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Old 03-20-2018, 09:15 AM   #1
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Basement Insulation Ontario


I don't have a current insulation project. Just trying to better
understand the insulation method I see most often. Guess the
point of this thread is to share what (little) I know and get
alternative explanations for the techniques I've seen.
No doubt this method is described in the OBC (Ontario Building
Code), but I don't have a copy and wouldn't know where to look
if I did.
I have theories for most of the things I've observed but I'm more
certain about those theories for some things than others.
My memory is weak when it comes to when changes in the OBC
occurred so any timelines are more like guesses.
Lastly, I'm skipping styrofoam insulation as I've never seen that
used by new home builders.

Up till the 80's or 90's basements were uninsulated. By 2000 all
new homes required insulated basement. Common method was:
-tar paper attached directly to entire outside concrete wall
-2x4 wood stud wall built in front of wall with ~1" space behind it
-stud wall may have had plastic underneath->not sure
-stud bays filled floor to ceiling with batt insulation -> R12?
-the joist space above the wall would get batt insulation pushed into
place against header joist
-6mil VB (Vapour Barrier) entirely covering/sealing from floor to top
of header joist

Some time between 2000 and 2010 this changed in one way:
-The stud wall is no longer insulated/VB'd to the basement floor.
Instead the bottom ~1" is uninsulated and the VB is tied tucked in
under the insulation and sealed to the wall somehow
-By this point there was definitely VB under the stud wall

So here's what I think are the purposes of the above:
-Tarpaper: Allows air to flow both directions so that any moisture will
not be trapped. Reduces chances of insulation getting wet from
moisture/condensation on concrete wall.
-Space of ~1" between concrete wall and stud wall: Further reduce
chances of insulation getting wet from contact with concrete wall by
reducing physical contact. Allow air circulation pocket to aid in removal
of any moisture that finds it's way in.
-VB: Keep warm moist air from moving outward through the insulation
where it would condense as it cooled.
-Change to NOT insulating bottom ~1': Allow enough heat to escape
down low to prevent freezing under the footings where it could shift
and crack the foundation and possibly everything above.

OK, guess that's it. Ready for further and/or different interpretations.
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Old 03-20-2018, 09:25 AM   #2
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Re: Basement Insulation Ontario


Current thought is rigid foam to serve as a vapor retarder and thermal break (to prevent condensation) and then further insulating value can be achieved through fiberglass or mineral wool between the studs in the wall. While you may have code saying otherwise, no vapor barrier is advised on below-ground walls to allow drying to the inside.
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Old 03-20-2018, 10:26 AM   #3
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Re: Basement Insulation Ontario


Noticed a typo in my previous post but can no longer edit it.
Replace ~1" with ~1' in paragraph below:

Some time between 2000 and 2010 this changed in one way:
-The stud wall is no longer insulated/VB'd to the basement floor.
Instead the bottom ~1" is uninsulated and the VB is tied tucked in
under the insulation and sealed to the wall somehow
-By this point there was definitely VB under the stud wall
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Old 03-20-2018, 12:17 PM   #4
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Re: Basement Insulation Ontario


Basement insulation has been required since at least the early 1980s, possibly before.

But it was only required down to half height and the r-value requirement was something like R6 or 8.

In the early mid 90s, they required full height r12 for a short time, then mike harris got elected and reversed most of the improvements in the code, went back to half height.

The code does not indicate how to insulate for the most part, just the r-value, nominal. (now it may be the actual r-value they look at)

For new builds, they don't put studs with insulate; they usually put fiberglass blanket insulation, it comes in a roll and vapour barrier included.

Doing it with studs is worse - the effective r-value of insulation with studs is below what the batts are rated for.

Vapour barrier and fiberglass is about the worst insulation method for basements. The barrier traps moisture from the foundation in the wall assembly and any moisture that gets in can't get out.

It's far better to have a 100% thermal and moisture break to stop condensation with an r-value of at least 10. Additional insulation can be put in the wall when finishing (or to get to full r-value required by code) and no barrier is required.

However, code may still require a barrier despite having the thermal break, solution is to install it to pass inspection, then rip holes in it before the drywall goes up.

The officials who come up with the code and a lot of the contractors who advise them don't understand building science.
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Old 03-21-2018, 07:41 PM   #5
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Re: Basement Insulation Ontario


Thanks for opinions above. Interested in hearing more.
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Old 03-21-2018, 08:11 PM   #6
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Re: Basement Insulation Ontario


Basements are indeed a challenge in that they can be very different in terms of moisture. Building a dry basement, emphasis on dry, is very difficult and expensive and success will require good landscaping and soil drainage. Most basements that appear to be dry are not even if no water has been seen ever. If the soil around the house has any moisture content, as in green grass (thanks Airman) then that moisture around the walls and under the floor will be migrating into the basement. That is where omitting the VB comes in as if blocked that limited amount of moisture will accumulate until it inside the walls matches the outside. Add anything that mold likes to eat and you have a problem, including fiberglass insulation.

Any indication of water and you have a worst case condition before you start and moving forward requires a lot of planning (moisture management) and more money.

Bud
to be continued
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Old 03-21-2018, 09:14 PM   #7
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Re: Basement Insulation Ontario


Not sure what all is in our current code but all the builders are doing the same procedure. The framing is inspected, the insulation is inspected and the all the exterior walls are drywalled and taped and filled

Top of wall is fire stopped between the top plate and the sill plate on the foundation.
2x4 wall does not want to touch concrete and as the inside of our foundations are a little wavy because we se ready forms the standard is to build it 1' away from the top of the foundation and plumb down.
The fire stopping can be used to make the whole process easer, If 2x10 is available when we frame the house we use it for sill plate, then when we build the walls in the basement we just add a top plate next to the 2x10. Then plumb down to the floor which lays out the bottom plate. If the upstairs is square the basement matches it exactly. Sill gasket under the bottom plate. Some of the fire stopping is lost to plumbing and HVAC. Electric wire holes are sealed with that foam for that the boxes are installed with the formed plastic boxes and the wires are poked thru that and sealed. Vapour barrier is sealed with acoustic seal to the top and bottom plate around door and windows . Taped joins in the barrier must be taped over solid backing.
The rim joist is insulated and can be done with foam board if the ceiling is slated for drywall.

I see in some areas TGI floor joist in the ceiling must now have drywall because of there fast burn thru weakening, I think that is a good idea.

If you don't let air travel to the cold zone you don't have condensation and moisture on the inside is an HVAC problem.
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