My new house has a flat roof surface wich will be used as a terrace of 1600-1700sq.ft. wich needs waterproofing + protection for pedestrian traffic and other possible wear Construction is with QL ICF 8" walls i have already install tapered insulation with a drainage pattern ( what is the correct english term for that product/system ? ) of EPS material at first i was considering EDPM membranes and such single ply ...then i learned about how i would have to setup some pathways and be carefull not to puncture it with tools or weights it is also quite expensive, and since i have no experience on installation, it would either be labor intesive or cost me alot to have it installed then i found about RoofKrete from UK wich are supposdly finishing roof with a 1/4" layer of concrete of special constitution ( mortar with carefully chose aggregates, latex and probably some kind of hydrophobic addmix ) using high % of steel reinforcement( ~ 10% fine WWM ) i have had some dicusission with north american waterproofing solutions ( hycrete, cementaid, krystol ) and all do not garantee that a membrane of concrete using their product would be totally waterproofed on a flat roof.. ( i want to use 1-2" of concrete ) now i am running out of idea my latest scheme would be to install a quick PVC membrane,with some basic glue and ballast and then have a 2" concrete slab with hydrophoic addmixture poured on it i believe that it is the only way i would feel safe about waterproofing i have to say that i am a bit scared about concrete cracking in long term, and water getting in from there then with a lower membrane, water couldn't get in the house, but what about freeze/thaw? would it make the concrete crack from pressure while freezing under it ? we have very cold winters here ( quebec ) i could also use a dimpled membrane like delta-ms on top of the PVC membrane, so that water finds a way easily under the concrete, if it ever gets there? i really wish to find the best waterproofing solution, wich will garantee me of tranquility for the next 25-30years and that is why i am up to singleply + concrete to try and get best of both world sorry if this post is long, and all mixed up i may have slept a bit too much this morning and my head is still full of complexe ideas :) thanks all for your time

Discussed with roofing company here ,
and it seems that EPDM is the cheapest and probably the best way for base waterproofing
they can order almost any dimensions under 50 by 150
so i could use a 50 by 40 and cover 90%of my roof without any seams/joints

so then i'd need to find a proper membrane that could be used on top of the EPDM
before the concrete, that would leave a path flow for water/ice if it ever leaks from the concrete

thought about using dimpled membranes like the one from Delta-MS
but it won't allow water to go through it ..thus will not work properly

need to find anything that will allow water through but won't all jamm under concrete while pooring

that'll be hard....cement particles are very fine :(

Cement, yes. Concrete, No :).

panelcraft : mmm ..i thought that concrete was made of cement paste + aggregates + addmixtures??
i don't get your smiley .. :p

i just thought about using very dense geofabric on top of some air space board of some type
it just needs to be punctured all the way through

Does your tapered insulation have rabbetted edges on the bottom of the insulation boards?  Is this what you mean by a drainage pattern?  If so, that is meant to let water drain through the insulation when the insulation is on TOP of the membrane.

Do you have roof drains or does everything drain to the edges?

What is the insulation installed over?  Metal deck?

Your roof membrane (PVC, EPDM, whatever) that you will install over the insulation will be your primary line of defense. 

The concrete overlay will serve as ballast and help with drainage and give you a terrace finish, but I would not depend on it as a true waterproof surface unless you have no roof penetrations and can somehow deal with flashing at the edges, etc.

1" concrete is silly to think about.  2" concrete will not work as a terrace (or almost anything else) even with fiber reinforcement.  3" is absolute minimun. 4" is better if you are going to use it for a terrace and consider it as a waterproof surface, and then you should have a good water/cement ratio mix with >4500psi

Your roofing installer and manufacturer need to approve whatever you are doing in order to get a warranty, but I would use a protection board (such as Carey Board) over the membrane and put the concrete over that.  I do not think a drainage plane under the concrete is needed, but again, consult the manufacturer/installer.  You will get some drainage benefit from the concrete, but it is not really a secondary membrane.  There is no downside to Hycrete admix, etc., but not much benefit, either in this application unless you go with a very robust slab. 

