I need some help on using lightweight concrete for the decking of a
balcony versus wood decking. How is the supporting structure laid out?
I found a concrete company that installs it a lot but they said they
just show up and pour and don't pay much attention to the structure. I
talked to my engineer and he just said the dead weight would go from 15
to 30.

What type of underlayment is used? Is a vapor barrier neccessary?
Whats the best way to attach railings?

Thanks

Targus

well, since noone else is answering, i'll give it a shot.

as your engineer indicated, you will need to beef up the framing.

if this is outside and exposed to weather, i would recommend treated
plywood for underlayment. also treated joists, etc. of course. I
think you would want a layer of 30# felt on top of the plywood. there
are many ways to attach railings and it really depends on what type of
railing system you desire. wood? metal? vinyl? cables? polycarbonate?
you could drill through the lightweight concrete or you could attach
posts to the rim.

How is the supporting structure laid out?

I talked to my engineer and he just said the dead weight would go from 15
to 30.


If you're paying an engineer and he can't handle this, you need a new
engineer. Plus, without anyone here knowing anything about the rest of
the structure that you have there, ie how it's supported, what it
adjoins, etc., how can they help you?

Hi, without more details, it's hard to say. But generally, you deck
with pressure treated plywood, seal all the joints, brush on a vapor
barrier, or roll on vapor barrier, then do the concrete.

I'd make dang sure you consider sloping the decking away from the house
otherwise you'll have standing water at the low spots. By the way,
light weight concrete is still heavier than heck, so yes, beef up the
supports.

good luck, tim1198

Thanks to all for helping. My engineered drawings show a wood deck
with 14 lb/sqft dead weight I believe. The concrete guy finally told
me most of his balcony pours are 3 to 4 inches thick. That means
adding 29 lb/sqft to the dead weight for a total around 40 lb/sqft
which isn't really too bad.

I got lucky yesterday and happened across a 32 unit building being
built with concrete balconies. Looks like 2x10's with 4x10's at each
end and across the front edge and posts. They were using that glued
plywood but I couldn't tell how thick it was or what they had for vapor
barrior so all your help was greatly appreciated. The concrete stuck
out over the edge about 4 inches.

Thanks.

wrote:
Thanks to all for helping. My engineered drawings show a wood deck
with 14 lb/sqft dead weight I believe. The concrete guy finally told
me most of his balcony pours are 3 to 4 inches thick. That means
adding 29 lb/sqft to the dead weight for a total around 40 lb/sqft
which isn't really too bad.

Ummm, yes, it is too bad. You have a balcony. Code requires a 60 PSF
design live load. If your designer skimped and designed it as a deck,
it was designed with a 40 PSF live load. Lightweight concrete figure
125 PCF, which is about 30 PSF for 3" and over 40 PSF for 4". Even if
it was designed properly, adding that much dead load puts you in
dangerous territory without any people on the balcony.

I got lucky yesterday and happened across a 32 unit building being
built with concrete balconies. Looks like 2x10's with 4x10's at each
end and across the front edge and posts. They were using that glued
plywood but I couldn't tell how thick it was or what they had for vapor
barrior so all your help was greatly appreciated. The concrete stuck
out over the edge about 4 inches.

What is the purpose of the concrete? Is it a finished surface or a
substrate for setting tile? Why do you need 3-4"?

R

What is the purpose of the concrete? Is it a finished surface or a
substrate for setting tile? Why do you need 3-4"?

I want a solid surface on the balcony to keep anything from dripping
through. I'm having lightweight concrete poured on the second floor as
a sound barrier so it seemed like the thing to use. The location is a
couple blocks back from the Pacific Ocean which means wind, salty air
and lots of rain, fog and moisture - maintenance is an important issue.
I don't want to be painting something every year.

The 3-4 inches is not my idea. The concrete supplier says that is
usually what they pour on outdoor applications. I found a building
nearby with concrete balconies and they look to be 3 inches thick, with
a cold joint every 6 or 8 feet and had cuts in the top closer than that
( I didn't measure).