Insulating the attic - underside of the roof

[Mike.VA]

I am getting ready to start adding insulation on the attic ceiling/underside of the roof and plan to us the:
Attic Ventilation Channel (plastic or polystyrene foam vent, not sure yet) then followed up with R-15 Kraft Faced Insulation Batt.

I understand how to connect the soffit vent and the roof ridge vent to have good flow under the ventilation channels, but how do you do it when there is no roof ridge vent? My ridge vent stops about 4 feet for each end.

 

[-Brent-]

Does the soffit vent end, too?

 

[Mike.VA]

Does the soffit vent end, too?

The gabels have soffits as well is what I think your asking all the way up to the peak.

 

[Voi]

I am getting ready to start adding insulation on the attic ceiling/underside of the roof and plan to us the:
Attic Ventilation Channel (plastic or polystyrene foam vent, not sure yet) then followed up with R-15 Kraft Faced Insulation Batt.

I understand how to connect the soffit vent and the roof ridge vent to have good flow under the ventilation channels, but how do you do it when there is no roof ridge vent? My ridge vent stops about 4 feet for each end.

Is it a standard gable or hip roof?

If you want to insulate under the roof deck you really need each truss bay ventilated.

A reasonable alternative might be to put in the equivalent of a collar tie between the upper chords and sheetrock under that. Non structural, it will only hold up your ceiling material. That way the soffits in areas that don't run straight up to a ridge vent can still have some airflow to the vent.

Will that work with your plans or need for headroom?

Also, if you're planning on using baffles for continuous ventilation from soffit to ridge they are not ideal for that situation. It's better and often the same cost to make your own baffles with rigid foam, depending on how long of a run you need.

 

[Mike.VA]

http://www.garagejournal.com/forum/showthread.php?t=351813

Here is my thread on my garage. The roof is standard.

Head room is not an issue, I will take photos of the area tonight and add them. I like where your going with this, something I didn't consider.

I don't understand the rigid foam alternative. Can you explain in more detail? I want to insulate after installing the vents to be able to use the attic.

 

[Voi]

I don't understand the rigid foam alternative. Can you explain in more detail? I want to insulate after installing the vents to be able to use the attic.

You would basically be making your own baffles. The stock ones don't have as much volume of airflow and are less effective the longer you run them together.

With rigid foam you're basically making your own baffles and determining the volume of air flow by how far you space them away from the roof sheathing. You're also getting the full width of the truss bay for air flow don't have to deal with the stock baffles compressing.

If you do create this mini attic space with non-structural collar ties you would just stop your baffles there.

Obviously as you increase air flow you are taking away from the depth available for insulation. Evidently there are ways to calculate how much volume of ventilated space you need but I don't know how to do it or where to find that information. I believe there is an article on GBA. I'll look for it.

Ultimately at some point if you give too much space to ventilation you're not getting much in the way of insulation. I would also price closed cell spray foam which would go right under the roof deck and you could insulate over that as long as you get the right ratio of foam and fiberglass for dew point control. Again, there is an article on GBA about that. Then you'll be using the full space available for insulation and wouldn't need that mini attic space.

A similar option is rigid foam above the roof deck and insulation below, again paying attention to dew point control. Only worthwhile if you're also due for a new roof.

[EDIT] Both the closed cell foam and rigid foam above the roof deck would allow you to have a non-ventilated roof.

 

[Voi]

The site built baffle article is only available to GBA members. I am not a member otherwise I'd just read the relevant parts and summarize it for you.

I just looked at your thread and noticed your attic trusses already have a collar tie of sorts. Does that type of truss continue from gable to gable?

If so I think this will be pretty easy. It's just a matter of how much insulation you want and how much you're willing to spend to get it. Obviously rigid foam above the roof deck is out of the question with the build apparently being recent.

I suspect in your climate and with that roof pitch you won't need extreme ventilation. You could cut 2" foam to fit between the upper chords and push it into the truss bays and have 1.5" ventilation space. That should be more than enough ventilation. I say this assuming those upper chords are 2x4.

