Insulation question

[DCarr]

Not exactly a HVAC question, but it does affect both.

With 2" x 6" walls ... what is the thickest insulation I can use ... R 19 ? Or can I use / will I benefit from using R 32 ?

TIA

 

[kaffine]

If you are using fiberglass I would say R-19. Forcing more in isn't always better. If compressing it would give higher R values they would do it and sell it that way. If you want higher R values you will have to go to a diffrent insulation like spray foam but that is expensive.

 

[bimmer1980]

kafine is correct. more is not better in the case of fiberglass insulation. It is the little airpockets that provide the "insulating". When you pack it in, you just provide a way for the heat to conduct thru the fiberglass fibers.

You could think about a 1" layer of polystyrene on the outside of the wall... that would increase the overall R-value of the wall when combined with the R-19 fiberglass insulation.

there are some cellulous insulation solutions out there that are dense packed.....

 

[DCarr]

Thanks for the info. I wasnt certain of the thickness of each. I have a foil / Fiberglass / Plastic insulation up against the metal. I was told it has an R 11 value

 

[Dolfan]

I've got a slightly different question on insulation.

My attic space has no insulation in between the rafters up against the roof, but the entire top of the ceiling has blown in insulation, which I thought was typical. Recently our A/C for that level wasn't performing real well and a technician commented that the duct work is in the hot attic space and in addition there is no insulation in the rafters?

I agree that the duct work running through 110-118 degree spaces isn't great but most home ours I haven't seen that space insulated, am I wrong? The house was new built in 2000 and had to meet code for Georgia.

Honestly with the size of this roof I don't know that I can afford typical batting insulation in all the rafter space, must be 4500sq ft of roofing space!

 

[trbomax]

Just insulate the ductwork.I find it hard to believe that a contrcter would even put ductwork in that is not insulated any more.

 

[Dolfan]

Just insulate the ductwork.I find it hard to believe that a contrcter would even put ductwork in that is not insulated any more.

The ductwork is that flexible type with the outer layer of reflective material and about an 1.5" of insulation. But I think he is saying that with the extreme temps we get in the summer in the Atlanta area that the upper unit is putting out cold air but then it is fighting the attic temps to get it to the registers without warming due to the temps.

We have had about 10 days of 92-96 degree days and it struggles when it is in that range, in the 87-92 range it seems fine.

 

[trbomax]

He needs to do a temp rise check between the discharge side of the evap coil and the registers.If the system is good, the discharge temp should be around 50 deg.at the registers and maybe 40-45 at the coil.If its up around 65-70 at the reg,,then check the temp at the evap.this will tell if its going into the attic or just not there in the first place.The system should be running for at least 1/2 hr to do this.

 

[Dolfan]

He needs to do a temp rise check between the discharge side of the evap coil and the registers.If the system is good, the discharge temp should be around 50 deg.at the registers and maybe 40-45 at the coil.If its up around 65-70 at the reg,,then check the temp at the evap.this will tell if its going into the attic or just not there in the first place.The system should be running for at least 1/2 hr to do this.

Your spot on, I'm going to spend some time this weekend with my pyrometer and look at the registers to ensure they are sealed well, get good readings on all the registers and check in the attic for leaks, should be easy with the difference in temp being around 30-40 degrees!!!!

 

[jklingel]

You can get R-21 fiberglass insulation for 5.5" spaces, but I'd sure use cellulose, mineral fiber, or cotton.