crawlspace will run colder and more humid. If you go with the latter putting at least half the R value below the joists and air tight (with say, 2-3" of unfaced EPS rigid board, for lowest cost) will keep the joist edges well out of mold/rot danger, and the crawl could be vented to the outdoors. Then again, if the same EPS were laid atop your cement-parge crawlspace floor and insulated the foundation walls you'd be in about the same place, with less labor, and have a warmer-dryer crawlspace. (R8 of EPS will run you about the same money as R5 in XPS, but it'll be twice as thick- you have some headroom to work with.)


In the AE research article they do make reference to insulated floors vis a vis insulated walls :           



                                                                                                              " Energy Savings

While moisture reduction was consistent, energy

savings varied with climate, insulation and duct

placement.

In Flagstaff, researchers monitored energy use

throughout a single heating season. While the homes

with insulated floors used 20 percent less natural gas

than the controls, those with insulated foundation walls

used 53 percent more.

This seemed counterintuitive; ducts are a notorious source of heat loss. With

all the Flagstaff homes’ ductwork in the crawl space, one would expect better

performance from the warmer, wall-insulated crawl spaces. But according to

Cyrus Dastur, the Advanced Energy building scientist who directed the research,

those homes’ lack of floor insulation let heat radiate from the first floor to the

crawl space, robbing more heat from the house than was saved by keeping the

ductwork warm.

The research makes it evident that in cold climates, it’s better to insulate the floor

above the closed crawl space than to insulate the foundation walls. "

I realize it's Flagstaff, but perhaps adding a regulated exhaust fan (like the Tjernlund unit -- they make a compelling argument for their product) and some tiny amount of make-up air to the CS I can make our plan work.   Or, perhaps going back to the other idea of running an HRV air supply and stale air return duct -- with a low wattage in-duct heater -- will accomplish the conditioned air movement required.  That is the opinion of the SummerAir folks, who make HRV's. 

Another concern is that by making our humungous CS a conditioned area, the CS would have to be heated to near the same temps as upstairs living area.  It seems logical that the un- or under-insulated floors will otherwise transfer their heat to the coldest area -- down to the CS and it heatsink floor.  Methinks that insulating the subfloor to the max will mitigate this problem. 

Have you read David Hill's article on this subject?  (he manufactured our Eneready HRV) It is very interesting as it adds a new element of radiant barrier to the mix.  I talked with him a while ago, and as a local (Vancouver) he suggested venting the CS with a small exhaust fan.  Here's his take on CS modifications:  

Radiant Barriers in Crawlspaces                                           Feb. 3, 2010

 

Although R-2000 attributes little insulating credit to radiant barriers, leading Canadian building scientists 60+ years ago recognized their benefits in housing. Today we thank Dr. Don McAdam for reintroducing this ‘insulation’ to us. Over the last 3 years he has patiently made 2 in-depth technical presentations to TECA members complete with a convincing demonstration and a follow up in TECA News.

 

While radiant barriers are simple to use and appropriate in specific applications they are complicated to explain. Unfortunately they are misapplied in wall cavities and the poor performance which results has discredited them for use across the board.  Radiant barriers shine in retarding heat flow downward*. Attached to the underside of a wood joisted floor system is the sole winter heat retaining application where radiant barriers can be effective.** If the floor is radiant heated floors they are even more beneficial as an ‘insulation’ method.

 

The total floor heat loss down downward is made up by adding up the 3 separate and independently acting floor losses, conduction, convection and radiation.

 

Conduction     There are 2 downward conduction paths through a wood joisted floor system: conduction through the wood of the joist itself and conduction through the air between the joists. Both losses operate independently. In the case of a 2 x 10 joist system, heat conducts down through both the 9- 1/4"  joist itself and also through the 9-1/4" depth of air contained between the joists. Because dry wood has an R value of approx. 1 ¼ per inch thickness, the R value of a 2 x 10 is about R12. Unfortunately, regardless of the insulation material used to fill the joist space, these 2x10’s always conduct some heat. However, in a 16” o/c joist system the path width through the 1 ½” of wood is only 9% of the gross floor area, so this and the fact that seasoned wood is a fair insulator, the conduction loss down through the floor assembly is small compared to either convection and radiant losses. The thermal bridge caused by the 2 x 10 could be reduced by substituting a TJI (with a thin 3/8” web) or by installing rigid board insulation sheathing wall-to-wall under of the joists.