You could then drywall or even put another lay of foam over the trusses to reduce thermal bridging and upping the R value. But that's a lot of foam and a lot of labor and you give up some space in your attic. At some point you need to just price closed cell at full depth and be done. No sense putting in the 2" minimum closed cell for vapor barrier and trying to squeeze something else into the remaining 1.5" of space.

By the way you'd have no issues with dew point control with 2" of foam and only 1.5" of space remaining.

I believe at least one of the outfits specializing in reclaimed rigid foam is north of your in Maryland if you want to go that route.

 

[Mike.VA]

Voi,
Thanks for the reply and the suggestions. I will be learning as I go on this and your help is appreciated.

 

[larry4406]

Mike - my 2 cents from building homes day in and day out, and Energy Star certified ones at that.

I will assume you are using standard bat type insulation, as you indicated as such.

If it were mine, I would do the following:
- Put baffles at the bottom down near the truss tails. This is done to ensure that the soffit vents breath
- Put baffles up near the ceiling clip at the attic truss. The baffles are typically 4' long, so center it on the clip
- Pad the angled ceiling clip at the attic truss to net about 12"
- Pad the uprights ("kneewall") of the attic truss to net 5.5"
- Install thermoply on the back side of the now padded attic kneewalls
- Put solid blocking between the attic truss bays under the attic truss uprights to close the bays
- Install R-49 at at attic bottom chord truss bays from perimeter to the solid blocking
- Install R-21 at the vertical attic uprights
- Install R-49 at the angled ceiling clip
- Install R-49 at the bottom chord of the attic piggy back truss (attic ceiling)
- Install drywall and finish. If not finishing, note that you should not leave the kraft paper of the insulation exposed as it is flammable. Instead use an FSK covering.

Your soffits now are able to vent to the dead attic space behind the knee walls, up past the ceiling clip, then up to the large space above the piggy back trusses, and then out thru the roof ridge vent.

 

[Mike.VA]

Larry,
Thank you for spelling that out.
I understand,,oh how I understand, (my builder and I have been going in circles about this)
I want him to continue the floor all the way to the wall, so I can use it.
Right now I don't have a ceiling/floor in the space between the attic and the bottom floor behind those truss.
I am a bit greedy and want that space for storage.
Am I crazy?

 

[Mike.VA]

Here is pic of sort of what I want to do.

 

[larry4406]

Mike - you could do that if you wanted that kind of storage. I thought you were finishing the upper area as well.

Still keep the baffles at the truss tails. Change the insulation at the bottom chord to your entire garage ceiling (no need for the bay blocking I described). Omit the attic kneewall padding, insulation, and backside thermoply. Omit the attic ceiling clip and above insulation.

Do all these omissions when/if you later finish upstairs, all except the truss bottom chord blocking.

 

[Mike.VA]

Larry,
Thanks for all the advice, it will save me lots of time and money installing the insulation the ways you suggested.

Here is my first load

Now to get working.

 

[larry4406]

Go Mike go! Nice to talk with you!

Running the insulation along the top chords with baffles from tails to void above piggy back trusses will allow the future upper attic space to be part of the same thermal boundary as the garage below. As we talked, be mindful if you ever want to create a separate living space for the attic vs conditioned storage. Not sure what R-value your top chords will support. Be mindful of exposed kraft paper (brown paper on insulation) as that goes towards the heated space in our area and is flammable. If it will be exposed, we use a FSK blanket wrap instead. FSK is the foil or white wrap you see in unfinished basements in our area.

 

[Mike.VA]

Larry,
Which one would be better:
1. EcoFoil ® Reflective Insulation 1/4"
2. Perma "R" Products R2.9 Unfaced Polystyrene Foam Board Insulation
3. Expanded Polystyrene Foam Board Insulation
for a good covering over the kraft paper batten insulation?

 

[larry4406]

Larry,
Which one would be better:
1. EcoFoil ® Reflective Insulation 1/4"
2. Perma "R" Products R2.9 Unfaced Polystyrene Foam Board Insulation
3. Expanded Polystyrene Foam Board Insulation
for a good covering over the kraft paper batten insulation?

