Whats code for attic insulation, how much R can you have ?

I was just wondering this. Does code limit the amount of R you can use ?

Not so much code as the fact that you can only put so much insulation in the attic.

I think that R50 (which is 15") is max 'cause after 15", the stuff just compacts and you achieve no more R value. Now the stuff he was blowing in was gray paper like stuff. Came in square bales and was fed into a hopper, then to a blower and up to the attic

That's what the contractor who is doing an addition told me a couple of weeks ago

Sw

Never heard of any thing code about that. I do know it has been proven that you can in fact over insulate a building and that in turns causes odd problems. A lot also depends on the type of insulation you use since some settle over time and in turn looses R value. The new spray in foam stuff in theory could be put in to a point you could have an R value of well over a thousand if you had the room to do so that is

We sold a house a few months back and needed 18" to satisfy the house inspector and bank loan for new buyer. You bet we had it blown in and house sold, yippe!!!

So do you think it's possible to get zero heat loss?

Big grin

Sw

I haven't heard of a max by code.
I would worry about weight on the ceiling between the rafters.

Here in cold country the minimum is R38 in the ceiling. That's only about 12".
You can have more.
It's important not to insulate over your vent chutes that go down between the rafters to the soffit vents. Roof hasta breathe.
You can extend the chutes if needed.
I blew in a lot more than 12" in mine. Towards the middle and gable ends it's closer to 20". Where the rafters meet the sides maybe 16".
New construction.
Inspector did poke his head up there and liked the extra.

Our hard foam insulator guy says. Houses don't breathe people do! He has sprayed quite a few homes and shops everywhere, sealing them up like a thermos bottle. My sons included,this is the second winter.

Doesn"t really matter how much insulation when there are air leaks letting cold air in and warm air out.
Windows are a terrible heat loser.

don't use the paper like stuff.it is nothing but
ground up news paper that is chemically treated.
will settle over time. need to use the new Owens
Corning itch free fiber glass.does a much better
job.

a good roof system needs to breathe. will trap moisture otherwise and cause a mold problem.that is why FHA requires a certain amount of vent space.i have re roofed houses where it has molded from the inside out.

This came up at the right time for me. I'm going to blow fiberglass in the new shop ceiling on Saturday and it will be 16". Lumber yard claims the power company will help on the cost if it's 16". I don't think they will help out on anything more than that.

Buick mentioned air leaks. This is more true than most of us realize. My old shop is 30x32 with a 13 foot ceiling and when I built it I went to excesses to make sure it was tight. It has six inches of fiberglass in the walls and 12" of cullulose in the ceiling. Back when I was burning wood I had gas heat also but it was set at just above freezing to keep the shop from freezing after the fire died out at night. The propane tank was a little 100 gallon job and one tank lasted till mid-march, and after that is wasn't needed till the next winter. One summer the big door got cracked (I know how it happened but don't ask) and I didn't fix it. Crack was maybe 12" long and spread possibly 1/8" at most maybe less. That next winter the tank ran out in February. Couldn't figure it out till I happened to be laying on the floor by the door and felt the slight breeze coming from the crack. So that crack wasted 35 gallons of propane for me that winter. A quick piece of duct tape over the crack would have saved me that much fuel.

Talking about blown insulation. That 12" of cellulose that was blown in the old shop attic in 1982 is now 6" of paper mache. This building has an uninsulated steel roof with a 4' ridge vent and the condensation drip over the years wrecked the insulation. The attic should have had better venting and maybe the steel should have been insulated.Jim

Been blowing insulation in attics for 35 years. Started out using the cellulose and got talked into using the fiberglass. Used it for a few years until I noticed one cold windy day that there was a pretty good draft coming in around the can lights. I ended up having to go back in the attic and cover them with blanket insulation. Also one time I was watching the guys blow the fiberglass in when somebody came in from the garage and slammed the door. The whole attic looked like it dropped a couple inches. Another thing if you get a little snow blowing in the vents which does happen around here, the fiberglass will let it go right through and onto the ceiling drywall. We lost a couple rows of tape one winter from that. So now we are back to using the cellulose. Here in SE SD. we are using R48 which is about 12 inches of cellulose. A lot depends on the installer as to what you actually get. A little more air and you get a lot of fluff which can add to the R value but lets more air in. One should actually have a bag count from the installer to see if your really getting the true R value you are paying for. The installer I now use for the cellulose injects a glue like substance with the insulation and that is supposed to keep it from settling. I saw in one house with fiberglas after a big wind storm one side of the ceiling had blown over to the otherside. Was enough air movement to pick it up. I would recommend the cellulose myself. I have it in my own home and would do it again.

I am going to use fiberglass bats. A single layer is R30 and I plan to eventually have two layers to give an R60. Minimum I would go anywhere in the country is R30 with R60 being better. If I was doing new construction I would be using foam.

I havnt ever seen a actual code on how much insulation in a certain area or any certain r-factor needed in a specific area. as far as i've been able to determine its all sort of determined by local codes or practices as far as any law would go. there are lots of places online that will give you basic recommendations for your general area ,but a whole lot depends on your heating cooling loads,type of construction etc.in MY place,ive got 18" of blown in fiber glass in the new part ive added on's attic,plan is to add about that much in rest of house when im done repairing ceilings and things.seems to be working well so far.

This is what i have gone to two rows of r30 running crossways against each other . Seems to have warmed up my place quite a bit. Im doing some remodeling and being able to just roll the bats up instead of having cello fall all over the place when i take out the ceiling plaster .

When we built our cabin we put 12" batts between the trusses, and thought that was adequate, but I am beginning to wonder. We spend more time up there (Canadian border) and it seems hard to heat. It is scissor trusses and I think I can take off one piece of steel on the porch soffit and blow some more on top. The concern I have is the 12" batts do not seal up around the vertical truss members.

Don't know for sure, but I've never heard of a max limit.

You do need airflow in your attic space though - cut that and you risk mold and rot. So that's a limiting factor of sorts right there.

But I think there's the rule of diminishing returns at play with insulation.

r120 would be twice as good as r60 but the difference would probably only save you about 15 cents a year in energy costs.

Keep in mind too that - depending on the materials used - if you stack insulation too high, it's going to start crushing the airspace out of the material at the bottom - lowering the rvalue.

In other words if you lay a strip of r 20 fiberglass insulation on top of another - it doesn't give you r40. It'll certainly be BETTER than r20 - but it may not be as good as you think because the lower layer is squeezed more than it should be.

And on top of that, as somebody else mentioned, the weight between joists directly on your ceilings is a serious concern. Put too much insulation and over time you could get some bowing and cracking in your ceilings.

I think the codes you might be referring to could be more like FHA or Va or HUD "STANDARDS". I haven't built one with their financing in a while but it used to be they had minimums for ceiling R values. Around here sidewalls have to be a certain R value to meet code but that is probably because they are closed up and the buyer wouldn't be able to verify it otherwise as opposed to looking in an open attic space.