Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

1970s-80s house

Status
Not open for further replies.
wrantler

wrantler

Structural
Aug 19, 2022
109
CA
Well I was house hunting today and came across an interesting one. The house was built sometime between 1975 and 1983. It says the foundation is 'slab' which seems typical in the area I am in. When I got there the realtor told me there was an issue with the foundation and that they had a concrete slab jacking specialists in to repair it (and showed me the receipt). It said they drilled holes and pumped 1.5m3 of grout to level the foundation slab for a cost of $5k. So I looked around and clearly the floor did not seem level. I could see daylight under some of the interior walls and there was some cracks in the drywall they tried to repair and paint over, and some they did not.

I am not familiar with how these slab foundations were built in this area but it looks like a grade beam around the perimeter walls. Interior slab is poured after. From the pics it looks like the interior slab portion has settled more since they leveled it (or they never 'leveled' it in the first place). The original flooring in the kitchen did not look tampered with so I don't think they really tried to do much other than keep it cheap and try to pass the buck on to the next guy? But 1.5m3 over some of the settled areas comes to almost and inch so that seems to make sense.

In the pictures the red lines represent walls that I could see daylight under. Yellow line is the crack in the ceiling.

Now for questions:
1. From how the trusses look pretty much all the interior walls are non load bearing?
2. If #1 is true one could pretty much knock out the walls to the kitchen/dining/laundry rooms and open it up? They seem to be hanging from the roof trusses?
3. Has anyone seen this happen before to a slab foundation and fixed it on the semi cheap?
4. Has the fill under the slab consolidated and wont settle anymore?

Well this house is priced quite low (for the reasons above). And it is in a nice area. So I am actually thinking about it at this point. I would redo the flooring and renovating anyways so I am mostly concerned about the sinking floor issue....it has to feel right and maybe you guys can help with my dogs breakfast.

house1_nyv28l.png
20231022_135155_xuxkuy.jpg
20231022_135224_y8vhdv.jpg
20231022_135446_ponczp.jpg
20231022_135655_ssso7y.jpg
20231022_135701_y8bd1f.jpg
 
Replies continue below

Recommended for you

Sort by date Sort by votes
You need to hire a local structural engineer to evaluate in detail. Particularly before removing any walls. And fixing the floor properly looks expensive.
 
Upvote 0 Downvote
wrantler - you're mostly a commercial/industrial structural engineer, correct?

Residential isn't that much different. The approach some contractors take to it is...but the physics are the same and I apply the same rigor to residential engineering as I do to commercial. After all, a house is Risk Category 2 just like a shopping center!

So I'd take a look at the trusses and the roof line. Any signs of sagging? Distress in the trusses? Look closely to confirm that the trusses were not intended to bear on any of the interior walls.

Jacking slabs is not cheap. For my own house: I'd start by having a Ground Penetrating Radar scan of the slab to see if there are any voids under the slab. This may require the removal of finishes - I don't imagine it would work well with carpet. Then I'd survey the floor to create a contour map and determine the elevation differences. That plus any estimated voids would give me a good idea of how much jacking is required and I'd work with a jacking company to come up with a targeted plan to jack in the right areas.

But that's also why I don't have a house on a slab (among other reasons).
 
Upvote 0 Downvote
I mostly do bridges these days. Luckily I seem to be ok at it and we have tons of rotting infrastructure that needs work. I Have done a couple residential things in the past but it was years ago - and I would not say I know this area well.

I really did not want to sniff around too much on my visit as it was an open house. I would like to go again on a booked showing so I can snoop harder without being watched.

The roof line did not seem to sag from the outside. And I did not notice anything inside. I would like to get in the attic tho. I guess I am thinking that the trusses would just span exterior to exterior wall as the span is pretty short.

@phameng are these houses on slabs an issue in your area. If so that I pretty much what I am looking for - run away signs.

Oddly enough I think the old man lived here for the last twenty years with the house like this. He died and his estate is selling it. The estate did the 'fix' and tried to patch it up.


