[ben1216]

I am installing a bonus room over my non temp controlled garage. The garage ceiling is concrete. The area above the garage originally was a screened in porch. i have 7" from slab surface to my existing main structure floor. i planned on starting by building a 2x4 sill plate and continuing with walls as usual. i was then going to vertically fasten a 2x6 against interior studs basically forming a rim joist and then continuing joist as usual. double stacking 2" foam board between joists. after 3/4" subfloor and carpet i should meet existing floor darn near close enough with carpet being installed. My big question here is i know i need a vapor barrier. when and how should i install it? im doing a usual sill foam sealer pad. should i just lay 6mil plastic over the whole slab and build on top of that? If so, should i run the plastic all the way to the edge of the slab? sill foam on top of that? then i was thinking i really like dmx. could i put that down before i even start the rim joist against the walls and have the whole flooring system over top of that?

thank you all for the help in advance. next nice day im starting this so im ready for discussion haha:biggrin2:

 

[Nealtw]

Is the floor level?
Can you post a few pictures

 

[ben1216]

 

[ben1216]

the slab is pretty darn level. Im going out today to pressure wash it. i did just find some liquid concrete vapor barrier sealer products that i didn't know existed. liquidam ez and hydrohalt for example. What if i just paint the entire slab with a product like this?

 

[Nealtw]

the slab is pretty darn level. Im going out today to pressure wash it. i did just find some liquid concrete vapor barrier sealer products that i didn't know existed. liquidam ez and hydrohalt for example. What if i just paint the entire slab with a product like this?

Why would you need a sealer if it is above the garage? Doubt it would hurt anything but what moisture are you afraid of?

 

[ben1216]

Why would you need a sealer if it is above the garage? Doubt it would hurt anything but what moisture are you afraid of?

a heated surface and a cold surface meeting causes moisture. am i wrong?

 

[Nealtw]

a heated surface and a cold surface meeting causes moisture. am i wrong?

If warm moist air comes in contact with a cold surface the moisture will condense, Sealing the inside will not stop that. Insulation and stopping air movement will prevent that. :wink2:

 

[Nealtw]

I would consider building the walls and just fill the floor with layers of foam board and glue down the T&G over that.

What is your plan for the roof like?

 

[ben1216]

I would consider building the walls and just fill the floor with layers of foam board and glue down the T&G over that.

What is your plan for the roof like?

so you wouldnt even consider sealing the concrete first? as you can see i tore off a bonus room that was already there. it was a crap of a job though. also didnt have hvac, which i will be running to it through the existing rim joint. there was batt insulation in the floor to begin with. the faced side was down and there was sign of moisture, meaning the facing was basically glued to the slab from years of moisture hit the batt facing. thats more or less why im concerned with moisture. although the whole structure was basically floating before. they only tied the floor joist touching the house to the rim joist and the rest floated. but i guess that could also mean air got under the exterior joist causing the moisture damage. they had no barrier as well on those exterior joists.

im running the old roof pitch (sign of tear out in pic and roof line) starting from back of bonus room(side of house garage is on) and extending it straight to match same pitch as front of house. then adding gable on existing house and end of bonus room

 

[Nealtw]

im running the old roof pitch (sign of tear out in pic and roof line) starting from back of bonus room(side of house garage is on) and extending it straight to match same pitch as front of house. then adding gable on existing house and end of bonus room

Did I miss something or are the windows up stairs a problem?

 

[ben1216]

no, look at the old roof line going right under them. im continuing that pitch all the way to the face of the front of house.

so do a sill sealer and leave it at that?

 

[Nealtw]

no, look at the old roof line going right under them. im continuing that pitch all the way to the face of the front of house.

so do a sill sealer and leave it at that?

We generally but something between wood and concrete everywhere be the sill gasket for sure.

So the roof like this.

 

[SeniorSitizen]

To prevent concrete surface condensation of the new space the concrete floor needs to be warmed by insulating the garage ceiling . We have the same situation with the basement ceiling being concrete with the exception the room below is living area and therefore the upper concrete surface is room temperature. Carpet and Vinyl or other is all that's necessary.

 

[Nealtw]

To prevent concrete surface condensation of the new space the concrete floor needs to be warmed by insulating the garage ceiling . We have the same situation with the basement ceiling being concrete with the exception the room below is living area and therefore the upper concrete surface is room temperature. Carpet and Vinyl or other is all that's necessary.

Insulating below the slab would only help if you were heating the slab. Insulation between the slab and the room makes more sense.

No, warm moist air and you have no condensation.

 

[SeniorSitizen]

Insulating below the slab would only help if you were heating the slab. Insulation between the slab and the room makes more sense.

No, warm moist air and you have no condensation.

If the slab is insulated from below the surface of the living area is warmed by room temperature. Keep the upper surface of the concrete above dew point temperature and there is no condensation. Insulate above the surface and attempt to keep warm air from reaching the cold concrete surface and that's where the problem lies. Seal with everything and method available and eventually that will fail, if it was ever actually sealed to begin with, which i have my doubts. We read frequently about that portion of basements that's above grade that should have been insulated on the exterior.

 

[Nealtw]

If the slab is insulated from below the surface of the living area is warmed by room temperature. Keep the upper surface of the concrete above dew point temperature and there is no condensation. Insulate above the surface and attempt to keep warm air from reaching the cold concrete surface and that's where the problem lies. Seal with everything and method available and eventually that will fail, if it was ever actually sealed to begin with, which i have my doubts. We read frequently about that portion of basements that's above grade that should have been insulated on the exterior.

So you think heat is going to radiate down thru a wood floor, air space, heat 6 to 8 inches of concrete. Two weeks of 35* and the top of that slab with be 35 * The only time there is benefit to insulation under a slab is when you have

hydronic​

heat in the slab.

I live on a basement slab with out insulation and my floor is 55* year round.
I have friends that put 4" of foam under their slab with no added heat and their floor is 55* There is not enough heat to warm the floor.

 

[ben1216]

We generally but something between wood and concrete everywhere be the sill gasket for sure.

So the roof like this.

the rear pitch above my grill/garage is correct. but it stops at garage and comes straight down. just like signs of old exterior wall. on the contrary that pitch continues straight to the front of house and meets existing roof facing.

 

[Nealtw]

the rear pitch above my grill/garage is correct. but it stops at garage and comes straight down. just like signs of old exterior wall. on the contrary that pitch continues straight to the front of house and meets existing roof facing.

That's really low slope.

So a new footing and pier at the front corner? Or are you extending the garage out to the front?

 

[ben1216]

the garage you see is the back of my house. i think you have everything backwards.

 

[Nealtw]

the garage you see is the back of my house. i think you have everything backwards.

I did... :biggrin2: