Spray foam crawlspace insulation which way?

[stv1991]

Going to be foam spraying the crawlspace of a building in northern, MN. Building is sitting on a concrete footing with a four block height above the footing. The ground under the building is partial sand and one corner is sitting on ledgerock and ground is mostly uneven underneath. There is a gas tankless water heater under the building as well as a water pressure tank.

Question is: do we spray the concrete walls, rim, and floor joists to insulate this crawlspace OR do we spray the concrete walls, rim, and floor of this crawlspace and keep the floor uninsulated and let the heat from the building radiate down below?

1) is the sprayfoam strong enough to be crawled on once it sets up without breaking?
2)if we spray the floor & walls will that let the ground below freeze and thus have a higher chance of the building shifting due to frost?
3) if we spray the floor joists & concrete wall will heat radiate down and prevent building shift?
4) not spraying the floor would allow easy access to plumbing & wiring I see as an advantage
5) what are the moisture concerns for each method?

Pros/Cons/Suggestions for either method? Bowl or upside down Bowl?

[James Eggert]

Each of your approaches is a mess!!! I suggest you review the proper way to do this with the AHJ.

Fill out your profile to continue after reading this!

Quik answers
you spray the walls. rim and floor system BUT, because of the fuel burning appliance in the crawl space you now need an ignition barrier...costly because that has to be either a dw cover, an osb cover, or intumescent spray! all cost time and money. The placement of mechanical equipment is the crawl is probably going to bite you.....

1. the foam cannot be crawled on, see the note above about the intumescent ignition barrier.
2. short answer, the building does not freeze OR shift within the envelope, because the footings are below frost and the walls per the IEEC requires insulation either on the exterior or the interior.
3. I can't answer this because I'm LOL
4. This advantage does not exist in the real world.
5. Typical soil cover is a 6-10mil underlayment with stone or a rat slab!

I can appreciate your questioning, albeit somewhat limited in the approach. Review the spray foam issues with the installer.....please don't tell me you want to buy a couple of the large tanks and do it yourself!!!

[Mark Parlee]

Jim
Is is conceivable that if all of this is insulated from the inside that no residule heat keeps the footings warm, they freeze and heave. This would be a problem if for some reason the footings we not deep enough to begin with.
why do I second guess things now that I mainly do consulting?
somethings changed in my thinking.

[James Eggert]

Mark
Think about it this way, the footings are placed at the prescribed frost guided depth, so they don't freeze, such as a simple footing/wall combo backfilled both sides except you keep the inside dirt typically 18" below the framing. In this scenario, nothing freezes.

Now, if you leave the inside down to top of footings, and then install a vb on the ground, you can either install stone or a 3"ratslab. In this scenario the backfill material is supposed to hold the footings against exterior forces, and of course if you pour a ratslab that would be a moot point. So now the 18" is say 40" when you allow for a min 6" grade below top of wall and add in a top plate for the floor system. Again, once you place the prescribed rigid inside the foundation walls from top of wall and two foot below the exterior grade, whether mechanically heated, or simply using the ground's residual heat, the area doesn't freeze, therefore the footings cannot heave!

When we place 2" rigid under a slab it is to create a thermal break from the ground, and keep the slab at a constant temperature.

[Mark Parlee]

Jim
I was over-thinking it. Sometimes all of the crappy details I see gets the best of me and I play the what if game.

[stv1991]

Thank you for the replies. However, this is a unique circumstance and the owner would like to maximize the efficiency of this building.

As mentioned one of the corners of this building is built on ledgerock so that side of the building will not shift. However, the other three sides of the building are "floating" on the footings and are only about 18" below ground surface because they were not able to be placed below the frost line due to the variablility in depth/ruggedness of the ledgerock below the surface. Now with that being said, the three sides of the building that are not on the ledgerock have a drainage system just outside of the perimeter of the building and then the drainage system is covered by 4X8 sheets of rigid foam about 10-12" below ground surface and angled away from the building. The drainage system takes the water about 50' away from the building and actually seems to be doing a good job at keeping water away from the building. The rain gutters are also tapped into this system.

I have crawled around under this building and have looked at the footing and block wall and they are intact with no cracks or evidence of shifting. This building has been sitting this way for around 15 years at this point so it appears as if the system has some merit in holding the building solidly in place.
No, I will not be the one who sprays the foam under this building but the owner wants it done and has mentioned both ways. The bowl or upside down bowl with the spray.

Due to the "floating" footing, spraying the block walls, rim, & floor joists makes the most sense to me. It keeps the heat under the building and can prevent the ground from freezing and lessen the likelyhood of the footings being pushed up by frost.

