Rigid Foam to Rafters

[Bolson32]

Hi Guys,

I tried to find old posts regarding this but couldn't really find anything exactly like what I'm looking to do.

I live in Minnesota and my detached garage was built in the 50's and has a hip roof and only three horizontal 2x4s. I do use them for some light storage.

Walls were insulated with kraft faced fiberglass batts and have white painted OSB on them.

I have 2 questions and I think you guys are the ones to ask!

1:Can I put foil faced right foam right against the rafters? Hip roof will make it a bit of a pain but that's gotta be better than putting it between the rafters. There's a lumberyard around here selling it for $16 a sheet for 2" foil faced. That's a pretty damn good deal. If so, what's the best way to attach them? Will glue hold it? Does it need to be nailed?

2: Electric heater, would it be suitable for my 22x15 garage? Gas isn't much of an option, no real way to get a line out there but I'll have plenty of power and those forced air electric heaters are really affordable. I'd just like to keep it ~45 when I'm not out there. Turn it up when I am.

Thanks in advance!

 

[jives]

Some Dow Thermax, Atlas Infinish ES, and Rmax TSX8500 series, according to their data sheets, can be used as the finish interior on walls and ceilings. Whether local code will allow that is another story. Not sure if "regular" foil faced polyiso fits code.

 

[Bolson32]

Does code matter as much in a detached dwelling? What if I don't necessarily care and can rip it down if they want when I sell the place?

 

[Radix2]

I think it will work as a ceiling - there are a couple issues to consider.

Do you have soffit vents and ridge/can vents on top? - (will you have a vented space above the ceiling?) If not, then you want it sealed with spray foam

2" foam is going to be a pretty good barrier whether it is foil faced or not - and if you have a vented area above, as good as a typical drywall job, the issue is sealing places where air can flow past.

I would nail it up with plastic washer nails.

Code requires these standard foams (see Jives above) to be covered because of the flammability and production of fumes. You are going to have to decide if the risks are a concern to you.

With R10 on the ceiling, and insulated walls, I would think an electric heater would do a pretty good job on a 15x22. If you can do a 240v version it would really be plenty.

 

[Bolson32]

Thanks Radix2,

Flammability is a concern but given that there's already OSB on the walls, how much more flammable can it get?

I do have soffit vents and will put in a ridge vent next summer. Seems to be easy enough to do. This would essentially vent every rafter gap individually.

As for the washer nails, that's the way to go? Glue seems appealing as it doesn't compromise the insulation at all, but glue would be awfully permanent and if it ever had to come down it would leave glue streaks everywhere I'm sure. Also not even sure if it would hold.

As for the heater I was looking at this one.

http://www.menards.com/main/heating...692446960-c-6328.htm?tid=-8195239068561593776

The stuff I'm getting is called Rmax and it is supposedly about R13 at 2" I think that should be sufficient.

 

[Radix2]

Thanks Radix2,

Flammability is a concern but given that there's already OSB on the walls, how much more flammable can it get?

I do have soffit vents and will put in a ridge vent next summer. Seems to be easy enough to do. This would essentially vent every rafter gap individually.

As for the washer nails, that's the way to go? Glue seems appealing as it doesn't compromise the insulation at all, but glue would be awfully permanent and if it ever had to come down it would leave glue streaks everywhere I'm sure. Also not even sure if it would hold.

As for the heater I was looking at this one.

http://www.menards.com/main/heating...692446960-c-6328.htm?tid=-8195239068561593776

The stuff I'm getting is called Rmax and it is supposedly about R13 at 2" I think that should be sufficient.

I think you have a good plan. The flammability thing is that wood in general is pretty good against a few random sparks, but things like foam and paper can catch easier. It is similar to the big deal some inspectors make about uncovered paper faced fiberglass. Wood everywhere, but that bit of paper...

You could cover your foam with OSB or drywall pretty easily with some long screws.

 

[Longhair]

Bolson32, I just installed that same heater from Menards in my wife's (she shack) 14'x28'

Works Great!

 

[NUTTSGT]

Like Radix2 mentioned nails with the plastic caps should work but they may not in your case.

Generally the nails are aluminum and ringed. They can bend quite easily, epecially if those rafters are native lumber which can be harder than a pecker on a wedding night. You might need to use some screws with fender washers or strip the plastic caps off the nails to put them on the screws. Once you're done, you can cover them and the seams with foil tape.

 

[Bolson32]

Bolson32, I just installed that same heater from Menards in my wife's (she shack) 14'x28'

Works Great!

Awesome! Do you leave it on all the time or not? It recommends not letting it run unattended. I'd like to keep my garage at like 40 degrees at all times. I'm wondering if a different heater would be better for me.

Like Radix2 mentioned nails with the plastic caps should work but they may not in your case.

Generally the nails are aluminum and ringed. They can bend quite easily, epecially if those rafters are native lumber which can be harder than a pecker on a wedding night. You might need to use some screws with fender washers or strip the plastic caps off the nails to put them on the screws. Once you're done, you can cover them and the seams with foil tape.

I'm actually planning on using the 3" pole barn screws. They're a hex hex and have a rubber washer on them. They might be a little expensive but you're right, It's not pine and it's original. It's pretty damn hard. I'll just tape all of the seams and the screws when I'm done. Thanks for the feedback!

 

[Falcon67]

Flammability is a concern but given that there's already OSB on the walls, how much more flammable can it get?

LOL, we set off all our fireworks - snakes, spinners, candles, whatever - on a chunk of OSB because the ground was wet on 7/4. OSB has a few scorch marks, that's it. People seem to act like it's 4x8 sheets of crepe paper, it's not. It's as hard to light with a torch as a 2x4.

 

[Bolson32]

LOL, we set off all our fireworks - snakes, spinners, candles, whatever - on a chunk of OSB because the ground was wet on 7/4. OSB has a few scorch marks, that's it. People seem to act like it's 4x8 sheets of crepe paper, it's not. It's as hard to light with a torch as a 2x4.

Try some fireworks on some RMax foam for me and get back to me will ya?

 

[lakeroadster]

Try some fireworks on some RMax foam for me and get back to me will ya?

I was surprised, bet you'll be too. Polyiso... impressive stat's:

Fire Resistance Properties of Polyiso Foam Plastic Insulation Used in Wall Assemblies Facts and Comparisons

http://r.search.yahoo.com/_ylt=A0LE...uid=1031/RK=0/RS=Gs925dI4F.5GvjBpbq.18f2SrKU-

Based on the data presented in this technical bulletin, the following conclusions are substantiated:
1. Wood sheathing begins to burn at 400° – 500°F, while polyiso does not burn until temperatures greater than 800°.
2. Polyiso offers superior surface burning and flame spread fire-resistance properties in comparison to minimum building code requirements and other common combustible insulating and structural materials used for building envelope construction. Its flame spread characteristics are similar to gypsum wallboard.

 

[Bolson32]

Wow....I was really concerned about bumping it up against some conduit and one metal junction box that's against the ceiling in my garage. Maybe I shouldn't be.

I'll try and burn some tonight lol

Thanks btw, appreciate your curiosity and then sharing.

 

[Bolson32]

For those curious, this particular Polyiso is rated at 75 or less for flame spread index.

http://www.homedepot.com/catalog/pdfImages/93/93355af3-2f33-43db-9528-91ab4333f7c5.pdf

OSB appears to be Reported flame spread index in the range of 86 – 150 for 7/16”

Cool info

 

[woody6904]

strip the plastic caps off the nails to put them on the screws. Once you're done, you can cover them and the seams with foil tape.

Did this with my shop, bought a box of plasti cap nails and stripped em off to put em on drywall screws to hold the foil faced polyiso. Taped the seams but didnt worry about covering every screw, probably went a little crazy with the screws, lol, the insulation shouldnt come down.

Just used foil faced from menards when it was on sale. I understand not meeting code and such, but my thoughts are its a shop, in a barn, with a bunch of flammables, sitting next to a bunch of straw. If it catches on fire, the insulation is the least of my concerns.

 

[Bolson32]

Did this with my shop, bought a box of plasti cap nails and stripped em off to put em on drywall screws to hold the foil faced polyiso. Taped the seams but didnt worry about covering every screw, probably went a little crazy with the screws, lol, the insulation shouldnt come down.

Just used foil faced from menards when it was on sale. I understand not meeting code and such, but my thoughts are its a shop, in a barn, with a bunch of flammables, sitting next to a bunch of straw. If it catches on fire, the insulation is the least of my concerns.

Yea....the 60 year old very dry 2x4 double header that the conduit and junction box are nailed too are probably substantially more flammable than the insulation. I just want to be sure I'm doing it MOSTLY safe! The garage, while detached is only about 8ft from the house.

As for the screws I think I'll just buy a 5lb box hex head pole barn screws. They're about $30 but since I got all of the insulation for $190 I think I can afford it. I read somewhere (maybe the Johns Manville install guide) that you're only supposed to put them every 24". So essentially 3 per sheet on the studs. I might even just do the edges on every other stud or something. The stuff isn't very heavy.

 

[woody6904]

So essentially 3 per sheet on the studs. I might even just do the edges on every other stud or something. The stuff isn't very heavy.

I think i did 5 instead of three, but i ended up putting some insulation on top of the foil for some extra R value, so I wanted it strong enough to hold the weight.

 

[theoldwizard1]

Flammability is a concern but given that there's already OSB on the walls, how much more flammable can it get?

The problem is that some foams, once ignited, will melt and run in river of flame !

If your rafter are 16-24" apart you are probably okay. 2" is NO WHERE NEAR ENOUGH insulation for MN !! 4" minimum, 6" better. If you are doing layer, stagger your joints.

 

[Crazyjake8493]

The problem is that some foams, once ignited, will melt and run in river of flame !

Expanded polystyrene (styrofoam) will melt and drip. Polyisocyanurate is a thermoset material and will burn and char, but not drip.

I did a little test in the backyard with a piece of cheap Polyiso from Home Depot, the plain foil-faced sheet, not Dow Thermax. With a propane torch 10-12" inches away the foil would bubble but no ignition. At 6-8" away from the direct flame, the Polyiso would ignite, burn for several seconds, char, and eventually start to go out. No dripping. Plenty of sparks from grinding metal did nothing. If sparks or slag were allowed to sit on it, I'm not sure. I only used foam on my ceiling so that should never happen.

 

[lakeroadster]

I was surprised, bet you'll be too. Polyiso... impressive stat's:

Fire Resistance Properties of Polyiso Foam Plastic Insulation Used in Wall Assemblies Facts and Comparisons

http://r.search.yahoo.com/_ylt=A0LE...uid=1031/RK=0/RS=Gs925dI4F.5GvjBpbq.18f2SrKU-

The problem is that some foams, once ignited, will melt and run in river of flame .......

Expanded polystyrene (styrofoam) will melt and drip. Polyisocyanurate is a thermoset material and will burn and char, but not drip. I did a little test in the backyard......

Jake's test confirms the findings summarized in the link previously discussed, which states:
b. Polyiso will not melt or drip when exposed to fire. This is not the case for polystyrene (XPS and EPS), which produces molten material that would also be subject to adding molten fuel to the fire.

 

[jives]

Not all polyiso is the same due to different cladding. Some polyiso (Dow Thermax, Rmax TSX8500, Atlas Infinish) have reinforced facings that have Class I firing ratings and can be used as an interior finish without being covered over by sheetrock. At about $50-60 per 4x8 sheet, though, it ain't cheap.

 

[bczygan]

Hi Guys,

I tried to find old posts regarding this but couldn't really find anything exactly like what I'm looking to do.

I live in Minnesota and my detached garage was built in the 50's and has a hip roof and only three horizontal 2x4s. I do use them for some light storage.

Walls were insulated with kraft faced fiberglass batts and have white painted OSB on them.

I have 2 questions and I think you guys are the ones to ask!