Question...since the concrete really is not a true membrane, why not use precast brick pavers or something similar....unless you really want a concrete surface.  If you ever need to repair your roof, the concrete will be a real PITA and will make the repair VERY expensive, so it is a double edged sword.

Bruce

Buce : thanks for comments ...

my reps now are :

Regular tapered insulation (eps ) with a drainage pattern. .no rabetted edges or whatever other finicky
only regular square boards, installed side by side

the roof system will have 2 roof drains in the middle of the roof
( already dictated by the tapered insulation pattern/system )

this was installed over metal deck
on wich i installed cut EPS into the cracks, and then a 3" dense EPS board
and lastly the taperer from 0.5" to 4" thick system

right now, it is watertight only due to some polythene sheets installed and rolled over the edges of the roof
( temporary winter waterproof ....was late )

Have you ever heard of roofkrete ?
http://www.roofkrete.co.uk/
UK roofing solution company
they make 1/4" thick concrete roof membrane
wich they then seal with seal XX ( no info)
10%+ metal content, mortar mix with carefully choosed aggregates and some addmixutres ( i presume some latex )
been holding for 10 years + now, and they propose a lifespan of 50 years

ever heard about concrete Canoe championship ?
those concrete canoes are 1/4 to 1/2" thick concrete ..and they hold in 10 people, flex and don't crack
( 10-25% latex in mixture..well reinforced )

so i am not afraid about going with 1-2inches of concrete at all
+ addmixtures that make the concrete hydrophobic seems to be quite available
so if i can make the water run off the concrete ..i bet 95-98% of it will go straight into the drains

then, around here, temperature goes from +40c during summer, down to -40c during winter
we have 2-3 months of freeze/thaw cycle
and 2-3 months of -10c or lower temp during winter

if water ever gets between the concrete and the waterproofing membrane
what will it do once it'll freeze?
that is something that i am afraid of

so that is why i would like to install some air space/drain between concrete/membrane
so that if condensation or whater is happens there, it'll have place to freeze and move around
toward the drains

i do not have any roofing installer nor manufacturer
only a material supplier
i will do all that myself ..nothing special here for now

even at 4" regular concrete is not very waterproof
it get damp as a spong, unless u can seal surface very good

your idea of pavers, i thought of
problem is that they need to be smooth enough not to puncture the membrane
and then they won't participate at all to the draining layers... but could still work 100%

evern heard about Kryton ?
they seem to say that their product waterproofes concrete, and keep sealing small cracks if they ever appear

and about fibers, i know that regular fibers only help marginally in this kind of application,
but i want to investigate carbon fibers
i've seen a few graphs where those fibers in the correct form and proportion
leads to slabs as resistant as one with 3-5% rebars
+ shrinkage control benefits + 3d reinforcement

need to find a solid study on the subject

what about foam?  my semi flat roof was foamed and then covered with elastomeric paint.  cost about 2 bucks a square foot; also had crickets built to move the water toward the scuppers.

the foam expands and contracts somewhat with the heat and as long as you re apply the paint every 4 to 5 years the foam should last for up to 30 years.  Our temp differential is 10 deg. F. to 117 F.

JinMTVT, where in the world are you?

Jelly : east of Montreal, in quebec

we had a very cold january, with constant -30-35c on my outside thermo on almost every morning before the sun rise
and last summer we hit 35c a few days .. but usually more in the +20-30c range

let's say that our regular range goes more from -30c to +30c


Bruce: super information ...thanks again
i am still considerin every options ....and today my mind is ticking me to look a bit on the "greenroof" side
for ideas and systems

i called for availability of the 50x50' ~ EPDM today, and was told 2-4weeks maximum
wich is ok with me ( still 5-6ft of snow on the roof right now ;p )