On the otherhand, I can see the thought process of spraying the block walls, floor, & rim to keep the heat encapsuled in the whole building, crawlspace through to the living area. With this scenario, a crawlspace heater probably is not even necessary as the living quarter heat will also heat the crawlspace. My concern once again is now the area is insulated and the ground has a chance of freezing and allowing the footings to shift due to frost heave even though there has been no evidence of this happening to date. In my mind, it's still a risk.

With the spraying of the floor there would only be one heating system and with spraying the floor joists there would, for all practical purposes, be 2 separate heating systems to keep the interior & crawlspace heated.

Hopefully this sheds some light on this unique situation and can help decide on which way to insulate the underside of this building.

[James Eggert]

OK, you've added some details not in the first post.
1. The building is set on both footings AND on ledge. You say there is no evidence of any front heaving damage. Is the walls on the ledge "pinned" to it or is that not known?

2. Because I don't know how deep the top of the ledge actually is where the walls are placed whether pinned or not, the fact there is no discernible movement gives some credence to the sheer size of the ledge, such that the slope of the ledge probably helps keep water away from the foundation/ledge connection joint. The additional building drainage system also sounds like it is working well.

3. I don't agree with the bowl up scenario because you are asking a stable foundation to be heated on one side and being cold on the other. Right now there is of course some ambient temp shift from the heated space above, but keep in mind that the soil temp stays relatively stable as it gets deeper, so you are already achieving some, that is some, temp increase from the earth floor. I would not encourage increasing that temp within a building foundation that works as it was designed and installed.

4. In the event I'm not clear, I would NOT spray the earthen floor.

5. You still will need to resolve the presence of mechanical equipment and the spray foam on wherever you put it.

[Roger P]

What you appear to have is a Frost Protected Shallow Foundation. http://www.toolbase.org/PDF/DesignGu...dFPSFguide.pdf
Also see 2009 IRC R403.3 Frost protected shallow foundations.
The foam sheets around the perimeter are keeping the footers from freezing and heaving.

Cover the floor with a Class I (6 mil poly) vapor retarder and foam the walls and rim. Do not foam the floor or the ground. See 2009 IRC R408.3 Unvented crawl space. The interior insulation needs to extend a minimum of 12” below the exterior foam sheets.

2009 IRC N1102.2.9 Crawl space walls. As an alternative to insulating floors over crawl spaces, insulation of crawl space walls shall be permitted when the crawl space is not vented to the outside. Crawl space wall insulation shall be permanently fastened to the wall and extend downward from the floor to the finished grade level and then vertically and/or horizontally for at least an additional 24 inches (610 mm). Exposed earth in unvented crawl space foundations shall be covered with a continuous Class I vapor retarder. All joints of the vapor retarder shall overlap by 6 inches (152 mm)and be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152 mm) up the stem wall and shall be attached to the stem wall.

[stv1991]

OK, a couple more questions on this.

This is a seasonal place that can be heated year round and used as a home if that was the choice. Currently the owner is keeping the interior temperature around 45-50 degrees year round. The place is used occasionally in the winter. 1-4 weeks each winter. Again, the foundation and drainage system seem to be doing its job because even with no heat for a few winters several years ago, the foundation has not shifted. If just the walls and rim are sprayed, is the floor going to feel cold on the feet? Should a crawlspace heater be kept underneath to prevent the freezing of the water pipes? There is heat tape in the water pipe from the well to about 20 feet inside the crawlspace.

If the walls, rim, and dwelling floor were sprayed there would be two separate heating systems involved because of the barrier on the floor. With just the foundation walls and rim sprayed there would be communication of heat between the crawlspace and the dwelling. So again the concern is will the floor feel cold until both the crawlspace and dwelling temperatures equilibrate? And also, if the dwelling interior is kept at that 45-50 degrees is there going to be concern of water pipe freezing in the crawlspace when temperatures in northern, MN drop down to -40 degrees in January?

I guess the main concern here is that the owner would like to maintain comfort in the winters yet have the ability to keep the water system active year round in the most efficient manner as possible. And my job is to figure out which way is the best option.

Also, what are the concerns with spraying the rim if there is humidity? The crawlspace is always dry but what are the moisture trapping concerns with spray foam in crawlspaces?

So for the record, spraying the ground floor is not an option. Now the question is foundation walls & rim OR foundation walls, rim, & dwelling floor for the situation at hand.

Again, thanks for any input as this really has me thinking in several different directions as to what is best.