Insulated foundation ( passive slab )

[Nickfromwales]

That's why this place works so well. Instead of shouting the reason at you we just whispered it loudly   

[TerryE]

14 hours ago, IanR said:

It's really not a lot of work to set out the EPS formers.

 

But it does have to be done properly otherwise the pour will be a disaster.  This isn't just a case of putting out some EPS Leggo bricks.  Our SE had a Geo survey to validated the depth of hardcore base, drainage, etc. needed and this varies depending on the subsoil type.  As I have said on other posts, the guys were extremely particular about compacting this in 50mm layers to a survey level, and then adding a 50mm sharp sand layer.  They rejected the first batch of sharp sand because it had too many fines in it.  

 

When I asked the gang-leader why they we so particular, his comment was that the greatest risk in this type of pour was differential subsidence across the slab.  We've had one member here hit badly with this issue when his slab slumped by 25mm in one area because of poor compaction.  

 

Likewise the rebar design has to be properly engineered for the design loads and then properly installed and tied in. And the pour need to be properly compacted.  We've had another member whose installer didn't compact the slab so it failed inspection and had to be broken up, removed and reinstalled.

 

So yes, I agree with your basic thesis that this type of slab, when properly installed takes less work than a conventional beam and block foundation + insulation, USH and top screed, and both cheaper overall and better performing, but you need a skilled team.  But these skill need acquired, and you need to proper quality checks when doing the job, otherwise things can go badly wrong. 

 

I just think that a typical jobbing builder won't have these skills or quality check in place.

[Nickfromwales]

5 hours ago, TerryE said:

 

I just think that a typical jobbing builder won't have these skills or quality check in place.

More to the point, they don't understand or foresee the consequences of missing such basic but vital links in the chain. A lot of them rely on Bco's that don't double check everything, a disservice to the customer who has paid for that service. 

On a garage conversion I was involved in, one Bco asked for holes to be drilled into the garage slab to PROVE that it was thick enough to take 5 courses of block for the internal, and then watched as the outer lip of the footing was also drilled for the same. Once happy he left after giving strict instructions on what needed to be done to open and clean the cavity out. He asked for photos of everything if it was being covered before his return. 

On another job, the builders used a petrol disc cutter to make two lines in the slab. They got the labourer to chase out about 2-3" of the concrete, bought some concrete in bags, mixed it and troweled it back in. When the Bco came out he said "have you dug a suitable footing ?" They replied "yes, of course we have, look the concrete is still soft from the 'pour'". Bco said happy days and left. 

He wasn't so happy when he came back and they were trying to hide the pair of 3600mm concrete lintels that they'd tried to put in stead of steels. That wall was load bearing and taking the hip of the roof.  They beat my price by £2k, and bodged every single thing they did and cut every corner they could. They just kept redoing it until the Bco said that'll do. 

There are builders, and then there are men who bought building tools and a van. Huge difference. Check with at least two previous customers so you know if things went south on previous jobs. 

[RichS]

5 hours ago, Nickfromwales said:

There are builders, and then there are men who bought building tools and a van. Huge difference.

 

 

Never was a truer word written.

Edited January 10, 2018 by Nickfromwales

[Nickfromwales]

What typo ? 

[jack]

18 hours ago, Nickfromwales said:

What typo ? 

 

If you only knew how many of yours I correct on the sly...