 

The ‘still air’ between the joists however, is a very good insulator. A layer 9-1/4” thick provides approximately R50. The R value of the assembly drops to approximately R39 after factoring in the lower thermal resistance of the 2 x 10 itself. Dr. McAdam showed TECA members that glass fiber is a less effective insulator than ‘still air’ itself. After air movement has been properly stopped, adding any insulation between the joists displaces the thermally more effective ‘still air which actually decreases the insulating value of the floor assembly.***

 

Convection     When joints and gaps through the perimeter rim joist and holes through the subfloor drilled by the electrician’s and plumber’s are sealed, the air between the joists is heat trapped so it can not move. The upper layer of air in contact with the underside of the subfloor plywood is warmer, making it want to rise thereby maintaining the ‘trap’. This means that convection can not begin.

 

Radiation        In quality draft-free construction, radiation is by far the most significant contributor to main floor heat losses down into a crawlspace. The 70° F floor plywood  (80°F +/- if radiant heated) 'sees’ the crawlspace floor. The underneath side of the subfloor plywood is a highly effective heat emitter while the crawlspace floor is a highly efficient heat absorber, thermally a bad combination. It makes no difference whether the crawlspace floor is skim coated over poly or is simply poly. This radiant loss downwards occurs unabated 24/7 all year because the temperature difference between these 2 surfaces is held almost constant all year. A comfortable floor must be maintained @ 70°F minimum while the ground itself holds the crawlspace ‘floor’ to 40°F  +/-**** In summary, the radiant loss downward over the period of one year is significant because:

a)     the floor area is large,

b)      the loss is constant and significant, unlike that of the exterior above grade walls where the losses approach zero during the summer and milder weeks of spring and fall, and lastly

c)     a crawlspace, indirectly heated by losses from above will drive increased heat loss to the outdoors.

 

Radiant Barrier Types          Bubble wrap is sometimes used to insulate HWT's. The benefit in this mainly vertical application is the wrap’s built-in compartmentalized air cells. The internal trapped air bubble resists both conduction and convection making the wrap effective. In a crawlspace application, where the barrier is used horizontally however, the bubble wrap’s most significant contribution against downward heat loss are its 2 exterior shiny surfaces, not the trapped air between. Simply, even with its internal built-in R value, the extra cost of the ‘bubble’ product over the simpler flat shiny sheet is not warranted in this floor application.  

 

Summary       

1) A double-sided foil radiant barrier tacked to the underside of the floor joists will significantly reduce radiant losses to the crawlspace.

 

2) Sealing the rim joists and subfloor penetrations will completely eliminate the convective losses through this floor assembly.

 

3) The net result, ‘still air’ trapped within the 9 ¼” ‘thick’ joist spaces provides conduction resistance that’s superior to traditional 9 ¼” thick R28 batts. That is R39 overall as for compared to R28 for the batted joist system. Note, while the R28 correctly represents the batt’s R value, the ‘assembly’ R is reduced to R25 when one discounts for the effect of the joist’s thermal bridge. Joist thermal bridging was already factored in for the still air’s R39 resistance value.

 

A foil radiant barrier costs less than batt insulation to purchase and install. Note, a radiant barrier does not have to be sealed to the standards of an air barrier of the plywood subfloor above, for example, so any minor holes left in it to accommodate plumbing and wiring do not seriously degrade its barrier performance.  

 

Radiant Barrier availability              The closest source we have found so far is Rona:

L#KLt 1050    SKU: 10010945 Attic Insul Kit                      Description: 723389 Attic Insulation Kit IK00001-CDA             (roll) Size: 500 sq. ft.

 

 

Installation

• To Reduce Radiant Heat Loss: After all plumbing and wiring is done, simply staple the radiant barrier to the bottom of the joists. In the case of TJI floor system, there are more effective ways to install the radiant barrier, but they are less practical.

• To Reduce perimeter Radiant and Conductive Heat Loss and Eliminate Convective Loss:  Before installing the radiant barrier, install Iso Board in the rim joist cavities, shiny side facing inwards towards the centre of the house. Seal around edges of Iso Board and air leaks around plumbing/electrical penetrations in the subfloor. 

 

Notes:

            * Heat moves from warm to cold with equal ease up, down or sideways, only hot air rises. One only has to sit on a cold concrete paver to realize that heat goes down easily. 

 

**In a hot climate, radiant barriers make great heat shields. Shiny foil material may be factory applied to the underside of the OSB roof sheathing, built into a roof tile underlay board and used separately suspended below the roof sheathing or, laid directly on top of the attic insulation. Suspending the barrier, while the least practical, is the most effective as both shiny surfaces contribute to the barrier effect. Radiant barriers effectively block the line-of-sight radiation transfer from the underside of the roof sheathing to the attic floor almost as if the glass fiber attic insulation was not there. Radiant barriers are especially useful when direct sunshine heats the roof surface to high temperature during any season when this added gain would overheat the house.

