# Attic Insulation installation - air flow



## ipokrov (Dec 8, 2012)

Hello everyone!

I had some ice dams on the roof and want to add the second layer of insulation over the crosswise but to make sure my air flow is not blocked I want to do something like whats in the picture, but instead run a run a strip of plywood across the rafters, any reason its recessed like that ?

thanks for any input!

ilya 









http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/images/enerpedia/fig5-22_e.jpg


----------



## jlhaslip (Dec 31, 2009)

The insulation stops shown in that image are set back so that there is more insulation over the top of the wall plates, which is a good thing.


----------



## ipokrov (Dec 8, 2012)

hmm thanks, that a good point. but I took a picture and I think it should ok as I'm already have insulation under the top plate (R30) (i'm also replacing that insulation as well, its pretty bad now) that's not enough?


----------



## Nealtw (Jun 22, 2017)

How old is your house? Take another picture there when you have the insulation removed. You may have an open cavity down the wall that should be blocked too.


----------



## Bud9051 (Nov 11, 2015)

The dirty fiberglass insulation is due to air from basement flowing up through those wall cavities or air from the outside. 

Ceiling joists normally rest on top of that top plate. We need to see more of how that area is put together as Neal requested.

Bud


----------



## ipokrov (Dec 8, 2012)

the house was built in 1956. I pulled back the insulation, I was thinking of butting the insulation against the top of sheathing?


----------



## Nealtw (Jun 22, 2017)

You have a construction method I have not seen. It looks like they raised it up for more insulation.. If you do not have an open cavity down the wall. Just an air chute or the foam in your first post will work. As long as air can get in above the insulation.


----------



## Bud9051 (Nov 11, 2015)

A little confusing to the left as that looks like a gable end. 

 Note the wire disappears to the right behind the end of that rafter. 

Still can't quite see enough to detail how that was built.

Soffit area needs to be able to provide air to every rafter bay. Is that the bottom of the soffit we are seeing between the horizontal 2x? and 1x? above the wires?

As you remove more insulation we will get a better picture but baffles should be used to maintain air flow under the roof in every rafter bay. As mentioned you will need soffit venting into each bay but may want to block between the soffits and end of the insulation.

Bud


----------



## ipokrov (Dec 8, 2012)

its Massachusetts, its all different , but I know what you are talking about, my parent's house build in 1905 has the wall cavities coming all the way up to the top. I think you can drop a quarter in there and find on the first floor. it made it easy for me to run network cables in the house before the wireless networking was available. So you think my original plan will work? Not that I'm lazy, but it seemed pointless to build all these recessed cavities with top plate being above the insulation anyway, much easier to just run a strip of plywood across rafters and be done with it. 

Thanks
ilya


----------



## ipokrov (Dec 8, 2012)

if wifes allows  I will be finishing the electrical upgrade today (figured may as well do the wiring since I will be removing the insulation anyway) and will take more pictures.

Sorry for my ignorance, but what is "baffles"? I'm a bit of a russian and unfamiliar with terminology


----------



## Bud9051 (Nov 11, 2015)

In the picture with the two wires going down, it appears that is the top plate of your walls. The gap below that appears to open into the soffit cavity which is not the best as cols air and wind will be able to blow onto the end of the insulation. As Neal said I'm not 100% sure how that is build, but if you run the plywood (or rigid foam) under the rafters and block that gap below you should be good.

Another question is, how much soffit vent area do you have and will the soffit cavity provide air to every rafter bay?

Bud


----------



## Bud9051 (Nov 11, 2015)

In America we are all a bit of somewhere. Before ancestry dot com got going one of my great aunts was really into "where we came from". I have now inherited much of that information and made connections with much more. It is really interesting and a part of America we should all be proud of.

I was typing when you made the second post so your question, "baffles.
Google "Air flow baffles" and they are available at all box stores. Their purpose is to hold the insulation down from the bottom of the roof and maintain an air path to allow the ventilation to remove moisture and heat. 2" gap is considered good and the baffle function can be homemade or the staple in variety you buy.
http://www.greenbuildingadvisor.com/articles/dept/musings/site-built-ventilation-baffles-roofs

Bud


----------



## ipokrov (Dec 8, 2012)

Hi Bud, you are right, we all came from somewhere, I came from russia and my father is 100% russian, but on my mom's side I have mongolian, jewish and bulgarian  so russians come in different flavors too  in the end we are all humans living on a tiny ball inside an infinite universe. but when the snow melts and builds ice dams on roofs, we forget all that  

I don't think the snow or fain should make it up that far, otherwise I would have water running down the walls, I was thinking about running plywood like I have in this picture and tucking the insulation all the way in under the top plate abutting against the top of sheathing.

I will be a making a different post , hopefully someone will set my mind at rest.


----------



## ipokrov (Dec 8, 2012)

So my next question is this, in my rush to rewire the lights and finish the insulation, I cut too fast not realising that the boards I was cutting partially supported the dormer wall, when they built this house they went off a bit with framing and part of the wall closer to the exterior wall is almost completely on the joists and on the other end was only an 1 inch, so I rushed to home depot and picked up a 2x8 and inserted it under like this:










this is how it sits on it now, almost all of the bottom plate is on the joist:













So my questions are, on the left hand side ,the new beam is not resting on any structual member, it looks like its resting the strapping:










To reinsofce that I was thinkng of adding an angle braket

https://www.homedepot.com/p/Simpson...uge-Galvanized-Medium-L-Angle-ML26Z/202071149

or this one

https://www.homedepot.com/p/Simpson-Strong-Tie-3-in-x-5-in-7-Gauge-Heavy-Angle-HL35-R/100374913

which one do you think would work best? for the large bracket I was going to use 1/2 lag screws 3" long

if I use the 7-Gauge bracket with 1/2" lag screws, what diameter drill bit should I pilot with? 1/4? or 3/8

don't mind the decking screws, after I started to fasten with, I realized I need something bigger but it was later and stores closed, I picked some 4 1/2 headlok screws today.


----------



## Bud9051 (Nov 11, 2015)

I'm mostly an insulation and air flow guy so will let the carpenters handle the demo repair, been there done that.

I'm watching
Bud


----------

