Foundations for small porch - Need clarification on requirements

[lutonlagerlout]

zut alors jim!

last chance mate

you dont really have enough for a concrete/ insulation /slab

build,but help is at hand

if you concrete or screed what you have so its level and 118 mm below finished height

you can then use DPM,100 mm celotex or similar and 18 mm ply
laid on top

its called a floating floor and we use them a lot on garage conversions,where its difficult to get the insulation in without breaking the old floor out

better to be slightly low than high if that makes sense

cheers LLL

[Jim S]

Dagnabit LLL that sounds very much like a plan

Strangely I was discussing it with a friend last night and he thought he recalled an insulation product with a finishing ply face which could fit the bill. He couldn't recall a name. Anyone know of such a product.

Would I glue the ply to the insulation board? any other fixings? say at the edges?

I thought I was being wise leaving the original slab in place, but now it seems I should have dug out the lot to enable the proper ratios of hardcore/sand/insulation/concrete/ and screed. Just for a wee porch, too.

Thank you for great advice and hopefully all is not lost and a successful build is not far away. Wait till I start asking about the roof :p

Cheers
Jim

[lutonlagerlout]

there is a kingspan board with 6mm ply glued on but it is not suitable for your needs
mainly for warm deck flat roofs

just normal 100MM rigid insulation with the 18 mm board laid flat on top
the skirting holds it in place
LLL

[GB_Groundworks]

I've no heard the dpm below and above on floors tony, or seen a spec from engineer or had a bco comment is that a new thing from your building control guys?



Edited By GB_Groundworks on 1409264476

[lutonlagerlout]

they have been asking for it for 3 years here giles
only round the concrete
they reckon the cement can rot the kingspan
you can use a thinner gauge over the top buts its easier for us just to use the same stuff above and below
LLL

[higgness]

When, in my previous job, i used to sell insulation, I was told by suppliers/manufacturers to recommend a layer of 1000g visqueen on top of the insulation. This was because the cement could damage the foil on the insulation, thus reducing the insulation values, also the 1000g should help to keep the insulation in place when pouring the floor. Not all manufacturers were giving this advise. A call to the local sales rep for the insulation supplier should solve this, not the builders merchant, the manufacturer.

[Brucieboy]

It's probably the same reason that concrete shouldn't be placed against aluminium ((external in particular) without some form of barrier. The high alkalinity of the concrete, pH approaching 13, will gradually corrode the aluminium when sufficient moisture is available.

[Jim S]

Update:
I followed LLL's suggestion for the floating floor. Cemented base to rough level then used Floor Levelling Compound. Fitted DPM to bottom and up sides and also over top of brickwork at front and sides. 100mm Celotex cut to size and fitted. Finally good quality 18mm exterior plywood cut to size with approx 5mm gap all round.

Question: What's the best sealant to fill the surrounding gap to seal the ply to DPM. This may not be really required but I have not ordered the porch yet and although the floor is protected I want to be sure no rainwater gets into gap!

Thank you
Jim

[lutonlagerlout]

i have a feeling it shouldnt be sealed Jim to allow for expansion

LLL



Edited By lutonlagerlout on 1410107561

[Jim S]

Yes, that makes sense.

Would the right sealant not be flexible enough to cope with expansion?

Or perhaps I could seal the front edge as that is where any rain is likely to get in.

I'm a very slow worker as you've probably gathered so it could be winter before the porch is finally up :p

I've got tarps and boards on standby!

Thanks
Jim

[Jim S]

I have sealed the front and short sides with silicon as a "just in case" measure". When the porch is up I can easily remove it and leave the expansion gaps before final fixing with internal trim.

Thanks for all the help with this wee project. I've got three quite similar quotes for supply only of the units but I may have to go for supply and fit as these units are heavy and I may not be up to it.

I'll report progress on a new thread as and when things happen.

Thanks again, guys
Jim

[lutonlagerlout]

any decent window firm will offer a 10 years insurance backed guarantee and a fensa cert.

as a ball park we did something similar to yours recently with a composite door and it was around £3.5k =VAT

but the roof was already there we supported it with steel posts

cheers LLL