The Slab Overhang Issue
How did this happen? Is slab overhang a common happening? How do you avoid a mess like this? Well, the Surveyor, contracted out by the builders, came out twice (over a six month period) to measure up, placing painted sticks and ties about the property for both house designs. We can’t work out what happened exactly. Except maybe…
…the kangaroos jumped the fence and moved both sets of sticks about. Yep! The first lot were left in; and the new ones were added to mark out the slab boundary.
The other thing could be that we downsized the house therefore confused our measurements. We’ve still not gotten to the bottom of it all but it really doesn’t matter now. The way the situation was handled by our carpentry team who alerted us and by our concreting team, who found the right people for the job, it’s such a small issue in retrospect!
If you accidentally design a McMansion and decide to downsize, beware!
Because of this mishap, the slab (due to the pegs and measurements) was made to the incorrect dimensions—the frame on the south side, the cold side of the house, was too short by 40 ml, and another 40 ml in two other places on the northern side, leaving our custom-built, excellent Calco hardwood frame hanging over—not precariously so but, according to engineering good practice: It wasn’t safe to build a second story on.
And to answer the question: How common is this? People in the industry told us this happens a lot. Many builders don’t go to the trouble that we all went to. Life has been very stressful for him lately. He has to do so much. I can’t get government help for Oxygen or CIRS medications (some of them, but most, no!), testing cost a bomb. I’ve got my uni and my plans for a career from home but I don’t feel the disabled are given a fair go. Unless a fair go is just laying in bed getting sicker by the year!
Plus, another section on the north side (the sunny, warmer side, which is our passive heating side during Melbourne winters!) and the western side (the hot side where the sun sets) were too big by 40 ml, which meant the concrete had to be wet cut with an electric saw by a concrete cutter.
These are the drawings our engineer drew so that we could get a clear picture of the solution to the slab overhang:
Basically, we had a steel beam bolted onto the 3 edges of the slab to support the frame. However, right away from a building biology standpoint, it bothered me to think that some builders and owner-builders would construct a building straight over this because of the condensation issue that most likely would develop: basic building-biology science says that if you have metal that’s cold on the outside while warm on the inside (as most houses are in cooler weather) then condensation will occur… then mould! could follow.
Being concerned about the health of the building envelope, condensation for the above reasons and, for a mould sensitive person with CIRS, this is a nightmare of a mistake to make.
In my brain fog, attached to oxygen, I contacted Thomas at ProClima in New Zealand (whom I found out about from Building Biologist, Rapheal at EcoLibria at Torquay, who I found out about from Lucinda at Eco Health Solutions). Thomas then put me onto Andreas at Laros Technologies, here in Australia.
Thankfully, Andreas understood my concerns! I have CIRS
The irony of writing a book on how to Build and Eco-Friendly, Allergy-Free House that is mould free and having to deal with these issues aren’t lost on me. As far as my book and blog go, this is a fantastic event to document because, thanks to ProClima and Laros, we fixed the issue. (I have a whole chapter on mould and happenings that can and did! go wrong and how we overcame these issues.) Dan and I inserted this thermal break ourselves. Now, 12 months later, my thumb still hurts from holding the beam while Dan wedged that low voc, non-toxic ‘thermal break’, between the slab and the metal beam.
Other ProClima products we plan on using:
Intello Internal Airtight Wrap (post coming up on that)
And, hopefully having our house and cottage roof windows’ supplies (flashing and tapes) supplied by them. I’m trying to book Kale in from KLM plumbing to do the job. He’s the perfect plumber: on time; does what he says he will. We’ll be sure to get good instructions for our plumber from Andreas [check] at Laros!
An Energy Efficiency Weakspot
From an energy efficiency point of view: this would be a weak spot that would suck out heat from the building during winter. So although the solution from our engineer was a clever one that saved our house and budget, it didn’t take into account that, Melbourne, being a colder climate, that has such *lovely cold weather, which would keep the piece of steel cold on the outside and warm on the inside each time the house was heated: this would cause condensation given those conditions, which is a great way to end up with mould!
The solution was to create a thermal break along the piece of steal. This would be a guarantee against condensation because there wouldn’t have any heat conductivity of the steel leading to it in the first place!
The galvanised steal beam which is called a ‘RHS’ (Rectangular hollow section) bolted to the slab edge. The RHS had the dimensions of 150 X 50 mm; and was placed On the 3 sections under the overhang of the hardwood frame&msash;Southside and Northside.
Again, the slab was too big by 25 ml: the whole west side length of the house, jutting out with no purpose but to leach heat out of the house by poking out into the cold like that.
So then the builders and Dan found a concrete cutting mob to came out to the build. Whew! They bought with them a special saw and expertly cut the excess slab of by 25 ml, exactly!
Our frame was then nailed and glue together by Pristine Carpentry the ones who rang us alerting us to the fact that the house frame was too too big for the slab. When you take into consideration all the bricks, tin and metal that need to make up the house, that’s still only 40 ml hanging precariously over the edge of the slab. Earthquake anyone? Hyperbolic catastrophes aside:
The problem was: because of the steals temperature conductivity, it was a potential, most definite with time. Mould problem caused by condensation, which would have rose up the wall.
We could have used a hairdryer to meld the shape of the material to the beam but, we realised the pressure of the house would do this.
It was a hard lesson.
Note: It’s best to check yourself.
But it’s all taken care of one thanks to Laros and ProClima: sell truly environmentally-friendly and people-friendly products made for New Zealand weather.
Our solution to slab overhang came from Laros.
People and Places where we Received Assistance in Relation to Building Biology for People with MCS and Mould Illness (CIRS)