I was having a great 2021 year until about an hour ago when a tenant called and said his 12 x 24 ft. concrete front porch had collapsed!! I drove over and yes, 1/2 of his front 6 inch thick concrete slab has collapsed into the crawl space for no apparent reason. This is going to be a major repair. The part that did not collapse will (like the high-rise condo in Miami Beach) will have to be demolished and the entire 12 x 24 porch re-built. I told my tenant he may have to move out but for now just use the back door. His house (MH) is fine and was not attached to the front porch.

A crawl space under the concrete porch of a mobile home? Wow.... never heard of that, period, much less heard of one collapsing.

I imagine there must be some sort of bracing to hold up a 6 inch thick slab of concrete over dead space. Did the supports fail, erosion wear it out, or what "took it down"?

Like Sid, I'm surprised that there was a crawlspace under a concrete slab / porch for a MH. Is the slab yours & the mobile home his or do you own them both?

If there is a concrete floor in the bottom of the crawl space,

A little history first. Before 1975, there use to be a 1940's vintage house built on this lot. This front porch was originally built for that house. That house burns down and the lot was cleared of everything except the elevated (3ft) concrete slab front porch. This 12 x 24 porch has a cinder block foundation that supports the outside perimeter of the porch. Now, instead of rebuilding the house, someone bought the lot in 1976 and put a 1976 vintage SW mobile home in and butted it up against the existing front porch which made perfect sense.

Fast forward from 1976 to 2011 and I buy the MH and lot from the 3rd owner of the MH. Even in 2011, the concrete porch had a 'shallow spot' in the middle where rainwater would always pool. It was where this water would 'pool up' as to where the slab began it's collapse. Also, I noticed this morning when looking at a cross section of a broken 6 inch slab section, the original rebar used inside this concrete is all rusty looking. I don't know the full age of this concrete slab but it is at least 50 years which enough time for rebar to rust. T

Jason,

The perimeter cinder blocks did not collapse and they are still supporting the eight 4x4x7' wood posts which are supporting the metal roof above it. This 12 x 24 porch has a metal roof which I am so glad did not collapse due to the foundation wall not being affected. If that foundation block wall is still good, I want to keep it.

Not quite like yours... but here is my porch story....I had a front porch get hit by a car about 5 yrs ago. Took the front right pillar out. Dropping the porch roof down on the Escallade. I turned it into my insurance; got like 6200 and they went after they driver insurance company. Cheapest estimate to rebuild was 15k. Needless to say; I re built the front porch and pocket the difference.

Plenty,

Plenty,

Roy, sorry to hear of your current situation. I would be willing to bet that the underside of that structure was not periodically checked for decay. There should have been some sort of structure and floor to pour the concrete on originally that probably decade a long time ago and now the rebar in the concrete is weekend as well.

Sounds like it might have been built using steel tension cables. They put the cables in the concrete and after it sets a bolt protruding from each end is tightened putting the cable under high tension thus giving it strength for non-supported loads like you have. Fairly common in the 1960-70's. Unfortunately, the cable almost always fails without warning causing a catastrophic structural failure.

6x6,

This afternoon I went back and took a better look. Ys, there is some rotten wood underneath but I still think the rusted rebar is the culprit. Plus, I noticed the slab was originally poured at a depth of 6 inches in some areas and only 4 inches in other areas. Yes, this was probably a redneck concrete pour at the time it was first put in. However, the original slab lasted at least 50 years before it collapsed today and there is something to be said for that longevity.

Next week some serious work on this project will begin. I will know more then.

Roy,

But did you get your $5000 worth?

We had an entire bedroom ceiling of sheet rock simply fall down in one piece while baby napped. Fortunately his wooden crib stopped the drywall from crushing him!

Brad20K,

$5K worth of what? Hmm?? My morning coffee has not kicked in yet.

In the past, I have had entire sheets of drywall fall from a living room ceiling (unreported roof leak) in one house and in another house the kitchen floor collapsed due to a soft spot in the floor the tenant never reported either. Everything is fixable with money though.

I think he's assuming that you wouldn't have paid more than $5K for the place originally.

DJ,

Thanks for the clarification. Yep, this is one of those $5K houses and to this day has been my best cash cow of all time. Occasionally, Murphy's Law happens and this time 1/2 of the front porch collapsed.

My local municipal government had to demolish a concrete parking garage that they owned. It was not old. It became structurally unsound and could not be repaired. The engineers determined the main reason for the premature failure was the builders failed to use epoxy coated rebar (the green stuff). Over years, the concrete developed cracks and allowed water infiltration. The rebar started to rust, and rusty rebar loses adhesion to the concrete. The bond between rebar and concrete is absolutely essential to structural integrity.

Myob,

I was going to make a separate post on this but you beat me to it.

Why use 2x10's for the 12 x 24 perimeter walls? I was planning on using 2x8x12's for the perimeter walls (ie. rim joists) and also use 2x8x12's for my floor joists which will be 16in. on center with concrete block piers in the middle of the 12 ft. span.

I prefer to use the same dimensional PT lumber (2x8) for everything if possible.

Scott,

Ken,

There has never been a shortage of redneck builders in AL. And if I get a permit, guess what happens next. My current cheap property taxes will go up. The property tax people (appraisers) ride around town with building permits in their cars to verify that the work was done. If yes, an automatic tax increase.

3 years ago, I built another smaller deck at a rental house. I did not get a permit but I did call the rental house inspector and asked him for the lumber sizes and the spans etc. for a 8x8 ft. / 6ft. elevated deck. He did not have a clue. After I told how I wanted to build the deck, he said "yes, I guess that will be okay".

Chris (CT) - Yes this one was hollow under the slab. There is one cinder block pier in the middle of this 12 x 24 slab.

Myob,

besides being the quickest and the least work-- they are absolutely better way. Toe nails split the wood-- whether toeing from sides or top and bottom.

Roy you can put all the hangars up using a chalk line-- then just drop in the 2x8's.

It takes roughly 30 days for concrete to cure to 90% of its strength. It takes 100 years for it to achieve that last 10% of strength. But during that 100 years, things happen to the environment around the concrete.

Ray,

No concrete will be used to rebuild this. It will be like building a wooden deck that measures 12 x 24. My lumber cost will be around $1,600.00 and labor about $1,600. The best news is that my tenant will pay for it all with his rents. On the 1st, he made the first payment of $675.00.