2" foam board insulation under lift post???

[Lewisthepilgrim]

Hey guys, how thick did you guys poor your floor slab? I'm thinking 5" thick with 2" foam board underneath. But what about under the lift colums???

Did you do 3000, 4000 or 5000 psi concrete??

 

[skulldrinker]

Re: 2" foam board insulation under lift post???

If anything pour a small footing under the post location. No foam, nothing compressable.


3500 (5 bag) is for backyard patio and sidewalks

4000 (6 bag) is fir driveways and floors

5000 is for bridgedecks over the highway.

 

[K'ledgeBldr]

If you know exactly where the lift (legs) are going to be, I'd not place any foam board there and dig another foot down and about 3' square for a thickened slab at the mounting points.

I've seen it done as a separate footing- flush with finished floor- not a good finished look.

 

[22george]

Ask your lift manufacturer is my suggestion. That is what l did when l purchased my lift.

 

[Don1357]

None of these sound like the recommendations from a lift manufacturer. The one I plan on buying suggest a minimum of 4.5" with rebar. Throwing more cement under the spots the lift will be would not fulfill any particular requirements, as their engineer determined that 4.5" with rebar is all it took.

The whole "no foam under the post" fails to understand how a heavy load in a point on the slab gets transferred down. It gets distributed a lot more evenly, it is not like the post will break a hole on the slab.

 

[matt_i]

Couple of things come to mind.

Assuming you used F-250 (Foamular comes to mind) it has a 25.0psi rating, which multiplied by the 144 square inches in a foot, is 3600 psi which is almost double what an average soil (2000 psf) can be counted on to reliably bear weight upon.

However, with practical considerations, the rigid foam has to be "fitted" against the ground or a stone-base, and that's no easy task. The concrete, however, being a semi-liquid at first, will perfectly fit itself to the ground presented.

Last thing is that a 2 post lift is more like a set of 2 jib cranes than a set of posts. It requires the slab to be a part of bearing the overturning moment on each post.

If it were my personal lift I'd thicken the area falling between the posts and not fit the foam into the dugout area underneath it.

 

[1redTA]

I don’t understand why some of you are saying not to use the insulation under the lift. You trust the insulation to support the building plus everything inside of it but not the lift?

Also, why insulate the concrete if you are going to leave gaps? isn’t that defeating the purpose of the insulation?

 

[road_king]

As mentioned, look to the lift manufacture for required min concrete specs. Install the 2" rigid foam under the lift

 

[Buckgnarly]

Just do the thickness the manufacturer recommends and use the foam board. There is some WAY overthinking that goes on here.

 

[logical]

Do we even know its not a 4 post?

Sent from my garage.