 
Upvote 0 Downvote
They're very common around here. Most new houses are on slabs. Issues this bad on a slab with no load are rare, though. I've measured over an inch of drop in a slab bearing 2 floors and a roof deck that worked out to be almost exactly the expected consolidation of loose sand for the fill depth. In other words, they dumped sand in and poured the slab without consolidating.

I wouldn't want to deal with it. The trusses make it easy to knock out walls and rearrange things, but your plumbing is locked in unless you want to trench the slab. But this slab could be a can of worms. I'd price out gutting the place, pouring the slab, and doing your desired renovations and see how good it looks. Because there's a chance you could get to that point when you start digging into it.
 
Upvote 0 Downvote
I was also thinking they just dumped in some material and poured. I am not sure how else it could be this bad. Honestly I was hoping someone might talk me out of the gutting option. But I think that is what I will price out.

Its one of those 'shittiest house in one of the nicest part of town'.
 
Upvote 0 Downvote
Also price out ripping the whole thing down and building what you want in the nicest part of town.
 
Upvote 0 Downvote
Would one expect there to be reinforcing in this slab? I cant imagine it is very thick?
 
Upvote 0 Downvote
I could tear it down. I'd just have to live in it like this until I can afford to do that. Anyone wanna guess what the assessed value is?
 
Upvote 0 Downvote
V difficult to judge based on a a handful of photos, but looks to me like the interior slab or solid floor has settled over the last 40 years.

Pulling up the carpets would tell you a lot plus some exploratory digging to see what the walls are actually built on as it looks like a separate floor slab with better foundations for the walls.

As to removing walls - that ridge line on the roof looks very close to the line of the interior walls so again some investigations needed.

But what's the big downside?
Either just fill in the floors to get them level or remove, consolidate and relay the slab.
If that central wall is load bearing or at least difficult to tell if the trusses are "resting" on the interior framework then some sort of support beam might be required - not the end of the world.

So long as the outside walls look ok, seems very fixable.

All IMHO of course and you need some more local support, but do the numbers.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
Upvote 0 Downvote
Good point, LittlInch. If you prove they're non bearing walls, you could just fill on top of the slab. Though I'd still want to confirm there are no voids first.

Probably a 4 inch slab. If there's any wire, it's probably sitting on the stone under the slab.

Assessed value...twice the asking price? (I know nothing about the real estate market in BC.)

 
Upvote 0 Downvote
I would go to City Hall and see if they have any records. It is likely a frost wall atop footings. You need to figure out how that was done. If that was done poorly I would not consider this property. The slab repair is not a huge problem if the price is right and you are prepared to get involved.
 
Upvote 0 Downvote
The repair method varies quite a bit, requiring careful investigation per other's comments to answer your questions. If it can be proved that the slab is not intended to support anything apart from partition walls, then the repair is largely just to achieve a level floor (easier said than done).

I recently was contacted by a homeowner with a similarly settled slab-on-grade. He really thought the house was in a state of impending collapse. After asking him some questions, it really did not appear to be that severe or noticeably affecting his 2nd floor or roof framing. I spent a few hours reviewing all the provided info and drafted a ~$3k engineering proposal for destructive investigation to core the slab in a few places, auger some soil samples, and do some DCP testing to best inform the final signed/sealed repair plans. The homeowner was furious at the engineering fees and hung up on me when I didn't want to "just come see the house" for free. [dazed]
 
Upvote 0 Downvote
Did some recon calls today and got some anecdotal info. This fellow bought the house new in 1975 and lived there until he died recently. It sounds the owners think the settlement is from pouring the slab on some unconsolidated base. They attempted to fix it once 20 years ago. It settled again and it seems the estate tried to fix it again to get some more $$ for sale.

I spoke with the slabjacker company - which does seem reputable and honest. He said they pumped grout where it was convenient to the owner. Which was where they could tear back the carpet.

If this slab is on loose sand I dont think the slabjackers can really fix it without removing the slab. The grout injection might have even made it worse as the grout areas are supported but the others are not. Plus I would not want to sink a ton of money in a reno and have the floor settle again.

Say we assume the voids are all gone. I had thought one could remove all the interior walls and flooring and pour a leveling grout ontop to level the slab in one large pour. But if something settles it will surely crack

Anyone have thoughts on $/m2 to remove an interior floor slab. Thru a door via wheel barrow and jackhammer I guess?
 
