The Brew Cabin

Posted: **Fri Jun 22, 2007 5:49 pm**

In a barn I am hoping to work on, a previous contractor has installed an RC slab. This slab is 125mm thick and assuming it has been laid in accordance with the arch's plans it should sit on 1200 gauge DPM on 150mm compacted cleanstone hardcore that has been blinded.

I can see parts of the DPM coming up the sides of the slab into the wall cavities but it seems the DPM does not overlap in places and use of jointing tape has been ignored. I understand the membrane should overlap at least 150mm between sheets...

The DPM also just seems to be loose in the cavity. The barn does not have a DPC as it a couple of hundred years old. Is this OK to leave the DPM loose in the middle of the cavity? If so how much should it stick up above the slab and should it be in the middle of the cavity?

Unfortunately, it does seem that there are parts beneath the slab that will not be wrapped in the DPM as there are parts to the slab's side where no DPM is evident...

The plan is to lay Kingspan Thermafloor TF70 on the slab, then a vapour barrier, then a screed with underfloor heating pipes in it, then the floor finish.

Is it accpetable to put another DPM in or should the slab be broken up and a new DPM installed properly beneath a new slab?

http://www.insulation.kingspan.com/uk/pdf/tf70.pdf

The Kingspan website for TF70 does not talk about putting the DPM above the RC slab.

Posted: **Fri Jun 22, 2007 5:59 pm**

Crikey Ted it just seems to get worse. It sound as as if the internal blockwork has been built off the slab(for the slab dpc to be in the cavity), is that correct. If so the edges of the slab should have been thickened and tied in to the outside walls. (what walls are going to take the roof loading? often in conversions they design it so the new internal walls are carrying the roof loading) I would expect the slab dpc to be cut tight back in this instance. There should be a detailed drawing at 1:10 of this junction, compare whats on the detail to whats been done.

Posted: **Fri Jun 22, 2007 6:05 pm**

The slab does support the inner leaf.

Ski, don't be surprised - the whole construction should be condemned IMHO!

http://www.atkinson-law.com/CasesAr....ion.htm

The arch has done inspections but not picked anything up and the contractor is obviously a complete amateur and not suited to the job...

Posted: **Fri Jun 22, 2007 6:14 pm**

Is there a detail drawing for this though?

Posted: **Fri Jun 22, 2007 6:17 pm**

The first floor is supported off the inner leaf in places but the roof is on the outer leaf. Obviously if the slab has to come up, a lot of the first floor must too - how will we prop it?

Anyway, the roof needs to be redone too!

Posted: **Fri Jun 22, 2007 6:27 pm**

ski wrote:Is there a detail drawing for this though?

Not that I can find at present - so it should be built "according to best building practice" should it not; I don't think what we have here is good building practice!

Posted: **Fri Jun 22, 2007 6:38 pm**

No, if there is no detail there is no guide as to good practice. This sounds like another common fault, the owners(or whoever) have a set of plans that have gained deatiled planning and passed for building regulations but that does not make them construction drawings. I have seen this often, usually a client baulks at having to pay an extra chunk of cash for construction drawings and think well the drawings are good enough for building regs so you must be able to build it from them. This opens a can of worms because the architect can hide behind the fact that he was not employed to do construction drawings and the contractor can hide because he says there was no construction details. I would refer you to my comments on my last post in the celotex thread about getting a clean start.

Posted: **Fri Jun 22, 2007 6:48 pm**

Well the contractor still has to abide by manufacturer's instructions. So Visqueen's BBA and Visqueen's product and application details surely apply...??? Otherwise the manufacturer offers no guarantee....

Would you pay for something that has been installed without following the manufacturer's instructions?

The Brew Cabin

Dpm - Any solutions?