adding on a garage
 

We are building a garage where a car port was. What are the pros and cons concerning putting a vapor barrier under a concrete slab for the garage floor. We will be pouring over part dirt and part existing slab.
Thank for any advise

You need footings and a foundation. A slab doesn't have that.

We have just finished preparing for pouring the footings. We are wondering what to do when pouring the foundation. It will be poured over the existing carport slab plus over the dirt of the extra yardage that we are expanding to be the garage. Should a plastic vapor barrier be layed first before pouring the foundation?

A vapor barrier should be installed under the slab.
You should not be pouring concrete over dirt. There should be a drainage later of compacted gravel.

Can we assume that you do not have a plan or permits for this project?

If not then do whatever you want, I guess.

Andy.

where im at vapor barrier is required by code under the slab, for living spaces 2" of foam goes down as well.

the debate we've always had is does the plastic go down before or after the foam though..... if the plastic goes down first the plastic is more prone to tear... if it goes on top of the foam your gonna slip and slide all over the place when laying reinforcing mesh then placing concrete:huh:

We have permits and want to do quality work , not something that will cause problems down the line.

I have obtained many permits for garage conversions of all kinds. I have always had to create a set of plans showing how the construction was going to be done.
Can't get permits without them here.
Didn't you need construction docs where you are?

Andy.

Not in that detail.

I have found this (pouring on dirt) to be a very local issue.
Most places in LA and Orange Counties will allow this, as most of the ground around here is not silty.
We have no idea where the OP is located though.

Andy.

We are in Oregon ... lol very wet to say the least. Thanks for all the help. We will be putting down gravel and then a vapor barrier before we pour. the thing about the inspectors is that even though it doesn't have to be in the approved plans, they do check everything upon inspection.

The thing about a detailed plan going in is that any possible issues can be dealt with before construction starts. Having the inspector tell you what you did was incorrect after the fact, costs time and money.

Never hurts to do research or come here for help: R506.2.3 Vapor retarder. A 6 mil (0.006 inch; 152 μm) polyethylene or approved vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the concrete floor slab and the base course or the prepared subgrade where no base course exists.

Exception: The vapor retarder may be omitted:
1. From detached garages, utility buildings and other unheated accessory structures.
2. For unheated storage rooms having an area of less than 70 square feet (6.5 m2) and carports.
3. From driveways, walks, patios and other flatwork not likely to be enclosed and heated at a later date.
4. Where approved by the building official, based on local site conditions.
From: http://publicecodes.citation.com/ico...006_par004.htm


Gary