Insulation Question

[Bobber]

I'm considering building a new detached garage and want to put in a floor heat system. Because of that everything is going to need to be insulated.

Does anyone know if blown in insulation is more efficient than fiberglass mat insulation? It appears to be cheaper than the fiberglass stuff and I'm wondering if I could get by with 2 x4 walls with blown in insulation instead of 2x6 with fiberglass mat? I suppose the other option is to still build 2 x6 and blow in insulation however I'll lose a little space inside.

Thanks!

[Wesley]

Dpends on what temp you want to run your garage at...

[ISU_phoria]

They're pretty similar in r-value (cellulose actually being a bit better), so go with the cheaper option. (Have you taken into account the cost of equipment rental to blow in the cellulose insulation?)

Also, keep in mind, this is a garage, not a house. You shouldn't need to keep your garage at 72 F, (maybe 60), so I'd save the money, gain the space and go with 2x4 walls......especially with radiant floor heat, which heats objects, not the air, which will make you feel warmer than the air temp anyway.

IMO

Here's some more info....

Cellulose vs. Fiberglass

[Bobber]

I just want to warm the temperature warm enough to melt snow and ice, so mid 40's will be fine for me if the thermostat will go down that low. Once in a great while, I'll crank it up to 60, but want to save as much energy dollars as economically is practical.

[Phaedrus]

That could be kind of rough on your cars. The 40-60 degree range will encourage corrosion. And not be warm enough to really dry things out.

Just something to think about.

[MNclone]

This probably isn't for garage insulation, but I believe that blown in fiberglass is the way to go for insulation in a house. You can get an R-17 value in a 2x4 wall.
It is known as the Blown in Blanket System, or BIBS.
www.getbibs.com has some more information.

I spent a summer in college installing the stuff. Definately the way I will go when I'm building a house someday.
But the price is probably a bit steep for a garage.

[isufbcurt]

I had insulation blown into the walls of my house shortly after i first bought it and it helped. However this last winter I gutted the inside of my house and in the process but in fiberglass insulation and it was by far better that the blown in stuff.

JMO

[CyinCo]

The blown in insulation may compress after a period time leaving an un-insulated gap at the top of the walls. The top of the walls are the worst place for this gap to occur. Personally, I'd go with the fiberglass. I've always thought of blown in insulation as more of a retrofit insulation where you are adding insulation to an existing wall and don't want to tear it all open to install fiberglass.

[Bobber]

Originally Posted by Phaedrus

That could be kind of rough on your cars. The 40-60 degree range will encourage corrosion. And not be warm enough to really dry things out.

Just something to think about.

Good point, but I suspect most peoples attached garages do not get much warmer then that and can't say I 've ever heard of this being an issue?

[usedcarguy]

When you say cheaper, I assume you are talking about blown in cellulose. It's cheaper because they use shreded newspaper as filler which is much less expensive than fiberglass. But R-value is R-value regardless of the material used.

For the side walls, fiberglass bats are the best. The reason is that blown in insulation will settle. What ends up happening is that the top six inches of your walls end up being R-1 because there is no insulation there. And since heat rises, that is exactly where you DON'T want the void. The only arguement for using blown in on side walls would be in an old house application where you don't want to tear off the siding to put in insulation. Having a void at the top of a wall from settling is much better than having an entire wall with no insulation. As for the wall thickness, it really doesn't matter. Only 10-15% of heat loss is thru the side walls. Besides, by the time you figure the extra cost of construction of 2x6 walls and the negligible savings in heating costs, it's about a wash. If you are going to keep it cooler, then there's no reason to go 2x6. However on my house I did build 2x6 walls for the reason of extra strength and more importantly for additional sound deadening from the outside world.

For the ceilings, blown in insulation is better because there are no voids. However, there is the arguement of using blown-in cellulose vs. blown-in fiberglass. Cellulose is about half the money but is prone to settling over time due to the weight of it and its ability to absorb moisture and become heavier. When the insulation settles, the R-value decreases. Blown-in fiberglass does not settle but is more itchy if your doing it yourself and is more expensive, (about twice as much) but is the superior product. You can also blow in additional cellulose later when it does settle. Both types are available at Menards or Lowes.

As for your desired floor temp, don't worry about it being too cool and damaging cars. If you were to take a thermometer in a forced air heated garage at 65 degrees, you would find quite a difference in temp from the floor to the ceiling because heat rises and there is heat loss into the cold ground. By having the heat mass in the floor, you'll get the melting and drying right where you want it - at ground level. 45-50 degrees is ideal. Just don't forget to insulate below the floor with pink or blue board. They make a more dense version for under concrete applications.

When I did the ceiling in my shop I used bats because I'm a cheapskate and a little lazy. I criss-crossed two rows of R-19 for a total of R-38. The criss cross was to minimize voids.

Now if money is really no object then just spray in icynene. You can go 4 inches thick but have a higher effective R-value because there are zero voids with foam. The icynene people will say that bats suck and leave voids. In reality, it boils down to the quality of the installation. With the addition of Tyvek or equivalent and a quality bat installation, they are really splitting hairs and can not make the arguement for the extra cost.

In summary, you have to factor in ease, cost, and efficiency. With the side walls, having stuff tight is the more important than the wall thickness. Your money would be better spent on the ceiling rather than the walls. And with the cost of blown-in fiberglass, if you're on a tight budget you could go much thicker for less money with cellulose and have some money left over if you needed to blow in more later.

Hope this helps.

[Jerry1982]

What insulation will you put under the floor?

[Bobber]

I'll use the hard board insulation that's recommended. It's a couple inch thick hard foam.