Bruce:
i cannot install 4" of concrete on the roof,
my loading limit is quicly reach
it was designed for 70psf load
and the snow/ice/rain mix accounts for alot here
and concrete goes pretty fast :p

about pavers ...
this is owned by a friend of mine :
http://www.pavnat.com/
could probably have 50% off retail on those products..or something like that

you know what would/could be nice,
a designed layout, much a la Japanese inside gardens ..with concrete tiles like that
mixed with some easy to take care green spots
( i am trying to minimize time required to take care of the house as much as possible )

how would tiles like that settle on my roof? i guess it wouldn't be as stable as a concrete slab

do you know of any sub slab product that could be used?
i've seen some nice "wick drain" for green roof stuff
they are like dimpled membrane , but punctured and feature a geotex on top


about the thickness of the slab ..
i understand that roofkrete is more a layer than a slab,
but they do install it on top of wood compressed fibers and also directly over foam
and it is supposed to be able to whistand a big hammer threw at it easily ( from what i've read )
so i don't see how 2" wouldn't hold

again, i will have to get pricing info on pavers,
since the conrete way will start with a 2000$ disadvantage ( 1000$ pump, 1000$ for the concrete guys )
the rest is easy to DIY

about overflows,
i have thought about it
i think i could place a few holes at the correct places on the side walls
using some plastic pipe through all the materials ( the 3ft rempant is ICF , the remaining height will be wood probably )

that would make for a 4" difference from drain height to overflow pipes..
should be ok

A green roof is not going to be much, if any, lighter.  You will definitely want a root shield over your membrane if you use EPDM, PVC, etc.

Is 70psf your total capacity?  or just live load?  do you know the deflection criteria?

What is the deck span in the area you want to use as a terrace?

Think about reducing the amount of terraced area.  If you can limit the area and keep it over a bearing wall (as compared to the middle of a span), you might do better.

How will you deal with uplift?

Bruce

Hi Bruce

i installed the steel joists before pouring the last story of my house
so they are effectivly "jammed" inside the concrete..wich is so for each floor system

there is a 4 ft of concrete blocks over all of the roof steel joists
then all of the steel deck is screwed on the steel joists and perimeter reinforcing
with #14 screws , as many as we could install ( around 1500 on the 1600-17000 sq.ft. roof )

the "terrace" doesn't necessairly means that it will have a green roof section,
terrace is more used to describe the feel , design and use of this floor ( roof )

the span on the length ofthe joists ranges from 25' to 42' at the widest point...no supports at all
some joists are almost 3ft high with very heavy flanges

i will give a look at my engineering papers to see what live and dead load was specified,
but i know that the steel joist company over did it a bit ..so it should be fairly safe

i remember something like 40-60 snow loads ( center to perimeter )
PSF of course


I'd like to use ALL of it
there will be a 15 by 20 section with an access to the roof, with patio doors and some windows
this will also have an acess door to the greenhouse, wich should use around 20 by 20 of the roof

there will be a SPA on the far side of the roof ( already planned support..over did it a bit ..good for 100k LBS+ on a 10' by 10' area :p )


so then the EPS tapering system + some 3" EPS under it, was screwed on the steel deck with 3" washers
and some #10 screws

what exactly should i be afraid of in terms of uplift?
i don't believe that wind will ever get inside the house much,
not many windows that open :p
( only patio and rooms )


so ... i am still considering concrete VS pavers
i cannot find info on how pavers will behave on the drainage layer,
i don't want it not stable ...
but again..more options than a full concrete slab


installed the drain yesterday, already 4-6" of ice in the lowest points
haven't had time to isntall drains before that ...some of the water
got inside the walls through our basic poly sheets layup

I don't know if you need to be afraid of anything, but similar to building facades, negative wind pressure is usually higher than positive pressure.  Wind can lift the roof off a building and corners and edges are usually the biggest problem.  I know it is sonething we worry about on our commercial buildings and is something that our insurers are interested in.  Ballast is required in many situations.....pavers, concrete, gravel, etc. work well. 

Water will drain over and around the pavers as long as your membrane has slope.  Do protect the membran!

