Advise about house movement/cracking problem

Hi all

I have a mid 1950's Mt Gambier stone house that has cracks on the walls adjacent to the front door. They've been getting worse over the last few weeks but I put this down to the drought and Adelaide's reactive clay soils.

The other day while standing on the front door step I looked up and noticed the steel post that supports the roof over the front porch has broken loose. The porch roof is a simple steel reinforced concrete slab about 5 inches thick.

I've attached some photos so you can see what I'm talking about.

ISTBC but I suspect the reason for the support post breaking away could be related to having the front of the house paved about 7 months ago. Prior to the paving there were concrete paths surrounding the front porch which was probably holding everything in place.

Now the concrete paths have gone the porch step has dropped and taken the steel support post with it. As the entire weight of the porch roof is being carried by the walls adjacent to the front door I think this maybe the cause of the internal cracks getting wider.

I'll need to arrange for advise/quotes etc. to get this fixed ASAP.

Would it be a simple matter of inserting some sort of wedge between the support post and the porch roof to take the load off the walls? I'm concerned if the porch step continues to drop under the weight of the concrete slab roof the internal cracks will continue to widen.

I guess another option ($$$ :() would be to have the concrete porch roof removed and replace it with something lighter such as a steel or timber framed structure.

What are your thoughts about a solution for this problem?

Holy Dooley!

How long has the porch roof been unsupported?

Do you have any cracks in any walls on the opposite side of the house (the back)?

It looks to me like, as you said, the porch slab has moved (sunk) - but I cant see any cracks between the porch slab and the walls.

When they took the old paths away did they dig deeply near the porch?

You say you have reactive soil - can rainwater get down through the pavers? It is generally considered very bad practise to seal off soil surfaces next to foundations in reactive soils. Houses can heave - one side of a house rises higher than the other due to different soil moisture content.

This problem is very common. Here near Noosa there is a recent development with many million dollar homes built on swamp land - houses have tilted by up to 200mm (75mm is common) from just such paved areas. Plumbers tilers and chippies love it!

If it is only the porch slab that has sunk I would rip up the pavers, acrow prop the porch roof, jackhammer out the porch slab and extract the ironwork - then repour the porch slab and reinstall the iron work.

The cracked blockwork is a worry though - It appears as though the cracks go right up to the top plate of the front wall. Demolishing the concrete roof is going to make things worse perhaps.

If the house has heaved ie the back of the house has sank, I'd fill the cracks and sell it.

It looks like the porch ground slab is not supported properly. Taking away the other concrete has effectively increased the pressure on the soil under it and so is has settled. I think Dirty Doogie is on the mark with propping the porch roof and replacing the floor slab. But I would put a small footing/pier down there as well so it can't sink.

What ever you decide I would immediately wedge over the steel stauncheon OR put a substantial prop under concrete roof before it does more damage to the walls, and keep an eye on it should it settle further.

As for the cause (and I'm guessing here) as you had concrete perimeter paths before, I cant see the difference in replacing them with paving. I suspect there is another reason for your slab settling.

Did the paver folk deeply excavate or remove any large trees? Any leaking water pipes nearby, or excess water usage? Stormwater pipes broken/disturbed during paving?

Its going to be a trial and error method to eliminate causes, before you replace/underpin the slab.

Good Luck

Doers the paving cover a substantially larger area then the pre-existing conc footpaths?

As Doogie said, I can't see any cracks between the porch slab and the walls either. I'd say the slab & founds for that corner of the house have settled by at least the gap above the post. That's a fair amount and it's not good. :no:

The easy option is to sell up. Personally I'd temporarily (but thoroughly) wedge the gap, even if only to relieve the stress on the roof slab and improve safety levels by 100%, then wait another 12 months, reassessing the movement every month or so.

If the settling is only due to the pavers, the found's will find a new level and movement will stop. With luck, the damage is already as bad as it will get and you'll have had 12 months to put some pennies aside for permanent repairs. The blockwork's a worry, but it's not at the "tear down and rebuild it" point yet. However, if the movement continues I'd seriously consider making it someone elses' problem.

FWIW, I wouldn't bother pulling up the pavers. The horse has already bolted, shutting the stable door won't put it back in. :shrug:

I only became aware of the loose support post in the last couple of days.

The rear of the house hasn't cracked so I don't think the entire house has heaved.

The paving guy excavated the sourrounding area deep enough to accommodate 100mm of road base, 30-40mm bedding sand and the 60mm thick pavers (they link up to the driveway area).

