SIPS question for the Timber Frame experts

[scsmith42]

My house is a "chalet" style that was built in 1990.  It has a 12/12 pitch roof with a cathedral ceiling over 1/2 of the house (see photo below).  There are large laminated beams at the ridge and half way down that support 2 x 6 common rafters, which means that my ceiling insulation only has a value of R19 (and the electric bill bears this out!  ).

It's time for me to re-roof the house, and at the same time I am evaluating different ways that I can increase my ceiling insulation and reduce my electric and gas bill.  One option that I'm considering would be for me to strip off the old shingles and attach some additional 2 x 6's above the existing rafters, have about 4" of spray foam insulation installed, and then put sheathing and a new roof on top.

Another option would be to use foam board insulation instead of spray foam.

It occured to me today that the simplest installation would be to strip off the old shingles, install some SIPS on top of my exising decking, and then apply roofing on top of the SIPS.

At the end of the day, I'm interested in the best balance between cost, durability and efficiency gains.

Do y'all have any advice to share?  If the SIP route is a good way to go, can you suggest some reputable SIP manufacturers that are reasonably priced?

Thanks much.

Scott

[logman]

I get my sips from General Panel out of Johnson City, Tn.  They have the best prices around and are close by so shipping cost is low. 

[Thehardway]

Scott,

That's a lot of glass! I am suspecting the glazed area (typically less than R3) has a lot to do with your energy costs perhaps more so than the R19 roof.  Are your AC and heating bills equally high?  What is your solar orientation like in regards to your glazed walls?  Is the inside ceiling very warm to the touch in the summer?

I would definitely get an infrared thermal image done before tearing off the roof.  It is the best way to evaluate the thermal envelope performance.  One on the outside at about 5:00 AM during the winter months and one on the inside around 1:30-2:00 PM on a bright sunny day in the summer would give you a great idea of where your energy is disappearing to.  Better yet rent or buy a thermal imaging camera and you can really analyze every inch and fix all your problems.  Most problems occur around glass, doors, at the roof/eave connection, corners,  wall penetrations such as outlets, chimneys and vents and through the floors.
Should you find the roof is actually the culprit, I might try stripping off the old shingles, screw down some sleepers over the sheathing, spray the whole roof  with 2" of  Polyurethane foam and  install a  reflective corrugated metal roof screwing it to the sleepers.  This will not only make your roof airtight but will allow heat buildup on the back side of the metal to move up and out of the ridge rather than getting trapped on the back of the substrate, building up and pushing through the roof as with a typical cathedral designs.

I would probably stay away from the SIPS for several reasons:

1. Cost
2. Thickness would look strange and require a lot of re-work of rake and eave trim/flashings
3. Foam board  or spray applied direct to sheathing is easier to handle, cheaper and would achieve your purpose.


If it is the glass that is the culprit, your options are very limited but insulated curtains for night time can save a lot of heat loss and special coatings and films can also make an improvement.

The house looks very nice.

[scsmith42]

Bob, thanks for the insight.  The glass is all double pane, and it faces east.  There is a pine grove on that side of the house, so not much direct sunlight comes in.

The south side of the house does not have many windows, and yes it gets pretty warm upstairs in the summer time. 

That's good advice re the SIPs, at $5 - 6 bucks a square foot (I have about 2,800 sq ft of roof) it's a bit cost prohibitive.

Your advice about the alternatives makes sense.  I've run some numbers on screwing 2 x 4's directly over the existing rafters, filling in between them with spray foam applied directly to the existing sheathing, and then applying a new sheathing on top.  I've been quoted $1.50 per sq ft for the spray foam, with me providing the man lift for installation (which I already own).  Running some quick numbers, I would have about $1,800 in materials for 2 x 4's and new sheathing, plus the trim material that I would use. 

It looks like for less than 6K in materials, plus some labor, I can add 4" of spray foam insulation on top of the existing roof.  If that saved me $100.00 a month in utility bills, I would recapture my out of pocket costs in less than 6 years, not a bad ROI.

Plus, the combined thickness would be the same as a 2 x 10 rafter, which should not look unusual in terms of thickness.

Considering that my insulation is R19, it seems to me that adding insulation can't but help the situation.

[Jim_Rogers]

When you say "sips" that means osb foam osb, you may only need foam then osb on top. These cost less and do about the same thing.
You could try asking for these.
Some companies call them curtain walls for side walls, and nail base for roofs.

Good luck with your research.

Jim Rogers

[scsmith42]

When you say "sips" that means osb foam osb, you may only need foam then osb on top. These cost less and do about the same thing.
You could try asking for these.
Some companies call them curtain walls for side walls, and nail base for roofs.

Good luck with your research.

Jim Rogers

Jim, thanks for chiming in; I'll check into those as well. 

By the way, I just downloaded a drawing that you did back in 2004 of a Trestle Style Saw Horse...  Thanks for all of the great info that you have shared over the years.

[VictorH]

May I ask what kind of foam you were quoted at $1.50??  Was that per inch or for 2 inches.  Just curious since I spray foam myself and that seems cheap.  In my opinion you would want a closed cell foam.  Fantastic looking home.

[losttheplot]

Have you got decent ceiling fans up there?
Are they spinning in the right direction?

[ljmathias]

Not to run the hijack on fans too far, but I can never remember which way they're supposed to spin- one way in the summer, opposite in the winter.  Compromise I use is to have one spin one way and the other on the other half of the cathedral ceiling spin the opposite- hope is to create a circular pattern from one side to the other.  May not be the best way though...   

Lj

[John Mc]

Here in the Northeast, most folks run fans blowing down in the summer, and up in the winter (at least the folks that remember to change the direction). I don't know if that would change in your area... we don't have much problem with heat in the summer in Vermont. In hotter climates, maybe that would change if you had vents or windows you near the peak in summer in very hot a

Running up in the winter may sound counter-intuitive: heat rises anyway, why would I want to push more heat up to the ceiling? The reason is if blowing down you are fighting the air's natural tendency to rise. It's generally warmer towards middle of the house, so the air has a tendency to rise more there. Since ceiling fans tend not to be placed near the edges of a room, running them up boosts the natural flow, and tends to circulate air throughout the room better - rising up in the middle, settling down around the edges. Blowing down into the middle of the room and fighting this natural flow can basically slow or stop this circulation.

[scsmith42]

May I ask what kind of foam you were quoted at $1.50??  Was that per inch or for 2 inches.  Just curious since I spray foam myself and that seems cheap.  In my opinion you would want a closed cell foam.  Fantastic looking home.

Victor, that is for open cell foam.  A good friend of mine owns a business that installs spray foam insulation, and he cuts me a special deal.  That price basically is for filling up the entire space between the 2 x 4's.

Closed cell would be better, but it costs more, about $2.00 per sq ft if I recall.

[scsmith42]

Have you got decent ceiling fans up there?
Are they spinning in the right direction?

Yes, they run 24/7 for most of the year.  Right now they are set for blowing down, which is the summer setting.  I think that they are supposed to pull up in the winter....

Since the bedrooms are upstairs (adjacent to the cathedral ceiling), I need to keep the temps fairly consistent from ceiling to floor, otherwise we're baking at night in the summer time.

[Thehardway]

Scott,

Do you really need to go back with shingles?  The reason I ask is that with corrugated metal you could eliminate the sheathing altogether and realize further material savings.  If you do want to go back with shingles I would  use 2" of urethane rather than the 3 1/2" open cell.  the cost difference should be minimal for the insurance and additional performance it will provide.  The extra air space you leave under the sheathing will vent the roof and lead to longer shingle life as well. 

2" of urethane will easily outperform 3-1/2 of open cell.

As your friend can probably tell you, spray in polyurethane foam has some interesting properties which lead it to perform way beyond it's calculated "R" values.  2" of polyurethane 1.8lb. will perform equivalent to an R40 and is all you need to protect you from temperature ranging from -30 to +240.  In most cases, 4" of spray in polyurethane foam would be the maximum ever installed  on anything and performs at R 63+. After you go past 4" there is little or no additional ROI.

I say this because you really don't need 4" or even 3 1/2" over your R19 roof.  You just need to create a heat/cold barrier and then channel away buildup and eliminate conduction as much as possible and completely eliminate air passage through the roof membrane. 

You can find outdoor walk-in freezers which use 2" of urethane and are very efficient.  Think about an igloo cooler.  The better ones use only 1"to  1-1/2" of urethane and they will keep ice for 7 days.  Some of the best hot water heaters use 2" of urethane and they will lose less than 1 degree per hour and that is with 140-160 degree water and a 60 degree ambient.