Here is a link to tell you a bit more about uplift.
<http://www.roofingcontractor.com/CDA/Archives/5ec40f3784c58010VgnVCM100000f932a8c0____>

Bruce

We use 2'x2' concrete pavers (2") over a TPO roof for a walking deck.

Pavers are elevated above roof for water drainage and spaced with 1/2" gaps between pavers for water to get through.

With screw adjustable bases, we can make a sloped sub roof,  flat for the walking deck.

Removing one or more pavers for repairs or cleaning is very simple.

Waterproof layer is protected from traffic by pavers.

This should be designed in so there is the proper heights and structure. 
 
Typically we would have 1" minimum under paver at top of slope and 5" under paver at low point with 4" of drainage.


We would NEVER conceal the waterproof membrane under concete or anything that would prevent leak detection and repair.

My one and only presonal experience with supported pavers was not very good.  This was a VERY high traffic area outside a commercial shopping mall in Spain.  We had problems with the pedestals needing continual adjustment in order to keep the pavers from wobbling.  The contractor had a full time guy adjusting pedestals during the warranty period.

I suspect that it was a poor pedestal spec........what brands have you had success with?

I like the system because it gives a flat surface with no opportunity for ponding on the walking surface....all the drains and slopes are hidden from view.

Bruce

As i have told, i have no experience at all.
This is a personal project, for my personal home,
and i have never built or participate in a house project before..so its all first timer for me.

i don't quite know about the "pedestal" you are referring to, but i'll do a quick search for it ..

then i also like the idea of no water on surface ever ...since it'll always all just fall in the spaces and won't be seen again
Then, this is a residential house, we'll use the roof
but never as much as any commercial building
i don't want intensive service, but small adjustements from time to time don't quite scare me


snow as started to melt today ( sunny and +1C )
so i guess i'll have a snow free roof within 1-2 weeks now
then i'll start with the EPDM membrane
at least we'll be waterproof then :p

Bruce,  Not sure what the brand of pedestals was. The roofer bought them from Allied Roffing Supply in Denver.

We have used two different types:  First was just a 6"x6"x3/4" piece of plastic with four 1/2" tabs on top for spacing pavers. 
                                                         These were made to lay flat on the roof surface and conform to the slope.
                                                         We modified by adding cut offs from plastic 6x6 post.  Could make shims from 1/2" to 4".
                                                         Very labor intensive!

                                                         Second was screw adjustable pedestal that adjusted from 2" to 4". Again we used 6x6 
                                                         cut offs to add height over 4".   Much easier.

                                                         The shimming was caused more by the inconsistent thickness of the pavers.  
                                                         So we were shimming corners to lay flat.
                                                         These were all on low traffic single family patios, so some imperfection was ok.
                                                         Once they were shimmed in place we had very little problems.
                                                         
                                                         We have combined these two on roofs that only had 2 3/4" (3/4" for spacer and 2" paver)
                                                         on the high side. Used flat spacers with shims until slope was 4" for screw pedestals.            

Very easy to remove a couple of pavers to clean out underneath.  Also had a client drop a very expensive ring that fell thru the
gap and it was very easy to retrieve.  For a couple of days I was her hero!  Most of the decks we have done have been under
500 sf and it can get expensive, but you end up with a great patio, protected roof membrane and dry surface.

                                                      

 

 

What if one is not going to "shim" the pavers? would it look awfull ?

i have a 0.5" slope / 4ft ( 1/8"/ft )
and i don't think i'd care much if the pavers would follow the same slope

i wonder, you say it is very expensive

forgettin about the labour ( DIY here )
do you believe the material is very expensive ?

cause i have a bit over 1600sq.ft. to cover
i'd go a bit pricier than pouring concrete to have the paver possibility/design
but i won't do it if it costs 2-3 times more

We paid $3/corner spacer (non adjustable) and $21/ 2x2 paver

The minimum slope you have will probably not be an aesthetic problem, but unless you have very smooth and coinsistant slopes, you will do a lot of shimming to make the pavers work (three points make a plane.....4 points mean shims).  My experience was with adjustable pedestals that did not hold their adjustment.

Bruce