How to properly insulate attic?

[lorge1989]

My garage and my house are similiar in the sense that, they both are single story with an attic that I can walk upright in. I can only walk upright in the center (max ~6' clearance).

In my garage I simply insulated the ceiling with regular batt insulation, R-19. Which was fine, I do not heat the garage all winter. Just keep it at a decent temperature when in use.

My home is constructed similiarly I believe, with 2x6s in the cieling. Currently there is insulation on the underside of the roof. This creates a very hot attic during the summer months, and also a decently warm attic in the winter months. The current insulation is poorly done and I want to make sure that when I get a new roof put on I correct the insulation problem because I believe is has decreased the life of my roof and also contributed to some ice damming.

My attic is unfinished, used for storage. I do not care if it goes below freezing in the winter. I do care about prolonging my roof life, and preventing ice damns.

My thoughts on insulating the home attic is that I want to insulate the floor of the attic instead of the roof. Also I would like to increase ventilation up there.

Doing this is harder than it seems. Reason is, like I said I only have 2x6s on the floor, so just using batt insulation will only give me a R value of 19. I thought of using a combo of batt and foam board, and I think I can get that value into the mid 20s. Living in Buffalo, NY, our winters get cold and although this insulation layout will be better than before it is far from optimal.

There is a floor in the attic currently, that would have to be taken up to install the insulation. It is possible for me to fur the floor up to give me more depth for more insulation, decreasing clearance height.

Is the floor insulation better than the roof insulation idea?

Is there any disadvantage of insulating directly on the ceiling?

How can I increase my R value with limited space?

 

[Onewolf]

I think the best insulation would be closed cell spray foam below the roof sub-deck. Not cheap, but the best for insulation and structural integrity.

 

[-Brent-]

I have read A LOT on this topic over the last few months.

There's a lot of good info over at energyvanguard.com. For example, here's a blog article that you may find comforting to read: The Diminishing Returns of Adding More Insulation

The TLDR recap, after you get your home to the mid R20s, the graph shows heat flow benefits are not as drastic as the R value goes up.

Also, I have read a lot about radiant barriers. I would suggest you take a look at them and how you may be able to use them to your benefit in your climate. Out here, there's a big benefit to using them. After reading reviews and such, I chose Arma Foil.

When the shop is done, I'm going to address certain areas of our home where the insulation could be done MUCH better. Both space will be getting radiant barriers in addition to insulation.

 

[Danno1]

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There is an incredible amount of info here:

http://www.greenbuildingadvisor.com/


Also check the Fine Homebuilding website.


.

 

[lakeroadster]

Doing this is harder than it seems. Reason is, like I said I only have 2x6s on the floor, so just using batt insulation will only give me a R value of 19.

Can you sacrifice the storage area? If so place the batt insulation between the 2x6's... then another set of batt's on top, perpendicular to the 2x6's.

 

[DC73]

Is the floor insulation better than the roof insulation idea?

Is there any disadvantage of insulating directly on the ceiling?

How can I increase my R value with limited space?

I like the idea of a conditioned attic with insulation below the roof deck but you have to get it right. Proper details can vary with climate zone. Sounds like spray foam under the roof deck would be your best best. Avoids having to ventilate the attic, provides some structural rigidity, air seals and is a very good insulation.

Best to do some research on sites with more experts than you'll find here. In addition to the site already mentioned, check out BuildingScience.com and GreenBuildingAdvisor.com (which has a Q&A forum good for questions like these).

If you don't want to go with spray foam but still want to insulate under the roof deck, the Building Science website has had a few recent articles about how to create a conditioned attic without using spray foam. One of the important details they've come up with is to create a vapor diffusion channel at the ridge (similar to a ridge vent but only for vapor).

DC

 

[aptdweller]

has decreased the life of my roof and also contributed to some ice damming.

Bingo.
A "hot" roof is where the attic is in the conditioned space and the roof underside is insulated. Two downsides are short shingle lifespan and ice damming.

You would be better off with a vapour barrier and insulation in the floor of the attic. That, along with good ventilation will have your new roof lasting much longer. You could easily add a plywood floor over that to make a storage space.

There are a few ways to insulate, but I don't think you can go wrong with any of them. Personally, I would really think about cellulose if I had to redo my attic insulation. If cost isn't an issue, closed cell spray foam is about as good as it gets.

I'll second the Building Science website recommendation, though it is quite technical.

 

[jpcjguy]

Bingo.
A "hot" roof is where the attic is in the conditioned space and the roof underside is insulated. Two downsides are short shingle lifespan and ice damming.

You would be better off with a vapour barrier and insulation in the floor of the attic. That, along with good ventilation will have your new roof lasting much longer. You could easily add a plywood floor over that to make a storage space.

There are a few ways to insulate, but I don't think you can go wrong with any of them. Personally, I would really think about cellulose if I had to redo my attic insulation. If cost isn't an issue, closed cell spray foam is about as good as it gets.

I'll second the Building Science website recommendation, though it is quite technical.

Insulated roofline has minimal to no effect on shingle life:
http://www.greenbuildingadvisor.com/blogs/dept/building-science/insulated-rooflines-and-shingle-temperatures

 

[DalyArcher]

I agree with Lakeroadster. Evaluate what you are storing up there. Is it truly needed? Best to layer multiple bats. We have to insulate to r-40 in Northern BC I believe.

 

[DougWil]

.


There is an incredible amount of info here:

http://www.greenbuildingadvisor.com/


Also check the Fine Homebuilding website.


.

Good call.

There are conditioned attics and unconditioned attics. You have to decide what works best in your climate and with the building you have before planning insulation.

 

[lorge1989]

I have read A LOT on this topic over the last few months.

There's a lot of good info over at energyvanguard.com. For example, here's a blog article that you may find comforting to read: The Diminishing Returns of Adding More Insulation

The TLDR recap, after you get your home to the mid R20s, the graph shows heat flow benefits are not as drastic as the R value goes up.

Also, I have read a lot about radiant barriers. I would suggest you take a look at them and how you may be able to use them to your benefit in your climate. Out here, there's a big benefit to using them. After reading reviews and such, I chose Arma Foil.

When the shop is done, I'm going to address certain areas of our home where the insulation could be done MUCH better. Both space will be getting radiant barriers in addition to insulation.

I don't plan on getting up the suggested R-value, but I do want to get at least 25-30. I cool the house in the summer as we have many days approaching 90, and in the winter sometimes its below 0F for extended periods of time.

Thanks for the links!

.


There is an incredible amount of info here:

http://www.greenbuildingadvisor.com/


Also check the Fine Homebuilding website.


.

Can you sacrifice the storage area? If so place the batt insulation between the 2x6's... then another set of batt's on top, perpendicular to the 2x6's.

This is the ultimate question. Its an easy solution to just build up the floor, exept for the fact I have stairs up to my attic and it is very nice to be able to walk up there.

I agree with Lakeroadster. Evaluate what you are storing up there. Is it truly needed? Best to layer multiple bats. We have to insulate to r-40 in Northern BC I believe.

Sounds about right.

I'm right on the edge of 5/6.

Good call.

There are conditioned attics and unconditioned attics. You have to decide what works best in your climate and with the building you have before planning insulation.

I think I want to go with unconditioned. This is not my forever home and it would be nice not to have to heat/cool a space I will never live in.