No hardcore in an extension?!

[kk13]

We are in the process (2wks in)of building an extension (3x9m). The oversite is due to start next week. We have a few issues:

- The architect has specified 150mm hardcore but it seems the builder was not planning to lay this as the ground had not been dug out at all and he was planning to just lay the sand and the DPM etc - is this normal?
We have subsequently raised this issue with the builder and they are now proceeding to dig out the ground, although they are claiming MOT hardcore is already present from a previous patio. we are unsure if this is suitable for an extension. To us, the ground just looks like topsoil - we can see roots growing in it when we dig down into it!

- The architect also specified 80mm Celotex for the floor insulation - the builder decided to change this to Jablite which I believe is cheaper and inferior? He didn't tell us he had changed it. Since we now require a thicker layer of this insulation, he needs to make compromises with the other layers in the oversite (hence not doing the hardcore)

- The builder also just poured the concrete foundations over the existing drain which drains the kitchen and bathrooms without bridging it.

- The bricklayer put dishwashing liquid in the mortar - have just seen on the MyBuilder forums that this is unacceptable practice. How concerned should we be about this?

Any advice much appreciated.

 

[tony1851]

1. If the architect has specified 80mm Celotex, you will need more insulation as jablite is only about one-half as thermally efficient as Celotex; has the building inspector seen it?

2. They should NOT concrete directly over the drain because any slight settlement might crack it. The drain should be bridged with concrete lintels.

3 Washing-up liquid is not generally recommended because of the salt it contains, though a lot of brickies use it; probably the least of the concerns here.

 

[damanpunk]

Haha think you've been had for April fools mate!

 

[AdamCH]

Haha think you've been had for April fools mate!

Thought no April fools after 12:00 or the "fool" reversed - that was how we played it at our school anyway.

 

[kk13]

We wish it was an April fool sadly.

 

[theoldun]

U value of floor should be.0.22Wm2K
With a P./A ratio of 1.0, 80mm of FR celotex will suffice.
With Jablite Premium 70, you will need 140mm to comply
With Jablite 70 you will need 160mm to comply.

You can reduce your MOT sub base down to 100mm

Drain runs should never be concreted over in foundations unless sleeved or bridged with concrete lintels.

If washing up liquid is used as a plasticiser, you will be able to rake the joints out with your thumbnail in 10 years time.
Regards oldun

 

[RonnyRaygun]

Where you been Old Un?

 

[tony1851]

kk13;
It's not the end of the world regarding the under-floor insulation. You will still get some improvement compared with a plain concrete slab. Strictly, it probably won't comply but if the inspector picks it up, you can always put some additional insulation in the roof to compensate.

The drain, though, could be a problem and needs re-doing.

As regards the mortar, it may not necessarily be a problem IMO - if there is a reasonable amount of cement in the mix, you may be OK.

 

[^woody^]

The whole idea of having a set of specified plans, is to allow the builder to price for the work based on the specification, and then build the thing to the specification

Not to just do what he wants or thinks, or do what he did on the last job

I would stop the work and get these things sorted out now, before the builder carries on doing his own thing with the rest of the job

 

[AdamCH]

If the builder quoted for 150mm sub base & 80mm Celotex then that's what he should provide regardless of whether the substitution is okay with BC. If they are going to substitute then it should work at least as well not just to the point it satisfies BC.

Digging out the foundation will be fun

With this list of things gone wrong already you might be best to put you foot down and require it's all redone to spec - if you don't then what are they going to cut corners on to save money next?

Do you still have your architect involved? Might be worth getting them to take a look.

 

[tony1851]

It's easy to tell a builder to re-do this or re-do that but, at the end of the day, the builder will try to make up the loss somewhere, and other parts of the build will inevitably be skimped.

Now may be the time to part company before too much more work needs to be re-done.

 

[^woody^]

If the Op can't deal with the builders, then they could engage someone to actually manage the work and check the quality, before releasing any stage payments

OP, don't rely on the building control officer, they only check about five things and quality is not one of them

 

[kk13]

We have stopped the build until the potential issue with the drains is sorted out. Would thedrains still need support if they are redundant? Surely even if they are going to be redundant they risk collapsing with the weight of the foundations on top of them and thuscause the extension side to collapse?
There is also some question as to whether the neighbours drains run across the front of our house and join ours.

The owner of the company who we hired to do our extension has apologised profusely and offered to find us another ground worker if we wish to part ways with the one he subcontracted to initially. We will take a couple days to think about it but the Trust is definitely gone.