Mike - I'm not that knowledgeable. I suggest you call Southland Insulators in Manassas VA and talk with Scott Letcher.

 

[Mike.VA]

I have not reached out to him yet, due to still installing the vent baffles. [emoji856][emoji31]
After 6 runs now and at least a dozen nails pricks in my @&£¥€£¥ head I have found a trick, mostly due to my installation technique or there lack of would really be the point.
I was having the thin foam baffles rip every time when starting out at the soffit area when stapling onto the top of the wall.
My great mind, remember the ones with the nail holes came up with, a work around , wait for it,,,, the Duct Tape fix!!!!
Yep, that fixed it, I run a strip of the tape along the starting edge where I run the first staples across and now when stapling, the tape gives that strength to the baffle, and presto! No broken baffles and less holes in my head too.
Can't wait to get done with these and start the insulation.

 

[Mike.VA]

Have half of the roof done now with these baffles. This will be one task I really look forward to being over. [emoji19]

 

[larry4406]

Mike - looking good!

I hate insulation, drywall, and painting.

 

[Mike.VA]

I am finally almost finished with these *&^%^@ vent baffles and will need to install some 2x4's along the ends to attach the insulation to.

Now that brings me to the one thing ALL of us love to hear,,,,It's a new project (sort of) so it means a NEW TOOL purchase!!!

I need suggestions on a pneumatic nailer? This will be needed to instal nails onto a 2x4 going into a flat 2x4.

I would like to have one that is versatile for many other jobs as well.

Any suggestions??

 

[larry4406]

I have a Paslode Impluse framing nailer. Works fine for my needs, no compressor or hose needed. Small jobs works great. Would not use in a production environment due to slow cycle time of the purge cycle of the engine. Gas cells get expensive and battery charging takes time.

Our framers mostly use pneumatic Paslode framing nailers.

Not aware of a multi purpose nailer (ie combo framing and trim).

 

[Mike.VA]

The 24" insulation came in. Now I need a cool Evening to get up there and start this.

 

[larry4406]

Insulation and drywall have to be the worst diy phases...

Wish you the best Mike. Wear a dust mask, gloves, and long sleeves. Wash up later with cold water so as to not open your skin pores driving the insulation in further.

 

[Commendatore]

The key to getting insulation off is to rinse without scrubbing or scratching!

 

[Mike.VA]

Do you think I could get by crawling into a ziplock bag and do it? (Ha-yah!)

The fun is really getting to get started, I itch already just thinking about it.

 

[Mike.VA]

Have 90% of the vent baffles in and about 45% of the insulation in. This is one job I will really look forward to finishing.

 

[larry4406]

Looking good Mike

The kraft paper is flammable so make sure you cover with FSK if you intend to leave the insulation exposed (and have it inspected....)

 

[Mike.VA]

Is this the stuff I should use to cover the kraft batten insulation?

 

[larry4406]

Is this the stuff I should use to cover the kraft batten insulation?

Mike - Not real sure that is it. The stuff our insulators use is a foil covering over a kraft paper with threads woven in between in a diamond pattern. The apply this over batt insulation in exposed areas.

http://www.idi-insulation.com/wp-content/uploads/2015/10/Fi-foil-FSK-Shield.pdf

http://www.fifoil.com/products/air-barriers-vapor-retarders/fsk-shield

https://www.jm.com/content/dam/jm/g...nd Commercial/BID-0147_FSK25_BioBinder_DS.pdf

 

[Mike.VA]

Finished more of the attic last night. Also ordered some of that aluminum shield material.
Thanks Larry for pushing me to cover the kraft paper insulation.
Never can be too safe.

 

[larry4406]

Nice job. That gable wall is begging for a window

 

[Notgrownup]

That room is gonna be tight as a ticks a$$...I an in the process of finishing my ceiling but at 3/12 pitch I am blowing insulation, it seems like the cheapest way.

 

[Mike.VA]

Just checked on my order and noticed it had defaulted to our old address.
Called and could not change [emoji19], so had to cancel and reorder.

Now it will be delayed and I will not have it up before I start loading it.

Oh well. It won't be the first time I had to move things around in the attic.