Best way to repair a sagging 18" crawl space

tony66

To replace an old (50 year old) sagging floor over an 18" crawl space, is it better to pour in concrete or build another wooden floor?
Is the cost of concrete for a 400 sf space prohibitive? The advantage to poured concrete is that I can install radiant heat inside the concrete.

MacRoadie

There's no way to practically replace a raised foundation system with a slab on grade.

1. Your walls right now are sitting on a mud sill, rim joist/blocking, and a sole plate. These would need to be eliminated and replaced by a single mud sill (lots of shoring). The footings would need to be replaced as they will be too low. All interior and exterior walls would be affected.

2. All plumbing and electrical currently running under the floor would need to be re-routed either through the attic (electrical and potable water) or buried (sewer and potable water).

3. The entire crawl would need to be filled, graded and compacted.

4. Lots of other stuff, but you get the idea.

buletbob

Tony
what do you have on the floor now. carpet, strip flooring, What size are the current floor joist's and there span. and would you be willing to remove the center portion of the room floor to gain access to the crawl space? BOB

MacRoadie

I forgot to ask, do you have an aversion to rebuilding the wood floor? Are you really asking if you can rebuild the subfloor and pour lightweight over it with radiant heat?

tony66

The ranch has 3 types of flooring.
The greater part of the house is on concrete slab.
One room has a 3ft crawl space. This room was completely gutted and converted into my master bedroom. I installed a floor radiant heat system.

The TV room in question is over the 18" crawl space. It is covered by a very old carpet. I peeled the carpet in the corner and found the 18" crawl space for the first time. There is no access to this crawl space.
Because the floor joist is over 50 years old, and the floor is sagging, and I want to install radiant heat on this floor, I have the following options:

1. Repair the floor joist, which is old anyway
2. replace the floor entirely, with plans to install radiant heating on the floor i.e. above subfloor placement of the PEX tubes, using heat deflectors to direct the heat upwards, increase heat conduction with materials that has greater thermal mass, etc.
3. Remove the old floor and pour in concrete. The last option is quick and dirty. My original question was: the space is 400 sf. The total volume of cement is 400 x 1.5 (18 inches) = 600 cubic feet. Is this cost of labor and material prohibitive compared to a new wooden floor?

Yes, I am prepared to re-route all incoming utilities .

MacRoadie

Ok, now I'm even more confused. Where does the 1-1/2 inches of concrete go? If it's a slab on grade. it has to be 4" nominal to begin with.

As I said earlier, if you plan on pouring a slab, you'll have to raise the subgrade elevation in the crawl (the walls start 18" above grade as it stands) and you still have rim joists. mud sills, etc that have to go away.

Or am I missing something?

How are you planning to get from this:





to this:

buletbob

Tony
I would open up the floor, dig and pour the right amount of footings install a wood girder then jack it up and post or block up to the bottom of the girder. If your installing radiant heat you will have to insulate the floor joist cavity anyway, so then with the floor open you could see if you have the proper R-value. Doing it this way your supporting the floor if you want to put down a mud base for the heat system. BOB

tony66

The calculation of 400 x 1.5 is in cubic feet, meaning that the 1.5 ft is the 18" depth. It is NOT 1.5 inch thickness of concrete.
You have a good point about elevating the subgrade soil level. This would certainly reduce the amount concrete used. According to the Radiant Heat association recommendation, the optimal depth for buried PEX radiant hose is 8 inches to prevent heat loss downwards into the soil. You need to have at least 2 inches of rigid foam.
Ripping off the old floor and instal a new wooden floor is not a bad option too.

I may get a quote on these 2 options.

MacRoadie

I still don't see how you plan to address the wall framing. If you simply fill the entire crawl with concrete (22 CY is a crapload of mud for sure and around here it's $125.00 a yard, material only) you can still only pour to the top of the existing stem walls. You'll still have framing between that and the final floor level. How do you plan to address that?

buletbob

Tony, what type of material are you using for the finished floor? I sell a lot of radiant heat with my remodels here on Long Island. And never had a Dissatisfied customer, BOB

tony66

I buy them from Radiantec from Vermont.
I intend to install the PEX tubing over the subfloor, not under and not between the floor joists. I use floating finished laminated tongue and groove floor because of the inevitable heat expansion from the radiant heat.

buletbob

how much of a sag do you have with the floor? You should check out this site www.warmboards.com . I. use this product under all my strip flooring with excellent results. the floor cavity still has to have the proper R-value you do not want the heat to radiate down ward. The alum. plate only spreads the heat over the area. will not keep it from traveling down .