Factors That Makes Houses Crack

Here’s a list of things that make houses move and crack. How many of these can you identify in your house:

  • Downward movement
    • Consolidation of soft, uncompacted fill. Review the original soil test or order a new soil test.
    • Soft, squishy soil. Look for poor surface drainage that allows water to soak into the ground.
    • Settlement of backfill over sewers. Check council mapping for sewer plans. Look for sewer access hatches on or near the allotment.
    • Settlement of backfill over a stormwater pipe. Check council mapping for stormwater plans. Look for access hatches and field inlet gullies. Arrange an independent audit by a plumber.
    • Erosion of ground into a broken stormwater pipe. Review the plumbing layout on the site. Engageg a plumber to check pipes for breaks. Lodge a complaint with the infrastructure owner to get pipes fixed.
    • Tree roots. If trees are within 1 x times their mature height they could be affecting the house. Dig down to identify roots on the outside of the house. Remove trees or get a builder to install a root barrier.
    • Unstable slope slipping downhill. Engage a geotechnical engineer to assess the stability of steep slopes.
    • Mine subsidence. Review mine mapping and confer with a mine subsidence expert.
    • Slab heave caused by water seepage through the porous fill. A soil test will show if there is sandy, porous soil overlying clayey soil. Install an upstream soakage trench and divert water around the building.
  • Upwards movement
    • Poor site drainage causing slab heave. Identify low spots where water can soak into the ground and fill them with clayey soil sourced from elsewhere on the allotment.
    • Slab heave caused by setdown waffle pods under verandahs allowing moisture to seep into the ground. Ensure 50mm in 1000mm fall all around the dwelling. This should have been provided by the builder. Look for sandy soil or rocks around the dwelling that might be allowing water to drain under the patio area. Look for high floor levels in the rooms around the patio,
    • Footing heave caused by broken stormwater pipes. High points on floor surface levels above underground pipe locations. Engage a plumber o check and fix broken pipes.
    • Footing heave caused by broken sewer pipes. Engage a plumber to fix broken pipes.
    • Footing heave caused by broken water supply pipes. Turn off water supply. Engage a plumber to fix water pipes. Only happens in older houses where walls are set between concrete slabs. Unlikely in newer houses.
    • Tree roots placing upward pressure on footings. Look for large tr under the ground surface. Remove tree or remove tree roots. Install root barrier.
    • Brick growth. less likely but bricks do grow and some vertical lift could be experienced. Check and replace damp proof course.

5 Things to Look for When Inspecting a Suspended Concrete Slab

If you’re a structural engineer and you’ve just been asked to inspect a suspended concrete slab before it is poured, now is definitely a good time to go through the things you should be looking for when you carry out your inspection.

Here are my 5 most important things to check when inspecting a suspended concrete slab:

Continue reading 5 Things to Look for When Inspecting a Suspended Concrete Slab

This is a BIG House

Cornell Engineers was engaged by Brisbane Builder Rigoli Constructions to design the footings and slab for this massive house at Cedar Creek.

With 657m2 of single level slab on ground including 300m2 of verandah, this house is BIG!

Cornell Engineers designed the raft slab on ground for this house.

Massive raft slab on ground at Cedar Creek

Matt Cornell, director of Cornell Engineers explains:

There are special considerations a structural engineer has to take when designing a very large residential slab on ground. The decision to not have a control joint in the middle of the slab meant that this large slab had to be constructed and cured appropriately to keep shrinkage cracking to a minimum.

Once the slab was down, the builders did a great job of moist curing the slab which meant that the concrete had plenty of time to gain strength before the coverings were removed. This meant that shrinkage cracks were kept to a minimum.

Timber frame for big house at Cedar Creek

Now that the roof is on this big house, the plasterboard linings and internal fitout can commence.

The roof is on this massive house at Cedar Creek.

We’re looking forward to seeing this house finished. It’s going to be great!

Need a big house?

Need a big house for your family? Somewhere o hang out in a quiet spot in the country? Need a big slab? Contact Cornell Engineers to see how we can help.

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What Volume House Builders Don’t Want You To Know

The number one secret volume house builders don’t want you to know is that you are entitled to a certain standard of construction and finish in your home.

So picture this. You design and build your dream house with a volume builder. It all goes fairly smoothly. You move in. Three months later you see a crack or two in the walls.

“How bad does a crack have to be before it is a problem?”, you wonder.

The mass market builder supervisor says, “Don’t worry! Houses settle and move all the time. Wait 12 months and then we’ll come and do some repairs.”

But you do worry. You look at the crack as you walk past every morning. You see it every night. You worry some more. You show the crack to your friends. You hear horror stories about new houses and cracks. Is your house safe? Will you be able to sell it? Is my house falling down???

Ok. Take a breath.

Yes. Some level of cracking in a house is normal.

So now I’m going to reveal a secret which shouldn’t be a secret.

Queensland’s QBCC and Victoria’s VBA have both published a guide to what is an acceptable crack, deflection, sag and bow.

Check out the manual for your area and next time you complain to your site supervisor or warranty manager – arm yourself with what is acceptable and what sort of damage should be ringing alarm bells.

Here you go:
https://www.vba.vic.gov.au/__data/assets/pdf_file/0008/102896/Guide-to-Standards-and-Tolerances-2015.pdf

https://www.qbcc.qld.gov.au/sites/default/files/Standards_and_Tolerances_Guide_0.pdf