Note that radiant barriers (for either heating and cooling applications) only work when one or preferably both shiny surfaces have a minimum of ¾” air space in front of them. Their radiation ‘insulation’ properties are reduced to zero in the portion of their area which touches any  other construction material.

 

***Fiberglass batting of floor joist systems is still used today, in part as a legacy from drafty floor systems. However, batting is only a cure to a symptom. The best result which can be accomplished by placing batts here is to slow down the air movement through the joist system. Air leakage through slit openings between the plate and rim joist, joints in the rim joist and through holes in the subfloor causes high convective losses. This could be much more effectively accomplished by air sealing. Dense pack cellulose insulation, while it is seldom used for this purpose is an exception because it is a very effective draft stopper. Evidence of our misunderstanding about joist system air movement  contribution to heat loss is easy to see in renovation where pink and yellow figerglass batts removed from between garage/carport ceilings and heated bedroom floors above show large black dust stains from years of filtering the dust from moving air.

 

**** In locations when the ground is dry and hence has low conductivity and when the crawlspace floor is placed well below grade, 3 feet or more, the crawlspace floor centre may gradually warm up thereby reducing radiant loss from above. However many crawlspaces are shallow, are built in highly conductive wet soil, with some even allowing ground water to pass under enabling them to suck even more heat away. These high loss conditions depress crawlspace floor temperatures increasing the radiation losses from above.            

David A. Hill

Note:  Dave's process?  Easier said than done!  In the very beginning of this exercise I did contemplate installing radiant barrier.  In the end the product was returned to the supplier.  For one thing there it was too difficult to plan out the install as too many integrated utilities (plumbing, electrical wiring) were involved -- under and around joists, etc -- when it's up in place there'll be no map as to where any utilities are hanging.  Also, no local insulation installers knew how to put this stuff in correctly.  And, I discovered the absolute conductivity of the material frightened the heck out of us : what would happen if any electrical fault touched the massive sheeting of this under-joist install!! 
 

Posted By Dana1 on 28 Oct 2010 06:19 PM
In the Flagstaff floor vs. crawlspace foundation insulation experiement there was only wall insulation in the crawl, with nothing between the crawlspace air and the cold cold dirt (which is about 5C colder in Flagstaff than in Victoria.) With both the walls and floor of the crawl instulated there won't be that huge heat loss going out the bottom.

Was there something I was not understanding in the AE article?   Quote:  "While the homes with insulated floors used 20% less natural gas than the controls, those with insulated foundation walls used 53% more."   then..  "those homes' lack of floor insulation let heat radiate from the first floor to the crawl space, robbing more heat from the house than was saved by keeping the [ductwork] warm."   and.. "The research makes it evident that in cold climates, it's better to insulate the floor above the closed crawl space than to insulate the foundation walls."  Well, I think we qualify for cold climate compare to say, Florida   

Radiant barrier is all but useless when the temperature differences are less than 20C between the cold surface and hot surface, which is why they have no pay back in applications other than attics in hot climates. Unless the crawlspace got below 0C and stayed there often (not likely, in Victoria), you'd get pretty lousy performance out of it in this application (unless you keep your place 30C indoors all winter. :-) ) It is IN NO WAY equivalent to R28 batts in the joists at your delta-Ts. Your crawlspace floor is closer to 50F (10C) on the coldest day of the year than it is to 40F, if you've closed off the vents. And your sub-floor is closer to 60-65F than 70F (unless you have radiant heated floors.) In Saskatchewan there might be a winter benefit though. But with as little as R5 between the radiant barrier and the sub floor the delta-T between the RB and the crawlspace floor will be so small as to yield nearly zero benefit.

Sure glad I listened to myself on the first time around (and now you are confirming it) -- I felt the hype on that stuff had to be way off here in this climate.  Hard to understand why an engineer/designer (Dave) would postulate such a remedy.  Anyway, it could have been worse  ..but it wasn't installed and the the supplier took it back with no questions

But if you stuff R30 batts or something between the joists, the cold edge of the joist will be colder & damper. If you insulate between the joists and ventilate the crawl use outdoor air, and run it on dehumidistat control (which will mostly work in Victoria, but wouldn't in places with higher dew-points.


I think we will probably stuff the floor joists, get a Tjernlund ventilator http://www.tjernlund.com/retail/underaire.htm -- it has an integrated humidistat and low-temp shutoff t-stat, and use another opposing vent for a small amount of makeup air (to keep the CS from sucking in living space air).  As well, there is an existing 500w baseboard winter-use heater in the center of the CS, as well as a ceiling fan we installed a few years back.


I want to thank you for offering all this information for us to chew on.  If the above project doesn't satisfy our needs, then we may look biting the bullet and move on to insulating the walls, etc.

-dale