Block on flat, supergrund foundation, DPC required?

SRV

Hi,

Block on flat bungalow being laid to a floor-slab which is sitting on a supergrund foundation. External polystyrene insulation being used.


Is it necessary to use DPC under the blocks? I think maybe not. And a more airtight bond acheived without it?



While on the subject, .... is it necesary to use DPC anywhere else on this type of build? I cant think of any.


thank you..........SRV

sydthebeat

wheres the radon membrane? below the conc slab?
whats the floor make up? screed on insulation on slab on supergrud?

SRV

Hi Sydthebeat,

Ive attached an image showing the detail.

thanks

sydthebeat

SRV wrote: »

Hi Sydthebeat,

Ive attached an image showing the detail.

thanks

thanks srv, very interesting detail!!! i think i can imagine who its from.. 'norse' by any chance?

It appears in that detail that the radon upstand is doing the same job at the DPC. The DPC is typically there to prevent rising damp. There doesnt appear to be any chance of that happening. Being uber-paranoid there could be a chance that moisture may migrate from the external to internal along the horizontal part of the radon under the EWI. A possible solution may be to incorporate a DPC which runs from between the radon and floor slab up, internally over two block courses and steeped back into the block course.

SRV

yes, thats correct.

I know what you mean about the possibility of moisture creeping in along at the radon point. But this is an issue at every butt joint of the EWI polystyrene, were there to be a breach in defences, such as damage to the external render finish.
Also the mushroom head fixings provide means of transferring moisture to the block, were there a failure of render.

I am concerned about this possiblility but this concern ensures that I will see that the job is done correctly.

Thanks very much for the suggestion.

Could you visualise any other areas that may require dpc etc.?


SRV

fclauson

SRV

Supergrund is in the process of getting a NSAI cert - push them for what detailing will be approved and will not be on the Cert

Trev64

Hi SRV,
Your uploaded image is from the Viking System but you say you are using the Supergrund system?

Anyway, I've been looking into this area too and I've been reading the original Supergrund drawings here: http://www.supergrund.se/SuperGrund.aspx?pages=Document&subs=Constructor

They're in Swedish - but you can use google translate to good effect. The detail you are discussing is shown. The original AutoCad files are there too (lower list).

Have you considered using the Isoquick system? http://www.isoquick.de/en/aktuelles.html

Hope this helps!
Trev'

sas

Trev64 wrote: »

Have you considered using the Isoquick system? http://www.isoquick.de/en/aktuelles.html

Hope this helps!
Trev'

It's definitely a good system but it's considerably more expensive even before you including shipping.

liamolaighin

how much more would an insulated foundation cost than a traditional system. 3000 sq feet. A % difference would be a good indication.

Is it worth the extra output. aiming for an A3 rating anyways

galwaytt

You don't need it for A3. Or A2, either.

You can achieve A2 quite easily using a standard concrete raft foundation, and with insulation and floor screed, over.

sydthebeat

liamolaighin wrote: »

how much more would an insulated foundation cost than a traditional system. 3000 sq feet. A % difference would be a good indication.

Is it worth the extra output. aiming for an A3 rating anyways

Agreed with galwaytt.

Insulated foundation systems are, in general, expensive pieces of kit. Id consider them if i was designing for passive lebels, otherwise there are materials available on the market to reduce the thermal bridging at much less cost. Reaching A3 level is only slightly above min regs anyway, and by 2012 will be standard rating for building.