Foam board insulation question

[machwon169]

I am at the point where I'm going to insulate my garage. It's a 50x50x14. I just went and bought 1" thick polystyrene boards. 150 of them. Now before you guys get all upset I want to use them as a ceiling and a wall. Killing two birds with one stOne. My plan is to nail em up to my post 8 foot on center and nail em to the ceiling 4 foot on center. Then cover the bottom 4 feet tall with osb as a kick board sort of and also to help with accidental sparks and such. I will also be painting the foam board with water based latex with a fire retardant.

My question is where do I put a vapor barrier? On the walls I was going to do metal outside of building, vapor barrier 6 mil, foam board. For the ceiling I was going to do metal roof, attic space about 8 feet, roof trusses, vapor barrier to them and then foam board... is this how it should be done? I'm in the north east in NJ. I have a full length ridge vent and also I'm installing a gable vent on each side and one attic fan.

 

[matt_i]

R-6 walls and ceiling, which is what polyisocyanurate (silvery skin) boards are, isn't much.

If you have a stick frame you can do better. Also you can get R-30 in the ceiling if you pile loose fill cellulose above the ceiling.

Personally I wouldn't put a vapor barrier in a shop unless you are heating it with something unvented which is going to send mad moisture into the heated space.

Hate to be such a downer but adding a gable vent to a ridge vent system helps to defeat the ridge vent's proper operation...as it gives a short-circuit path of less resistance than drawing input/cooler air from the soffit vents.

 

[machwon169]

Heating it with a pellet stove.... closed flame... also I didn't know that defeats the purpose about gable vent... also I was thinking of doing the r6 with r19 on top of the board

 

[GYPSY400]

R-6 walls and ceiling, which is what polyisocyanurate (silvery skin) boards are, isn't much.

If you have a stick frame you can do better. Also you can get R-30 in the ceiling if you pile loose fill cellulose above the ceiling.

Personally I wouldn't put a vapor barrier in a shop unless you are heating it with something unvented which is going to send mad moisture into the heated space.

Hate to be such a downer but adding a gable vent to a ridge vent system helps to defeat the ridge vent's proper operation...as it gives a short-circuit path of less resistance than drawing input/cooler air from the soffit vents.

Agreed.. the foam board alone won't be enough insulation - especially in the ceiling. Vapor barrier goes on the warm side of the wall
Also in regards to venting, either gable or Ridge vent with the inlet air coming into the soffit , keep in mind that hot air rises.

Sent from my SM-G903W using Tapatalk

 

[yeldogt]

The foam "IS" a vapor barrier. Is it covered with foil .... the uncovered is not very strong.

It's not much of an R value -- where is the property?

Look up inside foam board wall details -- what's on the outside now? I'm an unvented attic guy -- but that's another thread.

 

[buddyboy]

yeah the foam is your barrier but that little r value it's not gonna matter.

as far as adding gable vents to an attic that has a ridge/soffit system: that's like adding a second engine in the trunk of your car to get better gas milage.

google how attic venting works. I know at first thought that adding more venting to an attic sounds like it will help things but actually it could hurt things . bad

 

[DC73]

You need a lot of help. Find it here: http://www.greenbuildingadvisor.com/qa

DC

 

[machwon169]

Ok I thought r5 would be ok for walls and then r5 foamboard with staggered r19 on top for ceiling would net me r25 for roof.

This space will only be heated when in it. During winter months here in NJ we only go to low 20s and prolly won't be out there then. But when it's mid 30s 40s I would like it to be 55-60 degrees

 

[rburke65]

You can update your location in your profile

 

[GYPSY400]

Ok I thought r5 would be ok for walls and then r5 foamboard with staggered r19 on top for ceiling would net me r25 for roof.

This space will only be heated when in it. During winter months here in NJ we only go to low 20s and prolly won't be out there then. But when it's mid 30s 40s I would like it to be 55-60 degrees

2500 sqft.. it will take forever to heat it from outside temperature.. I'd recommend either not heat it, or insulate the **** out of it and have a heat source that can keep it at a constant 50.

Also, if you don't insulate the pad, it will always feel cold.. it you do insulate the pad it will take a lot of time for the heat to dissipate. The pad when warmed up ( doesn't have to be radiant heat) acts like a big heat sink.

Sent from my SM-G903W using Tapatalk