Urethane also adds structural strength that open cells and fiberglass do not and it forms its own vapor barrier.

This all said, The "R" factor should be thrown out when it comes to insulating.  It is very misleading and does not reflect true performance. It was a specific test  made and created and by the fiberglas insulation industry to sell their product.  It's day has come and gone.

Another bonus is that if you happen to get rained on while you are doing your roof project which is likely, the polyurethane will shed the water nicely.  I wouldn't say the same for the open cell

[scsmith42]

Bob, thanks for the additional info.  My foam insulation guy stopped by yesterday, and recommended that I use 2 x 6's instead of 2 x 4's, and that he fill 5" of the 5-1/2" cavity up with foam.  His point was that a narrower air gap between the decking and the foam promoted faster air flow, which increased efficiency.

I concur re the closed cell, and will discuss this further with him.

Most likely the insulation will be a little bit overkill... but the additional cost for the 2 x 6's is only a few hundred dollars.

Now the really good news is that.....  my insulation guy just bought some additional land, and would like to get it cleared.  It was clear cut about 7 years ago, he needs to get the stumps and brush removed.  Since I have a D8 with a root rake, we're talking trade   

And.... my roofer may be purchasing some land and would like a small pond dug on the land.  We're talking trade too!      

I looked into metal roofing (all of my other farm buildings have it), but based upon the design of the house I think that a shingle that resembles a wooden shake would provide the best overall appearance.

[frwinks]

Urethane also adds structural strength that open cells and fiberglass do not and it forms its own vapor barrier.

Is there VB under the R19insulation?  Be careful not to create a double VB sandwich where the r19 insulation has no chance of drying out 

[shinnlinger]

If you look at my gallery I insulated me roof with a semi load of polyiso(5k but I sold 1/3rd of it and insulated my walls as well.).  SIPS are just too much $.

Dave

[Holmes]

   I think Thehardway is right on with his recommendation. It could be the best trade off you ever make. The urethane foam will save you money almost every day of the year.  Holmes

[scsmith42]

Urethane also adds structural strength that open cells and fiberglass do not and it forms its own vapor barrier.

Is there VB under the R19insulation?  Be careful not to create a double VB sandwich where the r19 insulation has no chance of drying out 

Good advice.  I'm not sure re the VB, but there may not be as the roof leak came through the ceiling.  A portion of the house has an attic; I'll see if I can crawl up there and look above the wall at the end of the cathedral ceiling to look for a VB.

I'm presuming that if/when we add the spray foam on top of the existing roof, we will want to block off the existing soffit and gable vents, and only use a new vent between the spray foam and the new sheathing?

[oklalogdog]

Well here's my 2 cents worth.  I built a rustic home in 1980 and used jumbo cedar shakes for shingles.  I floored my attic and of course filled it with junk.  To make the long story short I had to go into the attic numerous times to put stuff or get stuff.  During the summer the attic was warm but never unbearably hot.  Finally after 20 years the shingles were ruined in a devastating hail storm and the insurance adjuster talked me into replacing them with asphalt shingles.

That summer I went into the attic and it felt like the fires of Hell.  I had some old computer equipment up there with rubber feet and the rubber had melted.  Our utility bills skyrocketed and the A/C ran constantly just to keep up.  No telling how much the shakes saved me in utility bills over the 20 year span.  I am building my own home again now and I will definitely used the cedar shakes and plan to cut my own.  This was one of those lessons you find out the hard way I guess.

[scsmith42]

Well here's my 2 cents worth.  I built a rustic home in 1980 and used jumbo cedar shakes for shingles.  I floored my attic and of course filled it with junk.  To make the long story short I had to go into the attic numerous times to put stuff or get stuff.  During the summer the attic was warm but never unbearably hot.  Finally after 20 years the shingles were ruined in a devastating hail storm and the insurance adjuster talked me into replacing them with asphalt shingles.

That summer I went into the attic and it felt like the fires of Hell.  I had some old computer equipment up there with rubber feet and the rubber had melted.  Our utility bills skyrocketed and the A/C ran constantly just to keep up.  No telling how much the shakes saved me in utility bills over the 20 year span.  I am building my own home again now and I will definitely used the cedar shakes and plan to cut my own.  This was one of those lessons you find out the hard way I guess.

That's great info to know -thx.