No trees, pipes etc were removed in the process - just the old concrete path. The paving surface isn't sealed so rain (whats rain) is able to drain through ok.

I've also been keeping water up to the lawn and garden beds to minimise the effects of the ground expanding and contracting during the drought.

The concrete pad (not tied to the house foundations) looks to have moved a few mm away from the house. Will need to take a closer look along the edges to see if it has dipped.


Gathering from the replies replacing the concrete pad might be the go.

The next step then - ring around, have it inspected and get some quotes/ advise.

Will keep you posted.

Thanks

THanx I would be interested to know how it goes. Definitely put a prop under the roof slab or wedge up from the steelwork ASAP though.

The pavers are pretty much covering the same area where the concrete path used to be.

There is a small crack in the conc pad that doesn't show up in the photo. It wasn't there before the pavers went down so it's possible the pad has leant forward causing the post to come loose.

Will take a closer look at this when I get home tonight.

I have no advice to give, but would like to say, from what is shown of the house, looks like its a very nice place. Minus the cracks of course. :)

The pad looks to be a simple slab on grade. Foundation resistance is dependent on weight from surrounding soil and structure. Removing and replacing the nearby paving has likely compromised that function. I suggest immediately wedging the post to reduce damage to the slab roof and the rest of the house. Then support the roof with outboard props to remove load on the pad. Demolish the pad, and replace it with a new pad, with a deeper footing at the post location. The deeper footing reacts against the weight of deeper soil. I can't do calculations by long distance and jurisdiction, but a local builder or engineer can likely advise on the depth required.

Joe

Quote:

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Originally Posted by joe greiner

Demolish the pad, and replace it with a new pad, with a deeper footing at the post location. The deeper footing reacts against the weight of deeper soil. I can't do calculations by long distance and jurisdiction, but a local builder or engineer can likely advise on the depth required.

Joe

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I agree.

There are houses everywhere with cracks due to the drought!
I'm no expert but it seems to me that the concrete porch roof, no longer supported by the post, is exerting a lot of leverage on the walls. Its now a cantilevered structure. I can't see how the the roof is connected to the stonework, but its obviously a decent join, otherwise it would have parted! And put less stress on the walls too.
I would seriously consider taking it all down, digging up the porch slab, and rebuilding with decent footings. Maybe the new roof could match your house roof, with tiles? Keep the same steel post maybe. Would there be much of a weight difference between tiles with associated woodwork, and the existing concrete number? I reckon it would weigh heaps less and therefore less stress on the walls.

Good luck.

Removing the roof slab would be an option but trying to tile the area would involve moving the gutters and attaching extensions to the rafters. I think he will want to leave the roof structure alone.

Thanks for your thoughts and advise.

I've wedged in a temporary post to keep everything in place for now.

On Thursday a local underpinning contractor came around to have a look at it. He put it down to the corner of the house settling (where the pot plant is in the photo) as a result of the drought and the new pavers. He advised waiting for the winter rains before doing anything by which time the foundations will have found their level. Then he advised wedging a metal plate between the existing metalwork and the roof area and securing it with bolts. Once this has been done the cracks can be repaired. He said this type of problem is common place in Adelaide with the drought and the age of the house.


On Friday a general building contractor had a look at it. He said the drought is a factor but the concrete pad is also a problem as it's not substantial enough to support the weight of the porch roof and it's not tied into the house foundations.

His advise:

Option 1: dig up the pad and put in a new one with deeper footings and reset the support post.

Option 2: Remove the porch roof and pad, replace with lighter weight verandah structure and pad with deeper footings. He agreed that a tiled roof structure would be less weighty than the concrete roof but the guttering and stonework may need to be altered to accommodate it. He said a timber frame structure with colourbond roof would not require extensive reworking of existing house.

He's going to send me quotes for the 2 options.


I've got another general builder coming around onTuesday for a 3rd opinion.


At this stage I'm leaning towards option 2 - new roof and pad. Even before the drought and the new pavers I've had to repair cracks on the interior walls adjacent to the porch. I think the weight of that concrete roof will continue to cause cracks unless it is replaced with a lighter structure with proper footings.


Stay tuned.

Yes the porch roof will be heavy - if anyone tries to demolish it they would have to be careful. Machines like jackhammers are likely to send vibration into the blockwork of the walls and shake them. Given the walls are already cracked great care would be needed.