Upvote 0 Downvote
You need to consider how far you want to go with the reno. If you plan to take the structure down to the studs, and you have extensive mech/elec renos as well the value of the property is not much more than the raw land. The value of the raw structure is not a big part of a typical home (20%-30% new build). The problem with a reno is everything tends to cost 50% or more than new because the first step always involves demo. The next problem is you rarely get quotes because you never know what is hidden in the wall before starting. What is the value of the land and what is the potential value if you look at the comps in the area? Years ago I moved the home I grew up in. Before I did that I went thru endless scenarios how to reduce the size and change the interior layout. Every time I went too far with the interior renos it became obvious saving only the raw studs and framing was not cost effective.

I recall doing some concrete demo work some years ago as well. Before I started I asked one of the old time contractor for some tips. His advice in dealing with concrete demo was use the largest equipment you can. The hammering is not difficult. The work is removing the debris. I don't think anyone without knowledge of your area will have good estimates to remove the slab. How much you get charged will depend on your trade availability. For me I doubt I could find anyone that would charge less than $90/hr for this work, and it would only be a few since it is crap work. If I were in Vancouver I could call and find any number of companies that specialize in concrete demo work, and it would be far more cost effective. I would call a few trades and ask for budgets.

I doubt your problem is voids. I would expect you will find improper slab prep and/or fill materials that are problematic. Is this sand and gravels or clay materials? If clay, a very common problem is not to deal with runoff.
 
Upvote 0 Downvote
Or just break it up, remove the odd big bit, compact the broken bits and then pour in a truck load of grout?

Or drill a hole in it every say metre, pump grout underneath, then flood the place with self leveling grout?

Many ways to get a floor raised a bit and super flat.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
Upvote 0 Downvote
I really do appreciate everyone's feedback. I am thinking about things and will report back.
 
Upvote 0 Downvote
I'll just add that, for me, I'd be evaluating this mostly from the perspective of resale value. Can I get this back to good well enough that it ceases to be a disclosure item and a drag on resale value.

Most of us workaday types borrow heavily to acquire our homes. And I think that there's danger in treating any property as such a "forever property" that resale is not a concern.

Life happens and I'd not want to be chained to a mortgage on an unsellable house when it does. There could be a massive economic downturn in BC or a zombie infestation contained by the the Rockies... who knows? Maybe an Estonian supermodel love interest requiring a move to Milan?

Last year I got involved in assessing a home foundation where the house wasn't selling simply because it was built on a wood foundation which is weird around here. No performance issues. The retiring couple that owned the house wanted to cash out on their nest egg property in order to move closer to the families of their adult children. They'll be doing that with much lighter pockets than they'd planned for which was pretty sad to see.
 
Upvote 0 Downvote
PWF basements reminds me of a story of a review we did around 20yrs ago now. It was a very nice home and very well built by a contractor that was well respected. It would not sell because the home inspectors kept noting the walls had bowed 1/2" or 5/8". We had prepared a report indicating that it was per CSA PWF code, and I believe others had too. It still would not sell. In the end we helped the couple with a design to strip all the drywall, and add new studs as a precaution. Each stud was scribed to the slightly curved wall, and framed plumb. It was very costly. I am glad PWF foundations died a natural death. The earliest versions were an absolute nightmare. Near the end of their popularity they were much better, but still not my preference.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

m1208
  • Locked
  • Question
wood trusses subject to house fire
Replies
4
Views
117
dvd
dvd
magicming
  • Question
House floor post on exterior foundation wall 1
2
Replies
23
Views
758
PlinkoEng
P
XR250
  • Locked
  • Question
Steel Framed Balcony to House Attachment 1
Replies
16
Views
181
XR250
XR250
milkshakelake
  • Question
Lateral concerns for making an opening in a house
Replies
9
Views
179
Flotsam7018
Flotsam7018
structSU10
  • Locked
  • Question
1970s MBMA
Replies
1
Views
11
DanKile
DanKile

Part and Inventory Search

Sponsor

Back
Top Bottom