Drywall-insulating foam layers

[JHZR2]

Hi,

Given the discussion in the other thread about attic insulation and laying insulation batts parallel and perpendicular to the joists and all. Just wondering... Why don't folks layer drywall and foam boards (like the r-2 to r-4 types), at least on the upper story of a home? I get it that fiberglass batts and blown foam is r-10 and up, but it's also somewhat impractical, easily compressed, and can have all kinds of moisture and mold issues. I know that an R-4 layer doesn't prevent a ton of loss, but it would be so easily integrated into the ceiling, and so easy to put up, is this ever done?

Essentially adhere a 4x8 insulating foam panel to a 4x8 drywall sheet, jig it up, and screw that to the joists or studs.

 

[donnyj08]

generally because there are two different properties to insulating. there is and air seal and and R-value. R-value is simply the insulating ability of a product. Drywall, tape and mud combined creates and air barrier when done correctly. therefore the cheapest way to insulate ceilings is too use a fiberglass batt or cellulose blow in insulation.

Foam is and air barrier and an insulator both, so it is one of the best insulation's. Spray foam generally is air tight at 1/2in thick and has an r-value of 7 per 1 inch. It is however expensive. the best way to use foam as and easy insulator is to spray it on. if you drywall and spray foam in between the ceiling joist you would have an amazing barrier. and also increase the rigidity of the structure. adhering solid foam sheets to the drywall would not be as structurally sound.

from years of weatherization experience i prefer to use 1/2-1 inch of spray foam on all exterior walls with r-13 batt on top. then drywall. this will give you and air tight r-21 value and nearly sound proof walls. the ceiling is best dry walled and blown to R-48 using a cellulose compound insulation. cellulose is cheap, easy to add and will also become air tight when it settles tight. cellulose is also easy to add too later. simply blow more! of course you could spray on and inch or so in between ceiling joist before you blow cellulose

also spray foam the crawl space and band joist parameter at 2" thick to seal the foundation from outside. this brings the crawl/basement into the boundary of the home rather than excluding it.

do these things and the home will likely be incredibly tight. if the home has any gas appliances it may however be too tight. there are MVR's (minimum ventilation Ratios) that should be followed to insure the home has adequate air for the breathing of its occupants. MVR's will vary based on number of occupants including pets, and the type of appliances in the home.

 

[sleddriver]

You may find an answer for this on either Fine Homebuilding.com or GreenBuildingAdvisor.com.

 

[Shannow]

When I did my kitchen, on a North facing room (down here, that's sunny side), I put R 2.6 fibreglass batts in the wall cavities between the fibro outer clad and the inner gyprock (drywall)...it's the best insulated room in the house (for now, until I do all the rest of them).

 

[Boxnuts]

Originally Posted By: donnyj08

from years of weatherization experience i prefer to use 1/2-1 inch of spray foam on all exterior walls with r-13 batt on top. then drywall. this will give you and air tight r-21 value and nearly sound proof walls. the ceiling is best dry walled and blown to R-48 using a cellulose compound insulation. cellulose is cheap, easy to add and will also become air tight when it settles tight. cellulose is also easy to add too later. simply blow more! of course you could spray on and inch or so in between ceiling joist before you blow cellulose

I was seriously impressed with R-48 level of insulation. However I then remembered that your R value will be in US units whereas mine and others in the world will be in SI units, which means dividing yours by about 6. Even so R-8 in SI units is still very good.

 

[eljefino]

There might be a building code reason not to have it inside... flammability?

I stuck 1/2 inch 4x8 foam sheets on my exterior sheathing before putting vinyl siding up. Hung them horizontally to cover as many vertical cracks as I could. Tyvek too, to cut the wind.

 

[sciphi]

Slow down the movement of air and the house will generally be more comfortable. Insulation helps slow down air movement. Some air movement to keep the air fresh inside is needed, though. Don't want a "sick house" caused by insufficient fresh air!

 

[BMWTurboDzl]

Originally Posted By: donnyj08
generally because there are two different properties to insulating. there is and air seal and and R-value. R-value is simply the insulating ability of a product. Drywall, tape and mud combined creates and air barrier when done correctly. therefore the cheapest way to insulate ceilings is too use a fiberglass batt or cellulose blow in insulation.

Foam is and air barrier and an insulator both, so it is one of the best insulation's. Spray foam generally is air tight at 1/2in thick and has an r-value of 7 per 1 inch. It is however expensive. the best way to use foam as and easy insulator is to spray it on. if you drywall and spray foam in between the ceiling joist you would have an amazing barrier. and also increase the rigidity of the structure. adhering solid foam sheets to the drywall would not be as structurally sound.

from years of weatherization experience i prefer to use 1/2-1 inch of spray foam on all exterior walls with r-13 batt on top. then drywall. this will give you and air tight r-21 value and nearly sound proof walls. the ceiling is best dry walled and blown to R-48 using a cellulose compound insulation. cellulose is cheap, easy to add and will also become air tight when it settles tight. cellulose is also easy to add too later. simply blow more! of course you could spray on and inch or so in between ceiling joist before you blow cellulose

also spray foam the crawl space and band joist parameter at 2" thick to seal the foundation from outside. this brings the crawl/basement into the boundary of the home rather than excluding it.

do these things and the home will likely be incredibly tight. if the home has any gas appliances it may however be too tight. there are MVR's (minimum ventilation Ratios) that should be followed to insure the home has adequate air for the breathing of its occupants. MVR's will vary based on number of occupants including pets, and the type of appliances in the home.


Spray foam insulation is on my bucket list of home building. That and a perfectly clean and sealed crawl space.

 

[Kruse]

Originally Posted By: BMWTurboDzl

Spray foam insulation is on my bucket list of home building.


I like it also, but right now it is costly.
There's a house in my area being built that did the spray foam. You can put your hand on the foam and it is not cold at all. Even the 2X4 or 2X6 joints are a lot colder than the foam. But I've seen cost estimates (in this area) where it is $2 per sqare foot of blown in foam. That cost is the area of foam, not the area of the house. It does create a tight house, however.

 

[JHZR2]

Originally Posted By: eljefino
There might be a building code reason not to have it inside... flammability?

I stuck 1/2 inch 4x8 foam sheets on my exterior sheathing before putting vinyl siding up. Hung them horizontally to cover as many vertical cracks as I could. Tyvek too, to cut the wind.


I've seen many homes built this way - foam boards on the outside then wrapped and sided. Often when equipped with ($$$) electric heat in fairly cold areas. I figured, why not complete that box?

It may well be too tight though...

 

[BMWTurboDzl]

Originally Posted By: JHZR2
Originally Posted By: eljefino
There might be a building code reason not to have it inside... flammability?

I stuck 1/2 inch 4x8 foam sheets on my exterior sheathing before putting vinyl siding up. Hung them horizontally to cover as many vertical cracks as I could. Tyvek too, to cut the wind.


I've seen many homes built this way - foam boards on the outside then wrapped and sided. Often when equipped with ($$$) electric heat in fairly cold areas. I figured, why not complete that box?

It may well be too tight though...


My townhouse is built this way but without the house wrap unfortunately.