Installing Floor Joists on a cement floor. (roof, windows, color)

[beachouse]

I am going to install 2x6 floor joists on a cement floor , put fiberglass insulation rolled in between the joists and the floor will be 3/4" exterior plywood.

The cement floor is approximately 2 feet above the ground and 3" thick.

Do I need to put tar paper or something on the cement before the floor joists go down ?

I have read that the cement will corrode the wood , but sill plates sit on cement blocks in a house though ?


Thanks

[desertsun41]

Originally Posted by beachouse

I am going to install 2x6 floor joists on a cement floor , put fiberglass insulation rolled in between the joists and the floor will be 3/4" exterior plywood.

The cement floor is approximately 2 feet above the ground and 3" thick.

Do I need to put tar paper or something on the cement before the floor joists go down ?

I have read that the cement will corrode the wood , but sill plates sit on cement blocks in a house though ?


Thanks

Why are you doing this? I can answer your question but it's not up to me or you or anyone here. It's up to the Building Inspector unless you are in some very far out of the way unincorporated town with no rules.

Yes you are right that sill plates sit on cement. But they are pressure treated or the old term is wolmanized. This is regular Douglas Fir that is treated with Arsenic which is how you get that green color to it. All codes require wood that comes in contact with cement or block to be pressure treated. Concrete sweats and otherwise naturally gives off moisture which will rot untreated lumber.

In addition if standard wood is in contact with cement it will stay moist which will hold up a big sign for Termites to come make their home. A Termite can not eat into PT lumber.

What is this cement floor anyway? Is it an old slab?

[beachouse]

It is an enclosed porch with a cement floor.
I want to put the 2x6's , insulation ,plywood and carpet to keep the floor warm.

As I remember the pressure treated is only for outdoor use because of the arsenic, so I didn't consider it,because this is an open porch I am installing windows in .

[desertsun41]

Originally Posted by beachouse

It is an enclosed porch with a cement floor.
I want to put the 2x6's , insulation ,plywood and carpet to keep the floor warm.

As I remember the pressure treated is only for outdoor use because of the arsenic, so I didn't consider it,because this is an open porch I am installing windows in .

If it's an existing enclosed porch then technically but not legally you can get away with enclosing it. I wont go much into that or it will get deleted anyway. You still should use the PT when in contact with cement. I suspect your porch cement floor is pitched. Now what? You will have to play shim master or snap lines on each joist and rip them to the pitch so your floor will be level.

You said 2x6 joists. What is your span? I forget my span tables but I suspect a 2x6 should only span about 7'. More then that and your floor will bounce like a spring.

Be careful what ya do. You don't want to get into any trouble with the city inspectors. Going the legal route they will make you bring the whole new room up to modern code even if the rest of the house is 50 years old.

[beachouse]

As far as the span the joists will be supported by a 3" cement floor.

I am staying away from the pressure treated due to the arsenic and it would be indoors.Maybe some roof paper so the wood is not resting directly on the cement.