1:Can I put foil faced right foam right against the rafters? Hip roof will make it a bit of a pain but that's gotta be better than putting it between the rafters. There's a lumberyard around here selling it for $16 a sheet for 2" foil faced. That's a pretty damn good deal. If so, what's the best way to attach them? Will glue hold it? Does it need to be nailed?

2: Electric heater, would it be suitable for my 22x15 garage? Gas isn't much of an option, no real way to get a line out there but I'll have plenty of power and those forced air electric heaters are really affordable. I'd just like to keep it ~45 when I'm not out there. Turn it up when I am.

Thanks in advance!

A couple of things to consider.

In a hip roof, not every rafter space will continue up to the ridge, so venting is a concern.

From your description, it is a typical hip roof garage, with a ridge board and inadequate and undersized ceiling joists, used to tie the sidewalls together.

These type roof structures are ubiquitous and not designed to hold up much more than their own weight. Adding very much will cause the ridge board to fail, the ridge to become swaybacked and the sidewalls to bow out. If the sidewalls aren't tied together, they will blow out and the structure fail.

I have examples of this next door. And they haven't even had any load added to cause this.

The difficulty is that you need multiple layers to get adequate R value, and that can add too much load.

My first choice would be to fully fill the rafter spaces with a quality closed cell foam insulation, professionally installed.

Alternatively, I would install a complete row of properly sized and fastened ceiling joists and insulate at the ceiling. In fact, I would install these joists in any event.

Photos and measurements?

Is it a board roof?

How many layers of shingles, and are they due for replacement?

Bill

 

[Bolson32]

My first choice would be to fully fill the rafter spaces with a quality closed cell foam insulation, professionally installed.

Alternatively, I would install a complete row of properly sized and fastened ceiling joists and insulate at the ceiling. In fact, I would install these joists in any event.

Photos and measurements?

Is it a board roof?

How many layers of shingles, and are they due for replacement?

Bill

That would be my first choice too...but that would be multiple thousands of dollars and the ROI wouldn't be there. I'm not going to live here forever. 5-10 years tops.

Ceiling joists are a possibility but I like the ceiling storage. As for multiple layers...yea it would probably be beneficial to have R32 or R44 with 4 to 6" but I'm just not looking to keep it at 60 degrees and live out there. I'm looking to keep it at 38 and maybe turn it up when I'm working out there. Frankly R13 is probably more than the attic of my house had last winter and even then the heat bills weren't bad.

Structure is 16x23 I think...inside is 15x22. Board roof. 1 layer of shingles, pretty new. And you are correct, with this configuration some of the corner joists would not be vented. However my attic of my house wasn't vented at the peak until this fall and I didn't have any moisture issues in my attic and hell...I lived in the house. There will still be soffit venting, which is what the house had as well. I guess if I seal it up, I'm just not that concerned about it. I'm pretty sure city code doesn't require vented roofs, as evidenced by the fact that I was able to purchase the house and it passed inspection. I even had a local roofer tell me it was up to code. Is moisture more of a concern in a garage than a house? I feel like the bulk of the moisture in a house comes from showers, cooking, and water vapor released by the human body. I'm not sure what would generate a ton of moisture that wouldn't already be present in the air in a garage.

 

[bczygan]

Given your needs and wants and plans, I would simply attach a single layer and tape the joints. Use 3" ring shank capped nails. Done and done. Do NOT think of drywall. Not needed and too heavy.

I would seriously consider some 2x6 ceiling joists (To better tie the walls together than those 2x4's), at least 4' on center and closer 24" where you want some storage. Attach to walls with metal plates.

And we love photos!

Bill

 

[Bolson32]

Thanks Bill!

That's exactly my plan. I'll probably use 3" hex pole barn screws with the plastic washers, just in case I need to take one down it might be a touch easier. And as an DIY warrior I don't want to miss with the old hammer and pound holes in my new insulation.

I'll try and snap some pictures tonight!

As for the ceiling joists, I'll probably tack a few more up next summer once I get things moved around. I agree it would probably be a prudent venture.