THICKNESS OF R-30 RIGID INSULATION.

[NOOR]

Can someone tell me quickly what the thickness of r-30 rigid insulation is?:?

[King]

NOOR wrote:

Can someone tell me quickly what the thickness of r-30 rigid insulation is?:?

Depending on what type of insulation you are using...

For typical extruded polystyrene rigid insul. R value is 5 per inch, so u need 6" to get R-30.

[farker]

... well not exactly. It also depends on the density of the foam as well. Typ. EPS foam used in SIP wall & roof panels has a one pound density and only has a 4.1 R per inch. It is fairly common to have this density on other poducts as well. It would be better to call an insulation company directly to get the answer as well as see what is going to be readily available in your area.
Additionally, foams such as Polyurethane have an initial higher R value/inch than EPS but, as it out gasses nasty stuff over the first few years, it actually performs worse than EPS

[#9]

What product do you want to specify in yor area? What kind of rigid for what application? I always run to the internet first. A quick search of standad Owens-Corning rigid products claims R values of 5 per inch of material.

[secret]

I was looking at Dow's polyisocyanurate rigid roof isulation today and they claim at least R value of 6.5 per inch. Not too shabby!

Dow (and I assume all the major manufacturers) will list the R values with their associated product. You just have to do some navigating thru it all.

[stl-guy]

NOOR wrote:

Can someone tell me quickly what the thickness of r-30 rigid insulation is?:?

No really quick answer.

First, R-values for rigid insulation are no longer measured byR -Valuebut LTTR.

Long term Thermal Resistance. This is the in service thermal resistance of certain types of rigid board insulation.

There are three types of rigid insulation that can be considered. Extruded Polystyrene, Expanded Polystyrene, and polyisocynurate insulation.

Polyisocynurate insulationor"poly-iso" insulation has the highest R-value per inch of anyclosed cell type of foam insulation available. Poly-isoyields a maximum of R-7per inch depending on the manufactures claims. So 4" would be R-28 and about LTTR of 26.

This would be a minimum4" of rigid. There are few manufacturers that produce a 4" thick board or recommend it. Usually this would be achieved with two layers of board insulation.

To achieve the LTTR of R-30,by currentASTM standards,this would normallyrequire 2 layers of 2.5" poly-iso insulation. This can be upped slightly with a 1/2" layer of cover board, either wood fiber or gypsum based.

[BLUH2005]

check Carlisles,

I spec'd a rigid foam board that is R-8 per 1.5" panel

and used 3 layers with overlapping seams for a roof

[stl-guy]

BLUH2005 wrote:

check Carlisles,

I spec'd a rigid foam board that is R-8 per 1.5" panel

and used 3 layers with overlapping seams for a roof

That would probably be extruded polystyrene. R-8 per 1.5" is only 5.33 per inch. Each layer adds to the labor costs. 3 layers of R-8 still only gives you an R-24, not the desired R-30.