slipping sheet above foil faced insulation?

ryanrod

I'm building an extension and am about to pour the floor slab.

The ground floor construction consists of
hardcore well compacted, sand blinding, 1200 guage Radon barrior,
70mm Quinn Therm + 70mm Quinn Therm staggered joints (140mm total insulation) + perimeter insulation, 142 mesh for concrete slab. concrete slab to be 150mm.

I have insulation fitted and mesh installed over insulation ready for UFH pipes
to be tied to, build is open to the elements as walls are going up after slab.

I have just become aware that a slipping sheet is needed between the insulation and the concrete slab to prevent damage to the foil face of the insulation.

I have a couple of queries on this.

1) if I install a slipping sheet how will the water (rain has fallen) between radon barrier and slipping sheet escape?

2) If this is a big problem why don't they coat foil face with plastic in the factory?

3) Will the concrete effect the load bearing capacity of the insulation material by somehow eating into it?

The builder doing the floor says he has never used it.

muffler

1. cant comment as I cant see it.
2. You need to ask the manufacturers.
3. A separating layer of polythene will sort it.

RKQ

ryanrod wrote: »

1) if I install a slipping sheet how will the water (rain has fallen) between radon barrier and slipping sheet escape?

The slipping sheet is just a sheet of plastic over the insulation. Water shouldn't reach the radon barrier as its covered with 2 stepped layers of insulation and a sheet of plastic. Its a good idea to progress quickly - ie lay steel and ufh pipes the same day, pour slab the next day!

ryanrod wrote: »

2) If this is a big problem why don't they coat foil face with plastic in the factory?

This has become a "popular" idea but its not a critical detail (yet). Check with manufacturer.
Should say damaged foil isn't a problem as the foil needs an air gap to reflect heat, which isn't in a floor anyhow - so foil has a limited function in a floor.

ryanrod wrote: »

3) Will the concrete effect the load bearing capacity of the insulation material by somehow eating into it?

No - check with manufacturer. Plastic if used will prevent contact.

ryanrod wrote: »

The builder doing the floor says he has never used it. -

I've only seen slipping sheet used recently. Its not standard practice (yet)

sydthebeat

Aluminum is an amphoteric material, meaning it will react chemically with either an acid or an alkali. When portland cement is hydrating it releases free calcium hydroxide which is a very strong alkali. The pH of a fresh concrete mix can be more than 13. Consequently any material that reacts chemically with an alkali should be carefully considered if it is to be embedded in or placed adjacent to fresh concrete.

from: http://www.cement.org/tech/faq_aluminum.asp

have a read of this

ftp://imgs.ebuild.com/woc/C650369.pdf


I make it a standard specification to lay a 1200 gauge DPM over the insulation.

eg: http://i48.photobucket.com/albums/f242/sydthebeat/PICT0021.jpg

ryanrod

Thanks for the useful replys, thay have helped clear things up.

It's hard to get good weather 2 days in a row this time of year,
so I might have to leave out slipping sheet to allow water escape through
slab.

Cheers

sydthebeat

ryanrod wrote: »

Thanks for the useful replys, thay have helped clear things up.

It's hard to get good weather 2 days in a row this time of year,
so I might have to leave out slipping sheet to allow water escape through
slab.

Cheers

well, if you are going to incorporate a slipping sheet, your better off doing it the same days as the insulation so this situation doesnt arise.

if theres a large amount of water already theres theres no much you can do, short of pumping it...

ryanrod

live and learn I suppose

Carlow52

ryanrod wrote: »

Thanks for the useful replys, thay have helped clear things up.

It's hard to get good weather 2 days in a row this time of year,
so I might have to leave out slipping sheet to allow water escape through
slab.

Cheers

If u leave it out the concrete will eat into the alu foil and AFAIK will attack the insulation also.
In that event, as u said later, live and learn and follow the advice given re the slipping sheet.

conor2949

Just a few questions on the perimeter insulation in the floor -

1) Should you avoid using foil backed insulation on the perimeter of floor slabs - no matter which way it is facing it will be touching concrete be it the floor slab or the riser walls.

2) If you did use foil backed insulation with the foil back to the block riser wall - could you leave the 1200 gauge DPM run up the warm side of the insulation to prevent concrete "reacting" with the insulation face?

3) Should you finish the floor slab flush with top of perimeter insulation? could the lack of a solid concrete perimeter be problematic at any point later on in the build?

thanks
Conor2949

RKQ

conor2949 wrote: »

1) Should you avoid using foil backed insulation on the perimeter of floor slabs - no matter which way it is facing it will be touching concrete be it the floor slab or the riser walls.

Riser wall conc blocks are not an issue - wet conc in slab might react with foil but perimeter blocks are dry!

conor2949 wrote: »

2) If you did use foil backed insulation with the foil back to the block riser wall - could you leave the 1200 gauge DPM run up the warm side of the insulation to prevent concrete "reacting" with the insulation face?

No, install radon barrier / dpm as per standard detail. This detail addresses important damp and gas prevention issues. Do not try to alter without Professional advice.
By all means use a separate strip of 500 guage plastic to protect warm side of insulation from wet concrete. (18 inch roll of dpc might be useful to use)

conor2949 wrote: »

3) Should you finish the floor slab flush with top of perimeter insulation? could the lack of a solid concrete perimeter be problematic at any point later on in the build?

Yes - flush to top of slab, to standard detail. Wall insulation should overlap floor insulation. (Can be difficult to be percise on site - depends on wallties etc)
Vertical floor insulation has been a Building Reg. requirement for a number of years. It is very important.